Peanut meal enzymatic hydrolysis process optimization and effects of inorganic nitrogen fertilizer partial replacement with its products on potato growth and soil quality

Objective To optimize the enzymatic hydrolysis process of peanut meal, and investigate the effects of the resulting hydrolysate as a partial substitute for inorganic nitrogen fertilizer on potato growth and soil quality, aiming to promote the resource utilization of peanut meal waste and the sustainable development of potato production.

Method A 4-factor, 3-level Box-Behnken Design experimental design was used to optimize reaction time, initial reaction pH, reaction temperature, and enzyme addition amount for preparing an enzymatic hydrolysate (M) with high protein hydrolysis degree. Under field conditions, the effects of enzymatic hydrolysate and traditionally fermented peanut meal broth (F) on potato crops and soil quality were compared at inorganic N fertilizer substitution rates of 5% (M5, F5), 10% (M10, F10), 15% (M15, F15), and 20% (M20, F20).

Result The optimal conditions for peanut meal protein hydrolysis were: Reaction time of 4.5 h, initial reaction pH of 8.6, reaction temperature of 54.9 ℃, and enzyme addition amount of 900.8 U·g⁻¹, with an average hydrolysis degree of 25.02%. After optimization, the nutrient contents of enzymatic hydrolysate were: Total N 5.10 g·L⁻¹, total P 5.30 g·L⁻¹, total K 9.70 g·L⁻¹, and organic matter 50.40 g·L⁻¹. The M10 treatment exhibited the optimal effect on increasing the total potato yield and large potato production, with the total yield and large potato yield significantly increasing by 26.63% and 30.90%, respectively; Tuber N, P, K, and dry matter contents significantly increased by 19.04%, 22.47%, 29.32%, and 31.86% higher than those of the control, respectively. For the M20 treatment, soil pH significantly increased by 5.70%, compared with the control, while organic matter content and electrical conductivity significantly increased by 13.48% and 40.06%, respectively. The alkaline-hydrolyzable N content reached a peak of 106.26 mg·kg⁻¹ in the M15 treatment, which was 5.70% significantly higher than that of the control. The α diversity indices of the bacterial community in the M10 treatment were obviously higher than those in the other treatments. The relative abundances of the plant-beneficial bacteria Terrabacter, Sphingomonas and Arthrobacter in M5 treatment were significantly increased compared to F5 treatment.

Conclusion After process optimization, both the hydrolysis degree and nutrient content of peanut meal are improved. Replacement of partial inorganic N fertilizer with the enzymatic hydrolysate can be regarded as an effective measure for green potato production, but its long-term potential and large-scale promotion still need to be verified.