Evaluation of competition in the different intercropping ratios of soybean (Glycine max (L) Merrill) and Chia (Salvia hispanica L.) based on replacement method

Today, efficient agricultural systems such as intercropping are essential due to the optimal use of resources. Meanwhile, using the Legume plant in intercropping can increase the efficiency of biological nitrogen fixation and be a sustainable approach to meet the crop's nitrogen needs. Since the planting pattern and component crop greatly influence this biological process, selecting complementary species in intercropping can play an essential role in increasing flexibility and sustainability in farming systems.

In order to study the effects of intercropping culture on the agronomic traits of Chia and Soybean, a field experiment was conducted in a randomized complete block design with four replications at the research farm of Sari agricultural science and natural resources university in 2019. The planting ratios were 0:100, 25:75, 50:50, 75:25, and 100:0 (Soybean: Chia respectively) using replacement method. ResultsResults showed that intercropping had a significant effect on shoot height, No. branch, grain yield, components yield, and the N. derived from the atmosphere (Ndfa). In the Chia, reducing the number of planting rows in different planting ratios, shoot height, and 1000-seed weight increased in contrast to the number of inflorescences per plant. Different planting ratios had no significant effect on the number of branches per plant of Chia. The soybean crop had the highest no. of branches, the number of pods per plant, and the 1000 seed weight in the 25:75 planting ratio. The highest shoot height was related to the monoculture soybean (100:0), and with decreasing the number of soybean planting rows in intercropping, the shoot height decreased. Also, the Ndfa in intercropping culture was higher than in monoculture during different growth stages. Its amount increased with a decreasing share of soybean planting in intercropping. Biological nitrogen fixation in soybean intercropping cultivation with Chia increased 75 days after planting and then decreased. Besides, the pure stand of Soybean (100: 0) and Chia (0: 100) had the highest and lowest grain yield with an average of 4629.57 and 823.14 kg. ha-1, respectively. Considering the total yield of Chia and Soybean in intercropping cultivation and the compensatory ability to increase the yield of Soybean against the decrease in the yield of Chia, the effect of competition between the two crops is positive complementation. Calculation of land equivalent ratio (LER) revealed that the planting ratio of 25:75 had the highest efficiency by 22 percent.

Chia in intercropping can improve the yield components of Soybean while improving the efficiency of biological nitrogen fixation. Increasing the efficiency of intercropping cultivation in the planting ratio of 25:75 due to the increase of 75.37% is the share of the complementarity effect on grain yield, creating balance and facilitating inter-species competition.