Fertilizer-nitrogen residues: useful conservation and pollutant potential under maize

A study of the fate of labelled fertilizer nitrogen in cropped soil, with particular reference to leaching after harvest, is reported. The experiment was carried out in a chernozem soil with three replications and two treatments (I and II), with maize as the crop: I: NPK(120kgN.ha-1; 100kgP.ha-1; 126kgK.ha-1. II: NPK+OM(120kgN.ha-1; 100kgP.ha-1; 126kgK.ha-1 plus 5000kg of organic matter (ground straw) per hectare). A 4-m2 plot was fertilized with (15NH4)2SO4 containing 10 atom 15N% excess. Tensiometers and access tubes were installed for measuring water content and water pressure at depths of 30, 60, 100, 150 and 200cm. Harvested crop as well as soil cores taken after crop harvest were analysed for 15N. The highest content of fertilizer-derived NO3-15N at 0-60cm depth was 1ppm, and at 120-180cm depth it was 0.3ppm. Climatological data were also obtained. There was evidence that, after harvest, mineral nitrogen had moved to a depth of 2m and some 10% was derived from the labelled fertilizer. Organic matter additions tended to reduce both leaching of nitrate and the percentage of leached Ndff. (author)