Study On Water Use Of Maize-soybean Intercrops On The Loess Plateau, China

Food security has always been the top challenge to realize the sustainable development of human society and needs to be resolved urgently. Less and uneven rainfall distribution in time and space, accompany with low soil fertility on the Loess Plateau of China, which greatly limits water use efficiency and productivity of crop. To make efficient use of limited water resources and improve soil nutrient utilization plays an important role in agricultural researches in this region. The maize-soybean intercrops can provide extra nitrogen resource which benefits to yield increase and input of chemical fertilizer decrease, finally improve water use efficiency. Therefore, intercrops can improve the present situation of water shortage and lack of soil fertility, then provide theoretical basis and cultivated practices for crop cultivation on Loess Plateau of China. We conducted field experiments to evaluate the effects of different crop variety(maize: Zhengdan 958 and Yuyu 22, soybean: Zhonghuang 24 and Zhonghuang 13), three densities(low, medium and high) and five sowing proportions(sole-cropped maize, 2 rows maize and 2 rows soybean, 2 rows maize and 4 rows soybean, 4 rows maize and 2 rows soybean, sole-cropped soybean) on crop growth, physiological characteristics, grain yield, economic benefits, nutrient and water use, which provide based references for selection of crop cultivation and sustainable development of agriculture. The main results were concluded as follows:(1) Land equivalent ratio(LER) in maize-soybean intercrops under different variety, planting densities and sowing proportions was 0.90-1.29. LER was greater than one except two rows maize and two rows soybean in 2014, indicating that maize-soybean intercrops improved yield and land use efficiency on the Loess Plateau of China.(2) The competition indices(aggressivity and competitive ratio) of maize were higher than that of soybean, supporting the maize became as dominant species in maize-soybean intercrops. The actual yield loss(AYL) of maize was positive, indicating that maize had a yield advantage in maize-soybean intercrops. AYL of mostly soybean was negative indicated the yield loss in maize-soybean intercrops. AYL of intercropped systems was positive indicated the yield advantages of maize-soybean intercrops. System productivity index(SPI) of maize-soybean intercrops showed the higher productivity and stability of these intercrop systems. The intercropping advantage(IA) of maize was positive when intercropped with soybean, showed the positive economic profit of maize, and IA of soybean was negative indicated the decrease of soybean economic profit in maize-soybean intercrops. Consequently, IA of intercrop system was positive which proved that there were advantages of economic profit while maize and soybean intercropped. In addition, the monetary advantage index followed a similar trend to IA and showed a clear and high gain from intercropping. Therefore, intercrops advantages were mainly a result of maize yield and economic benefit improving in maize-soybean intercrops.(3) The grain yield and economic benefit of Zhengdan 958 intercropped with soybean(Zhonghuang 24 and Zhonghuang 13) were greater than that of Yuyu 22. The AYL, SPI and IA of Zhengdan 958 were higher than that of Yuyu 22, showing that Zhengdan 958 with drought resistant had greater capacity to enhance intercropping advantages relative to Yuyu22 in arid and semiarid of Loess Plateau.(4) Yield components factors of maize and soybean decreased with increase of intercropped density. Intercrop increased maize yield components including ear weight, ear length, ear width, kernal weight per ear, kernel number per row and 1000-kernel weight then to improve single plant even population yield of maize. Refer to soybean under intercropped, yield in intercrops decreased or equal to sole crop in single plant even population yield production due to pod number per plant, seed weight per plant and 100-seeds weight. The AYL of maize was positive indicated that maize had the yield advantage in intercrops compared to sole crop. Most of AYL of soybean in proportion of 2:4 and 2:2 were positive and negative respectively, indicating the soybean yield in proportion of 2:4 were higher than that of in proportion of 2:2.(5) Aboveground competition for solar radiation was probably important to grains formation. Our results found that there was no significant difference of photosynthetic rate in maize and soybean under intercropped. Belowground competition for soil water and nutrients was important to high resource efficiency. Our results found that nitrogen and phosphorus uptake of maize increased and that of soybean decreased when they were intercropped; intercrops had an effect on evapotranspiration of maize and soybean to improve water use efficiency(WUE).(6) Compared to WUE of sole-cropped soybean and average that of maize and soybean, maize-soybean intercrops improved WUE. Intercrop in proportion of 4:2 had the greatest WUE among all sowing proportions. Compared to sole crop, intercrop increased vertical and horizontal distribution of root(root length density, RLD), and changed root morphological characteristics, and increased root niche to absorb water to impove crop water use.(7) There was a negative relationship between RLD and LER in maize-soybean intercrop. Intercrop in proportion of 2:2, crops overproduced roots at the expense of reproductive biomass compared with other intercrop proportions, which showed that the key reason for yield and WUE increase was that there was a trade-off between root growth and yield formation when maize intercropped with soybean.