Nitrogen fixation by lablab (Lablab purpureus) and lucerne (Medicago sativa) rotation crops in an irrigated cotton farming system

Abstract

Cotton producers in Australia are interested in including legume green manure crops in their farming systems. Lablab and lucerne are 2 crops that have been considered for this role. The object of this study was to determine their biomass production, nitrogen fixation, water use and water-use efficiency within a 1-year out-of-cotton rotation. Both species were grown under full irrigation, and partial irrigation, where periods of moisture stress occurred. During the period of the rotation, lablab produced more biomass and fixed more nitrogen than lucerne. Its biomass production was increased (from 9655 to 16 024 kg/ha) by full irrigation compared with partial irrigation, while lucerne biomass similarly increased (from 6563 to 8040 kg/ha). Lablab also fixed more nitrogen (177 kg N/ha) than lucerne (111 kg N/ha). Lucerne used more water than lablab and thus lablab had higher water-use efficiency of biomass production and nitrogen fixation. The study indicates that lablab produces more green manure with greater water-use efficiency than lucerne within a 1-year out-of-cotton rotation.