Date Published: June 10, 2015
Publisher: Public Library of Science
Author(s): Yitao Zhang, Jian Liu, Jizong Zhang, Hongbin Liu, Shen Liu, Limei Zhai, Hongyuan Wang, Qiuliang Lei, Tianzhi Ren, Changbin Yin, Zhihui Cheng.
Intercropping is regarded as an important agricultural practice to improve crop production and environmental quality in the regions with intensive agricultural production, e.g., northern China. To optimize agronomic advantage of maize (Zea mays L.) and soybean (Glycine max L.) intercropping system compared to monoculture of maize, two sequential experiments were conducted. Experiment 1 was to screening the optimal cropping system in summer that had the highest yields and economic benefits, and Experiment 2 was to identify the optimum row ratio of the intercrops selected from Experiment 1. Results of Experiment 1 showed that maize intercropping with soybean (maize || soybean) was the optimal cropping system in summer. Compared to conventional monoculture of maize, maize || soybean had significant advantage in yield, economy, land utilization ratio and reducing soil nitrate nitrogen (N) accumulation, as well as better residual effect on the subsequent wheat (Triticum aestivum L.) crop. Experiment 2 showed that intercropping systems reduced use of N fertilizer per unit land area and increased relative biomass of intercropped maize, due to promoted photosynthetic efficiency of border rows and N utilization during symbiotic period. Intercropping advantage began to emerge at tasseling stage after N topdressing for maize. Among all treatments with different row ratios, alternating four maize rows with six soybean rows (4M:6S) had the largest land equivalent ratio (1.30), total N accumulation in crops (258 kg ha-1), and economic benefit (3,408 USD ha-1). Compared to maize monoculture, 4M:6S had significantly lower nitrate-N accumulation in soil both after harvest of maize and after harvest of the subsequent wheat, but it did not decrease yield of wheat. The most important advantage of 4M:6S was to increase biomass of intercropped maize and soybean, which further led to the increase of total N accumulation by crops as well as economic benefit. In conclusion, alternating four maize rows with six soybean rows was the optimum row ratio in maize || soybean system, though this needs to be further confirmed by pluri-annual trials.
Northern China has a very intensive agriculture with high inputs of seeds, irrigation and chemicals, because of high pressure of food security. This has caused severe environmental problems , including pollution of groundwater by nitrate from soils , gas emission to air , and soil acidification . Loss of nitrogen (N) during maize (Zea mays L.) growth season is an especial concern, as excessive application of N is often combined with heavy summer rains in this region . To ensure both food security and environmental quality, it is essential to seek best management practices, which include appropriate cropping systems that can efficiently utilize solar and soil resources with minimum nutrient inputs.
This study clearly demonstrated that intercropping systems presented advantage over maize monoculture. Intercropping system of maize with legumes reduced N application in the same planting area compared to maize monoculture, probably because of the enhanced biological N fixation by legumes . Both maizeǁsoybean and maizeǁred bean systems showed intercropping advantages in yield, economy, land utilization ratio and reducing soil nitrate-N accumulation, as well as better residual effect on the subsequent wheat crop. Previous studies had also reported beneficial effects of intercropping systems on yield, economy and the environment [6,33], which stresses the importance of using intercropping in sustainable agriculture to alleviate pressure in intensive farming systems with high inputs and outputs . Soybean is more important than red bean in China, with more consumption and relying on import , and decreasing planting area year by year . Therefore, considering maize intercropping with soybean as the best cropping system in summer in the present study is reasonable and necessary.
Compared to conventional monoculture of maize, both maize ǁ soybean and maize ǁ red bean had significant advantage in yield, economy, land utilization ratio and reducing soil nitrate-N accumulation, as well as better residual effect on the subsequent wheat crop. In particular, maize ǁ soybean performed best, and was thus identified as the optimal summer cropping system in this study. Intercropping systems could reduce N fertilizer use and increase relative biomass of intercropped maize, as a result of high photosynthetic efficiency of border rows and sufficient nitrate supply during symbiotic period. Noticeably, intercropping advantage was not inherent but began to emerge at tasseling stage after N topdressing for maize. 4M:6S was the best intercropping system in this study, as it had the largest LER, crop total N accumulation and economic benefit. In addition, compared to maize monoculture, 4M:6S significantly reduced nitrate-N accumulation in the soil after harvest of both summer crops and winter wheat, and it even slightly increased wheat yield. The most important advantage of 4M:6S was to increase biomass of intercropped maize and soybean, which further led to the increase of total N accumulation by crops as well as economic benefit. In conclusion, alternating four maize rows with six soybean rows is the optimum row ratio in maize || soybean system, though this needs to be further confirmed by pluri-annual trials.