Uptake of labelled nitrate by roots of winter barley on a direct-drilled or ploughed silt loam soil

This work investigated the availability to cereal crops of inorganic nitrogen at differing soil depths at different growth stages. Experiments were done in the field on a silt loam soil on which winter barley was grown after direct drilling or conventional seed-bed preparation after ploughing.At three growth stages (Zadoks 25, 31 and 45) nitrogen labelled with the isotope ¹⁵N was introduced to microplots (area 707 cm²) at depths 7.5, 15, 30 and 50 cm. After an interval of 2 or 3 days to allow uptake of this nitrate by the roots, the herbage growing on the microplots was harvested and tracer-nitrogen content measured.Labelled-nitrogen adsorption was greatest from 7.5 cm depth, and uptake approximately halved for each depth increment. This decline with depth was more pronounced on the ploughed plots. Irrespective of cultivation method, total tracer-nitrogen adsorption averaged over all depths was much the same at growth stages 25 and 31 (mid-March and April), but at growth stage 45 (late May) the uptake on the direct-drilled treatment was almost twice that on the ploughed. Nitrogen concentration was significantly smaller in the direct-drilled crop particularly at the May harvest (Zadoks 45) and this starvation may have been responsible for the greater utilization by the direct-drilled crops of a fresh supply of nitrogen.