<p>Converting a nutrient management plan from commercial fertilizers to poultry litter helps effectively utilize waste from the nearly 10 billion broiler birds across the United States. Nine field scale watersheds from the USDA ARS Grassland, Soil and Water Research Laboratory near Riesel, TX were evaluated for P inputs and P outputs to determine phosphorus budgets for 15 years of annual application of poultry litter ranging from 75 – 219 kg P ha^-1 yr^-1 on cultivated and pasture/grazed fields. The cumulative net P continued to increase regardless of the application rate and had a positive relationship with soil level P (Mehlich-3 P) and flow weighted mean concentration (FWMC) for dissolved reactive P for both cultivated and pasture managed fields. We assessed hydrological connectivity within two nested watersheds by using the before-after-control-impact (BACI) design. Results showed hydrological connectivity during high rainfall years whereas low rainfall years had minimal connectivity compared to the controls. These results suggest the P contributions from upstream fields receiving poultry litter, even at high application rates, did not exhibit a treatment effect during the low rainfall years at downslope monitoring stations. </p><p><br></p> <p>As nutrient source variability increases in nutrient management plans, improving our ability to differentiate P sources and their fate in soils is critical. We evaluated soils with unique P inputs: inorganic P, poultry litter, and cattle grazing for isotopic signatures by forming silver phosphate and determining the δ¹⁸O_P. Isotopic signatures of the oxygen molecules which are strongly bound to P, provided signatures of 17.09‰, 18.00‰, and 17.20‰ for fields receiving commercial fertilizer, poultry manure, and cattle grazed, respectively. Significant effort was made to determine critical steps in the method to successfully precipitate Ag₃PO₄for analysis. Results show adding a cation removal step as well as monitoring and adjusting pH throughout the method increases probability of successful Ag₃PO₄precipitation. Findings from this study provide a valuable framework for future analysis to confirm unique δ¹⁸O_P signatures which can be used to differentiate the fate of different phosphorus sources in agricultural systems.</p>

The use of agrochemicals, like neonicotinoid insecticides can threaten human and environmental health when they are transported from agricultural fields. To minimize environmental impact of neonicotinoid pesticides to non-target organisms, it is important to quantify the movement of neonicotinoids from agricultural fields and examine how conventional agricultural practices can be altered using best management practices to minimize neonicotinoid transport. We developed a proportional runoff sampler that is inexpensive, rugged, and adaptable to existing runoff quantification systems. The sampler accurately collected flow-weighted samples under a broad range of steady-state and variable flow conditions. We then incorporated the sampler, along with leachate and soil sampling techniques, in a two-year field study testing the effects of winter cover crops and different edge-of-field buffer strip plant types on movement of the neonicotinoid thiamethoxam (TMX) and its metabolite clothianidin (CLO) in treated agricultural fields. Due to dry weather and other complications, runoff and leachate data could not be statistically analyzed. Soil samples indicated that cover crops had no effect on insecticide retention, so cover crops may not be a viable strategy to prevent neonicotinoid transport. Soil TMX was higher in grass buffers than native forb buffers in 2020; however, this result was not repeated in 2021 when vegetative cover was more consistent across treatments. CLO concentration did not vary by buffer in either year. Therefore, buffer strip plant type may have less impact on TMX and CLO retention than other factors like plant density. / Master of Science / Since the 1950's high yield crops and the use of pesticides and fertilizers have helped farmers increase yields from agricultural land. Increased yields have helped food production keep pace with population growth, but the use of pesticides and fertilizers can pose a threat to human and environmental health. Neonicotinoid insecticides can kill not only agricultural pests but beneficial invertebrates like bees and butterflies when the pesticides leave agricultural fields. To lessen environmental impact of neonicotinoid pesticides to the environment, it is important to understand 1) how these insecticides move from agricultural fields, and 2) how conventional agricultural practices can be altered to minimize neonicotinoid transport. We first developed a runoff sampler that was inexpensive, low maintenance, and adaptable to existing systems used to measure runoff. The sampler collects water at a rate proportional to the runoff rate under constant and changing flow rates. We then used the sampler along with leachate and soil sampling techniques in a field study testing the effect of winter cover crops and the species planted in edge-of-field vegetated buffer strips on the amount of the neonicotinoid thiamethoxam (TMX) and its degradation product clothianidin (CLO) remaining in the soil of treated fields during two growing seasons. Due to dry weather and other complications, runoff and leachate data could not be statistically analyzed. Cover crops did not change soil pesticide concentration either year, so cover crops may not be a viable strategy for preventing neonicotinoid transport. Soil TMX was higher in grass buffers than native forb buffers in 2020; however, this result was not detected in 2021 when plant growth in buffers was more uniform across treatments. CLO concentration did not vary by buffer type in either year. Therefore, the species planted in buffer strips may not be as important to holding TMX and CLO in soils as other factors like plant density.

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科学研究費補助金 研究種目:一般研究(B) 課題番号:03452285 研究代表者:上杉 喜彦 研究期間:1991-1992年度