Field‐Scale Variability in Optimal Nitrogen Fertilizer Rate for Corn

Abstract

N to surface water is primarily by subsurface flow of nitrate (Schilling, 2002; Steinheimer et al., 1998), partic-Applying only as much N fertilizer as is needed by a crop has ecoularly when N fertilizer has been applied at rates exnomic and environmental benefits. Understanding variability in need for N fertilizer within individual fields is necessary to guide approaches ceeding crop needs (Burwell et al., 1976).to meeting crop needs while minimizing N inputs and losses. Our ob-Small-plot research has shown that experiments in jective was to characterize the spatial variability of corn (Zea mays L.) different production corn fields can differ substantially N need in production corn fields. Eight experiments were conducted in their need for N fertilizer (Bundy and Andraski, 1995; in three major soil areas (Mississippi Delta alluvial, deep loess, clay- Schmitt and Randall, 1994). Need for N fertilizer may pan) over 3 yr. Treatments were field-length strips of discrete N rates also vary widely over large fields (Malzer et al., 1996; from 0 to 280 kg N ha Ϫ1 . Yield data were partitioned into 20-m Mamo et al., 2003) though very little research has been increments, and a quadratic-plateau function was used to describe published addressing this issue. Attempts to predict the yield response to N rate for each 20-m section. Economically optimal amount of N fertilizer needed have met with limited N fertilizer rate (EONR) was very different between fields and was success in humid regions (Kitchen and Goulding, 2001). also highly variable within fields. Median EONR for individual fields ranged from 63 to 208 kg N ha Ϫ1 , indicating a need to manage NThe dominant practice for agricultural producers is to fertilizer differently for different fields. In seven of the eight fields, apply the same rate of N fertilizer over whole fields and a uniform N application at the median EONR would cause more than even whole farms. In fields with spatially variable N needs, half of the field to be over-or underfertilized by at least 34 kg N this practice leads to frequent mismatches between N ha Ϫ1 . Coarse patterns of spatial variability in EONR were observed fertilizer rate and crop N need. Overapplication is more in some fields, but fine and complex patterns were also observed in frequent since producers have an economic incentive most fields. This suggests that the use of a few appropriate manageto err more frequently in that direction: The cost of ment zones per field might produce some benefits but that N manageunneeded N fertilizer in areas of overapplication is less ment systems using spatially dense information have potential for than the cost of lost yield potential in areas of undergreater benefits. Our results suggest that further attempts to develop application. systems for predicting and addressing spatially variable N needs are justified in these production environments.

Responsive in-season nitrogen management for cereals

“…Another major factor contributing to low NUE in current strategies has been uniform application rates of fertilizer N to spatially variable landscapes, even though numerous field studies have indicated economic and environmental justification for spatially variable N applications in many agricultural landscapes (Mamo et al, 2003;Hurley et al, 2004;Koch et al, 2004;Scharf et al, 2005;Shahandeh et al, 2005;Lambert et al, 2006;Hong et al, 2007). Uniform applications within fields discount the fact that N supplies from the soil, crop N uptake, and response to N are not the same spatially (Inman et al, 2005).…”

“…The main advantages of the ground-based sensor approach over the current pre-season "yield-goal" approach is the ability to obtain spatial difference in crop N need and assess climatic conditions encountered from planting to the time of in-season N application before making N recommendation. The weakness of this system lies in the uncertainty in estimating yield from mid-season sensor measurements and the use of a fixed NUE factor, a value that varies spatially within fields (Scharf et al, 2005).…”

Using an unmanned aerial vehicle to evaluate nitrogen variability and height effect with an active crop canopy sensor

“…The economically optimal fertilizer N rate (EONR), a function of yield response to N fertilizer application, can vary widely as a result (Scharf et al 2005). The ability to detect variability in N supply within a field has been studied in depth Roberts et al 2010).…”

Categorical Analysis of Spatial Variability in Economic Yield Response of Corn to Nitrogen Fertilization

“…Large spatial and temporal variability in YR to N and economic optimal nitrogen rates (EONR) within corn fi elds are well documented (Mamo et al, 2003;Scharf et al, 2005). However, many factors can potentially aff ect YR within fi elds.…”