Improving soil physical properties and cassava productivity through organic manures management in the southern...

Cassava cultivation causes serious soil fertility depletion in Cameroon. Organic manures can contribute to maintaining the productivity and sustainability of cassava production systems due to their availability and cheapness. This study was conducted during two successive cropping seasons (2016/2017 and 2017/2018) in the Southern Cameroon, to determine the effects of organic manures on soil physical properties, and cassava growth and yield. Tithonia diversifolia fresh biomass (TB) and poultry manure (PM) were used as organic manures. Different treatments were used, namely: (i) control (no amendment), (ii) mineral fertilizer (MF (450 kg ha^-1 13-13-23 NPK + 100 kg ha^-1 Urea)), (iii) two rates of TB (applied at 10 and 20 t ha^-1), (iv) two rates of PM (applied at 10 and 20 t ha^-1) and (v) two rates of the mixture of TB and PM (applied at 5 and 10 t ha^-1 each). The experimental designed was randomized complete block with three replicates per treatment. The application of TB, PM and TB + PM (mixture) lowered bulk density by 14-22.6%, 21.5-26.2% and 18.2-25%, respectively. While total porosity and water holding capacity were increased with manure application by 9.8-15.1% and 13.3-30.3%, respectively. The mineral fertilizer had no significant effect on these soil physical parameters. Application of TB and PM either solely or mixed significantly improved growth of cassava. Stem height, stem diameter and canopy diameter increased by 34.3-60%, 17.4-30.4% and 19.7-32.7%, respectively. Organic manures performed better than the mineral fertilizer. Aboveground dry biomass and fresh tubers yield increased by 21.7-59.6 and 76.6-112.2% with organic manures, and by 23.2 and 68.5% with mineral fertilizer, respectively. The best performance of cassava in terms of fresh tubers yield (51.78 t ha^-1) occurred with the mixture of TB and PM applied at 10 t ha^-1 each. The study revealed that fresh biomass of Tithonia diversifolia and poultry manure can be used to improve cassava production and sustain soil productivity in the humid forest zone of Southern Cameroon.