Corn production and environmental implications under varying nitrogen and management practices

Abstract

Economic and environmental issues combined have increased the need for better understanding of the fate of nitrogen (N) applied to crop production systems. The objectives of this dissertation were to evaluate the effects of different N sources including conventional urea (CU), polymer-coated urea (PCU), stabilized urea with chemical inhibitors (IU), and anhydrous ammonia (AA) on N losses and yield. Besides N sources, their interaction with placement (deep- versus shallow-banded; broadcast/incorporation versus subsurface banding), tillage management (conventional tillage versus no tillage) and irrigation management (irrigated versus rain fed) were also studied. In the first experiment, split-applied CU increased yield and N uptake compared with preplant applied PCU or IU and decreased nitrate (NO3-) leaching compared with PCU in a sandy loam soil. Direct soil-to-atmosphere nitrous oxide (N2O) emissions were significantly less with IU or split-U than with PCU and there was a trend for greater emissions with split-U than with IU (P =0.08). Irrigation significantly increased NO3- leaching during the growing season, but had no effect on direct N2O emissions in the same experiment. Indirect emissions due to NO3- leaching were estimated to be 79-117% of direct emissions using the default value of EF5, thus signifying the potential importance of indirect emissions in evaluating management effects on N2O emissions. In the second experiment, no-till significantly increased N2O emissions in fertilized treatments in a dry year and decreased crop yield in the control treatment in a silt loam soil. There were no significant differences in N2O emissions, grain yield or NO3- leaching potential with AA placement depth. In the third experiment, mid-row banding (MRB) significantly increased N2O emissions compared to broadcast/incorporation (BI) for PCU and CU in silt loam soils. Nitrous oxide emissions were correlated to a greater extent with soil nitrite (NO2-) intensity than with nitrate (NO3-) intensity; N intensity being a measure of integrated N concentrations over time. Compared to BI, MRB reduced NH3 volatilization loss and the CU treatment had greater NH3 loss than PCU or IU had. All these experiments highlighted the significant roles that N and other management practices can play in mitigating N losses.