Effects Of Farm Field Management On N Use Efficiency.

We estimated N losses from agricultural fields in corn-soy-wheat rotation in the Mid-Atlantic region of North America. Atmospheric N₂O fluxes were measured using static chambers inserted into surface soils, and NO₃^- and PO₄^-3 concentrations in groundwater were measured in tile drain discharges. In one 15 ha corn field, the control area received 100% of the recommended N (150 kg N/ha, a mixture of UAN and biosolids), and the experimental area received only 80% of the recommended N (120 kg N/ha). Due to the dry, hot summer of 2012, there was little difference between the low corn yields in the control (54 bu/acre) and treatment (47 bu/acre) areas, but there was a significant reduction in the N₂O flux from the 80% N treatment area compared to the control (17 versus 41 mmol N₂O-N m^-2 y^-1). Similarly, groundwater NO₃^- and PO₄^-3 in tile drains of the 80% treatment field (14-17 mg NO₃-N/L, 3-7 μg PO₄-P/L) were ~half those of the control field (20-35 mg NO₃-N/L, 4-10 μg PO₄-P/L). In summers with normal rainfall, reduced yields and smaller differences in N₂O and NO₃^- fluxes could result from 80% N applications. In a second 15 ha field previously planted in soy, fall and winter N₂O fluxes in the winter cover crop treatment area were significantly lower than those with no cover crop (~1 versus ~4 μmol N₂O-N m^-2 h^-1). These results show that management of grain fields can significantly lower greenhouse gas emissions and reduce nitrate losses to groundwater.