Abstract:

This research aimed to determine the optimal intercropping row ratio of alfalfa （Medicago sativa） and maize （Zea mays） in the semi-arid area of the Loess Plateau in central Gansu. The experiment design was based on the traditional monoculture of alfalfa （A） and monoculture of maize （M）. Six intercropping configurations were set up： namely alfalfa/maize intercropping at ratios of 5∶2 （5A2M）， 5∶3 （5A3M）， 7∶2 （7A2M）， 7∶3 （7A3M）， 9∶2 （9A2M） and 9∶3 （9A3M）. The effects of the different intercropping row ratios on the dry matter yield， forage quality and utilization of water and nitrogen resources in the system were analyzed. It was found that： the dry matter yield of the system was highest in the 9A2M treatment （12.7 t·ha^-1）. This was 51.2% higher than the yield of M （8.4 t·ha^-1）. The crude protein yield of the system was highest （3.5 t·ha^-1） in the 9A2M treatment. In terms of nutritional quality， the treatment with the highest maize whole-plant crude protein content （9.0%） was 9A3M， and the intercropping row ratio had no significant effect on the acid and neutral detergent fiber contents of alfalfa. The highest water use efficiency of dry matter production was found in the 9A2M treatment （38.5 kg·ha^-1·mm^-1）. This was a 91.5% and 67.4% increase （P<0.05） compared to the M and A treatments， respectively. In terms of nitrogen fertilizer utilization， the partial factor productivity of nitrogen fertilizer in the 9A2M treatment （149.3 kg·kg^-1） was also the highest among the tested intercropping configurations， and was an increase of 55.0%， 61.2%， 39.8% and 29.7%， respectively， compared with the 5A2M， 5A3M， 7A3M and 9A3M treatments. A multi-trait analysis using a radar chart showed that the 9A2M treatment had the best overall performance and can be recommended for adoption in the semi-arid area of central Gansu.

Key words: alfalfa/maize intercropping, row ratio, dry matter yield, nutritional quality, water and nitrogen utilization