Interspecific competition, N use and interference with weeds in pea-barleyintercropping

Field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L.) were in tercropped and sole cropped to compare the effects of crop diversity on pro ductivity and use of N sources on a soil with a high weed pressure. N-15 en richment techniques were used to determine the pea-barley-weed-N dynamics. The pea-barley intercrop yielded 4.6 t grain ha(-1), which was significantl y greater than the yields of pea and barley in sole cropping. Calculation o f land equivalent ratios showed that plant growth factors were used from 25 to 38% more efficiently by the intercrop than by the sole crops. Barley so le crops accumulated 65 kg soil N ha(-1) in aboveground plant parts, which was similar to 73 kg soil N ha(-1) in the pea-barley intercrop and signific antly greater than 15 kg soil N ha(-1) in the pea sole crop. The weeds accu mulated 57 kg soil N ha(-1) in aboveground plant parts during the growing s eason in the pea sole crops. Intercropped barley accumulated 71 kg N ha(-1) . Pea relied on N-2 fixation with 90-95% of aboveground N accumulation deri ved from N-2 fixation independent of cropping system. Pea grown in intercro p with barley instead of sole crop had greater competitive ability towards weeds and soil inorganic N was consequently used for barley grain productio n instead of weed biomass. There was no indication of a greater inorganic N content after pea compared to barley or pea-barley. However, 46 days after emergence there was about 30 kg N ha(-1) inorganic N more under the pea so le crop than under the other two crops. Such greater inorganic N levels dur ing early growth phases was assumed to induce aggressive weed populations a nd interspecific competition. Pea-barley intercropping seems to be a promis ing practice of protein production in cropping systems with high weed press ures and low levels of available N. (C) 2001 Elsevier Science B.V. All righ ts reserved.