Effect of initial C/N ratio and turning frequency on quality of final compost of turkey manure and olive pomace

In Morocco, the potential of agricultural waste is estimated at 34.7 MT/year. Composting is an effective way for waste management. If badly monitored, it can affect the environment. Initial C/N ratio (C/Ni) and aeration appear to be major factors impacting the composting process. This work studied the effect of C/Ni and turning frequency (TF) on the olive pomace and turkey manure co-composting process and on the final compost quality. The study concerned the Moroccan agricultural region Chaouia-Ouardigha where these two by-products are abundant and not valued. Six heaps (H1 to H6), at three levels of C/Ni (20, 22, 28) and two levels of TF (once and twice a week), were studied. Statistical tests showed that the studied factors had no significant effects on pH, total nitrogen, electrical conductivity, and cation exchange capacity (CEC). However, C/Ni had a significant increase of 60% in nitrates. Varying from 20 to 22 or from 22 to 28, C/Ni reversed its significant effect on final C/N and CEC/organic carbon. TF reduced significantly OM and final C/N by about 22% and 9% respectively. The dendrogram showed that the six heaps could form at the end two groups: group 1 (four heaps) and group 2 (two heaps) with a similarity of about 75 and 90 respectively. C/Ni of 22 and TF of twice a week seem to be an optimum to produce a final compost of better quality. This work shows that (1) C/Ni and TF significantly impact several final quality parameters of composts from olive pomace and turkey manure, and (2) composting has a strong effect of reducing the variability between heaps initially different to produce very similar final composts. © 2022, The Author(s).