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. 15N enrichment techniques were used to determine the pea–barley–weed-N dynamics. The pea–barley intercrop yielded 4.6tgrainha−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 65kgsoilNha−1 in aboveground plant parts, which was similar to 73kgsoilNha−1 in the pea–barley intercrop and significantly greater than 15kgsoilNha−1 in the pea sole crop.

The weeds accumulated 57kgsoilNha−1 in aboveground plant parts during the growing season in the pea sole crops. Intercropped barley accumulated 71kgNha−1. Pea relied on N2 fixation with 90–95% of aboveground N accumulation derived from N2 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 30kgNha−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.