Antibiotics used in animal agriculture are of increasing environmental concern due to the potential for increased antibiotic resistance after land application of manure. Manure application technology may affect the environmental behavior of these antibiotics. Therefore, rainfall simulations were conducted on plots receiving three manure treatments (surface application, subsurface injection, and no manure control) to determine the fate and transport of pirlimycin, an antibiotic commonly used in dairy production. Rainfall simulations were conducted immediately and 7 d after application of dairy manure spiked with 128 ng g (wet weight) pirlimycin. Soil samples were collected from all plots at two depths (0-5 and 5-20 cm). For injection plots, soil was collected from injection slits and between slits. Pirlimycin concentrations were higher in soil within the injection slits compared with surface application plots at 0 and 7 d. Pirlimycin concentrations in the 0- to 5-cm depth decreased by 30, 55, and 87% in the injection slit, between injection slits, and surface application plots 7 d after application. Pirlimycin concentrations were 106 ng g in sediment and 4.67 ng mL in water from the surface application plots, which were 21 and 32 times that of the injection plots, respectively. After 7 d, pirlimycin levels in runoff sediment and water decreased 80 to 98%. Surface application resulted in six and three times higher pirlimycin concentrations in water and sediment than injection. These results indicate that pirlimycin is most susceptible to loss immediately after manure application. Thus, injection could be considered a best management practice to prevent loss of antibiotics in surface runoff.
Soil test correlation is continuously necessary to affirm critical soil test values (CSTV) for specific nutrients, as changes in crop management and development of new plant varieties may change CSTVs. The objective of this study was to determine the CSTVs of phosphorus (P) and potassium (K) for soybean [Glycine max (L.)Merr.] and corn (Zea mays L.) using three long-term trials in North Carolina. Soybean was cultivated in 2020 and corn in 2021 in three long-term trials established on research stations located in the Tidewater, Coastal Plain, and Piedmont regions of NC. In each trial, up to five rates of P (0-88.2 kg P ha −1 ) and K (0-186.8 kg K ha −1 ) were applied annually at planting. Soil and tissue samples were analyzed and yield measured. There was yield response to P in all site-years. The average CSTVs of P for corn and soybean were 51, 66, and 14 mg kg −1 for the sites at Tidewater, Coastal Plain, and Piedmont regions. The CSTV of P for Piedmont (14 mg kg −1 ) differs greatly from the current recommendation for NC (52 mg kg −1 ). The response to K fertilization was observed only in three site-years and the CSTVs varied from 49 to 93 mg kg −1 , while the current recommendation is setting the CSTV of K at 85 mg kg −1 . These results indicate it is necessary to develop further studies of soil test correlation for P and K in North Carolina to better estimate the CSTVs for the state.
Traditional surface application of poultry litter leaves nutrients vulnerable to loss through volatilization and runoff. However, injection can increase capture of these nutrients in agricultural fields. Therefore, a field experiment was conducted to determine the effects of poultry litter injection on orchardgrass (Dactylis glomerata L.) hay yield and quality. Poultry litter was injected or surface applied using the Subsurfer poultry litter injector at the recommended agronomic rate (high) and half that rate (low) in 2012 and 2013 in an established field of orchardgrass. Soil was sampled to 15 cm and analyzed for soil nitrate. No significant differences in soil nitrate were detected between treatments. Although not always statistically significant, first cutting orchardgrass yields tended to be greater with surface litter application. Injected treatments had greater protein concentrations than their respective surface treatment, showing greater nitrogen uptake, when protein was weighted by yield. Protein was the same for high surface and low injected treatments showing that similar nitrogen (N) uptake was achieved.
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