« Crop yield increases as a result of biochar application in tropical soils »

Cotton residues in Burkina Faso are slashed and burned directly in the field, leading to long-term losses of nutrients in soil-plant systems. Tropical sandy soils are highly weathered and depleted in organic matter and nutrients. The recycling of cotton stems through biochar production as alternative to slash-and-burn is here tested at field scale for improving soil physico-chemical properties and the resulting cycling of nutrients in maize (Koumbia, province of Tuy, Burkina Faso). The effect of biochar application rate (0 t ha-1, 10 t ha-1, 30 t ha-1) and its combination with various fertilizer quantities (0 kg ha-1, 100 kg ha-1, 150 kg ha-1) have been investigated. Soil physico-chemical characteristics, plant tissue nutrient concentrations and yields were analyzed.
Our results show that both biochar application rates significantly increased soil pH values, organic carbon (OC) concentration and phosphorus (P) and potassium (K) bioavailability. P (9% to 74%) and K (37% to 83%) uptake rates by maize are significantly enhanced while no effect on nitrogen (N) uptake rate has been observed. Identical yields between treatments with no biochar but different fertilizer applications reveal inefficient nutrient use in soil-maize systems fertilized uniquely by NPK. In contrast, our field experiment highlights an increase in total aboveground biomass in response to biochar application but no significant variation in terms of grain yield. Biochar amendment at 10 t ha-1 combined with low fertilizer input (100 kg ha-1) resulted in higher soil nutrient bioavailability and cycling in soil-maize systems in comparison to high fertilizers inputs without biochar (150 kg ha-1). The addition of 10 t ha-1 of biochar can make up for a decrease in fertilizer application in terms of phosphorus (P) and potassium (K) bioavailability in soils.
In this maize crop cultivated on highly weathered soils in a tropical savannah, biochar amendment can lead to a reduction of up to one third in the use of NPK external fertilizer. The recycling of cotton residues through biochar production highlights its ability to improve nutrient cycling in maize agroecosystems.