SOIL SAMPLING STRATEGIES FOR ESTIMATING RESIDUAL NITROGEN

Accurate fertilizer recommendations require representative soil sample s. However it is often prohibitively expensive to collect the number o f samples required to insure accurate recommendations. The objectives of this project were to determine inorganic N variability and sampling requirements in six fields with different cultural practices. Inorgan ic N concentrations and variability were evaluated in six corn (Zea ma ys L.) fields (20 to 80 acres) with management histories. Samples from the 0 to 2 ft soil depth were collected from a 200 ft grid. At each g rid point, five samples were collected along transects between corn ro ws. Soil samples were analyzed for ammonium and nitrate N, Sampling lo cation relative to the fertilizer band influenced inorganic N concentr ations. By considering water and N inputs into the row and interrow ar eas separately, the relative importance of residual N remaining in row and interrow areas of the soil could be estimated. This estimate can be used as a guide for management decisions. Results shows that the be st strategy for sampling banded fields may include collecting 15 to 30 composite cores from a zone located halfway between the row and the b and.