program. Much of the corn production in this area is on
irrigated sands where N leaching is the main factor reducing
N use efficiency. Minimizing the potential for N leaching
loss is the most important factor for improved crop production
profitability and environmental protection under
these conditions. This is especially important in areas with
coarse textured soils and a relatively shallow aquifer.
At the same time, there is significant irrigated acreage of
corn production on medium-fine textured soils. Denitrification
is the main cause for concern in these areas since there
is minimal potential for significant N leaching. The same
is true for dryland corn production on the claypan soils of
southeast Kansas and other scattered poorly drained soils
in the other parts of the central Plains. And for dryland
production in the western part of the Plains states, timing
applications so that N is moved into the soil profile with
limited precipitation is important for making most efficient
use of applied N.
Optimum N application rates in the central Plains are best
determined by carefully accounting for residual profile N
(profile NO3-N soil test) and expected contributions from
soil OM, previous legume crops, manure applications, and
available N from irrigation water. Estimated N uptake for
corn is about 1.5 to 1.6 lb of N/bu (Table 1; grain and
stover). This is in part the basis for Kansas State University
corn N recommendations. Nebraska N recommendations
are somewhat similar, but generally suggest