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1 DRIP IRRIGATION AS ALTERNATIVE TO SEEPAGE TO INCREASE WATER USE EFFICIENCY IN POTATO PRODUCTION By JOEL EDUARDO REYES CABRERA A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2013
2 2013 Joel Eduardo Reyes Cabrera
3 To Jesus
4 ACKNOWLEDGMENTS I am extremely grateful to God for providing me with life and health to finish this project. I express my sincere appreciation to Dr. Lincoln Zotarelli, who served as chair of my advisory committee. I feel fortunate to have had such a creative and endlessly patient advisor. Thanks to Dr. Zotarelli for his guidan ce during the course of this research. I am also thankful to him for welcoming me into his academic team. It was a great experience working with him. I would like to thank Dr. Diane Rowland, Dr. Steven Sargent and Dr. Michael Dukes for always answering my questions and providing valuable ideas and comments to better conduct this research and set attainable objectives. I wish to express my appreciation to the Florida Department of Agriculture and Consumer Services (FDACS) for funding this project. Special th invaluable assistance in the Hastings farm. I extend my sincere appreciation to Patrick Moran, Marcelo Paranhos, Danny Burch, Da rio Ramirez, and Guilherme Buck for their time and energy in collaborating with this project. Thanks to Meridith Hedgecock for helping with sorting and picking up roots. Thanks to Dr. Xin Zhao for allowing us to use the root scanner. I would like to thank the great graduate students that collaborate with this research: Libby Rens, Charles Barret t Christian Christensen, and Mildred Makani. Finally, I thank Heather Capobianco for reading sec tions of this thesis and providing her valuable comments to improve my manuscript
5 TABLE OF CONTENTS page ACKNOWLED GMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 6 LIST OF FIGURES ................................ ................................ ................................ .......... 7 ABSTRACT ................................ ................................ ................................ ..................... 9 CHAPTER 1 BACKGROUND AND LITERATURE REVIEW ................................ ....................... 11 The Potato Industry ................................ ................................ ................................ 11 Nort heast Florida Agricultural Water Management ................................ ................. 13 2 PERFORMANCE OF DRIP IRRIGATION SYSTEM ON POTATO BIOMASS ACCUMULATION, N UPTAKE, TUBER YIELD AND QUALITY CULTIVATED IN FLORIDA SANDY SOILS ................................ ................................ ....................... 23 Introduction ................................ ................................ ................................ ............. 23 Materials and Methods ................................ ................................ ............................ 28 Results and Discussion ................................ ................................ ........................... 32 Conclusion ................................ ................................ ................................ .............. 46 3 CHARACTERIZATION OF IRRIGATION AND WATER TABLE FLUCTUATION UNDER DRIP AND SEEPAGE SYSTEMS FOR POTATO PRODUCTION IN NORTHEAST FLORIDA ................................ ................................ ......................... 63 Introduction ................................ ................................ ................................ ............. 63 Materials and Methods ................................ ................................ ............................ 68 Results and Discussion ................................ ................................ ........................... 74 Conclusion ................................ ................................ ................................ .............. 80 4 SUMMARY AND CONCLUSIONS ................................ ................................ .......... 95 APPENDIX SAS CODES ................................ ................................ ........................ 97 LIST OF REFERENCES ................................ ................................ ............................... 99 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 108
6 LIST OF TABLES Tab le page 2 1 Tuber size classification used to evaluate marketable and non marketable yield after harvest Z ................................ ................................ ............................. 48 2 2 Anal ysis of variance summary for aboveground biomass accumulation, aboveground and tuber N uptake, and irrigation water use efficiency. ............... 49 2 3 Analysis of variance summary for tuber total and mark etable yield, tuber grades, internal and external disorders, and specific gravity. ............................. 50 2 4 Effect of surface drip, subsurface drip, and seepage irrigation method on aboveground biomass accumula ... 51 2 5 potato varieties as function of irrigation method ................................ ................. 52 2 6 Two year averaged marketable size (A1, A2, and A3) and undersized class .................. 53 2 7 irrigation treatment during 2011 and 2012 spring seasons. ................................ 54 2 8 Tuber external quality and spec ....................... 55 3 1 Analysis of variance summary for root length density (RLD) affected by irr igation, column, depth, and treatments interactions. ................................ ....... 81 3 2 Irrigation and variety treatments, irrigation depth, marketable yield, and irrigation water use efficiency for 2011 and 2012 potato season. ....................... 82
7 LIST OF FIGURES Figure page 2 1 Rainfall events and cumulative rain for 2011 and 2012 potato growing seasons in Hastings, Florida. ................................ ................................ .............. 56 2 2 Minimum, average and maximum wind speed from planting to 40 days after planting (DAP). Sprout emergence generally occurs at 28 30 DAP ................... 57 2 3 Aboveground biomass accumulation of potato varieties affected by irrigation treatment in 2011 season. ................................ ................................ .................. 58 2 4 Above ground biomass accumulation of potato varieties affected by i rrigation treatment in 2012 season ................................ ................................ ................... 59 2 5 cultivated in Hastings, FL during spring 2011. ................................ .................... 60 2 6 cultivated in Hastings, FL during spring 2012. ................................ .................... 60 2 7 Above ground (lines) in 2011 season ................................ ...................... 61 2 8 and in 2012 season ................................ ................................ ..... 62 3 1 A. Schematic representation of the irrigation treatments field tested. SUR and SUB shows the drip tape position referenced by the seed piece. ................ 83 3 2 Experimental layout in the field showing treatments distribution and block dimensions. SUR (1); SUB (2); and SEP (3) irrigated plots. ............................... 84 3 3 Time Domain Reflectometry (TDR) probes installed parallel to the potato row in seepage and drip irrigation treatments ................................ ........................... 85 3 4 surface, and subsurface drip irrigation during 2012 spring season. ................................ ........ 85 3 5 Cumulative rainfall measured at Hastings, Florida in potato seasons 2011 and 2012. B. Cumulative rainfall measured at different growth stages ............... 86 3 6 Cumulative irrigation and estimated evapotranspiration for drip and seepage irrigation methods used during 2011 and 2012 potato growing seasons. ........... 87 3 7 Comparison of a seepage irrigated bed during 2011 (A D) and 2012 (E H) at different crop growth stages. Field was wetter in the 2012 season. ................... 88
8 3 8 Potato root density (cm of roots per cm3 of soil) in five depth intervals (0 15, 15 30, 30 45, 45 60, and 60 75 cm) at 86 DAP in the 2012 season ................... 89 3 9 Daily and cumulative solar ra diation, minimum, average, maximum daily temperatures and cumulative daily growing degree days. ................................ .. 90 3 10 Spatial distribution of moisture in the soil profile for seepage, surface drip, and subs urface drip. ................................ ................................ ........................... 91 3 11 Water table level, rainfall, daily irrigation events, and volumetric soil water content at 0 10, 10 20, 20 40, and 40 50 cm depth in 2011 .............................. 92 3 12 Water table level, rainfall, daily irrigation events, and volumetric soil water content at 0 10, 10 20, 20 40, and 40 50 cm depth in 2012 .............................. 93 3 13 Volum etric water content and water table dynamics at 5, 15, 30, 45, 60, and 75 cm depth in potato row 1 (A F), row 5 (G L), and row 8 (M R) ...................... 94
9 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science DRIP IR RIGATION AS ALTERNATIVE TO SEEPAGE TO INCREASE WATER USE EFFICIENCY IN POTATO PRODUCTION By Joel Eduardo Reyes Cabrera August 2013 Chair: Lincoln Zotare lli Major: Horticultural Sciences Seepage is the traditional irrigation method for potato production in Florida Although inexpensive, it has low water use efficiency ( 20 70%). Drip irrigation is > 9 0% efficient and has the potential to produce potatoes in Florida. The objective of this study was to assess the feasibility of drip irrigation as alternative for potato production in Florida sandy soils. A two year field study was conducted to investigate the effects of two drip tape installation depths compare d to seepage (SEP) on field grown potatoes The drip treatments were s urface (SUR) drip tape installed 5 cm above seed, and subsurface (SUB) drip tape installed 5 cm below seed. Two fresh market potato and one chipping T he experimental design was split plot replicated four times. Granular fertilizer was applied to all treatments, similar to practices in the area W ater quantity applied, soil moisture content, and wa ter table level were q uantified. T uber yield and quality, aboveground biomass accumulation nitrogen uptake, and root distribution were also evaluated. ble yield by 28% and 42% compared to
10 produced significantly higher yield under SEP. A verage marketable yield under SUR, SUB, and SEP irrigation treatments were 17 1 0 and 17 Mg ha 1 produced 13, 13, and 24 Mg ha 1 ; produced 27, 20, and 28 Mg ha 1 D rip treatments required 48 % and 88% less irrigation water compared to seepage in 2011 and 2012, respectively which was translated into average irrigation efficiency (IWUE) of 8, 6, and 3 kg m 3 for SUR, SUB, and SEP, respectively. Aboveground biomass was higher under seepage compared to drip There were no differences in root distribution among irrigation treatments owed yield and quality improvement under SUR. Drip irrigation increased internal quality Particularly SUR reduced incidence of brown center disorders h ollow heart and internal heat necrosis It was concluded that SUR drip irrigation increased IWUE while maintaining yield and enhancing tuber quality
11 CHAPTER 1 BACKGROUND AND LITERATURE REVIEW The Potato Industry Potato ( Solanum tuberosum L. ) ra nks products in production volume, after wheat ( Triticum aestivum L. ), rice ( Oryza sativa L. ), and corn ( Zea mays L. ) and is a major food crop in many countries (Fabeiro et al., 2001; FAO, 2012). Potato is widely grown in the United States under many climatic conditions and management practices (Levy a nd Veilleux, 2007). Potato is the leading vegetable crop in U.S., contributing to about 15 percent of farm sales receipts for vegetables (USDA, 2012). The U .S. is the fifth largest potato producer in the world after China, India, Russia, and Ukraine (FAO, 2010). Average U.S. yields have increased over the last 15 years due to improved management practices and adoption of new farming technolog ies ( Guenthner 2010 a ). In Florida, potato production is an important component of vegetable sales. Florida is one o f the five states in U.S. that harvest potato in spring (Hochmuth et al., 2001). This production meets specific market needs, has great demand, and results in higher prices than fall potatoes. For instance, from 2007 to 2011, the average price for Florida potatoes has been $ 0.2 kg 1 higher than fall potatoes (ERS, 2012). Potato was ranked with the 6 th highest crop value in the 2011 season according to the Florida Department of Agriculture and Consumer Services (FDACS, 2012) Approximately 14,731 hectares o f potatoes are grown in Florida and 63% (~9,500 ha) of this production area is located at the Tri County Agricultural Area (TCAA) in northeast Florida. Moreover state production and harvested area for the 2010 2011 season
12 increased by 4 and 12 %, respectiv ely compared to the previous season (FDACS, 2012). Nationally, p otato tubers are a versatile staple that can be consumed either fresh or as processed products (chips, frozen, dehydrated, and canned). The fresh market potatoes in North America are classifi ed as russets, whites, reds, and yellows based on skin color. Potatoes grown in north east Florida are divided into two market categories: fresh and chip market (VanSickle et al., 2012). Fresh market tubers are sold based on their external appearance, and u sually prices for fresh potatoes are higher than those for contract based processing potatoes. Thus, growers aim to produce tubers with high quality features that look appealing to the public and ensure better economic returns (ERS, 2012; Fabeiro et al., 2 001). In terms of the U.S. chipping market, the re has been a steady increase (>50% since 1960) in processing use of potatoes to meet consumer preferences and has led to growers adjust ing production practices to meet contracts and adapt to this market trend (Guenthner, 2010b). Red LaSoda has been the most popular grown red skinned fresh market variety in the state However, yellow fleshed potatoes like Fabula are gaining popularity among consumers ( Guenthner 2010 b ; Hutchinson et al., 2009). In the chip market specific gravity values (measurement of solid content in tubers) for use in the ch ippi ng industr y (Hutchinson et al., 2002)
13 Atlantic is a highly valuable round white variety for the processing market and one of the most planted potato varieties cultivated in northeast Florida. It was released in 1976 by the United States Department o f Agriculture and gained wide popularity among growers due to its excellent chip and fry quality. Previous studies have characterized Atlant ic as a high yield, high specific gravity potato when compared with other varieties in different regions of the co untry. For example, Webb et al. (1978) conducted a three year experiment and found that yields of Atlantic exceeded those of Sebago which is a locally adapted variety, by 40% under Florida growing conditions. Atlantic ranked in the positions 8 th and 9 th o ut o f the most cultivated potato varieties in Canada and the continental U.S. during the 2008 season (NPC, 2010) North east Florida Agricultural Water Management There is a growing competition among urban, recreational, industrial, and agricultural u sers for water resources in Florida A ccording to the last U.S. population census; Florida is the state with the third largest population growth per year ( Campbell, 1997 ; Marella, 2004) thereby increasing water resource use from all sources. Therefore, red uced water resources coupled with g rowing environmentalist pressure and rising public interest for water quality and conservation is pushing water users, especially the agricultural sector, to evolve towards more efficient use of this resource (Boman, 1990 ; Alva, 2008 a ). Irrigation is the largest component of freshwater use in Florida accounting for 49% of total withdrawals from the Floridan aquifer The increasing demand on limited water resources and the need to minimize adverse environmental consequences of food production seem to press for an important role of efficient irrigation technology in the future of Florida vegetable production. The Floridan aquifer is the main source of
14 water in northeast Florida ( TCAA ) According to S t. J ohns R iver W ater M anage ment D istrict (SJRWMD) a griculture is the major water user in the TCAA with an esti mated average daily usage of 488 million liters of water per day during the potato irrigation season (Durden, 2000a). This high demand for groundwater during potato irrigat ion season causes problems related to drawdowns in the potentiometric surface of the Floridan aquifer, increased pumping costs as the water level drops down, and salt water intrusion into the aquifer (Haman et al., 1989; Vergara, 1994). T he Tri County Agri cultural Area (TCAA) contains Putnam, St. Johns, and Flagler counties This area extends from Palatka to south Orange Park in Jacksonville along the northeastern Florida shoreline, and consists of mainly potato, cabbage ( Brassica oleracea L. ), and other co le crops (Chen 2010). Potato production accounts for the largest planted area with 67% estimated row crop area in the TCAA. The potato growing season starts in late December or early January through late May or early June. After harvest, cover crops such as s orghum s udan g rass are generally planted to control wind and water erosion in the field during the summer/fall period s (Munoz Arboleda et al., 2006). In 2000, St. Johns, Flagler, and Putnam counties (TCAA) reported a daily water withdraw al for irrigatio n of 34, 18, and 12 million gallons per day, respectively (Marella and Berndt, 2005 ). Furthermore, Putnam and St. Johns have been identified as a water resource problem due to the seasonal ground water withdrawals for potato irrigation. Additionally, Flagl er County is projected to have critical water shortages in the near future due to the excessive water pumped for agricultural purposes and an increase in population (Vergara, 1994). This large water withdrawal from the aquifer has caused the
15 area to be ide resulting in the need to look for strategies to protect groundwater as well as enhance water use efficiency of crops (Durden, 2000 a ; Trippensee et al., 1995 ; Vergara, 1998). Seepage is the predominant irrigation technique in the TCAA for potato production This method is broadly used because it is low cost, has low maintenance requirements, and is effective in flatwoods locations where the natural water table is relatively high and can be readily raised. Conventio nal semi closed seepage systems use shallow open ditches to distribute irrigation water in the field and to maintain the height of the water table (Haman et al., 1989; Smajstrla et al., 2000). Water seeps laterally underground and moves from the perched w ater table by capillary action to the Soil moisture status is the principal factor determining the start of a water event, with water pumping in the seepage system continuing to prevent stress and yield loss in the crop ( Casey et al., 1997 ). Seepage irrigation has been extensively criticized due to its low delivery efficiency. This method is heavily dependent on soil characteristics and on the depth of the natural water table ( Pitts and Clark, 1991). The soils in the TCAA are mainly sand (>90%), with l ow organic matter content. Therefore, they are characterized by low water holding capacity ( i.e. average field capacity of 10 12%) T he inefficiency of the seepage system high san d content, irregular rainfall distribution, and the use of fertilizer s increase the risk for nutrients leaching often leading to nonpoint source pollution in the St. Johns River watershed ( Locascio, 2005; Munoz Arboleda et al., 2008). Under Florida climati c conditions with uneven rainfall distribution during the potato growing
16 season, farmers heavily rely on seepage to supply the crop with the water needed. However, during heavy rainfall events, the sandy soils have a limited ability to hold large volumes o f water and runoff of nutrients to drainage canals occurs, resulting in significant loss of nutrients offsite (Waddell et al., 2000). The aforementioned characteristics of seepage irrigation and the inaccuracy to determine thresholds that can be used for i rrigation scheduling result in the use of as soil water status commonly used for potato production However, irrigation scheduling based on these subjective evaluations is often inefficient and unsustainable on a long term scale This type of management interpretation can be avoided with technology that 1) monitors the soil moisture and 2) increases control of water delivery to the root zone. In addition, when soil is maintained excessively wet for prolonged peri ods, hypoxic conditions occur preventing adequate oxygen reaching the root and tuber and often increase the incidence of blights, rots, and wilts resulting in economic loss (Holder and Cary, 1984; Shock et al., 2007 b ). Soil moisture uniformity in the field is the most challenging characteristic of seepage irrigation and becomes a severe issue during tuber bulking when e xcess ive water application increase s the incidence of tuber internal and external disorders he maximum yield (Alva, 2008 a ). Thus, it is evident that sound water management will have a positive effect on the ability of the plant to absorb nutrients and increase the potential for higher marketable yield (Gudmestad, 2008; Shock et al., 2007b). A uni form, more efficient seepage schedule is difficult to achieve because of the complexity of the shallow water table dynamics Q uantification of the water table
17 contribution to crop needs is vague due to soil characteristics and water upward flux in sandy so ils ( Singh and Chauhan, 1996 ). Limitations of seepage irrigation are the inaccurate ability to determine when to stop irrigation, duration of the water event, and lack of distribution uniformity as well as its excessive dependence on the water table level, which makes it difficult to control since water table depth can widely vary in the field (Pitts and Clark, 1991). Dry years have an enormous impact on the water table level and directly impact pumping costs and water requi rements for seepage irrigation. T he need for a more efficient irrigation method is imperative in the TCAA as well as in other part s of the state of Florida, where agricu lture relies on seepage systems (Alva, 2008b; Camp, 1998 ; Durden, 2000b; Livingston Way, 2007). A conversion from seepa ge to more efficient irrigation alternatives will potentially reduce nutrient load s to the St. Johns River watershed and groundwater that migrates from potato fields (Munoz Arboleda et al., 2008). To improve the water application efficiency and reduce the leaching and runoff potential of seepage irrigation, alternative water application methods should be explored. Drip irrigation is a method of delivering water directly to the root zone through a network of low density polyethylene pipes. This method increa ses the control of water volume used and greater efficiency (80 95%) is achieved (Burt, 1998; Goldberg et al., 1976 ; Morison et al., 2008). Drip irrigation has also been defined as the frequent low dose application of water through emitters located close t o the crop root zone. It offers many advantages; some of them are : 1) reduction of evaporation and increase of plant transpiration; 2) reduction of weed population; and 3) prevention of drainage and
18 retention of nutrients in the root zone (Lamm et al., 201 1). The high frequency application of water improves soil moisture content and reduces the volume of water applied and lost by deep percolation ( Vazquez et al., 2006 ). The drip system contributes towards increasing crop yield potential, improvement of wate r and fertilizer use efficiency, and offers the possibility for automation and fertigation through the drip line. High frequency water events by drip irrigation reduce the use of soil as a water storage reservoir, provide daily moisture requirements to the root zone, maintain a high soil matric potential that reduces plant water stress, and enhance s wetted by emitters (Badr et al., 2010; Burt, 1998; Phene et al., 1992 ; Phene and S anders, 1975 ; Saffigna et al., 1977 ). Drip irrigation has been tested in different potato production areas in the world (Yuan et al., 2003; Onder et al., 2005; Patel and Rajput, 2007). Previous studies have reported similar marketable yield when drip and s prinkler were compared to produce potato. However, an average of 65 m m of water was saved with drip and higher root concentration was reported under the drip treatment (Shalhevet et al., 1983). Another study compared drip to seepage irrigation for tomato ( Solanum l ycopersicum ) production and did not find significant differenc es in terms of yield or quality; but in terms of water use seepage used an average of 3.5 times pan evaporation while the drip water use ratio was on average 50% of pan ev aporation (Pi tts and Clark, 1991 ). Water resource savings and increasing crop yield per unit of water are becoming a strategic importance for many areas in the U S (Morison et al., 2008). Drip irrigation is an option for growers to overcome potential agricultural drou ght in northeast Florida; it
19 provides water and energy conservation benefits that address many of the challenges facing irrigated lands, and applies water uniformly so that each part of the irrigated area receives the same amount of water (Badr et al., 201 0; Patel and Rajput, 2007). The high soil water content around drippers facilitates better water transmission to the surrounding soil and minimizes soil moisture fluctuations around the crop root zone; however thorough attention should be paid to capillari ty and gravity forces that are dependent on soil properties in the field (Segal et al., 2000). Although it has been documented that drip irrigation has an inherent >90% delivery efficiency, considerations such as grower management, installation, system pre ssure, and filtration play a fundamental role in attaining this efficiency. Drip tape can be used permanently or a single crop season based on installation depth. The determination of appropriate depth of installation and time of use involves consideration of crop value, soil texture, and crop root development pattern (Burt, 1998). Surface placement of drip tape generally implies a shallow drip tape positioning (<10 cm) that is retrieved after each growing season in most crops. On the other hand, subsurface drip can be installed anywhere in the depth of root penetration. Subsurface drip irrigation microirrigation emitters with discharge rates usually less than 7.5 L h 1 (ASAE Standards, 2001). Subsurface drip offers the potential to save water by reducing soil surface wetting and thus evaporation loss ( Ayars et al., 1999 ). Under subsurface drip, water moves by soil matrix suction and eliminates the effect of surface infiltration character istics, saturated condition of water during irrigation, and surface runoff (Badr et al., 2010; Lamm et al., 2011; Patel and Rajput, 2007). However, deep positioning of drip
20 tape can poorly deliver water to the root system of shallow rooted crops like potat oes (Clark et al., 1993). The effects of drip tape placement depth ha ve been previously evaluated on different crop systems. Clark et al. (1993) reported a significant increase of 5% in the marketable yield of field grown tomatoes when drip tape was positi oned 3 cm below the soil surface compared to drip tape placed at a 30 cm depth. Patel and Rajput (2007) investigated the effects of five different drip tape installation depths (0, 5, 10, 15, and 20 cm deep) in sandy loam soils (69% sand) and reported that tuber yield was significantly affected by the tape positioning; obtaining maximum yield when drip tape was placed at 10 cm below the soil surface Dukes and Scholberg (2005) compared the use of different subsurface drip tape depth placement versus sprinkl er irrigation for sweet corn on Florida sandy soils and found that drip tape placed at 23 cm deep used 11% less water than the sprinkler treatment and that no difference in marketable yield was obtained between treatments. In arid regions like Egypt, subsu rface drip irrigation has shown to significantly decrease water use when compared with surface drip. The use of subsurface drip in production areas like Arizona, Texas, and California has increased in previous years; however, this technology has to be thor oughly tested under different large scale crop production systems to overcome any possible flaw s The outcome of these tests has to be a user friendly system that provides farmers with better decision making tools to optimize water management (Lamm et al., 2011; Soussa, 2010; Thompson et al., 2003) It has been mentioned in previous studies that surface drip irrigation is usually used for higher value crops while subsurface irrigation is used for lesser value crops.
21 This discrepancy is due mainly to the far mer perception that subsurface drip is harder to manage because of lack of visible hints when there are irrigation problems and use of surface drip decrease this potential risk. Readily available water to ensure crop establishment is the most challenging i ssue of subsurface drip irrigation. The adoption of this technology usually tends to bring problems due to lack of experience and knowledge on how to implement it and among growers the biggest concern is the proper evaluation of its performance and measure ment of discharge uniformity since there is no visual guarantee that the entire farm production is being well irrigated, which increases economic risks (Lamm et al., 2011; Patel and Rajput, 2007). The implementation of drip for potato production in sandy s oils makes precise depth installation crucial to obtain maximum yield and quality. Therefore, a thorough evaluation of drip tape placement and its effects on soil moisture distribution, plant physiology performance, and tuber yield and quality are importan t to generate accurate guidelines for growers. The proper use of drip irrigation, either surface or subsurface, is a challenge where research efforts and outreach are necessary to develop reliable tools that can be used by farmers to ensure optimal irrigat ion practices specific for their local conditions (Lamm et al., 2011). The goal of this study was to investigate the feasibility of drip irrigation as an alternative strategy to conventional seepage irrigation to increase water savings for potato productio n in northeast F lorida It was hypothesi zed that drip irrigation will potentially reduce irrigation water requirements compared to seepage irrigation, while maintaining potato tuber yield and quality
22 Objectives The objectives of this research were as fol lows: 1. to e valuate the performance of drip irrigation sy stem as a water delivery method for potato production in northeast Florida (Chapter 2 and 3 ). 2. to e valuate the effects of drip irrigation on potato plant growth, nitrogen accumulation, yield and tuber i nternal and external quality (Chapter 2). 3. to investigate soil moisture and water table dynamics as influenced by drip and seepage irrigation systems (Chapter 3).
23 CHAPTER 2 PERFORMANCE OF DRIP IRRIGATION SYSTEM ON POTATO BIOMASS ACCUMULATION, N UPTAKE, TU BER YIELD AND QUALITY CULTIVATED IN FLORIDA SANDY SOIL S Introduction Potato ( Solanum tuberosum L. ) is a high value crop in Florida. In 2011, potato production covered roughly 15,000 hectares of the state and received a crop value of $ 144 million. The Hast ings area, also known as the Tri County Agricultural Area (TCAA), encompassed 63% of the Florida potato area (USDA, 2012). In the TCAA potatoes are grown in sandy soils using seepage (subsurface) irrigation. Groundwater is pumped from deep wells and deliv ered to furrows spaced 18 m apart using semi closed pipes. Within each 18 m there is a group of 16 potato rows (0.35 m height) furrows and seeps laterally underground Farmers use a weir s tructure to hold the water back in ditches along the border of the field to raise the water table level (Livingston Way, 2010 ). The goal is to bring the water table up to just below the root zone of the plants located between two water furrows. Hence, the seepage method is based on water table management (Livingston Way, 2010; Singleton, 1996; Smajstrla et al., 2000). The advantages of seepage are its low cost, low maintenance, and effectiveness in places like northeast Florida where a natural high water ta ble occurs and plentiful supply of water exists (Haman et al., 1989). However, seepage water use efficiency ranges from 20 % to 70% because much of the large quantity of water pumped is not available for crop use but is used solely to maintain the water ta ble level (Locascio, 2005 ; Dukes et al., 2012 ) In addition, seepage has low uniformity of water distribution,
24 high percentage of deep percolation and high runoff potential in the field ( Clark and Stanley, 1992 ). Seepage also causes wide soil moisture fluc tuations in the field as a result of lateral flow and distance from the water furrow s (Smajstrla et al., 2002 ). Consequently, due to the length of time that the water table is high, soil saturation tends to occur around the root zone reducing aeration and affecting the ability of the plant to efficiently uptake nutrients which adversely impacts tuber quality A proper drainage system is required to lower the water table and avoid damage caused by excessive soil moisture and rainfall However, drainage als o brings additional issues regarding accurate water level control. For example, unexpected heavy rain can have severe negative consequences when the water table is high. It results in loss of nutrients via runoff and percolation. However, if seepage irriga tion ceases for a prolonged period the potato hill is the first soil layer to be drained of moisture due to evaporation and high hydraulic conductivity of sand (infiltration rate 19 mm hr 1 ) resulting in plant stress (Gudmestad, 2008; Livingston Way, 2010 ). Potato is extremely sensitive to water stress and water excess Tuber yield, grade, and quality can be reduced by either over or under irrigation. Over irrigation creates low oxygen conditions in the soil and increases nutrient leaching from the active root zone, which stresses the plant. Under irrigation of potato has a detrimental impact on nutrient uptake with further biomass and productivity reductions due to the plant sensitivity to water depletion (Shock et al., 2007). It is well documented that po tato plants rapidly close their stomata as response to slight reductions in water supply (Alva, 2008a) The timing and duration of water stress during different growth stages decrease plant canopy and biomass accumulation.
25 The low tolerance for water stres system is typically in the upper 30 cm of soil) makes readily available water a priority in order to avoid this type of detrimental situation ( Onder et al., 2005 Shock 2010; Wang et al., 2006). In additio n, the occurrence of tuber physiological disorders such as brown center, hollow heart, growth cracks, bruise susceptibility, and heat necrosis have been associated with wide variations in soil moisture content. A direct relation between low soil moisture c onditions and misshapen tubers has been reported (Eldredge et al., 1996; Shock et al., 2007). Face d with the need to increase water use efficiency by agricultural systems, a lternative water delivery methods to seepage irrigation are being sought by produce rs to improve water management and savings uniformity of distribution and minimize tubers affected with the aforementioned disorders Irrigation methods with high distribution uniformity are important to minimize losses and avoid to irrigate based on ina ccurate measures of soil appearance and intuition (Fereres et al., 2003; Shock et al., 2006). Drip irrigation has been tested in the past in severa l potato production areas in the U.S. in an effort to conserve overall production water use Additionally, a reduction in off site nutrient movement due to l owered water volumes applied more frequently is achieved, which results in reduced soil water fluctuation thus retaining fertilizer for a longer period of time in the root zone (Eldredge et al., 2003; Shock e t al., 2006; Shock et al., 2007).
26 In addition, tuber shape defects during the bulking period can be significantly decreased and potato yields increased by minimizing drastic fluctuations of soil moisture content in the root zone (Gunel and Karadogan, 1998 ; Phene et al, 1976). Another factor affected by irrigation practices is t uber specific gravity The specific gravity is a measure of starch content of tubers and an important factor in processing. Yuan et al. (2003) tested five water regimes based on the evaporation values measured by a standard pan evaporation (0.2 m diameter) and found that tuber specific gravity tends to decrease as the amount of water applied increases and vice versa. Other studies reported that more frequent irrigation events have al so shown potential to increase the specific gravity value (Gunel and Karadogan, 1998; Westermann et al., 1994). Waddell et al. (1999) reported a significant marketable yield increase (>4 Mg ha 1 ) and tuber with highest specific gravities under drip irrigation compared to sprinkler Any irrigation strategy must provide appropriate water quantities to the crop during specific developmental stages. There are five growing stages of the potato crop: 1) sprout development, 2) vegetative growt h, 3) tuber initiation, 4) tuber bulking, and 5) maturation (Lynch et al., 1995; Miller and Hopkins, 2008; Yuan et al., 2003). The tuber initiation and bulking stages have been identified as the most sensitive stages to water stress. Inadequate irrigation during the tuber initiation and bulking has been shown to reduce growth and tuber production of marketable size (Ojala et al., 1990; Onder et al., 2005, Steele et al., 2006). Thus, more profitable potato productions can be achieved through efficient irriga tion methods that keep soil moisture content constant throughout
27 the season meeting the development specific plant water requirements ( Shock et al., 2007 ) The national potato market is divided into two categories, fresh (or table stock) and processed prod ucts (chips, frozen, dehydrated, and canned). Fresh market tubers appealing external attributes, such as skin, shape, and uniform color. On the other hand, external qualit y appearance is less important for tubers with processed destination as it is to obtain high specific gravity values (ERS, 2012; Hutchinson et al., 2009). In Florida, early potato varieties maturing in less than four months are grown. In decades. igh market demand high specific gravity, adaptation to Florida conditions and high yield potential makes it popular among growers. However, ible to brown center, internal heat necrosis, and hollow heart ( Hutchinson et al., 20 02 ). For varieties in Florida. Additionally, yellow consumers and gr less sensitive to the physiological disorders for which is susceptible However, it has been reported (Hutchinson, 2003; Hutc hinson et al., 2009; Webb et al., 1978). In the context of shorter water supply and expected pumping regulations for potato production in northeast Florida, drip irrigation may provide advantages for growers to enhance water use efficiency as well as achie ve better control of soil
28 moisture and nutrients in the potato root zone. However, valid concerns about adverse effects on tuber yield and quality could produce a negative response from growers to adopt this alternative irrigation method The purpose of th is study was to evaluate the effects of two drip tape depth s on aboveground biomass accumulation, plant N uptake, varieties grown in northeast Florida. The hypothesis tested was that use of drip irrigation can maintain productivity and quality of chipping and fresh market potatoes. Materials and Methods The f ield experiment was designed to assess the response of potato varieties to irrigation methods The experiment was conducted at the Unive rsity of Florida Partnership for Water, Agriculture, & Community Sustainability at Hastings, Florida (29 The soil in the experimental field was classified as sandy, siliceous, hyperthermic Ar enic Ochraqualf and belongs to the Ellzey series (USDA, 1981) The proportions of the particle fracti ons in the topsoil (1 m) layer we re 94% sand, 2.5% silt, and 3.5% clay (Campbell et al., 1978). Natural slopes we re less than 2%. The water table level is normally within 25 cm of the surface on an average of 6 months annually (USDA, 1981). The area was laser leveled in 2011 and rows ( 78 m long, 0.35 m height) were formed with 1.01 m distance between row centers. It is a common practice in the TCAA to hill r ows to improve drainage and facilitate harvest operation At planting, granular fertilizer was banded in the soil surface on top of the potato row, and subsequently incorporated The fertilizer rates applied were 56, 1 12 and 1 68 kg ha 1 of N, P 2 O5, and K 2 O, respectively. In addition, side dress fertilizer application (84 0 140 kg ha 1 ) was performed when shoot emerg ence was 13 and 33 days after planting (D AP ) in 2011 and
29 2012, respectively F inal side dress N fertilization (84 kg ha 1 ) was done when plants were 15 20 cm tall at 46 and 40 DAP in 2011 and 2012 seasons, respectively No fertilizer was supplied through the drip irrigation system The experiment was laid out in a randomized complete block design with treatments arranged in a split plot consistin g of surface drip (SUR), subsurface drip (SUB), and seepage (SEP) as main factors and potato varieties: Atlantic, Fabula, and Red LaSoda as sub factors in four replications Buffer plots were installed between seepage and drip irrigated plots, requiring a total land area of 2.31 ha (5.7 ac) Plots were 21 m long. Entire beds ( 16 rows ) were used for s eepage plots In the case of drip, beds were divided by half (8 rows) and each section received one drip treatment Potato tubers were mechanically planted on F ebruary 17 and January 17 of 2011 and 2012, respectively. Seed pieces (57 85 g) were planted within 20 cm spacing in the row, 15 cm deep. Seeds were ridged immediately after planting. Drip lines of 16 mm inner diameter, 0.200 mm thickness, 20 cm dripper sp acing, and 500 L h 1 /100 m discharge rate (RO DRIP, John Deere Water, Moline, IL, USA) were installed approximately 5 cm below the seed piece before the seed was planted for subsurface (SUB) treatment; and 5 cm above the seed piece one day after planting f or surface treatment (SUR). Temperature, relative humidity, solar ra diation, and wind speed data were obtained from a weather station located in the experimental site. Daily reference evapotranspiration (ET o ) was retrieved from the Florida Automated Weathe r Network (FAWN; www.fawn.ifas.ufl.edu). Crop evapotranspiration (ET c ) was calculated from the product of crop coefficient (K c ) and ET o (Doorenbos and Pruitt, 197 7 ). The growing
30 season was divided into four stages and a specific K c was assigned to each one The crop stages and respective K c were as follow: i niti al (0.6), development (1.15), mid season (0.75), and late (0.6) (Allen et al., 1998) After plant emergence, 6 m section s w ere marked in the center area of each other row in the plot to quantify yiel d. The number of plants counted were based on the number of stems present in this six linear meter area and used to calculate plant density in each plot. The plant density (32,864 plants ha 1 ) was used as a reference for further conversion of biomass and t ubers into megagram (Mg) per hectare. Biomass accumulation was measured by harvesting biweekly the above ground section of two representative plants in each plot excluding plants in the plot border Sampling procedures were started when the plant populatio n was well established and plant size was considered homogeneous, which occurred 34 and 55 DAP in 2011 and 2012 respectively. Samples were collected using scissors for clipping each plant at the soil surface; tissue was stored in paper bags for transport b ack to the laboratory where stem and leaf tissues were separated within 24 hours of field collection. S amples were dried at 65 C until constant weight and ground using a tissue grinder (Laboratory Mill Model 4, Arthur Thomas Company, Philadelphia, PA) for dry matter determination. Leaves, stems, and tuber samples were digested using the aluminum block digestion procedure of Gallaher et al. (1975) and nitrogen was quantified by the Kjeldahl method at the Analytical Research Laboratory (Univ. of Fla., Gaines ville) using U.S. EPA method biomass and N accumulation throughout the crop growth stages.
31 Biomass accumulation logistic curves were fitted by adapting the equation pres ented by Witty (1983) as follows: Crop aboveground biomass accumulation = N / [1+ e K (t l ) ] N is maximum crop growth, k is crop growth rate constant, t is time in days, and l is time to half maximum biomass accumulation. At plant maturity when the plant tops bega n to senesce ( which occurred 89 and 92 DAP in 201 1 and 2012 respectively ) killed using the chemical desiccant Rely 280 (Bayer CropScience, Research Triangle Park, NC). The herbicide was applied at a rate of 1535 ml ha 1 tops were not vine killed be cause chipping varieties do not require this practice. The final harvest occurred on 109 and 112 DAP in 2011 and 2012, respectively. Total and marketable yields were determined in 3 6 m 2 of each plot, which was equivalent to 6 m sections replicated six time s During the mec hanical harvest, tubers from the s e section s were separated and labeled according irrigation treatment and potato variety After harvest, tubers were immediately washed and graded into various size classes on the grading line ; t ubers with m echanical injuries, greening, decay or misshapen were separated and quantified. The tubers were graded according to size parameters based on the USDA Standards for Grading of Pota toes (2011) as follows: tuber were deemed of marketable size if they had a d iameter between 48 and 101.6 mm, equivalent to categories A1, A2, and A3 (Table 2 1). The diameter was measured at the largest dimension at any angle from the longitudinal axis regardless of the position of the stem end.
32 A subsample of 20 marketable tubers was randomly selected from each harvested row. Each tuber was sliced in to quarter sections cross sectiona l l y and long itudinal for visual evaluation incidence of brown center, hollow heart, internal heat necrosis, corky ring spot, and any sort of tuber fle sh damage affecting the quality of the tuber. Brown center was further divided into three categories: light, moderate, and heavy based on the damage level of the tuber tissue. Specifi c gravity was measured by weigh ing a set of 20 potato tubers in air and d etermining the ir volume in water. The specific gravity was calculated using the formula: Specific gravity= (tuber mass (g))/ (tuber volume (cm 3 )) After harvest, the experimental area was planted with s orghum s udangrass (var. Sugar Grazer). Before the follo wing potato season the cover crop was incorporated to the soil to add organic matter. The treatments were tested as a two factor analysis of variance ANOVA (SAS Institute Inc. Version 9.2, Cary, NC). The PROC GLIMMIX of SAS was used to determine treatments main and interaction effects for the response variables total and marketable yield, aboveground biomass, N uptake, and internal and external tuber disorders. Irrigation and variety treatments were treated as fixed effects. Season, block, and replications were treated as random effect in the statistical analysis. A n ormality test was performed to check statistical assumptions. When treatment means were significantly different, a Fisher Least Significance test was used to determine where the differences occu rred. Results and Discussion Climate conditions Cumulative rainfall from planting to the harvest day was 116 and 178 mm for the spring of 2011 and 2012, respectively. Calculated ET c in the
33 same period was 380 and 306 mm in 2011 and 2012, respectively. Alt hough precipitation was higher by 62 mm during 2012 season, 38% of rain occurred at the end of the season during tuber bulking, after the potato vine s were desiccated for the fresh market varieties (Figure 2 1 ). Rain after vine kill was 5.3 and 68 mm in th e 2011 and 2012 seasons, respectively. The subsequent cover crop planted after the first potato season was not fertilized to evaluate the ability of the sorghum sudangrass to grow with the residual nutrients left in the field. In the TCAA, vegetable grower s are allowed to fertilize the subsequent cover crop with nitrogen at a rate up to 67 kg ha 1 (60 lbs ac 1 ) Thus, the cover crop in the experimental area showed reduced growth and very low biomass was incorporated to the soil which had a negative impact on wind erosion protection in the following potato season In the beginning of 2012, high windy conditions during the potato sprout development stage (between 33 and 40 DAP) adversely affected the emergence of the plants (Figure 2 2 ) Potato r ows were mec hanically covered with soil several times to protect seed pieces and surface drip tape The wind erosion caused a delay in emergence and a decrease in the amount of established stems, especially under drip treatment, where the drip tape was also displaced from the original location or damaged during labor to reform the potato hills. This damage was more severe in replicates 1 and 2 for the drip treatments that were located at the highest position of the experimental s ite Landscape anchor pins were used alo ng the drip tape to keep it in the row during windy conditions. Irrigation of the experiment started 30 DAP (3 days before th e windy conditions). Th e wind gusts highlighted one of the possible deficiencies of using drip
34 tape in sandy soils in northeast Flo rida at the beginning of the crop season ; where the localized irrigation w ater bulb did not maintain enough moisture in the soil surface and dry soil was easily eroded In addition, early irrigation with drip is risky because it could lead to prolonged per iods of saturation following planting and initial sprout development which could increase seed piece decay as well as poor and erratic tuber emergence (Shock et al., 2006). Seepage plots were also affected but to a lesser extent due to higher soil moistu re in the rows and between rows. The use of cover crops to improve organic matter that can retain soil moisture during the beginning of the season is fundamental to minimize damage by wind erosion in seepage and drip irrigated plots In both experimental y ears, weather in northeast Florida was influenced by the cold phase of ENSO (El N io Southern Oscillation), with the predominant phase categorized as unusual ly cold ocean temperatures in th e Equatorial Pacific (NOAA, 2005 ). La Nia creates warmer than normal temperatures in t he southeast continental U. S In the spring of 2011 and 2012 the Florida peninsula was under abnormally dry conditions, total rainfall amount was lower than normal, a nd temperatures were above normal There was an interaction of year by irrigation treatment and year by variety for tuber yield, biomass accumulation, and aboveground N uptake. Th e interactive effect of year and irrigation was attributed to the different p lanting dates between seasons (17 February 2011 vs. 17 January 2012) and the fact that the drier conditions in 2012 required the use of irrigation (drip and seepage) to supply moisture for optimum crop establishment and development.
35 Biomass accumulation an d N uptake There were no interactions between irrigation and variety treatments for biomass and plant N uptake. Irrigation, year, and DAP influenced biomass and N accumulation significantly (Table 2 2) Due to a significant year effect, biomass and N upta ke were analyzed separately for each season (Figures 2 3 to 2 8 ) Aboveground biomass accumulation was significantly ( p <0.05) higher under SEP treatments for all tested varieties in both years aboveground biomass accumulation was 1.9, 2.0, and 2.5 Mg ha 1 for SUR, SUB, and and 3.1 Mg ha 1 accumulation was 2.0, 2.0, and 2.3 Mg ha 1 for SUR, SUB, and SEP, respectively. The SEP treatment increased aboveground biomass accumulation by 22, 13, and 23% for both drip treatments. During the 2012 growing season, the aboveground biomass accum ulated was 300 kg ha 1 greater on average than in 2011 for all varieties. This was attributed to planting 30 days early in 2012 compared to 2011 season and cooler temperatures at the beginning of the 2012 season The SEP treatment promoted a higher abovegr ound biomass accumulation by 1.20, 0.73, and 1.26 Mg ha 1 Similar trends of aboveground biomass accumulation observed in 201 1 occurred in 2012. Although above ground biomass accumulation was significantly lower for all the tested varieties under the drip treatments, this result did not negatively impact tuber dry matter Figure 2 5 and 2 6 ). Nonetheless tuber biomass reductions
36 under both drip treatments compared to SEP irrigation, which was consistent with the reduced aboveground biomass production Similar results as was have been rep orted where reduced aboveground biomass production has a negligible effect on tuber biomass which is consumption of the potato crop (Smith et al., 2002) Under seepage, t he plant uptakes water beyond their current needs and store it I n the case of drip irrigation, the plant was more efficient with the available water supplied. This was observed varieties where the reduced vegetative growth did not impact tuber dry weight m in the same fashion and tuber dry matter was significantly lower under both drip treatments. Nitrogen uptake was evaluated in aboveground and tuber tissues. In 2011, cumulative aboveground N uptake was not significantly different among irrigation treatme as 62, 61, and 78 kg ha 1 for SUR, SUB, and SEP, respectively. There was veground N uptake. 67, 65, and 75 kg ha 1 for SUR, SUB, and SEP, respectively. Above grou nd N uptake was significantly different for SUB (72.1 kg N ha 1 ) and SEP (103.2 kg N ha 1 ). The SUR (84.1 kg N ha 1 ) treatment was not significantly different from SUB and SEP. In 2012, SEP significantly increased the aboveground N accumulation for by 30 and 23% for SUR and SUB, respectively. The SEP treatment also increased the aboveground N accumulation
37 to SUR and SUB, respectively. Abo veground N accumulation was not different for 1 on average) among irrigation treatments In terms of tuber N accumulation, the only difference found amo ng irrigation treatments in 2011 and 27% higher N accumulation in tubers compared to SUR and SUB trea tments, respectively (Figure 2 7 ). No significant difference was found among irrigation treatments for However in 2012 tuber N a ccumulation was statistically similar between SUR 1 1 ) (Figure 2 8 ). When compared to SUR and SEP irrigation, the SUB treatment reduced N accumulation in tubers followed the same pattern for both year s with significant ly higher accumulation of 32% under SEP treatment than in the drip treatments These results suggest th at there is with surface drip placement. It is important to state that fertigation (application of liquid fertilizer through the drip tape) was not explored for these trials. Granular fertilizer was used for all trea tments to allow a fair comparison between irrigation treatments. Fertigation has proven to be a very effective way to fertilize vegetable crops This technique may also be beneficial to production of potatoes in the TCAA The SUR treatment showed similar r esults in terms of tuber nitrogen accumulation compared to SEP, and offers potential for developing fertigation strategies that can deliver nitrogen close to the root zone minimizing leachate in sandy soils
38 Fresh p otato t uber total and marketable yield P otato harvest occurred 109 and 112 DAP in the 2011 and 2012 season, respectively. The re were interact ion s of year by irrigation, year by variety and irrigation by variety, for total and marketable yield (Table 2 3). The effect of irrigation method was ana lyzed within each of the three varieties and the performance of each variety was evaluated within irrigation treatments In addition, the interaction of year by irrigation and variety treatment was also evaluated (Table 2 6). arketable yield in both years when SUR and SEP irrigation was used. The average marketable yields were 26.6, 19.8, and 28.1 Mg ha 1 under SUR, SUB, and SEP, respectively. For and 16.7 Mg ha 1 for SUR, SUB, and SE 12.8, and 23.5 Mg ha 1 for SUR, SUB, and SEP irrigation treatments, respectively. The SUR and SEP treatments produced similar mark However, SUB with drip tape installed 5 cm below seed drastically reduced tuber marketable yields The reduction was on the order of 28 and 42% for (Table 2 5). both drip irrigation methods tested compared to the SEP treatment. Th e greater yield reduction of may be a result of a low tolerance of this variety to rapid soil moisture fluctuations caused by both drip irrigation treatments. The generally lower yield with SUB for all the tested varieties could indicate poor capillary movement upwards from the emitter to the root zone in sandy soils causing a lack of moisture supp lied to the
39 plant and some level of water stress experienced throughout the season. In chapter 3 the evaluation of root distribution showed that 69 77 and 61% of root length was in the 0 15 cm upper soil layer for SUR, SUB, and SEP respective ly. A larger root growth under SUB irrigation showed greater exploration area to uptake water, which could indicate water stress caused by low soil moisture content during initial growing stages. The low capillarity rise has been stated as the most frequen t shortcoming of subsurface drip (Lamm et al., 2011; Patel and Rajput, 2007). This underperformance of SUB in sandy soils is consistent with previous studies findings. Attaher et al. (2003) evaluated the performance of surface and subsurface drip in potato es and reported significantly lower yield under subsurface compared to surface drip irrigation Subsurface drip tape placed at 0.15 m depth did not maintain optimal levels o f soil moisture content in the upper soil layer due to predominant horizontal water movement from emitters. Potato tuber size distribution There were interactions between irrigation and variety treatments for tuber size classes A1 (4.8 6.4 cm), A2 (6.4 8.3 cm), B (3.8 4.8 cm), and C (1.3 3.8 cm). Irrigation and variety single effects we re important for grading classes A3 (8.3 10.2 cm) and A4 (>10.2 cm). The treatments interaction for grading sizes A1, A2, A3 and undersized (the sum of size classes B, C, and A4) is presented in Table 2 7 1 tuber size A1 for SUR, SUB, 1 when SUR, SUB, and SEP, respectively. Tuber size A1 results was not significantly different when SUR and SEP were used as irrigation method varieties.
40 1 under SUR, SUB, and SEP treatment. variety. SEP produced 34 and 40% increment of A1 tubers when compared to SUR and SUB, respectively. S imilar results w ere obtained treatments. However, SEP produced statistically better results than the drip treatments 7 ). T he S EP treatment yielded higher percentage of tubers under the A3 category than drip treatments for the three varieties tested. This significant reduction of tuber size A3 for all varieties under drip irrigation could be a consequence of the minimal schedule a djustment carried out for drip during the experiment. Although small changes in irrigation events and their duration occurred during the study, a fixed watering schedule was used to supply crop and evaporation losses. The drip irrigation schedule can be fu rther improved to increase the number of tubers with marketable size. It has been stated previously that drip irrigation can improve yield and quality of potatoes. However, significant tuber size reduction occurs if the emitter wetting front does not provi de enough moisture to the root zone throughout the whole season, which demands particular attention (Attaher et al., 2003). Additionally, difference among varieties in response to drip irrigation influence s the number and size of tuber s to be produced. Mor e research is needed to develo p specific crop coefficient (K c ) values and scheduling for drip irrigation that better matches specific variety requirements in sandy soils.
41 Tuber internal quality and physiological disorders Interaction was observed between irrigation and variety treatments for hollow heart, internal heat necrosis, and brown center internal disorders. In 2011, SUR and SUB treatments significantly reduced o and SUB treatments, respectively. No significant difference was found among irrigation 8 ). Although specific causes of hollow heart are not entirely understood, it is known that there is high tendency for in Florida conditions (Hutchinson et al., 2006; Webb et al., 1978). Hollow heart is mainly produced by stressful conditions during growing stages, especially due to subsequent periods of moisture level variations (Bussan, 2007; Christ, 1998). The reduction adequate soil moisture throughout the season whereas seepage failed to supply continuous moisture levels to the area where tuber s actively grow. Lynch et al. (1995) reported bulking stages, which followed by a period of rapid recovery can cause the development of cavities in the internal cell tissue. The SUR and SUB treatments minimized drastic soil moisture fluctuations during the whole season, impacting soil temperature directly, Another important physiological disorder occurring under TCAA growing conditions is internal heat necrosi s (IH N ). The IH N
42 1997). In 2011, SUR and SUB treatments reduced the severity of IH N and 61%, respectively when compa red with the SEP treatment. However, in 2012 SUB produced higher incidence (>70%) of internal heat necrosis compared to the other N ( Hutchinson et al., 2006 ). Our results showed that is possible to significantly reduce the appearance of IHN with SUR drip irrigation compared to SEP. On the other hand, the h igher incidence of IHN for the SUB treatment in the second season can be a result of reduced soil moisture capillarity failing to provide moisture to tubers growing near to the soil surface where high temperatures occurred. The appearance of brown center, which is categorized as light, moderate, or heavy depending on the severity and size of dark tissue in the tuber was also significantly reduced with SUR and SUB treatments. The increased reduction of light and heavy brown center incidence was obtained when SUR was used to irrigate by 90 and 100% on average the occurrence of light and heavy brown center, the incidence of light and heavy brown center was not statistically significant among irrigation treatments for
43 Tuber external quality and specific gravity Th ere was interaction between irrigation and variety treatments for growth cracks external disorder S ingle main effects of irrigation and variety treatment influenced the occurrence of greening, m isshapen and decay external disorders Greening and growth c racks disorders were further discussed in this chapter because of the severe detrimental impact these disorders provoke in f resh market and chipping tubers in the TCAA. Greening is a disorder caused by tuber exposure to abiotic factors. Irrigation treatmen a statistically significant difference in with a 65% reduction of green tissue in 2011. However, in 2012 the amount of green tu tested drip irrigation in silty soils and reported additional benefit of this method due to the gentle localized water application compared to furrow and sprinkler irriga tion (Shock et al., 2006). We did not find difference in the incidence of greening among irrigation The similar incidence of tuber greening disorder among treatments was explained due to the sandy soil in the are a which is easy to erode and tuber exposure occur However, potential exists to set and refine drip irrigation duration so that water is carefully delivered to the root and tuber zone during tuber bulking stage without exposing shallow tubers to the envir onment. Growth cracking in tubers appears when soil moisture is replenished after a prolonged dry period (Jefferies and MacKerron, 1987). Growth crack is a fissure of the tuber tissue that heals but severely affects the cosmetic appea l of the tuber. In 201 1,
44 SUB treatments. However, in the second year there was no significant difference for this 78% the occur rence of growth cracks in 2011 and 2012, respectively compared to the SEP treatment. developing growth cracks under fluctuating environmental conditions. However, the use of drip ir rigation significantly reduced the number of tubers affected with this physiological disorder when compared to seepage. Ano ther external parameter evaluated was the number of rotten tubers. In 2011, tuber irrigated with SEP had fewer incidences of rotten t ubers compared to SUR and SUB treatments. In 2011, drip maintained high moisture content in the soil layers where tuber grew during the bulking stage and caused some tuber s to rot. In 2012, the v olume of water applied with drip was decreased during tuber b ulking stage by 35% (1.49 mm day 1 In 2011, SUR irrigation increased the percentage of rotten tubers by 31 and 27% compared to SUB and SEP, respectively. As mentioned previously, irri gation adjustments were carried out in the second season; however, presented the same level of rot under all irrigation treatments. The low performance of suggest that this variety is not well adapted to the characteristics of drip water delivery method.
45 Finally, there was interaction between treatments for specific gravity. Specific gravity is an important tuber quality attribute related to the processing of the tuber (Yuan et al., 2003). y with the highest that can be further improved with optimal irrigation management in the bulking stage. than seepage, but was not treatment; however it was not statistically different from SUR and SEP treatments. Yuan et al. (2003) found strong negative correlation between spec ific grav ity and amount of water applied indicating that s pecific gravity values increased as water applied decreased
46 Conclusion Irrigating potatoes in the TCAA with surface drip is an alternative to supply plant water needs. Surface drip maintained mark varieties. A closer delivery of water to the root and soil area where the tubers are constantly growing is a viable method to improve internal tuber quality for both varieties mentioned above. Yield loss due to tube r defects caused by seepage can be highly reduced with just watering the ridge area where the tubers are located. The SUR and SUB minimized the incidence of hollow heart, internal heat necrosis and brown center disorders in 2011 and 2012 seasons. Abovegrou nd and nitrogen accumulation by the potato plants was lower for all varieties under drip treatments compared to SEP irrigation. However, this result did not varieties i rrigated with SUR obtained higher yield than those irrigated with SUB. The in sandy soi water requirement should be further studied for this variety. schedule at the end of the season needs adjustment to minimize rotten tubers. Cover crops that increase organic matter content, and help retain moisture early in the season may effectively prevent the effects of wind erosion damage on seed pieces and drip tape.
47 Finally, more research is needed to combine SUR drip tape with fertigation, and automation practices for maximum water and fertilizer use efficiency to potentially be attained
48 Table 2 1. Tuber size classification used to evaluate marketable and non marketable yield after harvest Z Size i dentification code Diameter size range (cm) Classification C 1.27 to 3.81 Non marketable B 3.81 to 4.78 Non marketable A1 4.78 to 6.35 Marketable A2 6.35 to 8.26 Marketable A3 8.26 to 10.16 Marketable A4 > 10.16 Non marketable Z U.S. No. 1 are tube rs not less than 4.78 cm in diameter.
49 Table 2 2 Analysis of variance summary for aboveground biomass accumulation aboveground and tuber N uptake and irrigation water use efficiency (IWUE) as affected by season, irrigation, variety treatment, and trea tments interactions. Main effect D.F. Biomass accumulation N uptake IWUE above ground tuber Irrigation (I) 2 *** *** ** *** Variety (V) 2 ns ** *** *** Year (Y) 1 *** *** ns ns I x V 4 ns ns *** I x Y 2 ** ** ns *** V x Y 2 ns ns ns I x V x Y 4 ns ns ns ns Significant at p <0.05; ** significant at p <0.01; *** significant at p < 0.0001. ns: not significant; D.F.: degrees of freedom
50 Table 2 3 A nalysis of variance summary for tuber total and marketable yield, tuber grades, internal and e xternal disorders, and specific gravity, as affected by season, irrigation, variety treatment, and treatments interactions. Main effect D.F. Yield Size distribution Internal Quality External Quality S pecific G ravity TOT MKT A1 Z A2 A3 A4 HH Y IHN BCL BCH GT GC RT MS Replication 3 ** ** *** ns ns ns ns ** ns ** ns ns Irrigation (I) 2 *** *** *** ** *** ** *** ** ns *** ** *** *** Variety (V) 2 *** *** *** *** ** ** *** ** *** *** *** ns *** Year (Y) 1 ns ns ns ns n s ns ns ns ns ns *** *** ns I x V 4 ** ** ns ns ** ** ** ns *** ns ns ns I x Y 2 ** ns ns ns ns ns ns ns *** ** ns *** V x Y 2 ** ** ** ** ns ns ns ns ns ns *** ns ns *** I x V x Y 4 ns ns ns ns ns ns ns ns ns ns ns ** ns ns Significant at p <0.05; ** significant at p <0.01; *** significant at p < 0.0001. ns: not significant; D.F.: degrees of freedom Z Diameter size of classes: A1 (4. 8 6.4 cm), A2 (6.4 8.3 cm), A3 (8.3 10.2 cm) and A4 (>10.2 cm). Y HH: hollow he art, IHN: internal heat necrosis, BCL: brown center light, BCH: brown center heavy, GT: greening, GC: growth cracks, RT: rotten, MS: misshapen.
51 Table 2 4. Effect of surface drip subsurface drip and seepage irrigation method on aboveground biomass acc potato varieties cultivated in Hastings, FL dur ing 2011 and 2012 spring season Z 2011 2012 Variety treatments Irrigation treatment Aboveground biomass (Mg ha 1 ) Surface 1.9 b 2.6 b 2.0 a 4.4 b 3.7 a 3.3 b Subsurface 2.0 ab 2.2 b 2.0 a 4.3 b 2.8 b 3.2 b Seepage 2.5 a 3.1 a 2.3 a 5.5 a 4.0 a 4.5 a Z Values within columns followed by the same lower case letter indicate that means are not significantly different at p between potato varieties within the same irrigation treatment.
52 Table 2 5 potato variet ies as function of irrigation method (seepage, surface drip and subsurface drip irrigation) during 2011 and 2012 spring season Z 2011 2012 Irrigation treatment Variety treatment Tot al Yield (Mg ha 1 ) Surface 33.3 a 24.2 a 20.7 b 30.7 b 23.1 a 19.6 b Subsurface 25 .6 b 16.3 b 24.8 b 23.5 c 10.9 b 14.1 c Seepage 30.8 a 23.3 a 36.5 a 37.6 a 23.3 a 28.1 a Marketable Yield (Mg ha 1 ) Surface 26.3 a 16.1 a 12.7 b 26.9 b 18.7 a 14 .1 b Subsurface 19.9 b 12.0 a 16.4 b 19.7 c 7.8 b 9.2 c Seepage 23.5 a b 15.8 a 26.1 a 32.8 a 17.6 a 20.9 a Z Values within columns followed by the same lower case letter indicate that means are not significantly different at p <0.05 significance level a among irrigation treatments within the same potato variety
53 Table 2 6 Two year averaged marketable size (A1, A2, and A3) and undersized class by irrigation treatment Irrigation treatment Variety treatments Size class A1 (Mg ha 1 ) S urface 15.32 a Z 15.51 a 9.95 b Subsurface 10.58 b 7.70 c 9.04 b Seepage 15.44 a 11.64 b 15.09 a Size class A2 (Mg ha 1 ) S urface 7.26 a 1.81 b 2.49 b Subsurface 5.26 a 1.87 b 2.82 b Seepage 6.60 a 3.34 a 5.04 a Size class A3 (Mg ha 1 ) S urface 4.06 b 0.09 b 0.99 b Subsurface 3.95 b 0.35 b 0.93 b Seepage 6.08 a 1.74 a 3.39 a Undersized Y (Mg ha 1 ) S urface 1.94 b 2. 50 a 1.55 b Subsurface 2.04 b 1.59 b 1.74 b Seepage 2.68 a 1.85 b 2.40 a Z Values within columns followed by the same lowercase letter indicate that means are not significantly different at p betwee n irrigation treatment within the same potato variety. Y Undersized is the sum of size classes C, B, and A4.
54 Table 2 7 Tuber internal disorders a ffected by irrigation treatment during 2011 and 2012 spring seaso ns. 2011 2012 Irrigation treatments Variety treatments L a S oda L a S oda Hollow Heart Z (kg ha 1 ) S urface 30.6 b 0.0 a 0.0 a 152.9 b 0.0 a 30.6 a Subsurface 30.6 b 61.2 a 30.6 a 428 .1 b 0.0 a 30.6 a Seepage 764.4 a 0.0 a 122.3 a 1528.8 a 0.0 a 122.3 a Internal Heat Necrosis Z (kg ha 1 ) S urface 244.6 b 122.3 a 0.0 a 794.9 b 61.2 a 30.6 a Subsurface 1009.0 b 0.0 a 30.6 a 2598.9 a 91 .7 a 30.6 a Seepage 2568.4 a 122.3 a 0.0 a 1 498.2 b 30.6 a 183.5 a Brown Center Light Z (kg ha 1 ) S urface 122.3 b 91.7 a 0.0 b 0.0 b 30.6 a 0.0 b Subsurface 611.5 a 61.2 a 152.9 b 244.6 ab 0.0 a 122.3 b Seepage 733.8 a 152.9 a 580.9 a 458.6 a 183 .5 a 733.8 a Brown Center Heavy Z (kg ha 1 ) S urface 0.0 b 0.0 a 0.0 a 0.0 b 0.0 a 0.0 b Subsurface 0.0 b 0.0 a 0.0 a 30.6 b 0.0 a 61.2 ab Seepage 825.6 a 30.6 a 122.3 a 214.0 a 30.6 a 214.0 a Z Values within columns followed by the same lowercase letter indicate that means are not significantly different at p between irrigation treatment within the same potato variety and season.
55 Table 2 8 Tuber external quality and specific gravity affected by irrigation treatment during 2011 and 2012 spring season. 2011 2012 Irrigation treatments Variety treatments Greening Z (kg ha 1 ) Surface 790.1 a 197.5 a 524.7 b 1548.3 a 480.0 a 1413.2 a Subsurface 814.5 a 201.2 a 1669.4 a 1490.2 a 439.7 a 1515.3 a Seepage 608.5 a 39.14 a 1259.7 a 1271.9 a 864.7 a 1702.4 a Growth Cracks Z (kg ha 1 ) Sur face 563.2 ab 667.8 b 152.3 b 181.0 a 20.2 b 237.3 b Subsurface 291.1 b 467.2 b 468.4 b 291.7 a 274.6 b 415.2 b Seepage 945.4 a 3371.8 a 1759.3 a 354.1 a 941.1 a 1460.3 a Rotten Z (kg ha 1 ) Surface 3552.2 a 4954.4 a 5596.5 a 81.3 a 779.1 a 2204.5 a Subsurface 2183.7 a 1968.4 b 3880.6 b 204.9 a 636.6 a 1550.8 a Seepage 2520.6 a 1962.3 b 4059.8 b 302.1 a 1015 a 1622.9 a Misshapen Z (kg ha 1 ) Surface 77.7 a 303.9 b 22.6 b 21.4 b 23.8 b 134.5 b Subsurface 100.9 a 151.7 b 115 ab 25.1 b 130.9 b 236.7 ab Seepage 343.1 a 665.3 a 415.2 a 431. 1 a 636.6 a 565.0 a Specific Gravity Z (g cm 3 ) Surface 1.081 a 1.056 a 1.056 a 1.079 a 1.049 a 1.055 a Subsurface 1.077 b 1.056 a 1.058 a 1.080 a 1.046 a 1.052 b Seepage 1.071 c 1.050 b 1.055 a 1.08 0 a 1.046 a 1.055 a Z Values within columns followed by the same lowercase letter indicate that means are not significantly different at p between irrigation treatment within the same potato variety a nd season.
56 Figure 2 1 Rainfall events and cumulative rain for 2011 and 2012 potato growing seasons in Hastings, Florida
57 Figure 2 2 Minimum, average and maximum wind speed from planting to 40 days after planting (DAP). Sprout emergence generall y occurs at 28 30 DAP
58 Figure 2 3 Above ground biomass accumulation of potato varieties affected by irrigation treatment in 2011 season. Irrigation treatments were analyzed within each variety and presented as foll ows: Atlantic (A C); Fabula (D F ); Red LaSoda (G I). Nonlinear regression and coefficient of determination (R 2 ) is displayed for each treatment
59 Figure 2 4 Above ground biomass accumulation of potato varieties affected by irrigation treatment in 2012 season. Irrigation treatments wer e analyzed within each variety and presented as foll ows: Atlantic (A C); Fabula (D F ); Red LaSoda (G I). Nonlinear regression and coefficient of determination (R 2 ) is displayed for each treatment
60 Figure 2 5 Tuber d cultivated in Hastings, FL during spring 2011affected by surface (SUR), subsurface (SUB), and seepage (SEP) irrigation treatments Bars with same lowercase letter are not significantly different at p <0.05 significance l evel Figure 2 6 Tuber d cultivated in Hastings, FL during spring 201 2 affected by surface (SUR), subsurface (SUB), and seepage (SEP) irrigation treatmen ts Bars with same lowercase letter are not significantly different at p <0.05 significance level
61 Figure 2 7 Above ground (lines) and tuber (bars) nitrogen uptake affec ted by surface (SUR), subsurface (SUB), and seepage (SEP) irrigation treatment in 2011 season.
62 Figure 2 8 Above ground (lines) and tuber (bars) nitrogen uptake affected by surface (SUR), subsurface (S UB), and seepage (SEP) irrigation treatment in 2012 season
63 CHAPTER 3 CHARACTERIZATION OF IRRIGATION AND WATER TABLE FLUCTUATION UNDER DRIP AND SEEPAGE SYSTEMS FOR POTATO PRODUCTION IN NORTHEAST FLORIDA Introduction Florida is one of the few states in U.S. that produces potato ( Solanum tuberosum L ) in spring (Hochmuth et al., 2001). Th e potato production from Florida has great demand in the market and generally obtain higher sales prices than fall potatoes (ERS, 2012). Potato production covered roughly 15, 000 hectares in Florida, with a crop value of $ 144 million in 2011. Approximately 9,500 hectares of potatoes are grown in St. Johns, Putnam, and Flagler counties (Tri County Agricultural Area: TCAA) in northeast Florida (USDA, 2012). Potatoes are the majo r irrigated row crop in the TCAA with an average irrigation water requirement calculated to be 4 83 mm year 1 (1 9 inches year 1 ) (Singleton, 1996) Seepage is the most common water delivery method for potato production in this area of northeast Florida beca use it is low cost and effective in flat locations where natural shallow water tables can readily be raised (Haman et al 1989). Potato farms irrigated with seepage irrigation maintains the water table level just below the root zone by either adding or su btracting water (Smajstrla et al., 2000). The low water holding capacity in sandy soils requires constant water supply to avo id plant water stress (Dukes and Scholberg, 2005). Several factors such as increased demand and c ompetition for water resources, ir regular rainfall patterns, saltwater intrusion in the Floridan aquifer, and increased costs of production makes imperative to look for other alternatives that provide growers more
64 options to irrigate their crops and remain competitive (Badr et al., 2010; P ayero et al., 2008; Spechler, 1994). Previous studies have reported a straight correlation between saturated soil conditions created by seepage and its negative effects on root active uptake I rrigation management needs to be sound from environmental and economic perspectives primarily because potato is an expensive crop to produce, and secondly it is less tolerant to water stress than many other crops (Munoz Arboleda et al., 2006; Patterson, 2010; Shock et al., 2007). As stated by the South Florida Water Management District, water is the main limiting factor for crop production in Florida thus, implementing efficient water delivery systems is important to optimize the use of the available water supplies and improve crop yield potential (Badr et al., 2010; Pitts and Clark, 1991; SFWMD, 1986). Irrigation has to be precisely scheduled in Florida due to the irregular rainfall patterns during the growing season. An easily controlled irrigation method provides the benefit of adequate soil moisture that can be re adily extracted by plants and in case of heavy rain there is storage capacity in the soil for extra water (Onder et al., 2005). Irrigation meth od, scheduling and amount applied are the most important factor s to consider when delivering water to the crop ( Shock, 2010). It is possible to increase production by developing well scheduled irrigation programs throughout the growing season (Shock et al., 2003; Yuan et al., 2003). However, this is difficult to achieve with the seepage system due to its low water d istribution uniformity in the field.
65 R educ ing off site movement of fertilizer and keep nutrients close to the active root uptake zone is a challenge potato farmers c ould overcome with more efficient irrigation methods to grow potatoes (Alva, 2008 a ). I rriga tion technologies such as d rip irrigation increases the control of water use and offers many advantages for growers; some of them are 1) reduction of evaporation and increase of plant transpiration; 2) reduction of weed population: 3) when well managed, ex cessive water drainage is unlikely to occur and therefore nutrients are retained in the root zone longer (Burt, 1998; Goldberg et al., 1976; Lamm et al., 2011). Moreover, drip also offers a n opportunity to maintain ideal soil moisture levels where plant is not stressed. In general, d rip adoption raise s concerns among farmers about the profitability of investing in new irrigation methods with the uncertainty of economic returns. However, drip could be a n alternative for farmers to conserve water, reduce pump ing energy and the amount of fertilizer used because t he d rip tape used for irrigation c ould also be used to inject fertilizers. Although d rip irrigation has the potential to deliver water uniformly, it is necessary to thoroughly evaluate this technology in sandy soils conditions Because potato is grown in hilled rows, there is a micro topographic influence o ver the water distribution uniformity This difficulty can possibly be overcome d ue to the localized water application of emitters (Lamm et al., 2011 ; Shock et al., 2007). Installation depth of drip lateral is one of the most evaluated factors to produce drip irrigated potatoes. The drip tape depth varies among cultural practices and soil physical properties (Burt, 1998). For instance, Patel and Rajput (2007) studied the
66 effects of five different lateral installation depths (0, 5, 10, 15, and 20 cm) on potato yield grown in sandy loam soil. They found that drip lateral installation depth significantly affected yield, and reported maximum yield when drip tape was placed at 10 cm soil depth Additionally, the use of drip irrigation for vegetable crop production has been reported to diminish NO 3 losses to the groundwater, increase water and nitrogen fertilizer use efficiency, and when properly managed drip irrigation ha s the potential to greater water savings (Lamm et al., 2011; Thompson et al., 2003). Waddell et al. (2000) found that frequent application of small volume of water using drip irrigation had positive results in maintaining nutrients in a reacha ble distance to the crop root zone. Although groundwater has been an inexpensive and accessible source to grow potatoes in the TCAA, the expected declines in water supply combined with scarce rain to replenish aquifers, higher evaporative demand, higher e nergy and fertilizer costs makes imperative the need to adopt more efficient irrigation methods to produce crops (Pair et al., 1983). Furthermore, in order to produce potatoes, water conservation practices are crucial for farmers in the TCAA. Drip irrigati on may be an efficient and sustainable strategy that can optimize potato production in sandy soils and greatly enhance resources use efficiency (Ahmadi, 2010) Northeastern Florida salinity issues High soil salinity severely reduces potato yield (Levy and Veilleux, 2007). Saline water restricts root water uptake, reduce water infiltration rate, and have negative effects on soil aeration (Ayers and Westcot, 1985). Production of commodity crops heavily rely on groundwater supply in the entire state of Florid a. Aquifers are used as sources of freshwater to meet the agricultural
67 demands for irrigation (Basdurak et al., 2007). The Upper Floridan aquifer is the principal source of water for potato production in northeast Florida. Overpumping of the aquifer has ca used water level decline and upconing of saline water from deeper zones to move into the fresh water system, increasing chloride concentration in wells, hence affecting water suitability for agricultural and domestic purposes (Spechler, 1994; USGS, 2008). Crop establishment and growth can be severely impacted when saline water is used because salt is accumulated in the wetting front impairing the plant ability to uptake nutrients (Hanson et al., 1997). The groundwater withdrawals in St. Johns county increas ed 1.22 million gallons per day fr om 1965 to 1988. Saint Johns along with Putnam and Flager counties (TCAA) have been identified as one of the principal areas of saltwater intrusion in northeast Florida. It is urgent to determine the optimum irrigation man agement to meet potato water requirements without overpumping irrigation wells or wasting water and nutrients. Efficient irrigation methods, such as drip, aims to produce more yield with less water. Additionally, r eduction in the volume of water used to gr ow the potato crop c ould minimize salt water intrusion and facilitate natural replenishment of fresh water resources. Evaluation of potato response to drip irrigation in sandy soils is paramount to provide scientifically based information to growers. Drip tape is commonly placed 3 to 6 cm below the soil surface in Florida vegetable production. Deeper tape installation may not provide moisture to shallow root crops like potato, due to the limited wetting from a point source (Clark and Stanley, 1992; Clark et al., 1993).
68 Thus, the objectives of this study were to 1) evaluate the distribution uniformity of two drip tape placement 5 cm above and below potato seed piece and its effects on root distribution and fresh tuber yield 2) analyze the water table fluctuat ions as influenced by drip and seepage irrigation systems, and 3) determine an optimum depth of placement for drip tape in potato hills on Florida sandy soils. It was hypothesized that drip irrigation can reduce crop water requirements, improve irrigation water use efficiency (IWUE), and reduce water drainage and runoff from the crop area. Materials and Methods Experimental Design and Layout Field experiments were carried out at the University of Florida Partnership for Water, Agriculture, & Community Sus tainability facility in classified as sandy, siliceous, hyperthermic Arenic Ochraqualf and belongs to the Ellzey series (USDA, 1981). Prior to the start of the first season the area was laser leveled and raised rows (78 m long, 0.35 m height) formed. Afterwards, the field was fumigated (60% chloropicrin, 39% 1 3 dichloropropene) at a rate of 103 L ha 1 Potato seed pieces (57 85 g ted on February 17, 2011 and January 17, 2012. Total g ranular fertilizer banded and incorpora ted into the soil was at rates of 225 1 12 3 0 8 kg ha 1 (200 100 275 lbs ac 1 ) of N, P 2 O 5 and K 2 O, respectively. N itrogen applications w ere split at three times: at planting, at emergence, and when plants were between 15 and 20 cm tall. No fertilizer was supplied with drip irrigation. The potato seed piece was used as point of reference for the install ation depth of the drip tape Subsurface drip tape (SUB) was place d 5 cm below the seed piece before planting, and surface drip tape (SUR) was installed after plant ing 5 cm above the seed
69 piece. The drip system operated at an average pressure of 55 kPa. Pressure was regulated and kept constant at 138 kPa on the inlet of each drip block treatment, which accounted for head losses to the furthest plots. In the drip irrigated treatments, a single pressure compensated drip line (RO DRIP, John Deere Water, Moline, IL, USA) flowrate of 1 L h 1 at 55 kPa for each emitter, a 20 c m emitter spacing, 16 mm inner diameter, and 8 mm thickness was used to deliver irrigation water (Figure 3 1 ). Irrigation treatments were established and replicated four times on 2.31 ha (5.7 ac) field. Plots were randomized within the typical farm design of sixteen, 1 m wide rows per bed. Plots were separated by a 37 m (120 ft) wide buffer zone. This large zone was necessary to eliminate the influence of the high water table in seepage plots on the drip plots (Figure 3 2) Water furrows were spaced 18 m at the border of each bed and used for seepage irrigation and to drain excess water. Field row lengths were approximately 78 m. Field operations followed typical grower practices in the region. Potatoes were sprayed during the season to control foliar diseas es and insects. Temperature, relative humidity, solar radiation, and wind speed data was obtained from a weather station located in the experimental site. Daily reference evapotranspiration (ETo) was retrieved from the Florida Automated Weather Network (FA WN; www.fawn.ifas.ufl.edu). Crop evapotranspiration (ETc) was calculated from the product of crop coefficient (Kc) and evapotranspiration of reference for each specific growth stage (Doorenbos and Pruitt, 1975).
70 Soil bulk density was evaluated at the end o f 2012 season. It was measured in undisturbed samples of known volume. Average bulk density for the 0 15 cm layer was 1.30, 1.45, and 1.31 g cm 3 for SUR, SUB, and SEP, respectively. The average bulk density for the 15 30 cm layer was 1.52, 1.57, and 1.57 g cm 3 for SUR, SUB, and SEP respectively. Similar bulk density values were found at the subsequent deeper layers (up to 60 cm depth). Bulk density was slightly higher for SEP at 45 60 cm deep when compared to SUR and SUB D aily irrigation events were used for drip and seepage treatments. The s eepage schedule was similar to farmer practices in the area, which let spigots open and water run through lateral water furrows to raise the water table to a desired level and until soil surface appearance is wet. Dri p irrigation events were 15 minutes, running three cycles per day. In 2011, irrigation schedule remained constant during 36 days and was increased to 4 cycles per day until the last irrigation day because of plant water stress symptoms increased soil surf ace temperature, and visual indication that emitter water bulb was not replenish ing the evaporation losses. In 2012, drip schedule started with the previous 4 daily cycles with a depth of 5 mm, equivalent to 49,991 L ha 1 However, fluctuating climate fact ors and relatively dryer conditions made it necessary to increase the events from 4 to 6 cycles per day. This upgrade was done 28 days after irrigation started and remained this way for 13 days. On March 28 th (71 DAP) the duration of each event was increas ed from 15 to 20 minutes to increase the size of the water bulb in these sandy soils to provide enough moisture to the root system. On April 4th (78 DAP), the duration of irrigation events was
71 reduced to an initial 15 minutes and continued like that until the last irrigation day on April 19th (93 DAP, right after vine killing). In the spring of 2011, a system consisting of 5 cm T shaped filter s (Amiad filtration systems, Oxnard, Calif.), pressure gauges, a flowmeter, a single station controller with attache d solenoid (SVC 100, Hunter Industries, San Marcos, Calif.) and pressure regulator (PRFX 20, Senninger Irrigation Inc. Clermont, FL) were installed at the inlet of each drip irrigated bed. Water volume applied was manually recorded and quantified from posi tive displacement flowmeters (DLJ 200 Multi Jet Water Meter, Daniel L. Jerman Co., Hackensack, NJ) at the inlet of each drip and seepage irrigated block Irrigation events and duration w ere recorded from the treatments beginning at plant emergence until ir rigation was suspended before vine kill. Vine kill is generally scheduled 20 days prior to harvest, and it is a practice performed to desiccate the aerial part of the plant to induce skin set and larger carbohydrate concentration in the tubers of fresh mar ket varieties Irrigation water use efficiency (IWUE) was calculated as follows: IWUE= (MKT)/ (IRRI) Where MKT is marketable tuber yield (kg ha 1 ) and IRRI is seasonal water applied (m 3 ha 1 ) for each irrigation treatment and expressed as kg m 3 Monitorin g soil water content Volumetric soil moisture content was recorded every 15 minutes throughout the entire season using sixty time domain reflectometry (TDR) sensors (CS615 and CS650, Soil Water Content Reflectometer, Campbell Scientific Inc. Logan, UT, US A). Thirty sensors were installed in the seepage irrigated plots and thirty sensors in drip irrigated plots. Three soil profiles containing 10 sensors
72 each were designed to monitor soil moisture at different potato rows in the plots Sensors were located 5 cm above drip tape for SUR and SUB treatments. The sensors were buried in cross sectional pattern from the irrigation furrow and connected to a datalogger (CR10X and CR1000 datalogger, Campbell Scientific, Logan, UT) via channel relay multiplexers (AM16/3 2B multiplexer, Campbell Scientific, Logan, UT). Data was downloaded weekly throughout the season. They were buried at different depths with 15 cm increments and the lowest probe installed at 75 cm distributed across the potato hill (Figure 3 3). In additi on to these sensors, a handheld TDR (FieldScout 300, Spectrum Technologies, Aurora, IL) coupled with 20 cm rods was used to measure weekly soil moisture content in the experimental area. Water Table Monitoring Observation wells containing level pressure s ensors (piezometers) (PDCR 1830 Series, General Electric, CT, USA) were randomly installed in each experimental block to measure water table depths and observe the effects of rainfall and each irrigation treatment on the groundwater level throughout both p otato seasons. Each piezometer was installed in the field using global positioning system (GPS) receiver (60 CSx handheld GPS Navigator, Garmin International, Inc. Kansas City, KS, USA). Measurements of cable depth from soil surface to water table surface were taken during the installation in order to obtain an accurate reading of the water level fluctuations. Probes were coupled with dataloggers that operated wirelessly to upload the data every fifteen minutes to a compute r receiver located at the farm mai n office and through a special software making it available to a website. Devices were calibrated at the beginning of each season as well as operating system updated and regular maintenance practices were performed to keep the devices operating
73 appropriate ly. Piezometers were removed from the field periodically for a short amount of time when tillage practices were needed. Root length density distribution Root sampling of the variety Atlantic was carried out 86 days after planting in the 2012 season in ord er to quantify the length density (RLD) of the root system affected by three different irrigation delivery systems. rooting depth (Stalham and Allen, 2001). Samples were taken at two different surface positions on a transversal line across the potato hill: (A) a djacent to the plant main stem ; and 0. 15 m (B) away from the plant Soil cores were sampled at 0.15 m deeper increments (0 0.15, 0.15 0.30, 0.3 0.45, 0.45 0.6, and 0.6 0.75) until 0.75 m from the soil surface was reached (Figure 3 4 ) A soil auger (0.1 m diameter and 0.17 m height) was used to collect samples of the root profile of a representative plant randomly chosen in each plot. Samples were placed in plastic b ags labeled with irrigation treatment and depth to which they were extracted. Plastic bags were stored in the Horticultural Sciences department (Univ. of Fla. Gainesville) cooler room at 4 C until further cleaning. A spray nozzle (Metal Body 584, Gilmour USA, Peoria, IL) was used at constant low pressure to separate the soil and organic matter particles from the roots. Special attention was paid to weeds in order to minimize the effect of them in the sample. Roots were collected on a round sieve with 1.79 mm mesh screen (Model No. U, Seedburo Company, Chicago, IL). Once the soil and debris were removed, the material left in the mesh was washed into Pyrex glass dishes with enough water to move the material around. Roots were hand picked using tweezers and pl aced in petri dishes that were stored in a freezer waiting to be scanned.
74 The commercial software package WinRHIZO 8.0 (Regent Instruments Inc., Quebec, Canada) digital scanner was used to evaluate the length and volume of roots in the different soil dept hs sampled. Plastic trays (25 cm x 15 cm) were carefully washed and dried in order to avoid scratches that could be misread by the root scanner. Results and Discussion Irrigation started after potato sprouts were fully emerged, which occurred 26 and 30 day s after planting in 2011 and 2012 seasons, respectively. The length of irrigation period was 6 7 and 6 4 days in 2011 and 2012, respectively. It is a common practice among growers in the TCAA to start irrigation on an average of 25 days after planting. The m ain pump was shut off when a rainfall was expected. The calculated ET c from planting to harvest date was 380 and 306 mm for 2011 and 2012 respectively The average daily irrigation volume applied using drip was 3.51 mm, while seepage applied 6.24 mm to ma intain the high water table in 2011. In 2012 season, it was applied an average rate of 2.73 mm day 1 when using drip and 22.04 mm day 1 for seepage treatment (Figure 3 6) The difference in the volume of water applied for seepage irrigation between seasons was a combined result of drier conditions at the beginning of the 2012 growing season, which required a large volume of water to raise the water table and keeping the field wetter a longer period at the end of the season Seepage was managed based on the soil appearance a s the main indicator of adequate moisture for the crop, which is a n ina ccurate procedure for determining irrigation scheduling which c an be improved Figure 3 7 shows the soil moisture distribution in the same seepage irrigated plot at d ifferent growth stages for 2011 and 2012 growing season. In 2012, more water was applied with seepage irrigation during the vegetative growth and tuber initiation stages maintaining the water table at a shallow depth. Also,
75 erratic and heavier rain storms occurred in 2012, which also impacted the water table level. The rain gauge in the research site recorded 54.1 mm of rainfall between April 21 and 22, 2012 (36 mm in 2 hours). The water retention structures were lowered to drain excess water and due to the low irrigation uniformity of seepage a large volume of water is needed to raise the water table up to a desired level. Th e s e type s of extreme rainfall events hig hlight ed the lack of accurate control of the water table with seepage irrigation. T h is system keeps the water table close to soil surface thus increas ing the risk of run off and nutrient leaching during periods of high precipitation Root length density distribution The root length density (RLD) is often closely related to water and nutrient upta ke (Lesczynski and Tanner, 1976). The RLD in this study was not significantly different among irrigation treatments Depth of sampling was the only factor that significantly influenced RLD. Root density decreased rapidly at deeper soil layers, which is con sistent with results found in other studies for potato ( Munoz Arboleda et al., 2006; Stalham and Allen, 200 1 ) and tomato (Zotarelli et al., 2009). About 61 77% RLD was found in the 0 15 cm soil layer. The RLD decrease d in subsequent soil layers as follows: 16 33% in the 15 30 cm layer; 4 8% present in the 30 45 cm layer ; and <2% RLD in the 45 60 and 60 75 cm soil depth s (Figure 3 8 ). Although difference s among irrigation treatments or interactions between effects w ere not found, it is important to highlight that the largest RLD found was 2.26 cm cm 3 in the 0 documented (Joyce et al., 1979; Mackerron and Peng, 1990; Tourneux et al., 2003). Researchers mention the influenc
76 closer to the subsurface water front. We did not measure root development across physiological stages, but we believe that larger roots present in 0 15 cm soil layer could be an effect of low moisture in this layer and caused some level of water stress. Several studies agreed that regardless of genotype differences, commercially produced potato typically have root system s con centrated in t he upper 30 cm of the soil (Ahmadi et al., 2011; Lesczynski and Tanner, 1976; Shock et al., 2006). Our findings RLD values were similar under SUR and SEP treatments in the 0 15 cm upper layer (1.90 cm cm 3 on average). Irrigation Water Use Efficiency (IWUE) In both seasons IWUE values were higher for drip treatments. The treatment ranking was as follows: SUR>SUB>SEP for all tested potato varieties In 2011, the obtained IWUE values were 5, 6, and 4 kg m 3 for SUR, SUB, and SEP treatments. In 2012, the IWUE values were 10, 6, and 2 kg m 3 for SUR, SUB, and SEP respectively The SEP treatment had the lowest IWUE values due to the large volume of water applied to control the water tabl e level and produce marketable yield In contrast, drip treatment consistently achieved higher IWUE levels due to similar marketable yield to those of SEP; however, it was produced with less volume of water. The position of the wetting front is commonly used to describe the soil moisture distr ibution under different conditions (Badr et al., 2010). When using SUB the soil surface remained dried due to the low capillarity rise on sandy soils, but lower soil layers between 15 and 40 cm had volumetric water content higher than 15%, which is consid ered optimum in sandy soil conditions. The SUR treatment also demonstrated an ability to maintain moisture content s higher than 12% at depths between 0 20 cm ( Figure 3 10 ).
77 In order to make a fair comparison among irrigation systems, an entire area approac h was chosen to compare the irrigatio n methods used in this research Waddell et al. (1999) compared sprinkler and drip methods and used a similar approach for drip calculations. They converted the volume of water applied by drip to a depth using the entir e plot area, although half of the area was irrigated. Thus, following th is approach our drip treatments delivered 2.73 and 19.31 mm less water per day than seepage in 2011 and 2012, respectively. This was translated into irrigation water savings of 48% 88 % when using drip irrigation. Soil moisture dynamics One of our hypotheses was that drip irrigation can supply water to the potato plant without relying on water resources from the water table On average, t he water table was maintained 27 and 14 cm lower on drip irrigated plots than on seepage plots in 2011 and 2012, respectively ; with t he average water table dept h for seepage at 55.6 and 69.3 cm from the soil surface i n 2011 and 2012, respectively (Figure 3 11 and 3 1 2 ). However, there were large ranges in these water table levels, with fluctuations between 19 and 65 cm in 2011 and 36 to 91 cm in 2012 In both seasons rainfall had a significant response bringing the water table up during certain times of the season Rainfall contribution to the water tabl e depends on the water table level prior to precipitation outlet board management, and the row location in the field. The closer to the water furrow, the higher the impact of rainfall will be, with minimum effect in the center of the bed (rows 7 10). On a verage 1 mm of precipitation will bring the water table 4 cm towards the soil surface The r ain pattern was different in 2011 compared to 2012. In 2011, 85% of the total 116 mm occurred during the initial 55 days of plant development and growth. In
78 2012, although it rained 62 mm more, 68 mm occurred in the final stages of plant maturation, after the vines were killed. The second year of this experiment (2012) was the warmest recorded temperature for the United States (since 1895), displacing 1998 from this position. As stated by Pitts and Clark (1991), seepage irrigation is completely dependent on the depth of the water table, so dry, hot years, severely reduce seepage efficiency and increases cost of pumping due to the water level decline in wells (Vergara 1994). F igure 3 11 and 3 12 present soil moisture data and water table level at four soil layers for each irrigation treatment in three key growth stages during 2011 and 2012. In the SUR treatment the 0 10 cm sensor showed the highest moisture response a nd high water content was kept at this depth throughout the growing season. Sensor s at deeper layers showed minimum response to the drip treatments, which is a good indicator that water delivered was kept in the intended soil depth and deep percolation was greatly minimized. The depth placement of drip tape for the SUB treatment produced dry soil conditions in upper layer (0 10 cm) and kept high soil moisture content in the 10 20 cm layer. The TDR probes measured soil moisture content fluctuations related t o irrigation events determined by the drip tape depth placement. The targeted layer with SUR and SUB were the layers presenting the moisture content variations during irrigation events. L arge soil moisture fluctuations w ere observed throughout the season in both years in the seepage irrigation treatments Soil water distribution The s patial distribution of soil moisture in the soil profile varied according to the irrigation method used. For SUR and SUB volumetric soil moisture content values were between 12% and 32% between the 0 and 45 cm soil
79 depth layer (Figure 3 10 ). Vertical movement from the emitter was more pronounced than lateral movement in both drip treatments. Capillar y rise was more noticeable in the SUR treatment than SUB. The highest moisture content for SUB was attained at the 35 cm depth while SUR had relative high moisture values at the 20 cm depth and extending to the 45 cm de pth The availability of water in the upper layers for the SUR treatment may be the reason why this drip tape place ment performed better than SUB in terms of marketable yield for a ll the potato varieties (Table 3 2). On the other hand, the seepage treatment had relative low moisture values of approximately 8% in the top layer between the 0 and 10 cm depth s and excessiv ely high values ( >32% ) at the 30 cm depth and below which is consistent with raising the water table level up to the root zone. In both years, the effect of the perched water table to the volumetric water content (VWC) varied primarily as function of the depth at which the soil moisture content was measured, and secondly as function of the row distance to the water furrow (Figure 3 13 ) Minimum water table influence was measured in the 0 15 cm layer. It appeared that the 15 30 cm layer behaves as interface as it presented the most dynamic interaction between the depth of the water table and the soil content. As the water table raised, the VWC at 30 cm increased until constant moisture content was reached, suggesting that the water table can be lower withou t impacting the moisture content at 30 cm. The soil was permanently saturated at lower soil depths (45 75 cm).
80 Conclusion The localized water application of drip treatments maintained higher soil moisture in the upper soil layers. Water saved with drip i rrigation was 11.02 mm day 1 on average. Si milar marketable yield between surface drip tape and seepage were achieved, which means that water can be saved using drip irrigation while maintaining yield. In 2011, higher IWUE was obtained with SUR and SUB com pared to SEP for potato was not influenced by irrigation treatment. The higher root concentration (>90%) was found in the upper 30 cm of soil layer for all treatments, which is in agreement with other potato root studies. The ability to supply water with seepage to the sh allow potato root system is challenging. Potato roots are scarce and do not efficiently extract water from deep soil layers where the groundwater front is coming up in the seepage system However, water front coming from closely placed emitters can increas potentially nutrient uptake. It is concluded that surface drip irrigation can produce similar tuber yield for an ability to conserve water and the po ssibility of fertigating the crop through the system. Future research is needed to evaluate the feasibility of fertigation using SUR irrigation, and to adjust drip irrigation regimes to growth stages and crop evapotranspiration in sandy soils
81 Table 3 1. A nalysis of variance summary for root length density (RLD) affected by irrigation, column depth, and treatments interactions. Main effect D.F. RLD Irrigation (I) 2 ns Depth (D) 4 *** Column (C) 1 ns I x D 8 ns I x C 2 ns C x D 4 ns I x C x D 8 ns Significant at p <0.05; ** significant at p <0.01; *** significant at p < 0.0001. ns: not significant; D.F.: degrees of freedom
82 Table 3 2 Irrigation and variety treatments, irrigation depth, marketable yield, and irrigation water use efficiency for 2 011 and 2012 potato season 2011 2012 Irrigation treatment Variety treatment Irrigation depth Marketable Yield Water Use Efficiency Irrigation depth Marketable Yield Water Use Efficiency (mm) (kg ha 1 ) (kg m 3 ) (mm) (kg ha 1 ) (kg m 3 ) Surface Atl antic 270 26280 a Z 9.7 a 17 5 27000 b 14.1 a Subsurface Atlantic 270 19910 b 7.4 b 17 5 19680 c 10.3 b Seepage Atlantic 518 23460 ab 4.5 c 1411 32790 a 2.3 c Surface Fabula 2 70 16110 a 3.1 a 17 5 18710 a 9.8 a Subsurface Fabula 2 70 12020 a 4 .5 a 17 5 7820 b 4.1 b Seepage Fabula 518 15790 a 3.1 a 1411 17640 a 1.3 c Surface Red LaSoda 2 70 12710 b 2.5 a 17 5 14130 b 7.4 a Subsurface Red LaSoda 2 70 16410 b 6.1 a 17 5 9180 c 4.8 b Seepage Red LaSoda 518 26140 a 5.0 a 1411 20890 a 1 .5 c Z Values within columns followed by the same lowercase letter indicate that means are not significantly different at p<0.05
83 A B Figure 3 1. A. Schematic representation of the irrigation treatments field tested. SUR and SUB show s the drip tape position referenced by the seed piece position and SEP shows the water table rise. B. Drip tape layout in the field.
84 Figure 3 2 Experimental layout in the field showing treatments distribution and block dimensions. SUR (1); SUB (2); and SEP (3) irrigated plots. Seepage and drip plots were separated 36 m apart on average
85 Figure 3 3. Time Domain Reflectometry (TDR) probes insta lled parallel to the potato row in seepage and drip irrigation treatments to monitor soil moisture content every 15 minutes throughout the season Figure 3 irrigated with seepage, surface, and subsurface drip irri gation during 2012 spring season.
86 Figure 3 5 Cumulative rainfall measured at Hastings, Florida in potato seasons 2011 and 2012. B. Cumulative rainfall measured at different growth stages: Initial (0 25 DAP); Development (26 55 DAP); Mid season (56 91 D AP); Final (92 112 DAP)
87 Figure 3 6 Cumulative irrigation and estimated evapotranspiration for drip and seepage irrigation meth ods used during 2011 and 2012 potato growing seasons.
88 Vegetative Tuber Initiation Tuber Bulking Maturation Figure 3 7.Comparison of a seepage irrigated bed during 2011 (A D) and 2012 (E H) at different crop growth stages Field was wetter in the 2012 season. A B C D E F G H
89 Figure 3 8. Potato root density (cm of roots per cm3 of soil) in fiv e depth intervals (0 15, 15 30, 30 45, 45 60, and 60 75 cm) at 86 DAP in the 2012 season
90 Figure 3 9 Daily and cumulative solar radiation, minimum, average, maximum daily temperatures and cumulative daily growing degree days (GDD, temperature base of 1 0 C) during the 2011 and 2012 potato gro wing season in Hastings, Florida
91 Figure 3 10. Spatial distribution of moisture in the soil profile for seepage, surface drip, and subsurface drip.
92 Figure 3 1 1 Water table level, rainfall, daily irrigation ev ents, and volumetric soil water content at 0 10, 10 20, 20 40, and 40 50 cm depth for potato during three development stages (vegetative, tuber initiation, and maturation) in 2011 for SUR (A C), SUB (D F), and SEP (G I) treatments
93 Figure 3 1 2 Water tab le level, rainfall, daily irrigation events, and volumetric soil water content at 0 10, 10 20, 20 40, and 40 50 cm depth for potato during three development stages (tuber initiation, full flowerence, and maturation) in 2012 for SUR (A C), SUB (D F), and SE P (G I) treatments
94 Figure 3 1 3 Volumetric water content and water table dynamics at 5, 15, 30, 45, 60, and 75 cm depth in potato row 1 (A F), row 5 (G L), and row 8 (M R) on a seepage irrigated block without rainfall input during the 2011 season.
95 CHAP TER 4 SUMMARY AND CONCLUSIONS E fficient water delivery system s like drip irrigation are a potential option for potato growers in northeast Florida. However, it is necessary to determine an optimal drip tape depth placement to successfully grow potatoes and attain maximum yield potential. Surface drip tape (SUR) was installed 5 cm above the seed piece and subsurface (SUB) drip tape was installed 5 cm below the seed piece. It was evaluated the impact s of these two different drip tape placement to grow one chi S easonal water saving s with drip irrigation ranged between 248 mm and 12 3 6 mm ( 10 and 49 in ches ) in this study The varieties responded different ly to SUR and SUB drip tr eatments. In general, t he SUR treatment outperformed SUB and achieved statistically similar results t o the SEP treatment in terms of total and marketable yield Marketable yield was not significantly The SUR irrigation high efficiency and low dependence on the water table is paramount for sustainable potato production in sandy soils. In addition, t he soil moisture content can be easily controlled with SUR drip in the u pper soil layer (0 3 0 cm depth). According to this research findings ,>90% of the this upper soil layer. Despite these benefits, there are some challenges to using drip irrigation in commercial potato production systems. These include: increased labor, high p robability of tape damage from machinery, high potential for leak s to occur in the system wind vulnerability if soil is not adequately wet, and increased costs of production. However, the possibility of implementing fertigation and automation of drip irrigation system could
96 facilitate its adoption Additionally, the potential increase of marketable yield due to water and nutrient precisely delivered and maintained in the root zone can alleviate expenses and moreover augment economi c returns. Improving water use efficiency in the TCAA is a priority in order for growers to remain competitive in the marketplace. Future research should be conducted to evaluate SUR drip tape combined with fertigation practices as well as better tape installation and removal methods This will help elucidate the performance of different varieties un der an optimum supply of water and nutrient s. Furtherm ore, more precise recommendations can be provided to growers with the addition al benefit of increasing production efficiency and diminish nonpoint source pollution in the St. Johns River watershed
97 APPENDIX SAS CODES The SAS codes used for the statistical analyses performed are presented as follows: 1) SAS code for yield (TOT and MKT), size classes distribution, internal and external quality variables, and specific gravity. proc import datafile = 'c: \ rawdata \ Yield_2011 2012.xls' out =yield replace; sheet= 'Yield' ; run ; proc print data =yield; run ; proc sort data =yield; by year rep i rri var; run ; /*average across rows per plot*/ proc means noprint data =yield; by year Rep IRRI VAR ; var C B A1 A2 A3 A4 TOT MKT HH BR CRS I HN BCL BCM BCH GT GC Mis ROT SG; output out =yield_avg MEAN = C B A1 A2 A3 A4 TOT MKT HH BR CRS I HN BCL BCM BCH GT GC Mis ROT SG; proc print data =yield_avg; title 'Yield averaged across plot rows' ; run ; PROC GLIMMIX data =yield_avg; CLASS IRRI VAR Rep Year; MODEL MKT = IRRI|VAR|YEAR rep (irri)/ ddfm =kr; random rep year; lsmeans IRRI*VAR/ lines plots =meanplot (sliceby=VAR); lsmeans IRRI*VAR / slicediff =VAR slice =VAR; lsmeans IRRI*VAR/ slicediff =IRRI slice =IRRI; title ; run ; Note: the independent variables were changed one by one in the Model statement. 2) SAS code for biomass accumulation and aboveground N uptake:
98 proc import datafile = 'c: \ rawdata \ Biomass_2011 2012.xls' out =biomass replace; sheet= 'Biomass1' ; run ; proc print data =biomass; run ; proc sort data =biomass; by y ear rep irri var dap; run ; proc means noprint data =biomass; by YEAR REP IRRI VAR DAP ; var BIOMASS Nitrogen; output out =B iomass _avg MEAN = B iomass Nitrogen; proc print data =biomass_avg; run ; PROC GLIMMIX data =biomass_avg; CLASS IRRI VAR Rep Year da p; MODEL biomass = IRRI|VAR|YEAR|DAP / ddfm =kr; random rep dap year; lsmeans IRRI*VAR/ lines plots =meanplot (sliceby=VAR); lsmeans IRRI*VAR / slicediff =VAR slice =VAR; lsmeans IRRI*VAR/ slicediff =IRRI slice =IRRI; title ; run ; Note: Year effect was significant for biomass accumulation and N uptake. Thus, SAS codes were adjusted for further statistical analysis. 3) SAS code for IWUE PROC GLIMMIX data =IWUE_avg; CLASS IRRI VAR Year REP; MODEL IWUE = IRRI|VAR|YEAR / ddfm =kr; random rep year; lsmeans IRRI*VAR/ line s plots =meanplot (sliceby=VAR); lsmeans IRRI*VAR / slicediff =VAR slice =VAR; lsmeans IRRI*VAR/ slicediff =IRRI slice =IRRI; title ; run ;
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108 BIOGRAPHICAL SKETCH Joel Reyes Cabrera was born in Leon, Nicaragua. Joel received a Bachel or of Science degree in Agricultural Engineering from EARTH University in Costa Rica in 2009. During his junior year in 2008, he had the opportunity to come to the University of Florida as an intern and learn about irrigation automated controller s under Dr. Michael Dukes supervision. Upon completion of his B.S. he worked as research assistant under Dr. Johan Perret investigating the benefits of using ethanol byproducts as fertilizer sources in commercial sugarcane plantations. He has been interested in water conservation practices since he was in high school and developed a passion for plants while being at EARTH. In 2010, Joel decided to pursue a Master of Science degree and was a ccepted to The Gator Nation in spring After getting his degree, he plans to continue his professional career either in academics or industry working on sustainable water management and soil plant atmosphere relationships to maximize crop yield