Effects of substrate biofortification with broiler litter and phyto-mediated-nano-ZnO on Pleurotus ostreatus production and degradation of substrate contaminants

Abstract

The increase in human population and the effects of climate change have resulted in food insecurity, and this makes communities living in poor environments have no access to nutritious food. These communities suffer from protein and mineral deficiencies. The study was therefore undertaken to investigate the effect of biofortification of substrate with broiler litter and phyto-mediated-nano-ZnO on the yield and growth of Pleurotus ostreatus as a means of addressing these challenges. The other objective was to investigate the safety of Pleurotus ostreatus fruiting bodies for human consumption, and the safety of spent mushroom substrate for livestock feed by analysing for presence of heavy metals. The experiment was laid out in 5 X 6 factorial treatment combinations. The experimental factors were as follows: Urochloa panicoides (1 kg) was used as substrate with five (5) broiler litter levels- 0%, 1.25%, 2,5%, 5% and 10% BL and six (6) nanoparticle concentration- 0 mg/kg, bulk-ZnO 2 mg/kg, conventional ZnO 8 mg/kg, green-nano-ZnO 2 mg/kg, green-nano-ZnO 10 mg/kg and green-nano-ZnO 50 mg/kg. The treatments were replicated four times making a total of 30 treatment combinations and 120 experimental units. The treatments were arranged in a completely randomized design (CRD). The mycelial growth, fruiting body initiation, and total biomass of Pleurotus ostreatus on Urochloa panicoides substrate with varied broiler litter and nanoparticle concentrations were assessed. At each harvest, the fruit cap diameter and style length of mushrooms were measured using a tape measure, and the conversion efficiency ratio of substrate to fruiting bodies/biomass was calculated. Macro- and micro-nutrient content on various substrates were analyzed using the dry-ashing macro- and micro-nutrient procedure provided by AgriLASA. The analysis of variance indicated a significant difference in the impact of nanoparticle concentration and broiler litter on total biomass (P<0.05), but there was no significant difference in the interaction. Broiler litter had a statistically significant effect on fruit cap size and style length (P<0.05), but there was no significant effect of the different nanoparticle concentrations. AgriLASA's dry-ashing macro- and micronutrient approach was utilised to evaluate the transfer efficiency of macro- and micronutrients, protein and heavy metals. Mushrooms and wasted mushroom substrate recovered from 5 BL green-nano-ZnO 50 mg/kg, 10 BL control, and 10 BL green-nano-ZnO 50 mg/kg had increased levels of Fe and Zn micronutrients compared to other treatments.The transfer macro- nutrient and heavy metal efficiency ratio of Pleurotus ostreatus was unaffected by any nanoparticle concentration. The accumulation coefficient of macronutrient (N, P, Ca, Mg) and micronutrient content (Fe, Zn, Mn) were significantly different in Pleurotus ostreatus fruiting bodies harvested from different broiler litter treatments. Finally, the study established that treatment; '5 BL green-nano-ZnO 2 mg/kg' had the highest conversion ratio of 51.61%, followed by '5 BL green-nano-ZnO 50 mg/kg' with 33.59% and 0 BL control at 25.35%. The lowest biological efficiency was obtained from 2.5 BL green-nanoZnO 10 mg/kg at 0.58 %. The results therefore indicate that it is possible to boost oyster mushroom yield by substrate biofortification with appropriate broiler litter and nanoparticle concentrations. The study also established that the heavy metals Cr, Cd, and Se that were found in oyster mushrooms were within the acceptable human food safety level. Biofortifying liverseed grass with broiler litter and nanoparticle concentrations in oyster mushroom cultivation can contribute to the boosting of fruiting body crude protein content