Competition between weeds and spring wheat for 15N-labelled nitrogen applied in pig slurry

The changes in weed:crop competition as affected by the interaction of slurry distribution pattern with crop sowing pattern was examined, using the parameters dry matter (DM) production, nitrogen (N) uptake and recovery of applied N in spring wheat and weeds. Pig slurry enriched with isotopic nitrogen (¹⁵N) was applied either fully incorporated or in concentrated bands. The two slurry distribution patterns were combined with either crop density or distance between the slurry band and seed row. Spring wheat and weeds were sampled separately seven times during the season. A high and fast crop recovery of applied N coincident with a low recovery in weeds may be obtained by at least three management elements: sowing the crop with a high seed density, sowing the crop row close to the band-applied slurry N, and early sowing. The effects on crop DM, N-uptake and ¹⁵N recovery of a high crop density and a narrow distance between the slurry band and crop row appear clearly at the beginning of the spring wheat elongation phase. For weeds the effects were most pronounced for ¹⁵N recovery, and using DM as the only response variable may cause insignificant results. However, methods for N application may be part of a strategy controlling weeds, but to obtain satisfactory weed control the N management needs to be supplemented with chemical or mechanical weed management.