«A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Crop, Soil, and Environmental Sciences ...»
Analyzing the 12 N-fortified PL and BS granular fertilizers together in a factorial arrangement indicated a significant BS x DCD x binding agent interaction for TP lost (Table 5.3). Total P lost as a percentage of TP applied ranged from 3.8 to 16.9% and followed trends similar to TP load and TP runoff water concentration (Table 5.3). With the exception of water-bound treatments, BS additions generally decreased TP loss, runoff water load and runoff water concentrations by 50% froml3.8 to 6.0%, 2.8 to 1.2 kg P ha"1 and 12.4 to 6.3 mg L"1 (Table 5.3). Reducing TP loss is one of the most important aspects in reducing accelerated eutrophication in P-deficient waterways (Daniel et al., 1994; Sharpley et al., 1994). Barring water-bound granules, addition of DCD slightly reduced TP loss in formulations without BS but no clear effect concerning DCD additions was established (Table 5.3).
Dissolved reactive P runoff water concentrations were higher from inorganic TSP (4.2 mg DRP L"1) applications than any other fertilizer treatment used in this study (Table 5.2). Edwards and Daniel (1994) had similar findings as TSP had over twice as much DRP in runoff compared to fresh PL. Similar to findings from other research (Haggard et.
al., 2005; Toor et al, 2007), high heat during granulation and pelletization significantly increased DRP concentrations in pellets and granular fertilizers by 2 to 5 times of those found in fresh PL (Table 5.1). However, we found that N-fortified PL and BS fertilizer DRP runoff concentrations were similar too or less than fresh PL (3.0 mg L"1) (Table
equates to greater plant availability with less nutrient loss. Milorganite and BS applications had similar DRP runoff concentrations as no-fertilizer plots and pose little environmental risks regarding nutrient loading (Table 5.2). Dissolved reactive P loads among treatments were not significantly different (p = 0.200) and averaged 0.6 kg DRP ha'1. Variable infiltration rates resulted in large differences in runoff volumes between plots making DRP load measurements non-significant (data not shown) (Pote et. al., 1996). While the BS, no-fertilizer and Milorganite treatments had the highest percentage of TP load present as DRP (67.2, 63.4 and 62.2% of TP present as DRP in runoff, respectively), they also had the lowest TP load and the least overall P loss to waterways (Table 5.2).
Dissolved reactive P was released from N-fortified PL and BS granules in a BS x DCD x binding agent interaction when expressed as a percentage of TP load (Table 5.4).
Similar to results previously discussed with Milorganite and dried BS, runoff water from BS formulations generally contained 10 to 20% more TP as algae available DRP.
However, BS granules had lower concentrations of TP lost in runoff water overall (Table 5.3). Therefore, the overall environmental P risks were reduced when BS were added compared to no BS treatments. Dicyandiamide and binding agent treatments did not have any clear effect.
Fertilizer treatments were applied on a P basis; therefore, N data is only discussed as a percentage since different amounts were applied to plots (Table 5.1). Total N lost as a percentage of TN applied ranged from 0.0% (no-fertilizer added) to 7.6% (PLUBDCD
(3.9%) and Milorganite (3.2%). Similar losses to turf fertilizers suggest that N-fortified PL and BS granular fertilizers do not pose greater environmental risks than fertilizers already commonly used. Other research on Captina silt loam indicated similar TN losses between inorganic N sources and PL, with PL TN loss of 4.0% (Edwards and Daniel, 1993; Edwards and Daniel, 1994). Such rainfall simulation conditions estimate worstcase risk conditions and realized losses may be less.
The percentage of TN load present as NH4-N ranged from 15.5% (no-fertilizer control) to 47.7 and 61.0% (PL and BS, respectively) during rainfall simulations (Table 5.5). Total N load as NO3-N ranged from 0.1% (most treatments, Table 5.5) to 2.3% (nofertilizer control). Total N load present as organic N ranged from 37.2% (BS) to 82.2% (no-fertilizer control) (Table 5.5). Reducing the fraction of inorganic N in runoff is beneficial as inorganic N may accelerate eutrophication if N is limiting in the water body (Keeney, 1973; Daniel et al., 1994). Generally, PL, Milorganite, urea, and N-fortified PL and BS granule treatments had similar proportions of NH4-N, NO3-N and organic N represented as TN load (Table 5.5). Most N was present as NH4-N and organic N while NO3-N concentrations were generally an inconsequential factor in this experiment as it was in previous research (McLeod and Hegg, 1984; Edwards and Daniel, 1994). Organic N fractions may not be readily available for assimilation; however, urea N quickly undergoes hydrolysis in aquatic systems while other organic N compounds quickly mineralize (Keeney, 1973; Knud-Hansen and Pautong, 1993).
Looking exclusively at the 12 N-fortified PL and BS granular fertilizers, BS and binding agent additives had no significant effects on TN loss (Table 5.6). Any binding
alternative should be considered. A DCD main effect, averaged over BS and binding agent treatments, indicated that DCD treatments had more TN lost in runoff than those without DCD (4.9 vs. 3.6% TN lost, respectively). Dicyandiamide is a highly soluble compound with high concentrations of TN (666 g N kg"1) and was easily dissolved and transported in runoff water after rainfall simulations began. Reduction of N losses through denitrification pathways may prove DCD as a beneficial additive to turf fertilizers even though TN runoff losses were slightly increased (Slangen and Kerkoff, 1984). A BS main effect, averaged over DCD and binding agent treatments, indicated that granules with BS had less NH4-N and more organic N than treatments without BS.
Treatments with BS may pose a delayed risk to waterways as less N was readily algae available, but organic N will eventually mineralize.
Poultry litter (11.6%) generally had similar percentages of total solids lost as Nfortified PL and BS fertilizers (Table 5.7). Grinding PL into a fine powder (passed a 5.8 mm sieve) before granulation did not significantly increase total solid loss. Urea and TSP (5.4%) had significantly less total solids lost in runoff than PL (11.6%) (Table 5.7).
Edwards and Daniel (1994) indicated similar results with higher total solid concentrations in PL compared to inorganic fertilizers.
Comparing the 12 N-fortified PL and BS granular fertilizers, formulations without BS (13.6%) had higher total solid losses than formulations with BS (9.5%) in a BS main effect (Table 5.8). Biosolids additions to formulations decreased total solid losses and potentially results in lower chemical oxygen demands and nutrient inputs when runoff
without BS (82.3%) also had higher total fractions present as dissolved solids compared to BS treatments (66.7%) (Table 5.8). Lower dissolved solid fractions are desirable as dissolved solids are quickly decomposed and nutrients released in waterways (Keeney, 1973).
Nitrogen-fortified PL and BS granular fertilizers generally raised runoff water pH more than BS, Milorganite, no-fertilizer, and urea + TSP treatments (Table 5.9).
Formulations with BS had lower runoff water pH than those without BS (7.1 vs. 7.3, respectively), averaged over DCD and binding agent treatments. Poultry litter and BS both have liming capabilities; however, it appears that PL has more acid neutralizing capabilities than dried BS used in our study (Hue, 1992).
Runoff from soil amended with Milorganite, BS and no-fertilizer had similar EC (Table 5.9). These findings were similar to those by Ojeda and coworkers (2006) whom found similar EC as no-fertilizer controls in runoff water when using fresh, dried and composted BS. Poultry litter EC was similar to N-fortified PL and BS fertilizer formulations without BS and were higher than urea + TSP applications. Processing PL did not statistically increase salt concentrations over fresh PL so environmental risks were not increased.
Similar to N, P and pH results, a BS EC main effect was significant when comparing the 12 granular fertilizer formulations, averaged over DCD and binding agent treatments. Fertilizers with higher fractions of PL allowed more nutrients and solids to be lost in runoff resulting in higher EC (293.8 and 400.3 p.S cm"1 for no BS and BS
Using tap water compared to more expensive lignosulfonate and urea formaldehyde binders generally worked equally well in retarding N, P and solid loss in runoff water. Additions of DCD to formulations may increase nutrient loss from granules initially, but may be a beneficial additive for reducing N loss during the growing season.
Addition of BS to formulations may reduce N, P and solid concentrations in runoff water.
Using PL as the sole organic material in granular fertilizers did not generally accentuate nutrient loss over fresh PL, even though previous research indicated that pollution may be greater from granulated products due to grinding materials to pass a 5.8 mm sieve followed by high heat exposure. Using N-fortified PL and BS granular fertilizers proved acceptable as fertilizer sources in regards to environmental risks and generally posed less nutrient concentrations and loads in runoff water than commonly used inorganic fertilizer sources.
The authors appreciate research funding obtained through the Arkansas Soil Testing and Research Fertilizer Tonnage Fees Program administered by the Arkansas State Plant Board.
Reference to trade or company name is for specific information and does not imply approval or recommendation of the company by the University of Arkansas, Fayetteville or the University of Arkansas Division of Agriculture to the exclusion of others that may be suitable.
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