Spent Pleurotus substrate as organic fertilizer to improve yield and soil fertility: the case of baby leaf lettuce production.

BACKGROUND

Spent mushrooms substrate is the most important waste generated by edible mushrooms industry and can be re-used as organic fertilizer, following sustainable production principles. In the present study, Spent Pleurotus substrate (SPS) was used for organic fertilization of baby leaf production during two consecutive cycles (1st: October to December; 2nd: December to March) using two variety of lettuce (Doge and Imperiale). Different amounts of SPS in a mix with chemical fertilizers were applied: 100% SPS to fulfil the N needs of the crop and 50% of mineral N (T100 + 50), 200% SPS to fulfil the double N needs (T200) and 200% SPS to fulfil the N needs of the crop and 50% of mineral N (T200 + 50). SPS treatments were compared with an unfertilized control (T0) and chemical fertilization treatments. The crops coverage, Soil Plant Analysis Development index (i.e. SPAD) and yield were monitored during each cycle and soil samples were analysed to observe the effect of SPS on soil fertility.

RESULTS

Among SPS treatments, T100 + 50, which combined 50% mineral fertilization with SPS, yielded the best productive results among SPS treatments. This combination improved nutrient availability, whereas higher SPS concentrations (T200, T200 + 50) reduced yields due to nitrogen immobilization. The high initial soil nitrogen content limited significant changes in soil nitrogen, but SPS improved soil organic matter, active carbon and enzyme activity, enhancing microbial activity. Among the two lettuce varieties a difference in nitrogen uptake and utilization was observed.

CONCLUSION

Overall, the study highlights the potential of raw SPS as a sustainable organic fertilizer for baby leaf cultivation. Incorporating SPS alongside half of the crop's mineral nitrogen requirement offers a promising alternative to conventional mineral fertilization. After just two crop cycles, this approach maintains a good yield at the same time as enhancing soil organic matter and enzymatic activity, ultimately improving soil fertility. © 2025 The Author(s). Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.