Soil mineral nitrogen and the rating of CaCl2 extractable nutrients

Abstract

It was assumed that the determination of the mineral nitrogen (N_min) content in the 0.01 mol/L CaCl₂ could rely on measurements of single form NO₃^–-N, NH₄⁺-N or both, and even including other extractable nutrients. This hypothesis was verified based on some primary data from 17 fields: ten with oilseed rape and seven with maize as indicatory crops during three consecutive seasons in a production farm in Górzno, Poland. The contents of NO₃^–-N, NH₄⁺-N, P, K, Mg and pH were measured in soil prior to the spring vegetation start and after a crop harvest (autumn). Phosphorus in spring and NH₄⁺-N in autumn, were variables discriminating against the number of clusters. It was higher in cropping sequences (CSs) with maize than with oilseed rape. The reliability of N_min determination and distribution between clusters in spring based only on NO₃^–-N was fully corroborated for maize CSs. In autumn, irrespective of the CS, the decisive factor in N_min prediction and distribution over clusters was the NH₄⁺-N pool. This study resulted in the rating of CaCl₂ extractable nutrients, indicating their availability status, shortage or excess, on the background of the N_min temporary rating.