Nutrient uptake by wheat and associated weeds as influenced by management practices.
In field studies in 1984/85 at Pantnagar, Uttar Pradesh dwarf wheat cv. UP 368 was sown in rows 15.0 or 22.5 cm apart, at sowing rates of 100 or 150 kg/ha, or sown uni- or bi-directionally (where half of the seed rate is sown on one direction and the other half in the cross direction). Closer row spacing, higher sowing rate and cross-sowing significantly decreased the NPK removal by grass (Avena ludoviciana, Cynodon dactylon and Phalaris minor) and broadleaved weeds (Melilotus indica, Vicia sativa, Anagallis arvensis, Chenopodium album, Fumaria parviflora and Lathyrus aphaca) and by a sedge (Cyperus rotundus), compared with wider row spacing, normal sowing rate and one-direction sowing, and resulted in higher NPK uptake by the crop. Uncontrolled weeds over a period of 90 d depleted on average 69, 15 and 52 kg N, P and K/ha resulting in 48, 41 and 54% crop loss in N, P and K in weedy plots, compared with the crop in weed-free conditions. The uptake of NPK was greatest in grass weeds and least in the sedge; broadleaved weeds removed NPK at a moderate rate. Application of 1 kg a.i./ha of isoproturon was superior to 0.5 kg a.i. in reducing NPK removal by weeds and increasing NPK uptake by the crop.