Soybean Yield, Quality, and Economic Responses to Shade Net Levels

Introduction: Today, human societies face various challenges such as climate change and global warming, environmental degradation, and food security concerns. One of the approaches proposed in recent decades to mitigate the adverse effects of climatic factors and enhance agricultural productivity is the use of shading nets, which create favorable microclimatic conditions and consequently improve plant growth and yield. Therefore, the microclimatic effects of shading nets in soybean cultivation have the potential to increase yield per unit area, leading to higher income levels, improved livelihoods, and enhanced economic prosperity for farmers. Materials and Methods: To evaluate the microclimatic effects of shading nets on the quantitative and qualitative performance of soybean and farmers' income, a field experiment was conducted based on a randomized complete block design (RCBD) with three replications at the research farm of Sari Agricultural Sciences and Natural Resources University, located at ۵۳°۰۰'E and ۳۶°۳۳′N. According to the extended De Maitonne climatic classification, the study area has a humid temperate climate. The treatments included four shading levels: no shading (control), and nets reducing light transmission by ۳۰%, ۵۰%, and ۸۰%. Surface irrigation was applied, and soil moisture was monitored using a tensiometer. Irrigation was carried out when the soil water content reached ۷۰% (SWC-۷۰). Quantitative traits, including plant height, number of pods per plant, number of seeds per pod, ۱۰۰-seed weight, biomass, harvest index, and seed yield were measured. For qualitative performance, soluble protein content and seed oil percentage were analyzed. Water productivity was evaluated under three conditions: irrigation water productivity (WPI), irrigation plus precipitation productivity (WPI+P), and evapotranspiration productivity (WPET). The economic performance of shading nets in soybean cultivation was assessed using the indicators NBPD, BPD, and the ratios P/C and B/C. Results and Discussion: Increasing shading intensity led to a reduction in the number of pods per plant, number of seeds per pod, ۱۰۰-seed weight, and biomass. The highest mean pod number and seed number per pod were obtained under the ۳۰% shading treatment, while these traits decreased significantly under ۵۰% and ۸۰% shading. The greatest and lowest biomass values were recorded for the ۳۰% and ۸۰% shading treatments, with ۵۵۰۰ and ۳۸۰۰ kg ha⁻¹, respectively. A positive and direct correlation was observed between soybean biomass and grain yield, indicating that reductions in biomass led to significant decreases in grain yield. Conversely, plant height increased with shading intensity, with the tallest plants observed under ۸۰% shading, though this treatment exhibited lower grain yield compared to ۳۰% and ۵۰% shading. The highest harvest index values were recorded under ۸۰% and ۵۰% shading (۲۳.۴% and ۲۳.۶%, respectively), while the lowest value was found in the control (۱۹.۳%). Grain yield under ۳۰% shading increased by about ۱۰% compared with the control (۱۰۶۶.۷ kg ha⁻¹), whereas yields under ۵۰% and ۸۰% shading decreased by ۹% and ۱۶%, respectively. The highest soluble protein content was observed in the control and ۳۰% shading treatments (۴۱.۸ and ۴۱.۴ μg g⁻¹, respectively), and the highest oil content (۰.۹۳%) occurred under ۳۰% shading. In contrast, the lowest values of both protein and oil content were recorded under ۸۰% shading (۳۲.۲ μg g⁻¹ and ۰.۷۸%, respectively). Moreover, water productivity indices (WPI, WPI+P, and WPET) were highest under ۳۰% shading, followed by other treatments. Despite reduced irrigation water use under ۵۰% and ۸۰% shading, their water productivity remained lower than that of ۳۰% shading. Economically, the highest NBPD and BPD values were obtained under ۳۰% shading (۸۰۴,۶۵۳ and ۸۱۹,۱۶۳ million IRR m³, respectively), and the P/C and B/C ratios were also superior in this treatment, while the lowest economic indices were observed in the control. Conclusion: Different shading intensities significantly affected the quantitative and qualitative traits of soybean. Compared with the control, ۳۰% shading resulted in a notable increase in grain yield and the highest water productivity indices. Economic analysis also confirmed the superiority of ۳۰% shading in terms of profitability and efficiency. Therefore, using ۳۰% shading nets in soybean cultivation can serve as a practical and strategic approach to modifying the crop microclimate, enhancing yield per unit area, increasing farmers' income, and contributing to sustainable agricultural production.

کلیدواژه ها:

Food security ، Water productivity ، Protein ، biomass ، Economic indices ، B/C ratio