Abstract

Our study aims to assess the kinetic of the decomposition and nutrient mineralization process of organic manures from pigs’ dejection. A litter bag study was carried out during 12 weeks following decomposition and nutrient release process in ferralitic soil in southern Benin (West Africa). 200 g of pigs’ manures from four groups of pigs fed with four diets were considered as treatments: T1 (recommended diet composition, consisted of 15% Azolla pinnata + 55% provender + 5% coconut copra + 5% oil palm + 5% soybean bran + 10% rice bran + 5% kitchen waste), T2 (partially improved diet with Azolla pinnata, consisted of 30% Azolla pinnata + 65% rice bran + 5% oil palm), T3 (improved diet with Azolla pinnata, consisted of 47.5% Azolla pinnata + 47.5% rice bran + 5% oil palm), and T4 (improved diet with cereal bran, consisted of 15% Azolla pinnata + 40% rice bran + 40% wheat bran + 5% oil palm). Animals of six months age were fed during three months. A randomized complete block design with three replicates was set up for litter bag study. One component exponential decomposition model y = y₀e^-kt was found for all treatments. Nutrient mineralization was slow in the soil. Less than 50% of the pigs’ manures were decomposed after 12 weeks. In addition, manure from treatment T1 was richer in K, Ca and Mg than manures from treatment T3. High quantity (42.65%) of N was released in treatment T3.  Pigs fed with diet enriched with Azolla produce manure which has released high N proportion in the soil. This is an opportunity to sustain food crop production.

Key words: Pigs’ diet composition, Azolla pinnata, soil fertility, organic manure, decomposition rate.