Crop yield, nitrogen acquisition and sugarcane quality as affected by interspecific competition and nitrogen application

- Sugarcane-soybean intercropping systems enhance land productivity and nitrogen acquisition.
- The intercropping advantage of sugarcane-soybean system is mainly contributed by soybean.
- Sugarcane juice quality is not influenced by sugarcane-soybean intercropping systems.
- Excessive nitrogen applications will reduce the sugarcane juice quality.

While economic efficiency of sugarcane (Saccharum sinensis Roxb)-legume intercropping has attracted a lot of attention around the world, interspecific competition between sugarcane and legume has not been studied so far. A three-year (2009-2011) field experiment was conducted by using a randomized block design with two N application levels (N1, 300 kg hm−2 and N2, 525 kg hm−2) and four crop arrangement patterns (soybean monoculture, sugarcane monoculture, 1:1 row sugarcane-soybean intercropping, 1:2 row sugarcane-soybean intercropping). The crop yield and nitrogen acquisition of sugarcane and soybean, and quality of sugarcane juice were determined at the maturity stages of soybean or sugarcane. Land equivalent ratio (LER) was used to evaluate the potential advantages of the intercrops, aggressivity (AG), and competitive ratio (CR) which based on crop yield and nitrogen acquisition were used to evaluate interspecific competition between sugarcane and soybean. The results indicated that sugarcane-soybean intercropping system had intercropping advantages based on total LER in the three-year. Sugarcane had lower AG and CR values than soybean. The quality of sugarcane juice was not significantly different between intercropping and monoculture, except the excessive nitrogen application (N2) in 2011, which reduced the apparent purity and gravity of sugarcane juice significantly compared with normal nitrogen application (N1). This paper suggests that the intercropping advantage of sugarcane-soybean system is mainly contributed by soybean. The introduction of soybean in a sugarcane field does not significantly affect the quality of sugarcane juice.