Abstract
The frequency of heavy rains is increasing with climate change in regions that already have high annual rainfall (i.e., Sichuan, China). Crop response under such high-rainfall conditions is to increase dry matter investment in vegetative parts rather than reproductive parts. In the case of soybean, leaf redundancy prevails, which reduces the light transmittance and seed yield. However, moderate defoliation of soybean canopy could reduce leaf redundancy and improve soybean yield, especially under high-rainfall conditions. Therefore, the effects of three defoliation treatments (T1, 15%; T2, 30%; and T3, 45% defoliation from the top of the soybean canopy; defoliation treatments were applied at the pod initiation stage of soybean) on the growth and yield parameters of soybean were evaluated through field experiments in the summer of 2017, 2018, and 2019. All results were compared with nondefoliated soybean plants (CK) under high-rainfall conditions. Compared with CK, treatment T1 significantly (p < 0. 05) improved the light transmittance and photosynthetic rate of soybean. Consequently, the leaf greenness was enhanced by 22%, which delayed the leaf senescence by 13% at physiological maturity. Besides, compared to CK, soybean plants achieved the highest values of crop growth rate in T1, which increased the total dry matter accumulation (by 6%) and its translocation to vegetative parts (by 4%) and reproductive parts (by 8%) at physiological maturity. This improved soybean growth and dry matter partitioning to reproductive parts in T1 enhanced the pod number (by 23%, from 823.8 m−2 in CK to 1012.7 m−2 in T1) and seed number (by 11%, from 1181.4 m−2 in CK to 1311.7 m−2 in T1), whereas the heavy defoliation treatments considerably decreased all measured growth and yield parameters. On average, treatment T1 increased soybean seed yield by 9% (from 2120.2 kg ha−1 in CK to 2318.2 kg ha−1 in T1), while T2 and T3 decreased soybean seed yield by 19% and 33%, respectively, compared to CK. Overall, these findings indicate that the optimum defoliation, i.e., T1 (15% defoliation), can decrease leaf redundancy and increase seed yield by reducing the adverse effects of mutual shading and increasing the dry matter translocation to reproductive parts than vegetative parts in soybean, especially under high-rainfall conditions. Future studies are needed to understand the internal signaling and the molecular mechanism controlling and regulating dry matter production and partitioning in soybean, especially from the pod initiation stage to the physiological maturity stage.
Highlights
The increasing human population is projected to raise food demand globally by 50% in 2030 [1]
In the present study, we hypothesized that soybean produces extra leaves in the high-rainfall conditions, i.e., southwest of China, and a slight defoliation from soybean canopy would (a) improve the photosynthetically active radiation (PAR) transmittance at the soybean canopy, (b) delay the leaf senescence of remaining leaves by improving the light environment at the soybean canopy, and (c) increase the translocation of photoassimilate to pods and seeds, as well as the final seed yield of soybean under high-rainfall conditions. We evaluated these hypothesizes by comparing the defoliation of 15%, 30%, or 45% of the top leaves from the soybean canopy at the pod initiation stage with no defoliation treatment
At R3, R4, and R5, the average highest leaf greenness was measured in CK, while at R6 and R7, the highest leaf greenness was noted under treatment T1, whereas, at all sampling stages, the average lowest leaf greenness was noticed under the T3 treatment
Summary
The increasing human population is projected to raise food demand globally by 50% in 2030 [1]. The first four decades of the green revolution (from 1960 to 2000) witnessed substantial improvements in grain yields of staple food crops; the rate of improvement in crop yields has significantly declined in the past twenty years [2,3]. This decline was ascribed to the fact that the genetic approaches used for the green revolution are attaining their potential limits [4]. Failure to enhance the crop yields on the currently available agricultural land will increase crop prices and the destruction of tropical forest areas for crop production [6]. Meeting the predicted world demand for food crops will require new crop production practices or methods beyond that employed in the green revolution [11,12]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
