Potential use of soy whey, a food byproduct soybean, as an alternative fertilizer for crop cultivation

The extensive use of chemical fertilizers for agriculture poses sustainability challenges. However, the use of local resources can potentially reduce the reliance on chemical fertilizers. This study evaluated the potential of soy whey, a liquid byproduct of soy protein isolate extraction that has not been previously used as a fertilizer, as an alternative nitrogen-based fertilizer for two vegetable crops, komatsuna and potatoes. Initially, both crops were grown under complete replacement of chemical fertilizers with soy whey. Subsequently, both crops were grown with different ratios of chemical fertilizer and soy whey. Soy whey had a positive fertilizer effect on all tested crops, although the degree of effectiveness varied by species. In komatsuna, substituting nitrogen entirely with soy whey resulted in an increase in fresh weight compared to unfertilized conditions, although the fresh weight remained significantly lower than that with chemical fertilizer. With a 30% reduction in chemical fertilizer at the nitrogen base, shoot fresh weight and potassium uptake were comparable to those of the chemical fertilizer; however, the uptake of nitrogen and phosphorus was reduced. In potatoes, the replacement of chemical fertilizer with soy whey resulted in decreased tuber nitrogen levels; however, tuber weight, phosphorus, and potassium remained comparable to those of the chemical fertilizer treatment. With 30% less fertilizer, the tuber nitrogen content was not significantly different from that with chemical fertilizer. Overall, soy whey is a promising alternative fertilizer, particularly for crops with long growth periods. • Fertilizer effects of soy whey, a liquid byproduct from soy protein isolate extraction, on komatsuna and potato were evaluated. • For komatsuna, soy whey showed positive fertilizer effects, although the efficacy was not as pronounced as that of chemical fertilizers. • For potato, the tuber number and individual tuber weight in the soy whey treatments were almost same values as those in the chemical fertilizer treatment. • Soy whey is a promising alternative fertilizer, particularly for crops with long growth periods, owing to its slow nitrogen release