Manure-based composts influence soil quality after lettuce (Lactuca sativa L.) production

Declining soil fertility is a major constraint for vegetable crops like lettuce in sub-Saharan Africa. With the purpose of contributing to enhancing crop yields and soil productivity, while safeguarding the environment, this study aims to assess the effect of composts made from chicken droppings (CCD) and horse dung (CHD) on soil quality after lettuce growing. The phytotoxicity of the composts was assessed by testing the germination of two varieties of lettuce (V1: Eden and V2: Blonde de Paris) with aqueous extracts of the composts at different concentrations (0, 25, 50, 75 and 100%). For the field evaluation, treatments (C0: control without fertilizer, C1: 15 t. ha− 1 of chicken droppings, C2: 15 t.ha− 1 of horse dung, C3: chemical fertilizers) and varieties were distributed in a completely randomized block design with three replications. Physico-chemical soil analysis was carried out before (Ct) and after lettuce production depending on the treatments. Soil’s parameters determined included: pH, organic matter, carbon, C/N ratio, granulometry, cation exchange capacity, exchangeable bases, nitrogen, phosphorus, calcium, magnesium, sodium and potassium contents. The results of the phytotoxicity test showed that the lowest germination percentages were obtained at V1C2100%Ster + (48.33 ± 6.01%) and V2C2100% Ster + (53.33 ± 6.01%). These values were around the standard (50%), showing that these composts were non- toxic. The results showed that overall, the composts improved soil properties, with significant increases in P and Ca content. So, soil Ca contents of C0, C1, C2 and C3 were respectively 2, 3, 2 and 2 times that of Ct. CCD and CHD can be therefore recommended for growing lettuce and maintaining soil quality.