Categorical Analysis of Spatial Variability in Economic Yield Response of Corn to Nitrogen Fertilization
2011
Kyveryga, P. M. | Blackmer, T. M. | Caragea, P. C.
Despite growing interests in variable-rate nitrogen (VRN) fertilizer applications, we still lack basic knowledge and practical methodology for identifying major factors that can be used to guide VRN application to corn (Zea mays L.). The objective was to develop a methodology for identifying a predictable relationship between economic yield response (YR) to N and commonly measured soil and terrain attributes in the presence of spatial dependence. Six 30-ha no-till fields in central Iowa were studied during 6 yr. Urea-ammonium nitrate solution was sidedressed at 112 and 140 kg N ha⁻¹ in alternating strips replicated from 10 to 22 times. Yield responses to the high rate were calculated in a 20 by 25 m grid pattern and classified into profitable and nonprofitable categories within each field. Autologistic models were used to identify which (if any) of the following factors economically affected YR: elevation, apparent soil electrical conductivity (ECa), slope, topographic wetness index (TWI), or digital soil map units. Significant effects of some of the factors were found within 8 of 15 site-years. Within five of these site-years, well-drained areas with lower ECa and TWI, and higher elevation and slope had the higher probability of profitable YR, but these effects were not stable over time. Within the proposed methodology, a high spatial resolution of YR is used that increases the ability to identify areas profitable to N, and farmers can explore VRN possibilities by applying a small fertilizer increment below or above a uniform optimal rate in many alternating strips across fields.
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