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Relationships among Mehlich-1, Mehlich-3, and Water-Soluble Phosphorus Levels in Manure-Amended, Inorganically Fertilized, and Phosphatic Soils

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Title:
Relationships among Mehlich-1, Mehlich-3, and Water-Soluble Phosphorus Levels in Manure-Amended, Inorganically Fertilized, and Phosphatic Soils
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HERRERA, DANIEL A. ( Author, Primary )
Copyright Date:
2008

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Agriculture ( jstor )
Crops ( jstor )
Fertilizers ( jstor )
Manure ( jstor )
Nutrients ( jstor )
Phosphates ( jstor )
Phosphorus ( jstor )
Soil science ( jstor )
Soil water ( jstor )
Soils ( jstor )

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University of Florida
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University of Florida
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Copyright Daniel A. Herrera. Permission granted to the University of Florida to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
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8/1/2004
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436097520 ( OCLC )

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RELATIONSHIPS AMONG MEHLICH-1, MEHLICH-3, AND WATER-SOLUBLE PHOSPHORUS LEVELS IN MANURE-AMENDED, INORGANICALLY FERTILIZED, AND PHOSPHATIC SOILS By DANIEL A. HERRERA A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2003

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ACKNOWLEDGMENTS I would like to acknowledge Dr. Rao Mylavarapu, Dr. Willie Harris, Dr. Dean Rhue and Dr. Lee McDowell for being on my committee and for all the guidance and knowledge they have shared with me through my years of study. Special thanks go to BK Singh and all my undergraduate professors at EARTH University who believed and encouraged me to jump into this journey; and what a journey this has been! I thank all the professors I have had at UF; they have been a constant source of knowledge and inspiration. Tambin quisiera agradecer a mi familia y amigos en Costa Rica. Su apoyo incondicional ha hecho ms fcil estar lejos de casa. Mi profundo agradecimiento a todos aquellos que de una u otra forma han estado conmigo durante este tiempo. ii

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TABLE OF CONTENTS page ACKNOWLEDGMENTS..................................................................................................ii LIST OF TABLES...............................................................................................................v LIST OF FIGURES...........................................................................................................vi ABSTRACT......................................................................................................................vii CHAPTER 1 INTRODUCTION........................................................................................................1 2 LITERATURE REVIEW.............................................................................................5 Phosphorus, the Element, the Nutrient.........................................................................5 Phosphorus Nutrition in Plants.....................................................................................6 Phosphorus Nutrition in Animals.................................................................................6 Phosphorus Sources in Agricultural Systems...............................................................8 Natural Phosphatic Soils........................................................................................9 Inorganic Fertilizer..............................................................................................10 Inorganic Fertilizer Consumption................................................................10 Fertilizer Chemistry-Reaction Post Application..........................................11 Dairy Manure.......................................................................................................12 Soil Testing.................................................................................................................14 3 MATERIALS AND METHODS...............................................................................19 Site Selection and Sampling.......................................................................................19 Sampling..............................................................................................................19 Phosphatic Soils...................................................................................................19 Inorganically Fertilized Soils................................................................................20 Manure Amended Soils.........................................................................................20 Sample Processing and Analysis..................................................................................20 Mehlich-1 Extraction ...........................................................................................21 Mehlich-3 Extraction ...........................................................................................21 Water-soluble Phosphorus...................................................................................22 Total Carbon........................................................................................................22 iii

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Particle Size Distribution.....................................................................................22 Total Phosphorus Analysis by the Ignition Method............................................22 Statistical Analysis ...............................................................................................23 4 RESULTS AND DISCUSSION.................................................................................24 Soil pH, Particle Size and Organic Carbon................................................................24 Extractable Soil Phosphorus.......................................................................................25 Relationship among Mehlich-1 P, Mehlich-3 P and Water Soluble P.......................27 Phosphatic Soils...................................................................................................27 Inorganically Fertilized Soils..............................................................................29 Manure Amended Soils.......................................................................................32 Influence Al, Fe, Ca, Mg and OC on P Extractability................................................34 5 SUMMARY AND CONCLUSION...........................................................................42 APPENDIX A MEHLICH-1 AND MEHLICH-3 CONCENTRATIONS OF FE, AL, CA, AND MG IN PHOSPHATIC, MANURE AMENDED AND INORGANICALLY FERTILIZED SOILS..................................................................................................44 B X-RAY DETERMINATION OF THE MINERALS PRESENT IN PHOSPHATIC SOILS.........................................................................................................................45 LIST OF REFERENCES...................................................................................................48 BIOGRAPHICAL SKETCH.............................................................................................53 iv

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LIST OF TABLES Table page 4-1 Soil pH and OC for each of the three soil P sources................................................25 4-2 Mehlich-1 Phosphorus, Mehlich-3 Phosphorus, and Water Soluble Phosphorus for each of the three soil P sources...........................................................................26 4-3 Multivariable regression analysis for P= fn (Al, Fe, Ca, Mg and OC) in phosphatic soils........................................................................................................35 4-4 Multivariable regression analysis for P= fn(Al, Fe, OC) in inorganically fertilized soils*.........................................................................................................36 4-5 Multivariable regression analysis for P= fn (Al, Fe, OC) in manure amended soils at the 0-5 cm depth...........................................................................................38 4-6 Multivariable regression analysis for P= fn (Al, Fe, OC) in manure amended soils the 5-15 cm depth.............................................................................................39 4-7 Multivariable regression analysis for P= fn (Al, Fe, Ca, Mg and OC) in manure amended soils for the combined soil depth of 0-5 and 5-15 cm..............................39 v

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LIST OF FIGURES Figure page 4-1 Correlation between Mehlich-1 Extractable P and Water Soluble P in phosphatic soils...........................................................................................................................28 4-2 Correlation between Mehlich-3 Extractable P and Water Soluble P in phosphatic soils...........................................................................................................................29 4-3 Correlation between Mehlich-1 Extractable P and Water Soluble P in inorganically fertilized soils. ..................................................................................30 4-4 Correlation between Mehlich-3 Extractable P and Water Soluble P in inorganically fertilized soils. ..................................................................................32 4-5 Correlation between Mehlich-1 Extractable P and Water Soluble P in manure amended soils. ........................................................................................................33 4-6 Correlation between Mehlich-3 Extractable P and Water Soluble P in manure amended soils. ........................................................................................................34 4-7 Series of reactions following monocalcium and monoammonium phosphate fertilizer application in soils.....................................................................................37 vi

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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 RELATIONSHIPS AMONG MEHLICH-1, MEHLICH-3, AND WATER-SOLUBLE PHOSPHORUS LEVELS IN MANURE-AMENDED, INORGANICALLY FERTILIZED, AND PHOSPHATIC SOILS By Daniel A. Herrera December 2003 Chair: Rao Mylavarapu Major Department: Soil and Water Science Department The use of both organic and inorganic nutrients to maximize economic returns is a common practice in agriculture production. Soil testing is a tool used to predict crop response to added P fertilizer. It is commonly perceived that high soil test P concentrations indicate high potential for off-site movement and impact on surface water quality. Mehlich-1 and -3 are common soil extractants used in the southeastern US for estimating plant nutrient availability; water-soluble P, on the other hand, reflects the P concentration in the soil but not necessarily correlated with crop response to added fertilizer. Water soluble phosphorus (WSP) may give a better indication of environmental risk. Environmental risk from phosphatic soils naturally high in P is unknown. This study was designed to determine WSP levels of phosphatic, manure amended and inorganically fertilized P-sources in soils, correlate Mehlich-1 P and Mehlich-3 P concentrations with WSP levels in soils with different P-sources and to determine the influence of Al, Fe, Ca, vii

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Mg, and soil organic carbon (OC) on extractable P. Manure-amended and inorganically fertilized soils samples were collected from the MSRB, and phosphatic soil samples from both the MSRB and St. Johns River Basin. Mehlich-1 P was significantly correlated with WSP in phosphatic; inorganically fertilized, and manure-amended soils. Mehlich-3 P was not significantly correlated with WSP in phosphatic soils but it was in manure-amended and inorganically fertilized soils. In inorganically fertilized, although significant, correlations had a low r 2 value. No statistical difference was found on the WSP concentrations among the three P sources in soils. Soil magnesium (Mg) concentration was the inorganic parameter that best explained P variability in manure amended soils. Iron (Fe) and aluminum (Al) explained 66% and 77% of the P variability in M-1 and M-3 extractions, respectively in inorganically fertilized soils. Low WSP in phosphatic soils indicated the presence of crystalline Al-P minerals with low solubility in water. Significant difference was found (P<0.001) between (WSP/Mehlich-1 P) ratio in phosphatic soils with respect to inorganically fertilized and manure-amended soils. viii

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CHAPTER 1 INTRODUCTION Phosphorus (P) is a fundamental constituent in the metabolic cycle and biochemistry of all living organisms. While nitrogen (N) is commonly referred to as the most limiting nutrient for terrestrial plant growth, P is considered as the one limiting productivity in fresh water and aquatic systems (Sinaj et al., 2002). For successful crop production, P inputs in the form of mineral and/or organic fertilizer are often necessary to optimize productivity; on the other hand, elevated soil P concentrations under certain conditions can be a potential threat to the environment as they have led to eutrophication problems in sensitive surface water bodies (Brye et al., 2002). As point sources of pollution are controlled, diffuse non-point P sources such as agriculture are becoming the target of regulatory control (Sims et al., 1998). According to United States Environmental Protection Agency (USEPA) (2000) agriculture is the leading source of water quality impairments in rivers and lakes in the USA. Therefore, identification of factors contributing to potential P losses from agricultural operations is critical. The most common approach used to date has been evaluating soil test P level because it is already widely conducted at relatively low cost, and the general research base and field calibrations used for the test interpretation. For example, high soil test P has been found to correlate well with greater risk for offsite P movement through run-off (Pote et al., 1996; Sharpley, 1995; Torbert et al., 2002). Water-soluble P has been considered as the soil P fraction that is most susceptible for offsite movement. Soil P solubility in water likely controls dissolved reactive phosphorus 1

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2 (DRP) concentrations in runoff (McDowell and Sharpley, 2001; Pote et al., 1999; Sims et al., 2000) and correlates well with P concentrations leaching studies (Maguire and Sims, 2002). Mehlich-1(M-1) and Mehlich-3 (M-3) are the main soil test extractions used in the SE United States for estimating P availability for crop uptake. Soil testing for extractable P is a tool commonly used in agriculture to predict crop response to P application. Crop production has been the main emphasis and purpose of soil testing programs. Today, farmers are confident in the practical value of a soil test for P and how its interpretation determines whether or not additional P inputs are needed by the crop. However, over-fertilization is common in many areas, particularly those where it is the only feasible option to apply organic wastes (due to limited area available and/or high cost of transportation) or where high cash value crops are grown and fertilizer cost is not a major concern (Sims et al., 2000). While integration of soil testing and environmental risk assessment may be an option, the source of P is possibly another variable that needs to be factored into the already complex system. There are three main sources of P that warrant consideration: phosphatic soils, (a natural common feature in Florida), dairy manure amendments, and inorganic fertilizer applications. Phosphate minerals are the primary source of P for fertilizer. In Florida, P deposits were first discovered and mined in the 1880’s (Cathcart, 1986). Soils formed over phosphoritic deposits are often referred to as phosphatic soils. Phosphatic soils are defined as those where total-P increases with depth. Despite the high P-content (Total P) of these soils, mobility is thought to be limited, particularly in soils under severely

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3 weathered conditions because more stable P-forms (i.e. wavellite) are prevalent and therefore significant P-leaching is unlikely to occur (Wang et al., 1989) Inorganic P fertilizers are widely used in vegetables, strawberry, sugar cane, citrus, pine plantations and many other crops grown in Florida. They are used with a view to maximize productivity. The chemical reaction following a fertilizer application to the soil determines the end products, how much will be plant available as well as any potential for offsite movement. The solution around the fertilizer granule -as it reacts with the soilis known as the triple-point solution (TPS). Lindsay et al. (1962) found that as the TPS contacts the shell of soil surrounding the fertilizer granule it can dissolve soil particles yielding Mn, Ca, Fe, and Al (the latter two are common in Florida’s soils). They also measured a reduction in the Fe and Al concentrations with time, suggesting a co-precipitation in the forms of Fe and Al phosphates. In many areas, manures from confined animal feeding operations (CAFOs) are applied to farm crops to meet N requirements. This approach however results in exceeding crop P requirements, resulting in build up of soil bound P (Sharpley, 1996). In dairy manure, P fractions are dependent on the P concentrations in the diet. Dou et al. (2002) found that increase in dietary P concentrations from 3.4 to 6.7 g P kg -1 DM correspondingly increased water soluble P from 24.2 to 94.4 g cow -1 day -1 in the feces while the other P fractions remained small and with little or no variation. In the same study they also characterized the P in the feces; between 56 and 64% is water soluble and between 46 and 59% of total P in feces was determined to be inorganic. Although a high proportion of the total P in manure is in inorganic form, it is important to note that the reaction occurring upon soil application is different from that of inorganic fertilizer.

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4 Nutrient surpluses on farms and the consequent P build up in soils have caused accelerated P losses to surface water systems. To address concerns regarding P losses to the environment several states are now developing and adopting nutrient management strategies. Little work has been done comparing the water solubility and the source of P in soils in an attempt to understand the potential for offsite movement of P. Objectives In order to develop relationships among the three main P sources in the soil and the corresponding water solubilities and estimated plant availability, our study addressed the following objectives: 1. Determine water soluble P (WSP) levels of phosphatic, manure amended and inorganically fertilized P-sources in soils. 2. Correlate Mehlich-1 P and Mehlich-3 P concentrations with WSP levels in soils with different P-sources. 3. Determine the influence of Al, Fe, Ca, Mg, and soil organic matter (SOM) on extractable P.

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CHAPTER 2 LITERATURE REVIEW Phosphorus, the Element, the Nutrient P is classified as one of the macronutrient elements essential for plants and animals. Macronutrient refers to the amount (of the nutrient) required and not to their degree of essentiality to plant growth cycle. In world agriculture, P management is second only to N in importance as a limiting nutrient for the production of profitable yields. In soils, inorganic-P forms tend to be very stable because of their poor solubility and therefore, normally, are not associated with off-site movement (Black, 1968). Natural P concentrations in soils are very small and furthermore the availability level is much smaller. High P concentrations in native soils are rare and often can be related with past animal and particularly human activity in a given area (Brady and Weil, 1998). There is no doubt about the beneficial effects of P on agricultural production, however, it also is a high potential risk as a pollutant if off-site movement occurs into surface waters (Wood, 1998). The role of P on surface water eutrophication has been recognized for decades. However efforts in the USA to improve agricultural P management practices to protect water quality have intensified in late 1990’s (Sims et al., 2002). Although N and carbon (C) are the main nutrients required for aquatic biota growth in water bodies, their ease of air-water exchange have placed the main concern on P. For example, some water living organisms like blue-green algae can fix atmospheric N as well as C, resulting in P being the nutrient that limits or promotes eutrophication. 5

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6 Phosphorus Nutrition in Plants Phosphorus concentrations in most plants are much smaller than those of N, potassium (K) and calcium (Ca). Phosphorus is absorbed mainly in either of its orthophosphate forms (H 2 PO 4 or HPO 4 -2 ). Solubility of inorganic-P forms is pH-dependent, and therefore is sensitive to even small pH changes such as those taking place in the areas around the root (Tisdale et al., 1999). At the metabolic level, P is vital for multiple physiological functions in plants. As a component of DNA and RNA molecules, it is essential in genetic information and protein production. Phosphorus is essential for critical energy transfer functions of converting AMP and ADP to ATP. Also as phospholipids, it serves in maintaining the integrity of cell membrane structure (Marschner, 1995). In plants, P is also necessary for a normal development of the reproductive parts. It is considered essential for seed formation and is related with the success of the plant to reach maturity. Phosphorus also enhances forage, vegetable and fruit quality at the same time that it improves straw strength, particularly in cereals. It is also known as a stimulant of root growth, particularly lateral roots. Improvement in disease resistance is often seen when adequate levels of P are present in the plant (Tisdale et al., 1999). Phosphorus deficiency in plants is not pronounced or specific, and therefore may not be easy to diagnose; it may appear in leaves and stems as purple color development, from the edge in, however it is of little value because of low degree of specificity (Brady and Weil, 1998). Phosphorus Nutrition in Animals Phosphorus is the second most abundant mineral found in the animal body. Along with Ca, P forms the major part of mineral content of bone. In animal nutrition P is also

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7 closely associated with Ca and the requirements of one relate to the other. The ratio of Ca:P in bone is close to 2:1 and is rather a constant. In most animal diets a 2:1 Ca:P ratio is also sought, particularly in monogastric animals. Deficiency of P is a major problem in grazing livestock (McDowell, 1992). Involved in most, metabolic reactions, P has been determined to be one of the most versatile of all mineral elements. Phosphorus is present in organic compounds as phospholipids, phosphoproteins, nucleic acids, cyclic adenosine monophosphate, cyclic guanine monophosphate, inositol polyphosphates, coenzymes, and 2, 3-diphosphoglycerate (regulates O 2 released by hemoglobin) (Arnaud and Sanchez, 1996). Phosphorus is needed in every aspect of feed metabolism and utilization of fat, carbohydrates, protein and nutrients as well as high-energy phosphate bonds (ATP) and nucleic acids (RNA, DNA). It plays an important role in buffered systems such as blood and other fluids (e.g., rumen). It is fundamental in the rumen for cellulose digestion by microorganisms. Phosphorus deficiency is manifested in many ways, the most common ones being anorexia, decreased feed efficiency poor weight gain, reduced production (milk/eggs), fertility, and pica (eating disorder) (McDowell, 1992). From a dairy nutrition perspective, of all the dietary essential minerals, P represents greatest risk to the environment when fed in excess. Therefore, accurate and precise management of P content in the animal ration is vital for optimal animal performance and health while minimizing excreted P contents (National Research Council (U.S.), 2001). Phosphorus absorption is controlled by homeostasis., a more efficient, active transport mechanism, within the animal body is triggered when a low P diet is fed, reducing the excreted P. This mechanism is thought to be activated by low blood P. On

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8 the contrary a passive absorption mechanism predominates when normal to large amounts of P are fed. In other words, P supply in excess of the requirement reduces its absorption efficiency. Recycled P in saliva and excreted endogenous P complement the homeostasis controlling factors (National Research Council, 2001; Valk et al., 2000). Phosphorus absorption varies widely depending on the feedstuff being fed to the animal. In lactating dairy cows P absorption can range from 60 percent for forages and up to 90% for inorganic forms such as monosodium phosphates. In mixed diets, P excretion is inevitable; the amount to be excreted is dependent on the animal health, total P in the diet, animal requirements, age, P source and intake of other minerals such as Ca, Fe, Mg and Al (McDowell, 1992; National Research Council, 2001). Phosphorus Sources in Agricultural Systems Phosphorus deficiency has been documented to cause significant impacts to plant growth, crop yield and animal health. To maximize production, P fertilization has become a routine practice in agriculture; animal husbandry relies on P supplementation to avoid deficiency and urban settings rely heavily in the use of P fertilizers for landscaping purposes (lawn maintenance, golf courses, etc). There are many available options to supplement P into a system. In Florida, the existence of phosphatic soils provides a natural P source in some areas while manufactured fertilizers and manures from CAFO’s (particularly dairy operations) represent the most common sources applied externally. A description of these three sources and their characteristics is detailed below.

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9 Natural Phosphatic Soils Igneous rocks (as phosphate minerals) are the natural source of P in soils. The major phosphate deposits being mined today to produce P-fertilizer are located in Morocco and the US (Harris, 2002; McDowell, 1992). Phosphate deposits in Florida were first discovered and mined in the 1880’s (Cathcart, 1986). In 1892, the term “Hawthorn Beds” was first used to describe the P-rich material being quarried and ground to produce fertilizer near the town of Hawthorn in Alachua County, Florida. Now known as Hawthorn formation, this P-rich parent material also underlies areas of the MSRB, (Ceryak et al., 1983) an eco-sensitive region to P loading into the water bodies in north central Florida. Although stable-crystalline Fe and Al phosphates are the dominant forms of P in phosphatic soils, they do not account for the total P present in the soil (Wang et al., 1989). A complementary study was done, in which amorphous Fe phosphates were found to be an important component of the total P present in these soils, particularly near the soil surface (Wang et al., 1991a). Results show how M-1 was capable of extracting significant P concentrations particularly that associated with Fe and Al in non-crystalline forms. Results also showed how high concentrations of P affect the crystallization of Fe-containing compounds in phosphatic soils. Forms of P in Phosphatic Soils of Florida Phosphate minerals present in some phosphatic soils (identified in a cooperative effort between USDA-SCS and the University of Florida Soil Characterization Program) were characterized by (Wang et al., 1989). They found fluorapatite [Ca 5 (PO 4 )3F], crandallite [CaAl(PO 4 ) 2 (OH) 5 •H 2 O] and wavellite [Al 3 (PO 4 ) 2 (OH) 3 H 2 O] in the twelve pedons analyzed. They attributed the absence of variscite to its relatively unstable

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10 properties when compared with the ones found. Furthermore they concluded that fluorapatite is the most susceptible mineral to weathering, crandallite, an intermediate and wavellite the most stable, and common in Florida’s Ultisols. Inorganic Fertilizer In Florida agriculture, the use of inorganic P fertilizers to maximize productivity is a frequent practice in vegetable, strawberry, sugar cane, citrus, pine plantations and many other intensively managed crops. Inorganic Fertilizer Consumption World fertilizer consumption started to increase from the 1960’s. It reached its peak by the year 1989 when a total of 145.6 million metric tonn of fertilizer was consumed. Since then it saw a slight decline and subsequently leveling off in 1994. A small increase in 1995 however did not match the 1989 peak. In the United States alone, from 1960 to 1981, (peak year), the consumption went from 7.5 to 23.8 million nutrient tonn. This increase came along with an increase in cropped land and changes towards a more nutrient demanding-high yielding varieties. With the fertilizer use increment an increase in the fertility level of many soils also occurred. Constant P import into the system in quantities greater than those needed by the crop, built up the P content of the soils. This situation created an imbalance and brought about environmental concerns because of an increase in the eutrophication level of eco-sensitive surface waters, a current problem in Florida like everywhere else. This problem is enhanced in Florida by the low-P fixing capacity of the sandy soils and high annual precipitation (Humphreys and Pritchett, 1971).

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11 Fertilizer Chemistry-Reaction Post Application Application of water-soluble fertilizers is often followed by a series of in-situ reactions rendering a less soluble P-compound. As the P-rich solution diffuses out of the granule, the soil constituents around it may participate in adsorption/precipitation reactions. Depending on the type of fertilizer utilized, significant portions of the applied P can be chemisorbed before plant can uptake. In general monocalcium phosphate fertilizers have greater chances of interacting in such reactions than ammonium phosphates do (Sample et al., 1980). Most phosphate fertilizers consist of highly soluble P compounds that are not stable under soil conditions. The change in chemical form gives rise to products more suited for the soil conditions. Monocalcium phosphate (MCP) is the major component of superphosphate and is often present in mixed fertilizers (Lindsay and Stephenson, 1959b). As the dissolved fertilizer interacts with the soil, the resultant soil solution moving out of the fertilizer granule is known as meta-stable triple point solution (MTPS). The nature of the soil-fertilizer reaction products depends to a large extet upon the acidity developed as the applied fertilizer dissolved (Lindsay et al., 1962). The pH of the MTPS of MCP is around 1.48 in the first reaction band. Once the MCP reacted with a fine sandy loam soil it was found that the pH increased with time as well as a decrease in the P concentration in solution. It was also determined that the low pH of the MTPS dissolved Fe and Al from the soil constituents. Once in solution they reacted with P which was confirmed after a 3-month period, X-ray identification revealed the presence of amorphous Fe and Al-phosphates. The longer the reaction time the greater the amount of these precipitates (Lindsay and Stephenson, 1959a; Lindsay and

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12 Stephenson, 1959b). This is in agreement with the findings of Yuan et al.,(1960) who working with acid sandy soils found Fe and Al phosphates to be the primary fixed forms of added P. They suspected that some P remained as calcium phosphates after fertilizer application and became plant available with time. Additionally Humphreys and Pritchett, (1971) working with seven sandy soils of the Lower Coastal Plain region, described the reaction products after phosphate application. They found Fe-P and Al-P to be the dominant fractions in field conditions of the P retained by the soil seven to eleven years after the application. Dairy Manure Dairy farms have experienced substantial growth and intensification of their operations. This has increased the dependence in purchased feeds to meet animal nutrient requirements. Consequently, a nutrient imbalance has occurred where farm inputs exceeded outputs from the system, particularly in CAFO. Part of the imbalance (excess) is because the animal waste (manure); this results in an increase in soil-held P concentrations. Manure application to crops based on N requirements results in excess P because of a lower N:P ratio in manure than what the crop requires. When a limited area is available for land application, the same field receives manure for long periods of time resulting in increased P levels. Spray fields are usually located close to the barns to reduce the cost of transportation, a limiting factor in manure distribution (Daniel et al., 1998; Sharpley, 1996; Sims et al., 2000; Sui and Thompson, 2000; Whalen and Chang, 2001). Given the increased regulatory focus on P application there is a need to develop and implement management strategies to improve P balances on farms, maintain animal health and productivity while minimizing the effect of P on water quality. Manure storage

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13 and distribution according to P-based nutrient management plans are part of the optional strategies available. While this will likely result in increased cost or limiting dairy operation size, a reduction of excess P intake through diet manipulation is a cost-effective approach to achieving this goal. Reducing unnecessary mineral P supplementation will benefit not only the farmer as a lower cost in the feeding is experienced but also reduces the potential environmental effects (Dou et al., 2002). More precise diet formulation in dairy cows has reduced fecal P excretion without impairing animal productivity. Wu et al. (2000) found no differences in milk yield or other reproductive parameters through a complete lactation when reducing the diet from 4.9 to 4.0 mg P kg -1 . Furthermore, they saw a reduction of 23 % in the total P excreted. Above 70% of the total P (TP) in manures is plant available forms. Most of it is in readily available inorganic forms and/or becomes plant-available after application due to mineralization (Eghball et al., 2002). Dou et al. (2002) working with different levels of P in the diet found that raising dietary P concentrations from 3.4 to 6.7 g P kg -1 DM increased water soluble P from 24.2 to 94.4 g cow -1 day -1 in the feces while the other P fractions remained small and with little or no change. In the same study they also characterized the phosphorus in the feces. Between 56 and 64% is water soluble and between 46 and 59% of total P in feces is inorganic. It is important to highlight that although a high proportion of the total P in manure is in inorganic form, its reaction with the soil upon application is different from that of the inorganic fertilizers. Point and Non-Point Source Pollution Phosphorus may enter the water system at a specific point or location, known as point source pollution. Examples of this are discharge pipes of a factory or wastewater

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14 treatment plants. Phosphorus may also enter the environment from a non-specific diffuse area, which is known as non-point source of pollution. Eroded soil, nutrient leaching or runoffs from urban, residential and/or agricultural areas are examples of non-point source pollution. Phosphorus, attached to sediments derived from soil erosion, may reach lakes and streams and slow P release becomes an environmental concern. Point sources are more easily to locate and control, however non-point sources, such as those coming from agricultural operations are diffuse and complex and are therefore the focus of attention so that they can be controlled. Soil Testing Soil testing, Purpose and Scope In agriculture, now more than ever, the importance of an adequate supply of plant nutrients for crop production is being recognized. Nutrient deficiencies cause yield decreases while any excess of nutrient supply is uneconomical and environmental unsound. These constraints have pushed for a rapid and inexpensive procedure to better predict the nutrient needs of a specific crop in a given situation where soil, climate, crop variety and management factors exert considerable influence on plant nutrient composition and necessities (Marschner, 1995). Most of the essential nutrients are supplied to plants by the soil, and therefore it is important to know the status of soil nutrients. Soil testing can be defined as the chemical analysis of a given soil. It has become a precise and indispensable tool essential for the assessment of the fertility and productivity of a soil. Soil test should accurately determine the available nutrient status of a soil, indicate any serious deficiencies or possible toxicity for a given crop and form the basis for determining whether or not a fertilizer is needed (Tisdale et al., 1999). The effectiveness of the procedure is related to the extent to which

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15 the data has been previously evaluated and calibrated for a truthful interpretation of the analysis (Westerman, 1990). A soil-testing program is a result of a significant background research. The background research should indicate field-sampling techniques, test procedures, methodologies and an accurate correlation with crop needs. The soil-testing program starts with the collection of representative samples in the field where the objective is to reflect in the chemical analysis the true nutrient status of the whole field. It does not imply that all samples will give the same result but rather they will reflect the field’s natural variability. If the sample does not represent the field, it is impossible to provide a reliable recommendation (Westerman, 1990). Soil sampling schemes can be systematic as well as random. In both cases the final value is an average of the whole field. According to the field variability a more intensive sampling may be needed. Areas that vary in appearance, slope, drainage, soil type or nutrient management should be sampled separately. Depth of sampling is intended to reflect crop root system. In annual crops the depth of tillage is usually the depth of sampling, from 15 to 30 cm (Tisdale et al., 1999). Chemical analysis of the samples is another component in the soil-testing program. Composed of hydrochloric acid and sulfuric acid (0.05 N HCl and 0.025 N of H 2 SO 4 ), Melich-1 -or dilute double acid methodis a method used to determine nutrient concentrations in soils which have low cation exchange capacities (less than 10 cmol (+)/kg soil), are acidic in reaction (pH less than 6.5) and are relative low in organic matter content. According to Bray (1938), Ca and P readings from acid extractants can be higher

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16 than plant available concentrations because of the dissolution of calcium-phosphates compounds present in the soil. Soil pH (also known as soil reaction) is one of the primary variables of soil chemistry, affecting many soil factors that influence plant growth. The term pH is defined as the negative logarithm to the base 10 of the H-ion concentration; therefore for every unit increase in pH, the H-ion concentration increases ten folds. Increase in pH equals decrease in H-ion concentration (Tisdale et al., 1999). Plant nutrients, particularly P, K, Ca, Mg, B, Cu, Fe, Mn and Zn, are generally more available to plants in the pH range of 5.5 to 6.5 (Sartain, 2001). Plant available nutrient means the chemical form or forms of an essential plant nutrient in the soil whose variation in amount is reflected in variations in the plant growth and yield. The idea behind the soil test is to simulate plant extractability of the specific nutrient and the soil capacity to re-supply that nutrient to the soil solution from the nutrient pools that control availability. Many extractants have been developed for soil testing; the reactions controlling the nutrient supply to plants (availability) are closely related to the accuracy of the extrantant used (Tisdale et al., 1999). Environmental implications, besides nutrient bioavailability, have been the concern of soil testing laboratories during the past 10-15 years; many studies have been done on the subject. Laboratory research shows that soils with high to very high levels of soil test phosphorus (STP) are more likely to have high levels of WSP. This was confirmed with field studies which have shown that P losses by erosion, surface runoff, and leaching, lateral subsurface flow are greater when STP values are above the agronomically optimum range (Pautler and Sims, 2000; Pote et al., 1996; Sims et al., 1998).

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17 As environmental concerns about agricultural P intensify, the demand from environmental agencies for a systematic approach to use soil P testing in water quality protection efforts can be expected to increase (Sims et al., 2000). That is why agronomically focused soil testing procedures have been the subject of study in an effort to correlate them with environmentally focused testing procedures. For example, Pautler and Sims (2000), working with 122 soils from Delaware and 5 from the Netherlands found Mehlich-1 significantly correlated (P <0.001) with total P, oxalate-extractable P, Fe oxide-strip P and dilute salt (0.01 M CaCl 2 ) extractable P. Like Mehlich-1, Mehlich-3 was also found to accurately predict WSP, Fe oxide strip P and total P (Sims et al., 2002). Additionally, they found M-3 degree of P saturation to have a linear relation with oxalate P saturation method. Mehlich-3 was also found to have a close linear relationship with P removed from Fe oxide-impregnated strips (Indiati, 1998). Other soil tests procedures like Vermont-1, Vermont-2, Bray and Kurtz-1 (Magdoff et al., 1999) and Olsen (Heckrath et al., 1995) have also been used to assess potential for soil P loss to runoff waters. Research focused on environmental applications of routine soil testing procedures has encouraged regulators in many areas to consider setting environmental limits for soil test P as a relatively cheap method to target limited resources for reducing agricultural P losses. For example STP limits are now being considered in areas where intensive CAFOs created P surpluses and losses from agricultural areas have been identified as having a negative effect on surface waters (Maguire and Sims, 2002). In the state of Florida agricultural areas near lake Okeechobee (Nair et al., 1995), the Everglades (Reddy et al., 1998) and the MSRB are also being targeted due to nutrient loading,

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18 resulting in soil P enrichment. The use of STP is a reliable tool as long as other parameters are taken into account; particularly the source of phosphorus which can play an important role on P solubility and therefore on the potential environmental effects it may have on water quality.

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CHAPTER 3 MATERIALS AND METHODS Site Selection and Sampling Sampling sites were first identified and characterized based on three specific sources of P: inorganically fertilized, manure amended and native phosphatic soils. Sites for the inorganically fertilized and manure-amended soils were selected with help of the Suwannee River Water Management District; where the records indicated that the areas had received exclusively either inorganic fertilizers or dairy manure as nutrient sources for crop production. Phosphatic sites were native areas unimpacted by anthropogenic activities. Presence of phosphatic nodules (P-precipitates) and TP were the main criteria used to confirm the presence of phosphatic soils. All sites for inorganically fertilized and manure-amended soils were located in the MSRB. Sampling Manure amended and inorganically fertilized soil sites were all located in the MSRB; phosphatic soil sites were located in both the MSRB and the St. Johns River Basin. At each location sampling consisted of collecting composite samples at two depths (0 to 5 and 5 to 15 cm). The number of samples collected varied depending on the source of P. In manure-amended and inorganically fertilized farms, ten samples per field were collected, where as in native phosphatic soils five samples were taken. Phosphatic Soils Four sites were selected. Five randomly chosen samples were composited at each site; two depths (0 to 5 and 5 to 15 cm) were collected at each sampling location. An 19

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20 additional sample at a depth of 80-100 cm was collected in order to ensure a high TP concentration in the subsoil (e.g. that the soil was naturally phosphatic). Additionally X-ray evaluation was performed on the nodules present in the sample to identify the nature of the crystalline P forms present. Inorganically Fertilized Soils The inorganically fertilized farms presented a variety of crops grown: pasture for hay in two fields, peanuts, sorghum and pine trees in three fields and the last one had been fallow for 6 months (from May to November, 2002). Manure Amended Soils Six plots were identified where liquid dairy manure had been the only anthropogenic P-source added. Although inorganic P is present in manure, for the purposes of this study it was considered as an organic source. Sampled fields varied in size. However, the same total number of samples (10) were collected per field. In all cases, fields were located on a dairy farm, close to the barn facilities. Pasture was growing in all six plots; three of them were exclusively for hay purposes, two of them for grazing animals and one combined harvesting of hay and grazing animals. At each one of the manure amended and inorganically fertilized locations, ten sampling spots were chosen based on a field transect. No consistent sampling scheme was followed. However transect direction was intended to best represent the delineated area. In every selected spot two composite samples were collected, one from 0 to 5 cm and another from 5 to 15 cm depth from the soil surface. Sample Processing and Analysis Upon collection, samples were brought to the Extension Soil Testing Laboratory (ESTL) at the University of Florida where they were air dried in a hot room at 100 degree

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21 Celsius (C). Once dried, the samples were sieved and stored in plastic bags at room temperature. Soil pH Determination Soil pH was determined in a 1:2 (v/v) soil to destilled-deionized water ratio using a glass electrode. The pH meter was calibrated with 4.00, 7.00 and 10.00 standard buffer solutions prior to measurement. The procedure used was as stated in the manual for the Extension Soil Testing Laboratory (Mylavarapu and Kennelley, 2002). Mehlich-1 Extraction Mehlich-1 extraction (a dilute double acid mixture of 0.0125 M H 2 SO 4 + 0.05 M HCl) is calibrated for acid-mineral soils of Florida for various agronomic and horticultural crops (Mylavarapu and Kennelley, 2002). Five grams of soil were mixed with 20 ml of Mehlich-1 extractant solution (1:4 w/v), with 5-m reaction time and filtered using Whatman 42 filter paper. The collected supernatant solution was then analyzed for P, Ca, Mg, Fe and Al. The solution was kept under refrigeration until reading (maximum of 3 days). Nutrient concentrations were determined using Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES). Mehlich-3 Extraction Mehlich-3 extraction (a solution containing 0.015 M NH 4 F + 0.25 M NH 4 NO 3 + 0.001 M EDTA + 0.2 M CH 3 COOH + 0.13 M HNO 3 ) used 3.125 g of soil in 25 mL of solution for a 1:8 w/v ratio, given 5-m reaction time and then filtered with Whatman #41 filter paper. The supernatant was then analyzed for P, Ca, Mg, Fe and Al by inductively coupled plasma atomic emission spectroscopy (ICP-AES). When necessary, samples were refrigerated for a maximum of 3 days.

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22 Water-soluble Phosphorus Water-soluble phosphorus (WSP) was determined using a 1:10 (w/v) soil to deionized water ratio, 1-h reaction time (shaking) followed by filtration through a vacuum pump with 0.45-m Millipore membrane. From the recovered filtrate P was analyzed colorimetrically by the molibdate method (Murphy and Riley, 1962). Total Carbon Total carbon was determined by an automated combustion procedure at 1020 C using a Carlo-Erba (Milan, Italy) NA-1500 CNS Analyzer. For the procedure 0.05 g of soil sample were weighed on aluminum cups and then ignited in the combustion chamber. Total carbon was calculated based on known weights of the standard. Particle Size Distribution The classification system used to interpret the results is that of the U. S. Department of Agriculture. In the particle size determination, hydrogen peroxide was used in the organic matter removal. Upon organic matter removal, particle size determination was done by the pipet method, with sodium hexametaphosphate as the dispersing agent. Total Phosphorus Analysis by the Ignition Method One gram of soil was placed into a 50 ml beaker. It was placed for an hour in a muffle furnace at a temperature of 350 degrees C, then the temperature was raised to 550 degrees C, the sample was left in it for 2 hrs. Once the sample was cooled the ash was moistened with a few drops of DI water and 20 ml of 6M HCl were added. The solution was allowed to evaporate slowly on a hot plate. When the residue was dry, the temperature was raised to dehydrate the silica. Upon cooling, 2.25 ml of 6M HCl were added to the contents of beaker, then the beaker was warmed to dislodge the residue and

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23 the solution was quantitatively transferred (use a Whatman # 41 filter paper) in to a 50 ml volumetric flask collecting all the residues from the beaker. The solution was then ready for TP determination by the molibdate method (Murphy and Riley, 1962). Statistical Analysis Linear regression analysis was performed with the data analysis tool pack in Excel 2000 (Microsoft, 2000). Additional statistical analyses were performed using software of the Statistical Analysis System (SAS-Institute, 1989).

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CHAPTER 4 RESULTS AND DISCUSSION Soil pH, Particle Size and Organic Carbon The pH values for the phosphatic soils ranged from 4.9 to 6.6 at both soil depths (0 to 5 and 5 to 15 cm). The variation observed was mainly among sampling sites rather than within sites. The soil pH is generally influenced by several management factors including the crop grown, irrigation, and the type of fertilizer used, a factor that may have a greater impact in inorganically fertilized soils due to the wider pH range (4.6 to 7.1) observed. Similarly, soil pH values from manure-amended soils ranged from 4.9 to 7.5. In general the soil pH values from the three different P sources averaged 6.1 an acidic value, typical of the sandy soils commonly found in Florida. Particle size was determined for a composite sample from each one of the sites chosen. Clay content ranged from 0.2 to 5.4% while the percentage of sand varied from 84.7 to 98.0 %. Soils used in this study belonged to either sand or loamy sand textural classes. Because of the homogeneity in soil textural classes, this variable was left out of the statistical analysis. Organic Carbon (OC) values were found to be higher in the 0-5 cm depth than in the 5-15 cm depth (table 1). To avoid any anthropogenic influences, phosphatic soils samples were collected from areas inside a native forest, and as a result organic carbon accumulation in the topsoil was observed. The OC content for these soils ranged went from 0.3 to 2.1 %. 24

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25 Table 4-1. Soil pH and OC for each of the three soil P sources. P source Type Statistic Phosphatic Inorganic Fertilized Manure Amended Soil Organic Carbon (%) Mean 2.2 1.0 2..2 Range 0.3 – 2.1 0.5 – 10.9 0.5 – 8.0 SD 1.2 0.9 1.5 N= 30 120 120 pH Mean 5.8 6.0 6.3 Range 4.9 – 6.6 4.6 – 7.1 4.9 – 7.1 SD 0.5 0.5 0.4 N= 30 120 120 Organic Carbon content in inorganically fertilized soils ranged from 0.5 to 10.9 % with a mean of a range typical of these soils. Manured soils presented the highest mean OC value at both depths (0-5 and 5-15 cm) with a range of 0.5 to 8.0 % in the top 5 cm and 0.5 to 4.4 % at the 5-15 cm depth. Extractable Soil Phosphorus A wide range of soil test P values was observed for each one of the soil testing procedures used as well as the soil P sources analyzed (Table 2). Phosphorus concentrations using M-3 extractant were higher than M-1 P in inorganic fertilized and manure amended soils. The opposite occurred for phosphatic soils where M-1 extracted higher P levels, yet no significant difference was found between these two extractants regardless of the P source. The mean M-1 P concentration observed in each one of the three sources is well above the agronomic optimum level of 30 mg kg -1 (Mylavarapu, 2002). Although agronomic interpretation of soil test P levels indicate suitability for agricultural production, the solubility of the phosphatic minerals may not indicate at natural soil pH values is not the same and may not properly correspond with adequate plant growth in an agricultural setting.

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26 Table 4-2. Mehlich-1 Phosphorus, Mehlich-3 Phosphorus, and Water Soluble Phosphorus for each of the three soil P sources. P source Type Statistic Phosphatic Inorganic Fertilized Manure Amended --------------------------mg kg -1 -------------------------Mehlich-1 P Mean 297.9 a 64.3 a 278.6 b Range 25.1 1814.8 21.6 – 128.1 34.9 – 1350.0 SD 409.0 25.5 277.2 n= 30 120 120 Mehlich-3 P Mean 188.9 a 127.4 a 336.0 b Range 69.7 – 345. 4 64.1 – 234.6 109.0 1008.0 SD 84.6 39.4 212.6 n= 30 120 120 Water Soluble P Mean 10.6 a 5.7 a 30.6 a Range 4.4 – 22.5 1.3 – 9.6 2.0 – 150.5 SD 4.3 2.1 29.6 n= 30 120 120 Different letters in the same column indicate significant difference (P< 0.001). Extractable P concentrations for phosphatic soils indicated high P levels extracted with either M-1 or M-3 and relatively low WSP concentrations. No significant difference was found in WSP between sources but WSP/Mehlich-P was significant lower for phosphatic soils. In phosphatic soils, despite the high M-1 P and M-3 P levels, low WSP were observed. X-ray diffraction was performed in a sample from each one of the three locations selected. This sample was taken between 80 and 100 cm of depth. Fluorapatite was found in all of the three sites, wavellite in two of them and crandallite in one. Flourapatite is the mineral most susceptible to weathering, followed by crandallite, with wavellite being the most resistant (Wang et al., 1989). No significant difference was found among soil test extractants. In inorganically fertilized soils M-3 on average extracted nearly twice as much P than M-1 did and over 22 times that of WSP. Although these differences seem very clear,

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27 there was a lot of variation in the sample-to-sample relationship which resulted in no significant difference among extractants. In manure amended soils M-1 P and M-3 P concentrations were significantly higher compared to WSP levels (P < 0.05). The mean concentration for M-1 and M-3 P was 278.6 mg kg -1 and 336.0 mg kg -1 , respectively; while the WSP mean concentration was 30.6 mg kg -1 . Relationship among Mehlich-1 P, Mehlich-3 P and Water Soluble P Phosphatic Soils Significant correlation (P< 0.001) was found between WSP and M-1 P concentrations (Figure 1.) with r 2 = 0.41. The correlation between the two parameters remained the same when depths (0-5 and 5-15 cm) were analyzed independently, indicating that the P solubility was not influenced by depth. In phosphatic soils WSP concentrations were very low relative to the high M-1 values obtained. The two M-1 P values above 1000 mg kg -1 were from samples collected in soils where fluorapatite was present and the values were suspected to be due to the dissolution of fluorapatite when extracted with M-1; Wang et al. (1989) found Mehlich-1 to be capable of extracting high levels of phosphorus from soil minerals like apatite despite the fact that this form of P is only slowly plant available. In a follow up study Wang et al., (1991b) found that for phosphatic soils containing wavellite and noncrystalline-P associated with Al and Fe, Mehlich-1 P values were not correlated with total P values.

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28 y = 0.006x + 8.6R2 = 0.410.005.0010.0015.0020.000.0500.01000.01500.0Mehlich-1 P (mg kg-1)WSP (mg kg-1) Figure 4-1. Correlation between Mehlich-1 Extractable P and Water Soluble P in phosphatic soils. When comparing WSP with M-3 P in phosphatic soils (Figure 2) no significant correlation was found (r 2 = 0.002). Water soluble P levels were extremely low while M-3 P values observed were in the high to very high range for agronomic crops. There was no consistency in the levels of M-3 P observed. This variability is possibly due to the type of minerals that P is associated with in the soil. At given WSP level, the corresponding M-3 concentration ranged from 65 to 337 mg kg -1 (Figure 2). Mehlich-1 Fe and Al concentrations (Appendix A) were lower than those of Mehlich-3 in phosphatic soils. Amorphous forms of P, particularly those associated with Fe are well documented in Florida, particularly in phosphatic soils where naturally occurring high P levels perturbed the formation of crystalline Fe minerals (Wang et al., 1989; Wang et al., 1991a; Wang et al., 1991b). Amorphous forms of Fe and Al phosphates are 10 to 100 times more soluble than crystalline minerals (Wang et al.,

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29 1991a). Consistently, Ca levels in M-3 were lower than those of M-1. A two fold explanation could be given to this fact: first, the apatite did not dissolve in M-3 to the same extent as M-1 and second, the Ca being dissolved from apatite was quickly re-precipitating as it reacted with the fluoride present in M-3. It was also reported that the M-3 extracted more Al-P and Fe-P than M-1 because of the greater acid strength and the presence of complexing fluoride ions (Ballard, 1974; Sartain, 1980). y = -0.002x + 11.0R2 = 0.0020.005.0010.0015.0020.000100200300400Mehlich-3 P (mg kg-1)WSP (mg kg-1) Figure 4-2. Correlation between Mehlich-3 Extractable P and Water Soluble P in phosphatic soils. Inorganically Fertilized Soils. Extractable phosphorus levels in inorganically fertilized soils showed a wide range of values while the corresponding WSP concentrations remained low regardless of higher M-1 or M-3 phosphorus readings (Figure 3 and 4). The sampling depth had no effect on the correlation among M-1 P, M-3 P and WSP, and therefore the results shown in Figures 3 and 4 are for combined depths of 0 -15 cm.

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30 y = 0.05x + 2.3R2 = 0.420.002.004.006.008.0010.0012.000.0050.00100.00150.00Mehlich-1 P (mg kg-1)WSP (mg kg-1) Figure 4-3. Correlation between Mehlich-1 Extractable P and Water Soluble P in inorganically fertilized soils. In inorganically fertilized soils, Mehlich-1 P levels were mostly located in the high (31 – 60 mg kg -1 ) to very high (>60 mg kg -1 ) ranges according to IFAS interpretations for agronomic crops. Correlation of M-1 P with WSP (Figure 3) was found to be significant (P < 0.0001. r 2 =0.42). Although significant, the r 2 is relatively low. The chemical reactions following a fertilizer application depend largely on the type of fertilizer used. In acid soils, di-ammonium phosphate (DAP) reduces chemisorption (adsorption/ precipitation) reactions with Al and Fe because the triple point solution (TPS) leaving the granule has a pH of 7.48. Unlike DAP, mono-ammonium phosphate and mono-calcium phosphate fertilizers enhance chemisorption reactions in acid soils as the pH of the TPS can be as low as 1.01 (Lindsay and Stephenson, 1959a). Such an acid pH can result in the dissolution soil constituents such as Fe, Al, Ca, Mn; following fertilizer application, the reaction of a P saturated solution with these elements being dissolved from the soil

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31 promotes the formation of Fe and Al phosphates, which, under the conditions of the system will co-precipitate on the surface of the soil particles (Chu et al., 1962). The solubility of Fe and Al phosphates is expected to decrease with time (Lindsay and Stephenson, 1959a; Lindsay et al., 1962). Humphreys and Pritchett, (1971) working with seven sandy soils of the Lower Coastal Plain region, described the reaction products after phosphate application. Under field conditions, they found Fe-P and Al-P to be the dominant fractions of all the P retained by the soil 7 to 11 years after the application of inorganic fertilizer. Low concentrations of M-1 P and M-3 P that were observed probably came from samples where aged precipitates of Fe and Al phosphates were present. High M-1 P and M-3 P concentrations were also observed, which were expected to be plant available, newly-fixed forms of P. The forms of P found in inorganically fertilized soils had low WSP concentrations regardless of the level of extraction in either M-1 or M-3. Low water soluble P concentrations were found in all inorganically fertilized samples. These levels are expected to be from the readily available P pools of calcium phosphates with high solubility. The correlation between M-3 P and WSP was poor with an r 2 =0.28, however statistically significant (P < 0.0001) (Figure 4). The relation is not very different from that of M-1 P with WSP (Figure 3) although M-3 extracted higher levels of P than M-1. In M-3 there are three components that may help to extract greater quantities of P. EDTA acting as a complexing agent binding the metals associated with P, rendering more P in solution; acetic acid dissolving Ca-P and ammonium fluoride, extracting P associated with Al as it was a part of the P fractionation procedure to extract Al-P (Yuan et al., 1960).

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32 y = 0.03x + 2.2R2 = 0.270.002.004.006.008.0010.0012.00050100150200250Mehlich-3 P (mg kg-1)WSP (mg kg-1) Figure 4-4. Correlation between Mehlich-3 Extractable P and Water Soluble P in inorganically fertilized soils. Manure Amended Soils. The correlation between soil test extraction procedures in manure amended soils had the highest correlation coefficient than any other source of P. The correlation of WSP with M-1P and M-3 P was significant (P< 0.0001), with r 2 = 0.93 and r 2 =0.89 respectively (Figure 5 and 6). This concurs with the findings of (Pautler and Sims, 2000; Sims et al., 2002) who find that soil test phosphorus (M-1) was significantly correlated with WSP. Manure amended soils were determined to show the highest levels of WSP (Figure 5 and 6). In manure, >70% of the total phosphorus (TP) present exists as plant available. Most of the P in manure is in readily available inorganic forms and/or becomes plant-available after application due to mineralization (Eghball et al., 2002). Dou et al. (2002) working with different levels of P in dairy cows diets found that by raising dietary P concentrations from 3.4 to 6.7 g P kg -1 of dry matter resulted in increased water soluble P from 24.2 to 94.4 g cow -1 day -1 in the feces while the other P fractions remained small

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33 with little or no change. In the same study they also characterized the total phosphorus in the feces; between 56% and 64% of the total P is water soluble P and between 46% and 59% of total P in feces is in inorganic forms. These pools of phosphorus in manure are all extracted by the acidity present in either of the Mehlich extractants. That resulted in quick dissolution of phosphorus applied through manure present in these fields. y = 0.10x + 2.1R2 = 0.930.0020.0040.0060.0080.00100.00120.00140.00160.000.0500.01000.01500.0Mehlich-1 P (mg kg-1)WSP (mg kg-1) Figure 4-5. Correlation between Mehlich-1 Extractable P and Water Soluble P in manure amended soils. Nair et al., (1995) describing the forms of P in soil profiles from dairies in South Florida found that over 70% of the TP was associated with Ca and Mg, determined by using a 0.5 M HCl solution. The authors attributed this association to the high Ca and Mg in the cattle manure and to soil management practices like liming. They also concluded that this portion of P can be detected when using a soil test P like Mehlich-1. Because of the similar acidities and methods of extractions one can infer that Mehlich-3 would also be capable of extracting P present in this form.

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34 y = 0.13x 13.3R2 = 0.890.0020.0040.0060.0080.00100.00120.00140.00160.000.0500.01000.01500.0Mehlich-3 P (mg kg-1)WSP (mg kg-1) Figure 4-6. Correlation between Mehlich-3 Extractable P and Water Soluble P in manure amended soils. In manure amended soils the arithmetic mean of WSP was 30.6(a) and had significant difference (P< 0.0001) with respect to M-1 P 278.6(b) and M-3 P 336.0(b). This was the only case where significant difference was found among soil test extractants and WSP. This indicates that in the case of phosphatic and inorganically fertilized soils, although the relationship was significant at the 0.0001 level the mean separation was not significant. Influence Al, Fe, Ca, Mg and OC on P Extractability Multi-variate regression analysis based on the source of P was performed to weigh the influence of Al, Fe, Ca, Mg, and OC on the extractable P level with both, M-1 and M-3. The analysis was performed with and without Ca and Mg to see if the inclusion of these two elements made any difference. It was done by depth (0-5 and 5-15) as well as both depths together. While depth separation had no impact on the results, the addition of

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35 Ca and Mg into the model did in manure amended soils and helped explain the variability in M-1 P from phosphatic soils. Analysis of P= fn (Ca, Mg, Fe, Al and OC) in phosphatic soils was done (Table 4-3); these results were for the combined two depths studied. When Ca and Mg were excluded from the analysis, the other components failed to explain the variability seen in phosphatic soils. Both Ca and Mg were introduced into the equation once the X-ray diffraction revealed the presence of fluorapatite (a calcium phosphate) in two of the three locations sampled. Flourapatite or non crystalline calcium phosphates are more extractable than noncrystalline Al-P or Fe-P when the extractant has high affinity with Ca or has a strong acid component (Chu et al., 1962; Sartain, 1980; Wang et al., 1989; Yuan et al., 1960). Table 4-3. Multivariable regression analysis for P= fn (Al, Fe, Ca, Mg and OC) in phosphatic soils. Variable Partial R-square Model R-square Pr > F Mehlich-1 M-1 Ca 0.76 0.76 0.0001 M-1 Mg 0.1 0.86 0.0002 M-1 Al 0.04 0.90 0.006 Mehlich-3 M-3 Al 0.85 0.85 < 0.0001 Mehlich-1 extractions resulted in higher Ca levels in phosphatic, inorganically fertilized and manure amended soils compared to Mehlich-3 extraction. In Florida, no agronomic interpretation is given to Mehlich-1 Ca concentrations because of reduced accuracy of the readings and the effect M-1 has on dissolving Ca phosphates (Mylavarapu, 2002). Although the acidity produced by M-3 can also dissolve the Ca-P present, a precipitation reaction is expected to occur between Ca and F resulting in lower Ca concentration in solution, therefore lower Ca readings. The mechanisms involved in

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36 maintaining the P in solution are not well understood, however they have been observed and documented (Gartley et al., 2002; Mehlich, 1984; Sims et al., 2002). Table 4-4. Multivariable regression analysis for P= fn(Al, Fe, OC) in inorganically fertilized soils*. Variable Partial R-square Model R-square Pr > F Mehlich-1 M-1 Al 0.57 0.57 0.0001 M-1 Fe 0.04 0.61 0.0005 Mehlich-3 M-3 Al 0.66 0.66 0.0001 M-3 Fe 0.11 0.77 0.0001 *: No other variable met the 0.5000 significance level for entry into the model. Multivariate regression analysis in inorganically fertilized soils is presented in Table 4. When the two depths were analyzed independently, no difference was shown in the results as compared to combined analysis and therefore, the results shown are for combined depths (0cm). Furthermore, the introduction of Ca and Mg made no significant difference on the multivariate regression analysis (Table 4-4). From the results, it is noted that, despite the different P levels extracted by M-1 and M-3, Al and Fe were the two elements that explained the variability seen in the P concentrations. Several studies (Chang and Juo, 1963; Chu et al., 1962; Lindsay and Stephenson, 1959a; Lindsay and Stephenson, 1959b; Lindsay et al., 1962; Yuan et al., 1960) described Fe and Al phosphate to be the primary reaction products following Ca phosphate fertilizer applications, resulting in compounds that became more insoluble with time in acid soils. Figure 7 conceptualizes the reactions occurring upon fertilizer application to soils.

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37 Band 1= pH 1.48 – 3.0 MCP Band 2= pH 3.0 – 5.0 Fe-Phosphates Fe and Al coatings Al-Phosphates Soluble dicalcium SAND SAND phosphate (CaHPO4) Orthophosphate in solution Ca-Phosphates in solution MAP Band 1= pH ~3.47 (MSTPS) Figure 4-7. Series of reactions following monocalcium and monoammonium phosphate fertilizer application in soils.

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38 Results from the multivariate analysis of manure-amended soils showed significant difference when Mg and Ca were introduced into the equation and when independently run by depths. Therefore, separate results are presented by depth and also with and without the inclusion of Ca and Mg. Table 4-4 shows the results at the 0-5 cm depth with Al, Fe and OC as the only components of the analysis. Both Fe and Al concentrations resulting from either of the soil test extractants used were not able to adequately explain the P results obtained. Table 4-5. Multivariable regression analysis for P= fn (Al, Fe, OC) in manure amended soils at the 0-5 cm depth. Variable Partial R-square Model R-square Pr > F Mehlich-1 OC 0.57 0.57 <0.0001 Mehlich-3 OC 0.53 0.53 <0.0001 However OC was capable of explaining over half the variability with 95% confidence at P < 0.0001 (Table 4-5). Since OC forms the main component of sprayed manure such a relationship is possible. However, the fact that OC was able to explain the variability may not necessarily mean that the P present is bound to it. It has been documented that P existed mainly in inorganic forms (Nair et al., 1995; Nair et al., 1998; Zheng et al., 2002). Table 4-6, presents the results from the 5-15 cm depth from manure-amended soils. Aluminum, Fe and OC are the components included in the analysis. The main difference with respect to the surface samples (0-5 cm) is the reduced importance of OC, particularly in Mehlich-1 extractions were M-1 Al comes out to be the main factor capable of explaining the variability seen in the M-1 P concentrations. For the M-3 extraction, none of the elements (Fe or Al) were of importance in explaining M-3 P

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39 values. However, OC remained an important factor in the relationship with a partial r 2 = 0.48 (P < 0.0001). Table 4-6. Multivariable regression analysis for P= fn (Al, Fe, OC) in manure amended soils the 5-15 cm depth. Variable Partial R-square Model R-square Pr > F Mehlich-1 M-1 Al 0.57 0.57 <0.0001 OC 0.04 0.61 0.01 Mehlich-3 OC 0.48 0.48 <0.0001 M-3 Fe 0.06 0.54 0.007 For manure-amended farms, when Mg and Ca were included in the model, the importance of other factors changed (Table 4-7). Concentrations of Ca and Mg in cattle manure can be as high as 14500 and 5630 mg kg -1 respectively (Nair et al., 1995). Besides, Ca metabolism in ruminants is closely associated with that of P (Irving et al., 1973; McDowell, 1992). Therefore, close association of Ca and Mg to P in manure amended soils is expected. Table 4-7. Multivariable regression analysis for P= fn (Al, Fe, Ca, Mg and OC) in manure amended soils for the combined soil depth of 0-5 and 5-15 cm. Variable Partial R-square Model R-square Pr > F Mehlich-1 M-1 Mg 0.78 0.78 <0.0001 M-1 Al 0.07 0.85 <0.0001 M-1 Ca 0.03 0.88 <0.0001 M-1 Fe 0.01 0.89 0.0005 Mehlich-3 M-3 Mg 0.69 0.69 <0.0001 M-3 Al 0.08 0.77 <0.0001 M-3 Ca 0.03 0.80 <0.0001 OC 0.02 0.82 0.002 M-3 Fe 0.01 0.83 0.003 This model not only included more variables of significance than any other but it was also able to explain to a higher degree the variability between M-1 P and M-3 P

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40 concentrations. For M-1 the model showed an r 2 =0.9 with a 95% confidence interval and all other variables with a p 0.003. The relationships seen between WSP and M-1P and M-3P for the three P sources analyzed revealed the differences in the chemistry governing P reactions in each case. The poor relationship seen in phosphatic soils is due to the different solubility levels fluorapetite, crandallite and wavelite have when reacted with acid extractants, hence producing a wide range of P concentrations. For inorganically fertilized soils, the type of fertilizer and the time after the application have a strong influence on the WSP concentration as some fertilizers enhance P precipitation after application, particularly in soils where Fe and Al are present. A significant, however, low correlation was found in fertilized soils. Finally, a high correlation was seen between Mehlich extractants and WSP in manure-amended soils. Manure-amended soils had the highest values of WSP and Mehlich P. This fact can be misleading as high values do not represent the majority of the data. In other words the correlation increases because of the presence of such high values. If we were to focus on the lower range of the concentrations, the strength of the correlation will be reduced. This could be because of the natural capacity of the soil to absorb and retain nutrients in low levels. However, when the area is severely impacted with P loading, a higher portion of the P is present in the WSP fraction. Apparent difference exists in the WSP among the three P sources, particularly for phosphatic soils. Since there was no statistical difference, the (WSP/Mehlich-1 P) ratio values were statistically analyzed. Significant difference was found (P<0.001) between (WSP/Mehlich-1 P) in phosphatic soils with respect to inorganically fertilized and manure-amended soils, with no statistical difference between the latter two. This supports

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41 the point that phosphatic soils are less prone to off-site P movement due to the mineralogy and the form P is present in those soils.

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CHAPTER 5 SUMMARY AND CONCLUSION Summary This study was designed to evaluate the relationships among WSP levels in phosphatic, manure amended and inorganically fertilized soils, with Mehlich-1 P and Mehlich-3 P concentrations, and to determine the influence of Al, Fe, Ca, Mg, and OC on extractable P. Manure-amended and inorganically fertilized soils samples were collected from the MSRB, and phosphatic soil samples from both the MSRB and St. Johns River Basin. Mehlich-1 P was significantly correlated with WSP in phosphatic; inorganically fertilized, and manure-amended soils. Mehlich-3 P was not significantly correlated with WSP in phosphatic soils but it was in manure-amended and inorganically fertilized soils. In inorganically fertilized, although significant, correlations had a low r 2 value. No statistical difference was found on the WSP concentrations among the three P sources in soils. Significant difference was found (P<0.001) between (WSP/Mehlich-1 P) ratio in phosphatic soils with respect to inorganically fertilized and manure-amended soils. Conclusions Soils with Crystalline Al-P minerals forms had low solubility in Mehlich extractants Crystalline Ca-P minerals present in phosphatic soils can be dissolved by Mehlich extractants In phosphatic soils, M-1 and M-3 P concentrations did not accurately predict WSP Poor correlation was found between WSP and M-1 and M-3 P in inorganically fertilized soils 42

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43 Fe-P and Al-P precipitates in inorganically fertilized soils apparently become more insoluble with time Iron and aluminum together were positively correlated with M-1 and M-3 phosphorus concentrations M-1 and M-3 have high correlation with WSP in manure amended soils Magnesium was highly correlated with phosphorus in manure amended soils In the 0-5 cm soil depth OC was positively correlated with phosphorus concentrations Manure amended soils and inorganically fertilized had higher average concentrations of (WSP/ M-1 P) ratio than phosphatic soils.

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APPENDIX A MEHLICH-1 AND MEHLICH-3 CONCENTRATIONS OF FE, AL, CA, AND MG IN PHOSPHATIC, MANURE AMENDED AND INORGANICALLY FERTILIZED SOILS. P source Type Statistic Phosphatic n = 30 Inorganic Fertilized n = 120 Manure Amended n = 120 --------------------------mg kg -1 -------------------------Mehlich-1 P Fe Mean (SD) 23.4 (9.3) 11.7 (3.3) 11.4 (5.3) Range 9.8 45.2 5.9 – 20.2 4.5 31.2 Al Mean (SD) 345.7 (181) 189 (57.5) 213 (87.7) Range 102.1 – 780.0 93.3 – 338.3 62.2 466.8 Ca Mean (SD) 1320 (1151) 412 (138) 1186 (975) Range 104.8 4504.0 70.1 – 948.8 25.2 – 4552 Mg Mean (SD) 87.8 (46.3) 41.2 (19.9) 219 (196) Range 19.6 – 196.5 2.2 102.4 1.5 1251.2 Mehlich-3 P Fe Mean (SD) 143.4 (53.2) 117.9 (20.5) 94.3 (40.3) Range 61.4 – 232.2 73.8 161.1 10.6 162.9 Al Mean (SD) 700 (382) 485 (160) 452 (202) Range 130.4 1464.0 205.0 831.2 60.1 883.2 Ca Mean (SD) 790 (392) 353 (114.5) 953 (677) Range 140.6 1627.2 78.9 778.4 31.8 3057.6 Mg Mean (SD) 86.2 (47) 36.5 (17.3) 205 (183) Range 20.0 – 199.2 1.2 77.9 1.2 956.8 44

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APPENDIX B X-RAY DETERMINATION OF THE MINERALS PRESENT IN PHOSPHATIC SOILS. WWWF-A WWWF-A W= Wavellite F-A = Fluorapatite 45

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46 C C C C C= Crandellite

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47 F-A F-A = Fluorapatite

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LIST OF REFERENCES Arnaud, C.D., and S.D. Sanchez. 1996. Calcium and phosphorus., p. 245-255, In J. E. Zigler & L. J. Filer, ed. Present knowledge in nutrition, 7th ed. ILSI Press., Washington, D. C. Ballard, R. 1974. Extractability of reference phosphates by soil test reagents in absence and presence of soils. Soil and Crop Science Society of Florida Proceedings:169-174. Black, C.A. 1968. Soil-plant relationships. 2d ed. Wiley, New York. Brady, N.C., and R.R. Weil. 1998. The nature and properties of soils. 12th ed. Prentice Hall, Upper Saddle River, N.J. Bray, R.H. 1938. New concept of the chemistry of soil fertility. Soil Sci. Soc. Am. Proc. 2:175-179. Brye, K.R., T.W. Andraski, W.M. Jarrell, L.G. Bundy, and J.M. Norman. 2002. Phosphorus leaching under a restored tallgrass prairie and corn agroecosystems. J Environ Qual 31:769-781. Cathcart, J.B. 1986. The phosphate deposits of Florida with a note in the deposits in Georgia and South Carolina, USA, p. v., In A. J. G. Notholt, ed. Phosphate deposits of the world. Cambridge University Press, Cambridge; New York. Ceryak, R., M.S. Knapp, T. Burnson, and Florida. Bureau of Geology. 1983. The geology and water resources of the upper Suwannee River Basin, Florida. Tallahassee Florida. Chang, C.S., and S.R. Juo. 1963. Available phosphorus in relation to forms of phosphates in soils. Soil Science 95:91-96. Chu, C.R., W.W. Moschler, and G.W. Thomas. 1962. Rock phosphate transformations in acid soils. Soil Sci Soc Am J 26:476-478. Daniel, T.C., A.N. Sharpley, and J.L. Lemunyon. 1998. Agricultural phosphorus and eutrophication: a symposium overview. J Environ Qual 27:251-257. 48

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49 Dou, Z.X., K.F. Knowlton, R.A. Kohn, Z.G. Wu, L.D. Satter, G.Y. Zhang, J.D. Toth, and J.D. Ferguson. 2002. Phosphorus characteristics of dairy feces affected by diets. J Environ Qual 31:2058-2065. Eghball, B., B.J. Wienhold, J.E. Gilley, and R.A. Eigenberg. 2002. Mineralization of manure nutrients. Journal of Soil and Water Conservation 57:470-473. Gartley, K.L., J.T. Sims, C.T. Olsen, and P. Chu. 2002. Comparison of soil test extractants used in Mid-Atlantic United States. Communications in Soil Science and Plant Analysis 33:873-895. Harris, W.G. 2002. Phosphate minerals. Soil mineralogy with environmental implications. Soil Science Society of America, Madison, WI. Heckrath, G., P.C. Brookes, P.R. Poulton, and K. Goulding. 1995. Phosphorus leaching from soils containing different phosphorus concentrations in the Broadbalk experiment. J Environ Qual 24:904-910. Humphreys, F.R., and W.L. Pritchett. 1971. Phosphorus adsorption and movement in some sandy forest soils. Soil Sci Soc Am J 35:495-500. Indiati, R. 1998. Changes in soil phosphorus extractability with successive removal of soil phosphate by iron oxide-impregnated paper strips. Communications in Soil Science and Plant Analysis 29:107-120. Irving, J.T., F. Bronner, and G.A. Rodan. 1973. Calcium and phosphorus metabolism Academic Press, New York. Lindsay, W.L., and H.F. Stephenson. 1959b. Nature of the reaction of monocalcium phosphate monohydrate in soils: I. solution that reacts with the soil. Soil Sci Soc Am J 23:12-18. Lindsay, W.L., and H.F. Stephenson. 1959a. Nature of the reaction of monocalcium phosphate monohydrate in soils: II. Dissolution and precipitation reactions involving iron, aluminum, manganese, and calcium. Soil Sci Soc Am J 23:18-24. Lindsay, W.L., A.W. Frazier, and H.F. Stephenson. 1962. Identification of reaction products from phosphate fertilizer in soils. Soil Sci Soc Am J 26:446-452. Magdoff, F.R., C. Hryshko, W.E. Jokela, R.P. Durieux, and Y. Bu. 1999. Comparison of phosphorus soil test extractants for plant availability and environmental assessment. Soil Sci Soc Am J 63:999-1006. Maguire, R.O., and J.T. Sims. 2002. Soil testing to predict phosphorus leaching. J Environ Qual 31:1601-1609. Marschner, H. 1995. Mineral nutrition of higher plants. 2nd ed. Academic Press, London.

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50 McDowell, L.R. 1992. Minerals in animal and human nutrition. Academic Press, San Diego. McDowell, R.W., and A.N. Sharpley. 2001. Approximating phosphorus release from soils to surface runoff and subsurface drainage. J Environ Qual 30:508-520. Mehlich, A. 1984. Mehlich-3 soil test extractant; a modification of Mehlich-2 extractant. Communications in Soil Science and Plant Analysis 15:1409-1416. Microsoft. 2000. Excel, 2000, Redmond, WA. Murphy, J., and J.P. Riley. 1962. A modified single solution method for the determination of phosphate in natural waters. Anal Chim Acta 27:31-36. Mylavarapu, R. 2002. UF/IFAS Standarized Nutrient Recommendation Development Process for Successful Crop Production and Environmental Protection, pp. 4. UF/IFAS Nutrient Management Series, Gainesville, FL. Mylavarapu, R.and E. Kennelley. 2002. UF/IFAS Extension Soil Testing Laboratory (ESTL) Analytical Procedures and Training Manual. Nair, V.D., D.A. Graetz, and K.M. Portier. 1995. Forms of phosphorus in soil profiles from dairies of South Florida. Soil Sci Soc Am J 59:1244-1249. Nair, V.D., D.A. Graetz, and K.R. Reddy. 1998. Dairy manure influences on phosphorus retention capacity of spodosols. J Environ Qual 27:522-527. National Research Council (U.S.), S.o.D.C.N. 2001. Nutrient requirements of dairy cattle, 7th rev. ed. National Academy Press, Washington, D.C. Pautler, M.C., and J.T. Sims. 2000. Relationships between soil test phosphorus, soluble phosphorus, and phosphorus saturation in Delaware soils. Soil Sci Soc Am J 64:765-773. Pote, D.H., T.C. Daniel, A.N. Sharpley, P.A. Moore, D.R. Edwards, and D.J. Nichols. 1996. Relating extractable soil phosphorus to phosphorus losses in runoff. Soil Sci Soc Am J 60:855-859. Pote, D.H., T.C. Daniel, D.J. Nichols, A.N. Sharpley, P.A. Moore, D.M. Miller, and D.R. Edwards. 1999. Relationship between phosphorus levels in three ultisols and phosphorus concentrations in runoff. J Environ Qual 28:170-175. Reddy, K., Y. Wang, W. DeBusk, M. Fisher, and S. Newman. 1998. Forms of soil phosphorus in selected hydrologic units of the Florida Everglades. Soil Sci Soc Am J 62:1134-1147. Sample, E.C., R.J. Soper, and G.J. Racz. 1980. Reactions of phosphate fertilizers in soils, p. xviii, 910, In F. E. Khasawneh, E. C. Sample and E. J. Kamprath. eds. The Role

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51 of phosphorus in agriculture. American Society of Agronomy, Madison, Wisconsin. Sartain, J.B. 1980. Mobility and extractability of phosphorus applied to the surface of tifway bermudagrass turf. Soil and Crop Science Society of Florida Proceedings 39:47-50. Sartain, J.B. 2001. Soil testing and interpretation for Florida turfgrasses. Soil and Water Science Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. SAS Institute. 1989. SAS/STAT user's guide. Release 6. 4th. Ed. Volume 1. SAS Institute, Cary, NC. Sharpley, A.N. 1995. Dependence of runoff phosphorus on extractable soil-phosphorus. J Environ Qual 24:920-926. Sharpley, A.N. 1996. Availability of residual phosphorus in manured soils. Soil Sci Soc Am J 60:1459-1466. Sims, J.T., R.R. Simard, and B.C. Joern. 1998. Phosphorus loss in agricultural drainage: Historical perspective and current research. J Environ Qual 27:277-293. Sims, J.T., A.C. Edwards, O.F. Schoumans, and R.R. Simard. 2000. Integrating soil phosphorus testing into environmentally based agricultural management practices. J Environ Qual 29:60-71. Sims, J.T., R.O. Maguire, A.B. Leytem, K.L. Gartley, and M.C. Pautler. 2002. Evaluation of Mehlich-3 as an agri-environmental soil phosphorus test for the Mid-Atlantic United States of America. Soil Sci Soc Am J 66:2016-2032. Sinaj, S., C. Stamm, G.S. Toor, L.M. Condron, T. Hendry, H.J. Di, K.C. Cameron, and E. Frossard. 2002. Phosphorus exchangeability and leaching losses from two grassland soils. J Environ Qual 31:319-330. Sui, Y.B., and M.L. Thompson. 2000. Phosphorus sorption, desorption, and buffering capacity in a biosolids-amended mollisol. Soil Sci Soc Am J 64:164-169. Tisdale, S., W. Nelson, J. Beaton, and J. Havlin. 1999. Soil fertility and fertilizers : an introduction to nutrient management. 6th ed. Prentice Hall, Upper Saddle River, N.J. Torbert, H.A., T.C. Daniel, J.L. Lemunyon, and R.M. Jones. 2002. Relationship of soil test phosphorus and sampling depth to runoff phosphorus in calcareous and noncalcareous soils. J Environ Qual 31:1380-1387.

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52 US Environmental Protection Agency. 2000. The quality of our nation's water. A summary of the national water quality inventory: 1998 Report to Congress. EPA 841-S-00-001. USEPA, Washington, DC. Valk, H., J.A. Metcalf, and P.J.A. Withers. 2000. Prospects for minimizing phosphorus excretion in ruminants by dietary manipulation. J Environ Qual 29:28-36. Wang, H.D., W.G. Harris, and T.L. Yuan. 1989. Phosphate minerals in some Florida phosphatic soils. Soil and Crop Science Society of Florida Proceedings 48:49-55. Wang, H.D., W.G. Harris, and T.L. Yuan. 1991a. Relation between phosphorus and iron in Florida phosphatic soils. Soil Sci Soc Am J 55:554-560. Wang, H.D., W.G. Harris, and T.L. Yuan. 1991b. Noncrystalline phosphates in Florida phosphatic soils. Soil Sci Soc Am J 55:665-669. Westerman, R.L. 1990. Soil testing and plant analysis. 3rd ed. Soil Science Society of America, Madison, Wis. Whalen, J.K., and C. Chang. 2001. Phosphorus accumulation in cultivated soils from long-term annual applications of cattle feedlot manure. J Environ Qual 30:229-237. Wood, W.C. 1998. Agricultural phosphorus and water quality: an overview, In J. T. Sims, ed. Soil testing for phosphorus: environmental uses and implications. USDA-CSREES, Newark, Delaware. Wu, Z., L.D. Satter, and R. Sojo. 2000. Milk production, reproductive performance, and fecal excretion of phosphorus by dairy cows fed three amounts of phosphorus. J of Dairy Sci 83:1028-1041. Yuan, T.L., W.K. Robertson, and J.R. Neller. 1960. Forms of newly fixed phosphorus in three acid sandy soils. Soil Sci Soc Am J 24:447-450. Zheng, Z.M., R.R. Simard, J. Lafond, and L.E. Parent. 2002. Pathways of soil phosphorus transformations after 8 years of cultivation under contrasting cropping practices. Soil Sci Soc Am J 66:999-1007.

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BIOGRAPHICAL SKETCH Daniel Herrera was born in San Jose, Costa Rica on November 16th, 1976. He is the youngest son of Guillermo Herrera and Betty Duran. Daniel went to EARTH University in Costa Rica for his undergraduate education; there he received a degree in agronomy. After graduation in 1997 he did a year internship in Michigan with the Kellogg Company. A few months after returning to Costa Rica and working in his family farm, he went to work as teaching assistant at EARTH University. In January of 2001, after being accepted to graduate school he started a consulting company with his EARTH colleagues Minor, Freddy and Nestor. In August 2001 Daniel started his master’s degree at the Soil and Water Science Department at the University of Florida. 53