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«A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Crop, Soil, and Environmental Sciences ...»

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Phosphorus availability was shown to change after PL and BS were exposed to the drying and heat processes during pelletization and granulation. Toor and coworkers (2007) found differing DRP concentrations in PL granules depending on the extraction ratio used. For instance, at a 1:10 (granule:water, w:w basis) ratio the ground and heated

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increased to 1:200, DRP concentrations in fresh PL respectively increased until fresh PL extractants had more DRP than granulated PL. Toor and coworkers (2007) postulated that associations with cations changed during the heating process making P more soluble at low extraction ratios, but PL DRP ultimately increased as the extraction ratio increased.

Haggard and coworkers (2005) found similar results with pelletized PL having two times more DRP than fresh PL (1:10 extraction ratio); however, additions of alum successfully decreased these concentrations. Even after exposing BS to 105°C for 24 h, Ajiboye and coworkers (2004) found that most BS P remained in recalcitrant forms and would not likely cause water quality concerns while dairy, beef and hog manure had significant increases in the DRP fraction following heat exposure. Decreasing DRP in granular fertilizers is important since a linear relationship exists between fertilizer DRP concentrations and runoff DRP concentrations (DeLaune et. al., 2004; Haggard et. al., 2005).

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Binding agent selection is an important step in producing a suitable granule using agitative agglomeration processes (Komarek, 1967). Different types of binding agents can be utilized that fit into general categories based on their mode of action. Komarek (1967) proposed that binding agents hold agglomerates together by using a matrix, film, or chemical reaction. Holley (1981) refined this definition and proposed that the main modes of action were inactive films, chemical films, inactive matrix, chemical matrix, and chemical reactions. Binding agents which function by inactive and chemical films are products of choice for agglomerating dry and relatively inert organic products (Komarek,

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materials move through the agglomeration process. As dry ingredients and binding agents are mixed during granulation, the binding agent's surface tension pulls powdery substances into a sphere. The binding agent adds and/or dissolves salts found in the powdery dry ingredient resulting in a solid bridge formation between the dry ingredient particles after drying (Holley, 1981; Kaliyan and Morey, 2006). Chemical films work similar as inactive films, except chemical binding agents form the solid bridge between particles due to a chemical reaction and the process is not dependent on soluble salts (Holley, 1981).

Water, the most common binding agent used, showed promise for powdery substances and is the cheapest binder alternative (Holly, 1981; Hinkle and Rosenthal, 1991; Liu et al., 2006). Holley (1981) cited water as a universal binder due to its high surface tension for holding particles together and for positive lubrication qualities. Water initially acts as an inactive film binding agent due to surface tension during the green pellet stage (before drying); however, chemical films resulting from dissolution of soluble salts form solid bridges after drying and gives agglomerated dry products their ending strength (Holley, 1981; Kaliyan and Morey, 2006).

Lignosulfonates, organic by-products from the wood pulping industry, have beneficial strength and anti-dusting qualities when used in the fertilizer industry (Holley, 1981; Mickus et. al., 1988; Detroit, 1989; Lignin Institute, 1993). For instance, research conducted by the Tennessee Valley Authority indicated that urea made from lignosulfonate was stronger and cheaper than formulations containing formaldehyde, and lignosulfonate has since became a significant industrial binder (Mickus et. al., 1988;

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organic products due to an inactive film that forms post drying solid bridges (Holley, 1981). Solid bridge formation produced suitable granules during trials with ground alfalfa (Medicago sativa), limestone, and graphite (Hinkle and Rosenthal, 1991; Tabil et. al., 1997). Although lignosulfonate formed stronger granules than water alone in studies by Hinkle and Rosenthal (1991), lignosulfonate may not be the strongest binder available (Tabil, 1996; Tabil et al., 1997; Veverka and Hinkle, 2001).

Depending on formulation, urea formaldehyde resin compounds have been used successfully to make products ranging from slow-release fertilizers to adhesive agents for particle-board manufacturing (Christianson et al, 1988; Mikkelsen et al, 1994; Trenkel, 1997; Gabrielson, 2001; Georgia-Pacific Resins, Inc., 2006). Urea formaldehyde is formulated by reacting urea with formaldehyde, resulting in a mixture of methylene urea long-chain polymers (Trenkel, 1997). Nitrogen availability from these fertilizer sources depend on the length of the urea-formaldehyde chain, which is determined by the reaction time during manufacturing (Kaempffe and Lunt, 1967). As the urea and formaldehyde reaction continues, urea-formaldehyde chains increase in length making them more resistant to solubility and microbial activity; thus, offering a slow N release characteristic (Long and Windsor, 1960; Kaempffe and Lunt, 1967). Carter and coworkers (1986) experimented with different formulations of urea-formaldehyde fertilizers to determine their utility in flood irrigated rice systems. Overall, urea formaldehyde increased N efficiency, reduced NH3 found in floodwater, and increased soil N compared to urea treatments (Carter et. al., 1986). However, formulation, climate, and production systems all influence urea formaldehyde fertilizer utility and N-release characteristics (Cahill et.

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material into stable pellets by forming solid bridges from chemical reactions; made stable by thermosetting properties of the resin (Holley, 1981). Neyman and Derr (2002) proposed using urea formaldehyde as a pellet binder due to its inherent adhesive properties when blending with dry fertilizers while Tabil (1996) used a lignosulfonate and urea formaldehyde combination to provide superior alfalfa pellets compared to water and lignosulfonate binding alone.

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In the United States, Arkansas ranks first in rice (Oryza sativd) production (538 900 ha"1), fifth in cotton (Gossypium hirsutum) production (348 200 ha"1) and has a significant acreage of soybean {Glycine max L. Men-.), wheat (Triticum aestivum) and corn (Zea mays) (1 145 700, 331 900 and 247 000 ha"1; respectively) (National Agricultural Statistics Service, 2006). Extensive row crop agriculture equates to inorganic fertilizer needs that exceed 974 800 Mg per year in Arkansas alone (Arkansas State Plant Board, 2005). Southeast agricultural crops remove nutrients in ratios ranging from 4:1 to 23:1 (N:P) for corn (Zea mays) and tobacco (Nicotiana tabacum), respectively, while PL and BS average 3:1 (Edwards and Daniel, 1992; USEPA, 1995; International Plant Nutrition Institute, 2007). While PL and BS could replace significant quantities of inorganic fertilizer sources, nutrient concentrations in PL and BS do not match crop uptake needs and additional fertilizer would need to be used if these materials were applied on a P basis.

Nitrogen fortification may improve the utility of PL and BS for crop production.

Research by Hamilton and Sims (1995) found that PL was successfully transformed and

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compared to fresh PL. In their study, (NH^HPC^ and KC1 were used to produce fertilizer sources with N:P:K ratios of 5:5:1 and 7:7:5. Overall, greenhouse and incubation studies indicated that more plant-available N, P, and K was extracted over a growing season; however, NH4-N was quickly nitrified within 2 wk after application and NO3-N was the predominant N species. Similarly, municipal BS was successfully fortified with anhydrous NH3 and H2SO4 to produce an organically enhanced fertilizer with an analysis of 17:1:0 (Greer and Dahms, 1999). The fortified BS granules had comparable or superior fertilization capabilities compared to conventional fertilizer sources when used on rice, wheat, corn, and turfgrass research plots (Burnham and Jarrett, 2007).

Additives may also decrease environmental risks if incorporated into granular fertilizers. For instance, Moore and Miller (1994) found that additions of alum, quick lime, slaked lime, ferrous chloride, ferric chloride, ferrous sulfate, and ferric sulfate decreased water soluble P concentrations in PL from 2000 mg kg"1 to 1 mg kg"1 when applied to bedding material. Significant quantities of these additives can be incorporated into BS during the wastewater treatment process; thereby decreasing overall DRP concentrations (Maguire et. al., 2001). For instance, Penn and Sims (2002) found significant differences between the additive used in wastewater treatment processes and concentrations of DRP in BS materials and STP following BS applications. Reducing DRP in fertilizer and soil may effectively reduce overall nutrient runoff following rainfall events.

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There are many environmental and agronomic benefits for keeping inorganic N as NH4-N versus NO3-N. Raun and Johnson (1999) cited numerous N loss pathways that contributed to an overall world N fertilizer use efficiency of only 33%. Among the multiple N loss pathways, denitrification and leaching were cited as major areas where fertilizer use efficiency could be improved. For instance, a study by Drury and coworkers (1996) found that 26 kg N ha"1 yr"1 was leached from conventional tilled corn fields into subsurface drainage when only 115 kg N ha"1 was applied as urea, translating to a 23% N loss due solely to leaching. Similarly, significant quantities of N can be lost by denitrification. In a rice study, Norman and coworkers (1988) found that nearly all N was denitrified within 7 d after permanent flood was established on dry seeded rice in Arkansas. Preferential uptake of NH4-N by most plants is another reason to inhibit nitrification. Many plants prefer NH4-N compared to NO3-N because assimilation of NO3-N requires 20 ATP mol"1 whereas NH4-N assimilation only requires 5 ATP mol"1 (Salsac et. al, 1987). Energy savings and preferential uptake were partly responsible for increased crop dry matter production in a study by Huffman (1989). Numerous nitrification inhibitor products are available as fertilizer additives to reduce the nitrification process (Edmeades, 2004).

Dicyandiamide (HN=C[NH2]-NH-CN) was investigated as a nitrification inhibition product as early as 1918 and was shown to inhibit microbial activity without killing microbes; thus, having no net effect on soil microbial biomass (Cowie, 1918; Di and Cameron, 2004). The mode of action for DCD centers on the blocking of ammonia monooyxgenase enzymes in Nitrosomonas where NH4-N first undergoes oxidation to

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biodegradable with a half life of 18 to 25 days at 20°C on neutral pH soils (Amberger, 1989; Rajbanshi et. al., 1992; Hauser and Haselwandter, 1990; Di and Cameron, 2004).

Dicyandiamide efficacy increases under acid soils with only 4 to 10% undergoing mineralization 60 d after application; adding to effectiveness in acid soil loving rice production systems (Rodgers et. al, 1985). After application, DCD responds as a slow release fertilizer product that undergoes mineralization to end products of CO2, NH3-N and water by soil bacteria (Amberger, 1989; Rajbanshi et. al., 1992).

Dicyandiamide was shown to increase plant N assimilation and yield in several studies when applied on a 10% total N basis (1 DCD-N:10 total N). Norman and coworkers (1988) found that DCD increased rice plant N uptake of pre-plant applied N by 28% compared to no DCD treatments. Similarly, Wilson and coworkers (1990) found that DCD did increase overall rice plant N assimilation, decreased plant-soil N loss, but did not increase rice grain yields. A study by Wells and coworkers (1989) found that DCD additions increased rice yields and N efficiency in delayed flood production systems if N was applied at-planting; but properly splitting N during the growing season gave more consistent results. In all of the previous flood irrigated rice systems, N loss was decreased by reducing nitrification prior to flooding and thereby reducing denitrification after the permanent rice flood was established. Several studies indicated that negligible NO3-N concentrations were found in the soil after the flood was applied to rice (Norman et. al., 1988; Wilson et. al, 1990). Similarly, an Alabamian wheat study found that DCD additions did not increase grain yield, but there was evidence of reduced fertilizer NO3-N leaching throughout the soil profile (Bronson et. al., 1991).

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systems, previous research indicated that DCD reduced overall N availability, increased N volatilization and was toxic to certain plant species. An incubation study by Norman and Wells (1989) found that N from treatments with DCD was generally less available than treatments without DCD due to increased microbial assimilation. Ammonium-N is the preferred N source for microbes and increased NH4-N concentrations translated to increased immobilization; however, this immobilization did reduce overall N loss from denitrification after the soil was flooded. Similar results were seen in a study by Bronson and coworkers (1991) in wheat. Overall N loss was reduced by using DCD, but immobilization increased and N was not plant available. A field study in Alabama indicated that DCD-N was generally unavailable to corn as DCD-N plots had similar yields to the 0-N control (Reeves and Touchton, 1986). Increased NH3 volatilization may be another problem associated with favoring NH4-N species. Gioacchini and coworkers (2002) found that DCD exacerbated NH3 volatilization when combined with a urease inhibitor and applied to sandy loam soils, effectively decreasing overall wheat plant assimilation. Research in Alabama on cotton and sorghum found that DCD-N was toxic to plants and reduced cotton tissue dry weight and sorghum leaf chlorophyll concentrations below the 0-N check treatments when DCD-N was applied (Reeves and Touchton, 1986; Reeves et. al., 1988). Reeves and Touchton (1986) postulated that DCDN reduced the number of chloroplasts per cell and altered their structural integrity in cotton and sorghum as seen by Rufner and coworkers (1984) in radish {Raphanus sativus L. cv. Cherry Belle).

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