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

Field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L.) were intercropped and sole cropped to compare the effects of crop diversity on productivity and use of N sources on a soil with a high weed pressure. N-15 enrichment techniques were used to determine the pea-barley-weed-N dynamics. The pea-barley intercrop yielded 4.6 t grain ha(-1), which was significantly greater than the yields of pea and barley in sole cropping. Calculation of 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 sole 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 significantly greater than 15 kg soil N ha(-1) in the pea sole crop. The weeds accumulated 57 kg soil N ha(-1) in aboveground plant parts during the growing season 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 derived from N-2 fixation independent of cropping system. Pea grown in intercrop with barley instead of sole crop had greater competitive ability towards weeds and soil inorganic N was consequently used for barley grain production 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 sole crop than under the other two crops. Such greater inorganic N levels during early growth phases was assumed to induce aggressive weed populations and interspecific competition. Pea-barley intercropping seems to be a promising practice of protein production in cropping systems with high weed pressures and low levels of available N. (C) 2001 Elsevier Science B.V. All rights reserved.