Fallow Nitrate Accumulation in a Wheat‐fallow Rotation as Affected by Tillage System

Abstract

AbstractThe objectives of this study were to compare NO‐3‐N levels for three tillage systems, and to measure seasonal variation in NO‐3‐N levels during the fallow period of a winter wheat (Triticum aestivum L.) crop‐fallow rotation. The study was conducted on two sites, Duroc loam (Pachic Haplustolls) which was broken from native sod in 1970, and Alliance silt loam (Aridic Argiustolls) which had been cultivated 30 to 40 yr prior to establishment of the experiment, at the High Plains Ag Lab, Sidney, NE.No‐till, stubble mulch, and plow (bare fallow) treatments were established in 1970. In the first 2 yr at the Duroc site, the no‐till and stubble mulch tillage system soils accumulated 64 and 73% as much NO‐3‐N as the plow soil, respectively. Except 1975 and 1980, the NO‐3‐N accumulation from tillage systems from 1974 to 1980 was not different. From 1970 to 1975 NO‐3‐N accumulation in no‐till and stubble mulch soils at the Alliance site was different with no‐till and stubble mulch having 67 and 71%, respectively, as much NO‐3‐N as plowed soils. From 1976 to 1983, except 1981 and 1982, the NO‐3‐N accumulation under the different tillage systems was not different. The fallow portion of the experiments were sampled every 21 d between 1981 and 1983. Neither rate nor the beginning point of accumulation was affected at either site by tillage system. The date during fallow when a soil sample for N fertilizer recommendation was taken was important. A sample taken in July would only have 50 to 60% of the NO‐3‐N found at seeding time.