Species-specific interaction affects organic nitrogen uptake during intercropping of four important crop species: A useful index for selecting appropriate intercropping combination

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Intercropping has been an important practice for improving field production and its various aspects have been thoroughly investigated. However, only few studies have explored it from the perspective of organic nitrogen (N) uptake, especially under the rapid development of organic and no-tillage farming worldwide. In this study, two cereals (Triticum aestivum and Zea mays) and two legumes (Glycine max and Pisum sativum) were mono- and intercropped using microcosm experiments in a greenhouse, with a total of 10 combinations. The uptake pattern of in situ15N-labelled glycine by plants in each combination was investigated. The total biomass of wheat increased 1.6 times when intercropped with soybean, compared to its monoculture, but not at the expense of reduced soybean growth. Root:shoot ratios of maize increased 1.3 times when intercropped with pea compared with its monoculture. Intercropping with soybean decreased the uptake rates of 15N-labelled glycine by wheat compared to its monoculture. Although intercropping with other species increased the root:shoot in maize, it did not increase the glycine-derived 15N uptake rates. We conclude that interactions between agricultural plants are species-specific and can alter the uptake of N-derived from organic forms. These findings indicate that wheat-soybean intercropping can be a good choice for organic and no-tillage farming to improve production with the potential to reduce the application of synthetic N fertilizers.