Soil Nitrogen Parameters and Texture for Fertilization of a Spatially-Variable Field.

The objectives of this study were to determine i) if information about surface clay content and landform conditions like elevation can be used as auxiliary variables for estimating spatial variability of soil NO₃-N and ii) to use this information to determine profitability of variable rate N fertilization technology for non-irrigated corn [Zea mays (L.)] production in south central Texas across years.  A 64-ha corn field with variable soil type, elevation, and N fertility level was used for this study during 2004 to 2007.  Strips of variable rates of N (0, 60, 120, and 180 kg ha^-1) were applied to different sites within and across the field.  Yield maps showed distinct yield variation within the 64-ha corn field during 2004-2007.  Corn grain yield was negatively related to clay content in wet years and positively related to residual NO₃- N with depth in wet or dry years.  Residual NO₃-N to 60-and to 90-cm depths was more related to corn yield than from shallower depths.  The relationship of clay content to soil NO₃-N was weak and not temporally stable.  Yield response to N rate varied temporally in the whole field and in field segments designated by landform elevation.  Economic analyses indicated that applying variable-rate N fertilizer was not more profitable than conventional uniform N application when determined across years of variable rainfall.  Supply of N with depth combined with field variability in texture and landscape and weather conditions determined economics of alternative N management for this field.