N use by winter wheat established in cultivated and direct-drilled soils

Abstract

SummarysLabelled fertilizer N (15N depleted ammonium sulphate) was used to investigate both soil and fertilizer N use by winter wheat established in contrasting seed beds, these being soil cultivated to 20 cm depth or left undisturbed. The crop's response to, and recovery of, a range of N levels from 0 to 280 kg/ha given as a divided application in spring, were measured over two seasons. It was found that during the first season the direct-drilled wheat took up, on average, more fertilizer N but less soil N than wheat in cultivated soil, probably through differences in organic-matter mineralization. The different cultivation systems produced similar grain yields at all rates of applied N; however, when no fertilizer N was given, dry-matter production and soil-N uptake by the crop in the undisturbed soil were substantially less than by the crop in the cultivated soil. Crop recovery of the fertilizer N at harvest was between 29 and 40% of that given. After harvest, an average of one third of the applied fertilizer N was found in the top 60 cm of the soil profile. In the following season on the same plots a second winter wheat crop, receiving no fertilizer N, was drilled. At harvest there was shown to be an increase in grain yield and soil- and fertilizer-N uptake at the higher srates of N given in the previous season. In spite of this the recovery of the labelled residues was small, no more than 6% of the original application, or 15% of the residues remaining in the soil, irrespective of cultivation system.