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

Field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L) were inter- 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. 15N 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 had to rely on N2 fixation with 90-95% of aboveground N accumulation being derived from N2 fixation independent of cropping system. Pea grown in intercrop with barley instead of sole crop had a better 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 practise of protein production in cropping system with high weed pressures and low levels of available N