Impact of peat moss– switchgrass biochar mixtures on soybean performance with and without fertilization under controlled greenhouse conditions

Soybean (Glycine max L.) family Fabaceae, is an important crop known for its high-quality protein and oil content. This study examined how adding switchgrass (Panicum virgatum L.) biochar to peat moss growing media in a greenhouse, affected soybean growth, yield, and seed quality. A one-year experiment was conducted with three biochar rates (0%, 5%, and 10% w/w) and two fertilization regimes (fertilized and unfertilized plants), using the soybean cultivar OAC Strive. Plants were grown in pots with a modified Hoagland’s No. 2 nutrient solution and traits that measured were, total aboveground biomass, number of seeds, seed weight, number of pods, seed oil and protein content. Biochar was characterized for its properties, including nutrient content, SEM, metals, pH, electrical conductivity and ash content. Results showed that fertilized plants amended with 5% biochar produced significantly higher total seed weight (yield), total aboveground fresh and dry biomass, dry straw weight, and total number of seeds compared with the 10% biochar treatment. Higher values were also observed in the 5% biochar treatment compared with the control; however, these differences were not statistically significant. For the unfertilized plants all values are very low, indicating that fertilization is essential under the tested conditions. Unfertilized plants showed some minor improvements with biochar, but absolute values remained low. Seed protein content was about 44 to 45% for all the treatments while oil content ranged from 19.53% (5% biochar) to 20.28% (10% biochar). In general, adding 5% switchgrass biochar to peat moss under fertilized conditions improved soybean growth and yield, showing that it can be used as an effective and sustainable peat moss - amendment under greenhouse conditions. However, the 10% biochar treatment resulted in lower values than the control and significantly lower values than the 5% biochar treatment, suggesting the presence of a threshold effect.