Date Published: February 26, 2019
Publisher: Public Library of Science
Author(s): Lingyang Feng, Muhammad Ali Raza, Yuankai Chen, Muhammad Hayder Bin Khalid, Tehseen Ahmad Meraj, Faiza Ahsan, Yuanfang Fan, Junbo Du, Xiaoling Wu, Chun Song, Chuanyan Liu, George Bawa, Zhongwei Zhang, Shu Yuan, Feng Yang, Wenyu Yang, Paul C. Struik.
Different planting patterns affect the light interception of intercrops under intercropping conditions. Here we revealed that narrow-wide-row relay-intercropping improves the light interception across maize leaves in wide rows (60cm) and narrow rows (40cm), accelerated the biomass production of intercrop-species and compensated the slight maize yield loss by considerably increasing the soybean yield. In a two-year experiment, maize was planted with soybean in different planting patterns (1M1S, 50:50cm and 2M2S, 40:60cm) of relay-intercropping, both planting patterns were compared with sole cropping of maize (M) and soybean (S). As compared to M and 1M1S, 2M2S increased the total light interception of maize leaves in wide rows (WR) by 27% and 23%, 20% and 10%, 16% and 9% which in turn significantly enhanced the photosynthetic rate of WR maize leaves by 7% and 5%, 12% and 9%, and 19% and 4%, at tasseling, grain-filling and maturity stage of maize, respectively. Similarly, the light transmittance at soybean canopy increased by 218%, 160% and 172% at V2, V5 and R1 stage in 2M2S compared with 1M1S. The improved light environment at soybean canopy in 2M2S considerably enhanced the mean biomass accumulation, and allocation to stem and leaves of soybean by 168%, and 131% and 207%, respectively, while it decreased the mean biomass accumulation, and distribution to stem, leaves and seed of maize by 4%, and 4%, 6% and 5%, respectively than 1M1S. Compared to 1M1S, 2M2S also increased the CR values of soybean (by 157%) but decreased the CR values of maize (by 61%). Overall, under 2M2S, relay-cropped maize and soybean produced 94% and 69% of the sole cropping yield, and the 2M2S achieved LER of 1.7 with net income of 1387.7 US $ ha-1 in 2016 and 1434.4 US $ ha-1 in 2017. Our findings implied that selection of optimum planting pattern (2M2S) may increase the light interception and influence the light distribution between maize and soybean rows under relay-intercropping conditions which will significantly increase the intercrops productivity. Therefore, more attention should be paid to the light environment when considering the sustainability of maize-soybean relay-intercropping via appropriate planting pattern selection.
In China, intensive farming has been practiced with high inputs of chemicals, fertilizers, seeds, and irrigation, due to the high food security pressure. This situation has raised serious environmental problems , including groundwater pollution by leaching of nitrogen from soil layers , acidification of soil  and emission of harmful gases to air . The nitrogen loss during maize planting is an especial concern . To guarantee both food production and environmental security, we have to adopt best agronomic practices such as appropriate planting systems which have the ability to use sunlight and land resources efficiently with minimum inputs, for instance, intercropping and relay intercropping systems [6,7]. Relay intercropping is one of the important agronomic practices to increase seed yield [8,9]. However, as compared to intercropping systems, the advantage of relay-intercropping system is higher because in intercropping systems both crops almost have the similar growth periods and they required high amount of inputs to produce higher intercrop yields, whereas under relay intercropping system both crop species have different growth periods and have complementary resource use in time [7,8,10,11]. In addition, for maize soybean relay-intercropping system, the land equivalent ratio (LER, described as the relative farmland that is needed for sole crops to produce similar crop yields as intercrops) often reaches 1.7–1.8 when both crops planted at their optimal planting density, which increases its popularity among farmers, especially among small farmers . However, during the co-growth period per plant growth rates decrease and competition for sunlight, nutrients and land are exacerbated between maize and soybean under maize soybean relay intercropping system [11,12]. The reduced light intensity perceived by soybean plants promoted by maize canopy not only decreased the seed yield  but also lower the seed quality of soybean .