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SL210 Effect of Reduced Water Table and Fertility Levels on Subirrigated Tomato Production in Southwest Florida1 C. D. Stanley and G. A. Clark2 1. This is document SL-210, a publication of the Soil and Water Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Published November 2003 Please visit the EDIS Website at http://edis.ifas.ufl.edu. 2. C.D. Stanley, professor, Soil and Water Science Department, Gulf Coast Research and Education Center, Bradenton, Florida; Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611; and G.A. Clark, professor, Biology and Agricultural Engineering, Kansas State University, Manhattan, Kansas. The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean The Lake Manatee Watershed Demonstration Project (LMWDP) was established in 1990 with a long-term goal to accelerate voluntary adoption of agricultural improved management practices (IMP), which minimize nutrient loading (primarily nitrates) of Lake Manatee, a source of drinking water for Manatee and Sarasota counties in Florida. Agricultural activities in the watershed include citrus, fresh market vegetable, and cattle production. The initial stage of the LMWDP characterized the impact of existing management practices on nutrient loading and recommended IMPs to reduce off-nitrate movement. The LMWDP facilitated development and improvement of the fully enclosed subirrigation (FES) system as a recommended IMP (Clark, et al., 1990; Stanley and Clark, 1991; Clark and Stanley, 1992). Conventional subirrigation (seepage) in south Florida (Geraldson, 1980), uses lateral field ditches to convey water within the field. It is the most common irrigation system used for vegetable production on flatwoods spodic soils (Smajstrla et al., 1992). The naturally high water table is raised so water moves by capillary action into a raised nsoil bed about 20 cm (8 in.) high. Irrigation water is applied up to 24 h d-1to maintain an average field-wide water table approximately 40 to 45 cm (16 to 18 in.) below the bed surface. Applications adjusted to provide for daytime peak crop water use periods often exceed actual water use rates, so large amounts of surface runoff occur during low crop water use periods. Precise control of the water table level is very limited with the ditch systems and is determined by soil characteristics, rainfall, level of the natural water table, and any modification of a producer's irrigation application schedule. The use of subsurface drainage tubing to subirrigate field crops grown on flatwoods soils offers greater control of water table levels and conserves water (Stanley, et al., 1981; Rogers and Stanley, 1983). Vegetable producers often lease land and frequently rotate to different production areas, which makes use of drainage tubing for irrigation so expensive it is not an economically feasible option (Prevatt, 1981). The fully enclosed subirrigation (FES) system developed for fresh market vegetable production provides improved control of the water table when
Effect of Reduced Water Table and Fertility Levels on Subirrigated Tomato Production in.... 2 compared to conventional ditch-conveyed subirrigation. The FES system is a more precisely controlled application system with greater uniformity of application throughout the field (Clark et al., 1990; Stanley and Clark, 1991; Clark and Stanley, 1992). The FES system uses microirrigation tubing rather than open ditches to deliver water needed to raise water table levels. With manual control, the system saves 30 to 40% (Stanley and Clark, 1991) in irrigation applications by eliminating irrigation tailwater runoff from ditches, minimizing surface evaporation, and applying water more uniformly across the field. The FES system is suited to automated control of applications to maintain static water table levels using field-located sensors and system controllers which further increase irrigation efficiency. nWith subirrigation, lateral subsurface losses increase as maintained water table levels increase because field edge flow gradients are elevated. The result is a need for greater irrigation applications. If desired crop production levels could be achieved while maintaining lower water table levels, substantial amounts of irrigation water could be saved. At the same time, increased effective use of rainfall and reduced potential for field flooding could be achieved through greater available soil water storage above the water table. Water tables can rise to within 20 cm (8 in.) of the bed surface during heavy rainfall periods. Applied fertilizer is vulnerable to leaching as the water table drops back to its target control level. Growers commonly compensate for this potential loss by applying nitrogen (N) in amounts of 448 kg N ha-1 (400 lb N acre-1). The recommended N application rate (Hochmuth et al., 1988) for fresh market tomato production is 212 to 269 kg N ha-1 (190 to 240 lb N acre-1) based on 6542 bed m ha-1 (8686 bed ft acre-1). The primary objective of this study was to determine if fruit yield and quality levels can be maintained with reduced fertilizer application amounts in combination with managed lower water table levels. If so, nutrients and irrigation water could be conserved and the potential for nutrient leaching into water resources would be decreased. Materials and Methods This study was conducted at the University of Florida's Gulf Coast Research and Education Center near Bradenton, Florida, during the 1992, 1993, and 1994 spring growing seasons (March to June). A raised, plastic-mulched bed culture was used to grow each tomato crop (Geraldson, 1980). The study area was a contiguous block subdivided for three water table level treatments: 45, 60, and 75 cm (18, 24, and 30 in.) below the top of the bed. Plot areas 12 m (40 ft) wide and 91 m (300 ft) long were used for each water table level treatment with six beds spaced 1.8 m (6 ft) center to center, each separated by a 12 m (40 ft) wide buffer area to reduce water table influences between treatments. Microirrigation tubing (GEOFLOW, Inc.) with in-line 1.9 L h-1 (0.5 gal h-1) emitters spaced 60 cm (24 in.) apart was installed 40 cm (16 in.) deep with laterals spaced every 6 m (20 ft). The system was subdivided into irrigation zones for individual control of water table levels in each treatment area. Each water table level treatment area was instrumented with observation wells, water level recorders and loggers, and an electronic float switch irrigation control system. A solenoid valve which controlled irrigation applications was activated or deactivated depending on the float switch position and water table control height. A filtered and chlorine-treated (to prevent tube clogging) pressurized water supply pumped from a surface water source was used for irrigation. The soil is an EauGallie fine sand (Alfic entic haplaquods, sandy, siliceous, hyperthermic) with a natural water table level between 90 and 120 cm (36 and 48 in.) from the ground surface. Residual N in the rooting zone from previous cropping seasons is generally very low (< 2 mg kg-1) because rainfall between seasons leaches nutrients very quickly through this soil, which is approximately 95 to 98% sand. Preplant soil N determinations were made prior to each season to verify this condition. Gravimetric soil moisture determinations were periodically made during the season to determine the relationship between water table position and soil moisture gradient with depth to the water table. Pest management was accomplished with standard recommended practices for tomato production.
Effect of Reduced Water Table and Fertility Levels on Subirrigated Tomato Production in.... 3 nCommercial fertilizer used for supplying N and K was a blend of ammonium nitrate, calcium nitrate, and potassium nitrate. Fertilizer rate treatments were selected to range from the recommended rate to the maximum used by growers. The fertilizer rate treatments expressed here as kg ha-1 (lb acre-1) of N-P-K were: (1) 215-112-248 (192-100-221), (2) 309-112-356 (276-100-318), and (3) 403-112-465 (360-100-415). Even though the objective was to focus on N rates, K rates were adjusted with N to simulate current grower practice. The experimental design for the study was a split-plot with water table level as the main plot, split by fertilizer rate, and replicated in time by season. Within each season, four subplots were used for each treatment combination to increase observations. A commercial fresh market tomato (Lycopersicon esculentum Mill., 'Sunny') variety was grown in each season. Prior to field preparation, the FES system and float switches were activated to establish a 45 cm (18 in.) deep water table in all plots. Preparation of the 80 cm (32 in.) wide and 20 cm (8 in.) high production beds was accomplished in the following sequence: beds were formed on 1.8 m (6 ft) centers which provided a bed density of 6542 bed in ha-1 (8,686 bed ft acre-1); phosphorous was broadcast on the beds and lightly incorporated to a 7.5 cm (3 in.) depth; nitrogen and potassium fertilizer was applied in grooves 2.5 cm (1 in.) deep on the bed surface as two bands 20 cm (8 in.) on either side of bed center; fumigation with methyl bromidelchioropicrin was injected at a rate of 392 kg ha-1 (350 lb acre-'); and beds were covered with 1.5 mil black plastic two weeks prior to planting. Each crop was planted using transplants approximately six-weeks old at an in-row spacing of 60 cm (24 in.) in a single row in center of bed resulting in a plant density of 10,759 plants ha-1 (4,356 plants acre-1). Transplanting dates were 4 March 1992, 1 March 1993, and 3 March 1994. Float switches were adjusted to the plot treatment levels of 45, 60, and 75 cm (18, 24, and 30 in.) water table positions during the week of 16 March 1992, 22 March 1993, and 21 March 1994. The delay in 1993 was due to a severe storm that occurred on 13 March and caused extensive, uniform defoliation of transplants. Although complete plant recovery occurred, fruit set was delayed. Multiple harvests were performed for each season (27 May, 8 June, and 18 June for 1992; and 3 June, 14 June, and 21 June for 1993; and 19 May and 1 June for 1994) during which fruit yield and quality data were collected. Regression techniques were used for data analysis. Results and Discussion Results summarizing the effect of water table level and fertilizer rate on total marketable yield for all seasons are shown in Table 1. Regression analysis of the data revealed no significant interactions between fertilizer and water table level treatments. There were no significant differences for marketable yields among nitrogen fertilizer rates at individual water table levels, indicating that lower fertilizer rates were adequate to achieve acceptable production. Although no differences in marketable yield were measured between fertilizer treatments, visual differences were observed with respect to plant condition as the lowest N rate treatment [especially in the 45-cm (18-in.) water table level treatment] became visually N-stressed late in the season after the second harvest. Similar plant nutritional deficiencies were reported by Shih (1985) as a result of higher water table management levels. Only the N-rate treatment of 403 showed a significant quadratic response with respect to water table level (Table 1). Table 2 contains the marketable fruit size yield results as affected by fertilizer rate or water table level. No significant response in fruit size yield was observed among fertilizer treatments for any fruit size category or total marketable fruit production for all water table treatments combined. A significant quadratic response was observed among water table level treatments (all fertilizer treatments combined) for total marketable fruit production, but not for any fruit size category. Figure 1 shows the fluctuations for the water table level treatments during the 1993 growing season. Sharp upward peaks were caused by rainfall events. Development of a fluctuating diurnal cycle of the water table level for all treatments (during mid to late season) seemed to indicate that even though irrigation applications were made continuously during that period, the application rate was not
Effect of Reduced Water Table and Fertility Levels on Subirrigated Tomato Production in.... 4 sufficient to satisfy both plant water demand and the water required to maintain the water table level. Recovery to desired levels was always achieved overnight. A system malfunction caused an interruption in irrigation for the 75-cm (30-in.) treatment for about seven days (between days 55 and 62). This shows that even when irrigation was not applied and the water table level declined, the diurnal cycle still existed. Figure 1. Water table level fluctuations for the 45, 60 and 75 cm water table level treatments (A, B, and C respectively) for the spring 1993 season (*indicates a rainfall incident). The on/off cycles for each water table level treatment (controlled by the field-located float switches) were continuously logged throughout the growing seasons. Figure 2 illustrates a typical period (16 to 20 March 1992) following significant rainfall for the spring tomato season. This figure shows how the 45 cm (18 in.) treatment initially required irrigation applications earlier than other treatments and more frequently during the high evapotranspiration demand period (daylight hours). Although this study was not designed to quantify water use differences among treatments, based on the irrigation application times made during this period, the amounts applied to the 60-cm (24-in.) and 75-cm (30-in.) treatments were 45 and 30% of the amount applied to the 45-cm (18-in.) treatment, respectively. These data indicate that more water is required to maintain a higher water table (based on application frequency) than a lower water table. Figure 2. Irrigation system on-off cycles for the 45, 60 and 75 cm water table level treatments (A, B, and C respectively)from 16 March to 20 March 1992. Soil moisture gradients in soil profiles of the water table level treatment areas and the surrounding buffer areas (to collect data at water table depths other than the maintained levels) were measured using gravimetric sampling at soil depths between the water table and bed surface to determine differences in capillary fringe among treatments. EauGallie fine sand has a volumetric moisture content of approximately 10% at -10 kPa (near field capacity). Capillary rise from the water table is not sufficient to maintain a soil moisture content above 10% in the upper 15 cm (6 in.) of the bed when the water table level is below 60 cm (24 in.) (Figure 3). This information may help explain why significant quadratic relationship among water table levels for total marketable yield. Figure 3. Volumetric soil moisture content at the two depth intervals of 0 to 15 and 15 to 30 cm below the bed surface as influenced by water table level. Excessive rainfall during growing seasons had a significant effect on maintaining the target water table levels. Table 3 shows biweekly rainfall amounts received for each growing season. Rainfall amounts
Effect of Reduced Water Table and Fertility Levels on Subirrigated Tomato Production in.... 5 were either near or below normal [average rainfall for the period is approximately 30 cm (12.0 in.)], Aside from the daily fluctuations discussed earlier, the water table was maintained satisfactorily using the float switch arrangement. Conclusion These results indicate no particular advantage to maintaining a water table above 60 cm (24 in.) or to applying N fertilizer at rates greater than those recommended. The results indicate that more effective nitrogen management for subirrigated tomatoes can be accomplished without decreased production by: 1) using the FES system to maintain a water table level near 60 cm (24 in.) below the bed surface, and 2) using a nitrogen rate lower than generally used in commercial practice and near the recommended rates of 212 to 269 kg ha-1 (190 to 240 lb N acre-1). Maintaining a lower water table level should expand the available rooting zone and the ability of the plant to use nitrogen within the greater soil volume, and increase effective use of rainfall. Literature cited Clark, G. A., C. D. Stanley and P. R. Gilreath. 1990. Fully enclosed subsurface irrigation for water table management. Proc. Florida Tomato Institute, 19-30. Veg. Crops Special series Rep. SS-VEC-001. FL Coop. Ext. Ser., Univ. of Florida, Gainesville. Clark, G. A. and C. D. Stanley. 1992. Subirrigation by microirrigation. Applied Engin. in Agric. 8:647-652. Geraldson, C. M. 1980. Importance of water control for tomato production using the gradient mulch system. Proc. Fla. State Hort. Soc. 93:278-279. Hochmuth, G. J., E. A. Hanlon, P. R. Gilreath, and K. D. Shuler. 1991. Effects of K rates on yield of tomato at three commercial production sites. Soil and Crop Sci. Soc. Fla. Proc. 50:169-172. Hochmuth, G. J., E. Hanlon, B. Hochmuth, G. Kidder, and D. Hensel. 1993. Field fertility research with P and K for vegetables interpretations and recommendations. Soil and Crop Sci. Soc. Fla. Proc. 52:95-101. Hochmuth, G. J., D. N. Maynard, and M. Sherman. 1988. Tomato production guide for Florida. Univ. of Florida Coop. Ext. Ser. Circular 98-C. Gainesville, FL. nPersaud, N. S., S. J. Locascio, and C. M. Geraldson. 1976. Effect of rate and placement of nitrogen and potassium on yield of mulched tomato using different irrigation methods. Proc. Fla. State Hort. Soc. 89:166-169. Prevatt, J. W., C. D. Stanley, and A. A. Csizinszky. 1981. An economic evaluation of three irrigation systems for tomato production. Proc. Fla. State Hort. Soc. 94:166-169. Rogers, J. S. and C. D. Stanley. 1983. Subsurface irrigation of staked tomatoes. Soil and Crop Sci. Soc. Fla. Proc. 42:65-69. Smajstrla, A. G., D. S. Harrison, D. Z. Haman, and F. S. Zazueta. 1992. Irrigated acreage in Florida. Fla. Coop. Ext. Ser. Circ. 1030. 5 pp. Stanley, C. D., J. S. Rogers, J. W. Prevatt, and W. E. Waters. 1981. Subsurface drainage and irrigation for tomatoes. Soil and Crop Sci. Soc. Fla. Proc. 40:92-95. Stanley, C. D. and G. A. Clark. 1991. Water table management using microirrigation tubing. Soil and Crop Sci. Soc. Fla. Proc. 50:6-8.
Effect of Reduced Water Table and Fertility Levels on Subirrigated Tomato Production in.... 6 Table 1. Marketable tomato fruit yield for N fertilizer and water table level treatments for 1992, 1993, and 1994 spring growing seasons. Water Tabel Level 45 cm 60 cm 75 cm zNitrogen Treatment ----------kgha-1 x 103-------------LinearQuadratic 215 89.0 91.5t1.5 85.8 NS 30993.496.087.2NS 40387.4100.786.4 ** Linear NS NSNS **Significant quadratic relationship at 0.01 levels of probability, respectively; NS no significant relationship. zNitrogen treatments expressed as kgha-1. Table 2. Marketable tomato fruit yield and size as a result of N fertilizer and water table treatments for all spring growing seasons. Fruit Size Medium Large Extra Large Total N rate (kgha-1) --------------kgha-1 x 103--------------215 20.327.241.3 88.8 309 20.628.243.5 92.3 403 22.829.938.6 91.4 Linear NSNSNS NS Water table level (cm) 45 20.025.135.1 80.2 60 19.926.139.7 85.7 75 17.024.935.4 77.3 Linear NSNSNS Quadratic NS NS NS ** **Significant linear or quadratic relationship at 0.01 level of probability; NS = no significant relationship.
Effect of Reduced Water Table and Fertility Levels on Subirrigated Tomato Production in.... 7 Table 3. Biweekly and total rainfall for 1992, 1993, and 1994 spring growing seasons. Rainfall cm (in.) Weeks 1992 1993 1994z 2 35.94 (2.34)3.63 (1.43)0.0 (0.0) 4 54.10 (1.60)4.57 (1.80)2.39 (0.94) 6 75.54 (2.18)6.17 (2.43)0.15 (0.06) 8 91.93 (0.76)0.25 (0.10)6.25 (2.46) 10 110.0 (0.0)0.58 (0.23)0.43 (0.17) 12 130.05 (0.02)3.00 (1.18)0.03 (0.01) 14 1511.3 (4.45)0.79 (0.31)--Totals 28.83 (11.35) 19.00 (7.48) 9.25 (3.64) z 1994 Season was finished after 13 weeks.