Influence of prescribed fire intensity and grass mulch on soil erosion and runoff under rainfed maize in Nigeria

Abstract

The experiment was conducted at the Teaching and Research Farm, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria to investigate the influence of prescribed fire intensity on soil erosion and runoff, a situation that occur regularly in the study area. The experimental site is within the rainforest ecosystem of the Southwest Nigeria, and usually experiences a significant amount of rainfall every year. This encourages rainfed farming around the study area with most farmers using prescribed fire for land preparation before planting. It is presumed that bush burning causes erosion and degradation of other soil properties. The study therefore investigated the influence of prescribed fire of two intensities and mulching on runoff and soil loss, runoff coefficient, phosphate and nitrate contents of the runoff water. The treatments consisted of fire intensities of 200 °C (with effect correspondingly felt at a maximum of 2 cm soil depth) and 500 °C (with effect correspondingly felt at a maximum of 5 cm soil depth), grass mulch, and control (bare soil without vegetation or plant residue). Each treatment was imposed on a plot of 1 m2 arranged in a randomized complete block design with triplicates, for three cropping seasons, and prescribed burning at the start of each cropping season. The first season was from May to August 2019, second season was from September to December 2019 while the third season was from September to December 2020. Runoff volume, soil loss, phosphate and nitrate contents in runoff were measured using bounded erosion plots of polyvinyl chloride (PVC) materials with a harvesting container (25 L) installed at about 1 m deep. The 200 °C prescribed fire plots had higher soil loss than that of 500 °C. The runoff in the 200 °C prescribed fire plot were 13.36 mm, 10.80 mm and 12.78 mm during the first, second and third seasons respectively, while those of the 500 °C prescribed fire were 12.88 mm, 7.63 mm and 11.96 mm in the same order. Soil loss from the 200 °C prescribed fire plot was an average of 2.46, 3.40, 1.77 Mg ha−1 in the first, second and third seasons respectively, while the 500 °C prescribed fire plot lost an average of 1.70, 1.23 and 2.17 Mg ha−1 in the same order. The Average concentration of nitrates in the runoff under 200 °C prescribed fire were an average of 0.14, 0.21, and 0.38 mg L−1 while for 500 °C, they were 0.18, 0.19, 0.81 mg L−1 in the first, second and third seasons respectively. Nitrate and phosphate contents of the runoff were not significantly influenced by prescribed fire. The fire intensities did not have a significant impact on the total runoff and soil loss under maize in the prescribed fire plots. The slash and pack plots without burning experienced the highest runoff and soil loss. However, grass mulch plot reduced total runoff and soil loss. Therefore, grass mulching of soil is encouraged to mitigate soil erosion in maize fields.