The comparison of nitrogen use and leaching in sole cropped versus intercropped pea and barley

The effect of sole and intercropping of field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L.) and of crop residue management on crop yield, NO3- leaching and N balance in the cropping system was tested in a 2-year lysimeter experiment on a temperate sandy loam soil. The crop rotation was pea and barley sole and intercrops followed by winter-rye and a fallow period. The Land Equivalent Ratio (LER), which is defined as the relative land area under sole crops that is required to produce the yields achieved in intercropping, was used to compare intercropping performance relative to sole cropping. Crops received no fertilizer in the experimental period. Natural N-15 abundance techniques were used to determine pea N-2 fixation. The pea-barley intercrop yielded 4.0 Mg grain ha(-1), which was about 0.5 Mg lower than the yields of sole cropped pea but about 1.5 Mg greater than harvested in sole cropped barley. Calculation of the LER showed that plant growth resources were used from 17 to 31% more efficiently by the intercrop than by the sole crops. Pea increased the N derived from N-2 fixation from 70% when sole cropped to 99% of the total aboveground N accumulation when intercropped. However, based upon aboveground N accumulation the pea-barley intercrop yielded about 85 kg N ha(-1), which was about 65 kg lower than sole cropped pea but about three times greater than harvested in sole cropped barley. Despite different preceding crops and removal or incorporation of straw, there was no significant difference between the subsequent non-fertilized winter-rye grain yields averaging 2.8 Mg ha(-1), indicating an equalization of the quality of incorporated residue by the NO3- leaching pattern. NO3- leaching throughout the experimental period was 61 to 76 kg N ha(-1). Leaching dynamics indicated differences in the temporal N mineralization comparing lysimeters previously cropped with pea or with barley. The major part of this N was leached during autumn and winter. Leaching tended to be smaller in the lysimeters originally cropped with the pea-barley intercrops, although not significantly different from the sole cropped pea and barley lysimeters. Soil N balances indicated depletion of N in the soil-plant system during the experimental period, independent of cropping system and residue management. N complementarity in the cropping system and the synchrony between residual N availability and crop N uptake is discussed.