Optimizing tree shade gradients in Emblica officinalis-based agroforestry systems: impacts on soybean physio-biochemical traits and yield under degraded soils

Agroforestry is seen as a strategy to sustainably boost agricultural production by creating favorable microclimatic conditions. However, tree shade can significantly reduce crop yield, making it important to assess the balance between the positive and negative impacts of tree cover on food security, especially as climate change alters weather patterns. To understand this relationship, a trial was conducted to evaluate how tree canopy influences crop yield in degraded soils. This study examines how different levels of natural tree shade affect the physiological and biophysical constraints of soybean (Glycine max) in an Emblica officinalis-based agroforestry system. The study assessed the effects of shade intensities (S1-0%, S2-40%, S3-50%, and S4-60%) on physio-biochemical and yield traits of two soybean varieties: KDS-726 (V1) and MACS-1188 (V2). Increased shade led to significant reductions in net photosynthetic rate (16.21%, 25.32%, 40.08%), transpiration rate (6.45%, 21.14%, 39.61%), and stomatal conductance (22.86%, 39.79%, 55.91%) due to reduced light availability over control (S1-0%). Chlorophyll content and NDVI increased up to 50% shade but decreased beyond this, indicating limited photosynthesis. Higher shade levels also increased total phenol, proline, and other antioxidants, indicating increased stress. Soybean yield parameters decreased with increasing shade. The highest seed yield was in open conditions (2.15 t ha⁻¹), with reductions of 24.65%, 39.53%, and 59.53% under S2-40%, S3-50%, and S4-60% shade. KDS-726 produced 20% more seed yield than MACS-1188 (1.35 t ha⁻¹). Correlation analysis revealed that higher phenolic content and internal CO₂ levels, indicators of stress, negatively impacted seed yield (− 0.51 and − 0.49, respectively) due to reduced photosynthesis. A Crop Status Index (CSI) was derived to identify the shade threshold level in agroforestry for the first time. The highest CSI was recorded under open conditions, statistically comparable to values under 40% and 50% shade, and lowest in 60% shade. This suggests that moderate shading (up to 50%) does not significantly affect the crop’s overall status, while higher shade levels (60%) impose severe stress. Understanding the shade threshold helps manage understory crops to maximize light and reduce stress. Additionally, it demonstrates the potential of fruit-based agroforestry to rehabilitate degraded lands, enhance crop yield, increase fruit production, improve the environment, and meet India’s GROW report commitments of land degradation neutrality by restoring 26 million hectares of degraded land by 2030.