Decomposition of green manure in the dry and rainy seasons in Mali and Burkina Faso

Factors to consider when recommending green manure to farmers.

Fig 1. Initial nitrogen (N) and phosphorus (P) concentrations in leguminous and non-leguminous tree leaves in the dry and rainy seasons.

Fig 2. Decomposition of leguminous and non-leguminous tree leaves in the dry and rainy seasons.

Soil fertility decline poses a major threat to food security in the African Sahelian region. Historically, soil fertility in the region has been maintained through shifting cultivation with long natural fallow, however, increasing population pressure has shortened fallow periods. As a result, nutrient lost through crop yields are not replaced due to unavailability and high cost of inorganic fertilizers¹. Curbing this problem has led to the promotion of green manure from various agroforestry practices such as alleycropping, improved fallows, border tree plantings and woodlots. The ability of green manure to release nutrients into the soil is based on type of green manure (leguminous or non-leguminous) and the season of harvest and application (dry or rainy). Considering these factors, our study sought to compare the seasonal variation in green manure nutrient concentration and decomposition rate based on green manure type.

Materials and methods

The study was undertaken in Koulikoro (Mali) and Saria (Burkina Faso) using leaves from leguminous trees (Faidherbia albida & Pterocarpus lucens) and non-leguminous (Khaya senegalensis & Vitellaria paradoxa) harvested in both dry and rainy seasons. Decomposition of these leaves were studied using the litterbag technique in both dry and rainy seasons.

Results

Whereas seasonality had no effect on nitrogen (N) concentration of non-leguminous tree leaves, N concentration in leguminous tree leaves was 43% lower in the dry season than the rainy season (Fig. 1). Irrespective of season, N concentration in leguminous tree leaves was 2-folds greater than in non-leguminous counterpart. For phosphorus concentration, it was only in the rainy season that leguminous tree leaves was 175% greater than non-leguminous counterparts. Irrespective of leaves type, decomposition rate in the dry season was 5-times lower than in the rainy season, but in both seasons, it was greater for leguminous tree leaves than non-leguminous ones (Fig. 2).

Conclusion

For efficient utilization of nutrients from green manure by crops, it is important to understand green manure seasonal nutrient variation and decomposition rate, and green manure type.

Related literature

Nord, A., Snapp, S. & Traore, B. Current knowledge on practices targeting soil fertility and agricultural land rehabilitation in the Sahel. A review. Agron. Sustain. Dev. 42, 79 (2022).