Management practices such as fertilizer or tillage regime may affect nitrous oxide (N₂O) emissions and crop yields, each of which is commonly expressed with respect to area (e.g., kg N ha or Mg grain ha). Expressing N₂O emissions per unit of yield can account for both of these management impacts and might provide a useful metric for greenhouse gas inventories by relating N₂O emissions to grain production rates. The objective of this study was to examine the effects of long-term (>17 yr) tillage treatments and N fertilizer source on area- and yield-scaled N₂O emissions, soil N intensity, and nitrogen use efficiency for rainfed corn ( L.) in Minnesota over three growing seasons. Two different controlled-release fertilizers (CRFs) and conventional urea (CU) were surface-applied at 146 kg N ha(-1) several weeks after planting to conventional tillage (CT) and no-till (NT) treatments. Yield-scaled emissions across all treatments represented 0.4 to 1.1% of the N harvested in the grain. Both CRFs reduced soil nitrate intensity, but not N₂O emissions, compared with CU. One CRF, consisting of nitrification and urease inhibitors added to urea, decreased N₂O emissions compared with a polymer-coated urea (PCU). The PCU tended to have lower yields during the drier years of the study, which increased its yield-scaled N₂O emissions. The overall effectiveness of CRFs compared with CU in this study may have been reduced because they were applied several weeks after corn was planted. Across all N treatments, area-scaled N₂O emissions were not significantly affected by tillage. However, when expressed per unit yield of grain, grain N, or total aboveground N, N₂O emissions with NT were 52, 66, and 69% greater, respectively, compared with CT. Thus, in this cropping system and climate regime, production of an equivalent amount of grain using NT would generate substantially more N₂O compared with CT.

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Irrigation and N fertilizer management are important factors affecting crop yield, N fertilizer recovery efficiency, and N losses as nitrous oxide (N2O) and nitrate (NO3−). Split application of conventional urea (split‐U) and/or one‐time application of products designed to perform as enhanced‐efficiency N fertilizers may mitigate N losses. The objective of this study was to compare the effects of controlled‐release polymer‐coated urea (PCU), stabilized urea with urease and nitrification inhibitors (IU) and split‐U on direct soil‐to‐atmosphere N2O emissions, NO3− leaching, and yield for fully irrigated and minimum‐irrigated corn in loamy sand. Indirect N2O emissions due to NO3− leaching were estimated using published emission factors (EF5). Split‐U increased yield and N uptake compared with preplant‐applied PCU or IU and decreased NO3− leaching compared with PCU. Direct 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 significant effect on direct N2O emissions. After accounting for significantly increased yields with irrigation, however, N losses expressed on a yield basis did not differ and in some cases decreased with irrigation. Post‐harvest soil N and soil‐water NO3− in spring showed the potential for greater N leaching in minimum‐irrigated than fully irrigated plots. Indirect emissions due to NO3− leaching were estimated to be 79 to 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.

Digital soil mapping has been widely used to develop statistical models of the relationships between environmental variables and soil attributes. This study aimed at determining and mapping the spatial distribution of the variability in soil chemical properties of the agricultural floodplain lands of the Bara district in Nepal. The study was carried out in 23 Village Development Committees with 12,516 ha total area, in the southern part of the Bara district. A total of 109 surface soil samples (0 to 15 cm depth) were collected and analyzed for pH, organic matter (OM), nitrogen (N), phosphorus (P, expressed as P2O5), potassium (K, expressed as K2O), zinc (Zn), and boron (B) status. Descriptive statistics showed that most of the measured soil chemical variables (other than pH and P2O5) were skewed and non-normally distributed and logarithmic transformation was then applied. A geostatistical tool, kriging, was used in ArcGIS to interpolate measured values for those variables and several digital map layers were developed based on each soil chemical property. Geostatistical interpolation identified a moderate spatial variability for pH, OM, N, P2O5, and a weak spatial variability for K2O, Zn, and B, depending upon the use of amendments, fertilizing methods, and tillage, along with the inherent characteristics of each variable. Exponential (pH, OM, N, and Zn), Spherical (K2O and B), and Gaussian (P2O5) models were fitted to the semivariograms of the soil variables. These maps allow farmers to assess existing farm soils, thus allowing them to make easier and more efficient management decisions and maintain the sustainability of productivity.

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