Other measurements, including differences in yield and stalk nitrate concentrations, confirmed the variability in N sufficiency. Aerial color photographs showed N sufficiency varied in spatial patterns related to landscape position and other factors. Spatial variability of N sufficiency poses the same problem for conventional tissue testing as it does with a visual rating system. Analysis of a sample collected from an area with a mixture of N deficiencies and excesses provides little useful information. This is important because an essential step in moving toward site-specific management of N is learning what should be considered a site to sample.
Effective use requires some skill, but the test can provide important information at little cost.
Checking for strips of N-deficient corn that coincide with fertilization patterns can reveal problems caused by nonuniform applications of fertilizer. Spatial patterns in corn color or firing can be used to show how fields should be divided to collect soil or plant samples. This information subject to a usage policy .