Productivity and resource use in cotton and wheat relay intercropping

Keywords: Grain yield; lint yield; phenological delay; light use; nitrogen use; resource use efficiency; modelling; profitability; water productivity. From the early 1980s onwards, farmers in the Yellow River cotton producing region intercropped cotton and winter wheat; currently on more than 60% of the total cotton acreage. The driving force for intercropping was the need to increase household income by producing a cash crop, while maintaining the production of a major staple food. This study aims at analyzing the productivity and resource use of cotton-wheat relay intercropping systems. Wheat is sown in strips with interspersed bare soil in October and harvested in June of the next year, while cotton is sown in the interspersed space in the wheat crop in April and harvested before the next wheat sowing in October. Crop growth, phenology, productivity, quality, resource use efficiencies and profitability of mono- and intercrops were studied at the plant, field and system levels. The measurements were carried out in field experiments during three consecutive years with monocultures of wheat and cotton and four intercropping designs differing in strip and path width as well as number of rows per strip. The intercrop systems were identified by the number of rows per strip of wheat and cotton, as 3:1, 3:2, 4:2 and 6:2, respectively. All intercropping systems showed an advantage in land productivity compared to growing of monocrops. The fiber quality of cotton was not affected by intercropping. The land equivalence ratio was 1.39 in the 3:1, 3:2 and 4:2 systems, and significantly lower, 1.28, in the 6:2 system. All systems thus provide a substantial land use advantage. Resource (light and nitrogen) use efficiencies of intercropped wheat were similar to the monoculture; however, the resource capture decreased, because part of the land space was assigned to cotton. For intercropped cotton, light use efficiencies were similar to the monoculture; the amount of light intercepted decreased due to a delay in development and growth during the seedling stage and by the extent of canopy closure after the wheat harvest. The relative nitrogen yield total of intercrops was higher than the land equivalence ratio. Nitrogen use efficiency of cotton was decreased. The analysis of the N balance sheet showed that in the intercropping systems N was considerably more prone to losses than in the sole cotton. Conventional N-management in intercrops results in high N-surpluses that pose an environmental risk. Water productivity, both of wheat and cotton, was lower for the intercrops than for monocultures. The lower WP in the intercropping systems compared to the sole crop is a concern for the sustainability of these systems; water productivity needs to be enhanced. A simple mechanistic model for cotton (SUCROS-Cotton) was developed to explore the prospects to optimize intercropping systems. This model simulates cotton development as well for intercrops as for monoculture. The findings suggest that the productivity and resource use efficiencies of cotton-wheat intercropping can be improved by modifying the conventional management practices and by system optimization. It is concluded that the intercropping systems increase farmers’ income under a wide range of wheat and cotton prices.