Transformation, leaching and uptake of fertilizer nitrogen applied in autumn and spring to winter wheat on a heavy soil

Abstract

AbstractThe concentrations of ammonium and nitrate in the surface layer (0–6 in.) of a heavy soil with and without fertilizer N were measured from October 1957 to September 1958 on plots growing winter wheat and in bare soil. Ammonium sulphate or ‘calcium nitrate’ supplying 100 lb. of N/acre was applied in the autumn, in the spring, or half in autumn + half in spring. Both forms of fertilizer applied in the autumn were lost from the surface soil by the following March. Autumn‐applied nitrogen was not taken up by the wheat during the autumn or winter. Nitrogen applied in the spring was rapidly taken up by the crop, but remained in the surface soil of the bare plots until June, when prolonged and heavy rain leached the nitrate into the lower soil layer.At the time the ears emerged, much more mineral nitrogen had been lost from the soil top‐dressed with fertilizer in the spring than was accounted for by the increase in nitrogen uptake by the above‐ground parts of the wheat.The yields of grain and straw at harvest were not increased by the nitrogen fertilizers, whenever applied. The nitrogen contents of both grain and straw were increased by applying fertilizers, and there were consistent but small increases in the total nitrogen uptake by the wheat on the fertilized plots. The uptake of the fertilizer nitrogen had its greatest value in the samples taken at ear emergence when on average 27 lb. of N/acre of the 100 lb. applied was recovered. At harvest, wheat from the fertilized plots contained 18 lb. of N/acre less than at ear emergence.