Agroforestry Technique for Minimal Extra-Labour: Influence of Chromolaena-Cajanus Combination on Soil Chemistry and Biology, and Yam Yields

Despite the beneficial effects of legumes on soil fertiliy, their adoption by farmers remains low due to the extra labour entailed. Lifting this constraint is of paramount importance in sustainable agriculture. This issue was dealt with in the present study which was carried out in central Côte d’Ivoire through assessing the response of soil (chemical and biological parameters) and subsequent yam yield to two fallow systems: natural C. odorata fallow (control) vs. Combination of C. odorata and Cajanus cajan. The mixed plot was obtained by loosely introducing at the onset of fallow C. cajan which withstands competition by C. odorata. Soil chemical parameters, abundance and diversity of decomposer macrofauna, microbial parameters and subsequent yam tuber yield were measured. After a 30-month period of time, the P content in C. cajan leaf litter increased in the mixed plot. The density of diplopods in leaf litter was lower in the mixed fallow while the average order number in soil was higher. No significant change occurred in earthworm abundance and diversity, nor in microbial activities. SOM and available P increased in the mixed fallow, as well as nitrates. Yam yield increased by 35 % in mixed plots, the controlling factors being soil C and nitrates contents, and leaf litter P, K and Ca stocks (GLM). Although the tested fallow appeared promising, the study should be repeated over a longer period taking into account other macrofauna decomposers for a better understanding of the mechanisms underlying the observed changes.