Effects of grass-legume mixture on plant production and inorganic nitrogen acquisition

Abstract

Intercropping of grasses with legumes has been practiced to improve crop production for centuries, but interspecific facilitation between grasses and legumes may not always occur. To clarify whether competition or facilitation occurs between grasses and legumes, biomass production and nitrogen (N) acquisition of legumes and grasses were investigated in different cropping regimes. Two grasses (Zea mays and Sorghum bicolor) and three legumes (Glycine max, Medicago sativa and Vigna radiata) were monocropped or intercropped under field conditions. A short-term 15N labelling experiment was carried out to quantify the biomass production and N uptake by grasses and legumes growing in different cropping regimes for 104 days. Productions of three legumes significantly decreased as intercropped with both grasses (at least a 20 % decrease for all legumes), while that of both grasses kept relatively stable. All the plants consistently showed a preference for NO3− relative to NH4+ and were not influenced by the cropping regimes. NO3− uptake rate by G. max when intercropped with Z. mays or S. bicolor at 0–5 cm soil depth was only 58.8 % of monocropped ones. NO3− uptake rate by M. sativa and V. radiata when intercropped with S. bicolor were significantly higher (at least 3.5 times) than that in monocropped ones at 0–5 cm soil depth. Furthermore, NO3− uptake rate by M. sativa when intercropped with S. bicolor was 3.5 times higher than that in monocropped at 5–15 cm soil depth. In addition, intercropping did not change the NH4+ uptake rate by any plants in any cropping regimes. Intercropping decreased the production of all three legumes, but did not change the production of the two grasses. Intercropping strongly affected NO3− uptake by legumes and not by grasses. Moreover, positive linear regressions between NUE or production and total N uptake for monocropped rather than intercropped plants indicate that higher N uptake rates facilitate the production and NUE for plants. Intercropping M. sativa with S. bicolor could be worth trying in agricultural practice for the high N uptake rate by M. sativa in the intercropping system.