Responses of Branch Number and Yield Component of Soybean Cultivars Tested in Different Planting Densities

Abstract

Increasing planting density is one of the key management practices to enhance soybean yield. A 2-yr field experiment was conducted in 2018 and 2019 including six planting densities and two soybean cultivars to determine the effects of planting density on branch number and yield, and analyze the contribution of branches to yield. The yield of ZZXA12938 was 4389 kg ha−1, which was significantly higher than that of ZH13 (+22.4%). In combination with planting year and cultivar, the soybean yield increased significantly by 16.2%, 31.4%, 41.4%, and 46.7% for every increase in density of 45,000 plants ha−1. Yield will not increase when planting density exceeds 315,000 plants ha−1. A correlation analysis showed that pod number per plant increased with the increased branch number, while pod number per unit area decreased; thus, soybean yield decreased. With the increase of branch number, the branch contribution to yield increased first, and then plateaued. ZH13 could produce a high yield under a lower planting density due to more branches, while ZZXA12938 had a higher yield potential under a higher planting density due to the smaller branch number and higher tolerance to close planting. Therefore, seed yield can be increased by selecting cultivars with a little branching capacity under moderately close planting.

High Density and Uniform Plant Distribution Improve Soybean Yield by Regulating Population Uniformity and Canopy Light Interception

“…Soybean yield in various countries, including China, has improved in recent years mainly because of genetic improvement, increased inputs (e.g., irrigation and fertilizer), and better field management practices, such as the optimization of planting density and tillage methods [5][6][7][8][9]. Increasing the planting density of soybeans can remarkably improve light interception and canopy photosynthesis, resulting in a significant increase in total dry matter accumulation and seed yield [9][10][11]. In the United States, a soybean record yield of 10,414 kg ha −1 was recorded in 2007, with a planting density of 520,000 plants ha −1 in Missouri by Kip Cullers [12].…”

“…According to their results, higher seed yield was positively correlated with higher plant populations. Xu et al [9] showed that the soybean yield could increase significantly by 16.2%, 31.4%, 41.4% and 46.7% for every increase in planting density of 45,000 plants ha −1 , within the range of 135,000 to 315,000 plants ha −1 . These studies collectively show that higher planting density improves seed yield.…”

“…However, high planting density or dense planting alone does not necessarily lead to higher grain yield for soybean or other crops [9,15,16]. Benjamin [17] found that uneven distribution of individual plants in a specific planting density can affect plant growth, leading to yield losses at the crop canopy level.…”

“…Moreover, crowding planting can decrease the leaf thickness and photosynthetic rate of soybean due to reduced light intensity in the population, resulting in poor yield or even failure of harvest [24][25][26]. Strong light radiation, which mainly occurs in the sparse section of soybean fields, has been shown to promote the growth of axillary buds, leading to numerous branches and thus enhancing the production capacity of a single plant [9]. Although soybean plants have a strong branching compensation ability for seedling loss, soil waste and light leakage loss occur when the distance between individual soybean plants is too large, leading to lower yield [23,27].…”

“…Several lines of evidence regarding spatial plant distribution indicate that the consistency and uniformity of canopy populations can reduce competition among plants in a specific population and ensure efficient use of light energy and nutrient resources [25,28]. Soybeans exhibit a strong self-compensation ability, especially when the number of seedlings is insufficient, and can increase branching to improve yield [9,29]. The main objective of crop production is to obtain the maximum production benefit, that is, to obtain high yield as far as possible under constant input.…”