PREDICTION OF SOIL AND NUTRIENT LOSS RATES FROM RILL EROSION IN BIU AREA, BORNO STATE, NIGERIA

Abstract

The study was conducted on monthly and annual bases between March and December during 2020 at Biu area of Borno state consisting of six different sites (Piku, Kigir, Dam, Mirnga, Mandaragrau and Gunda) to estimate annual losses of soil and nutrient (N, P, K, Ca, Mg and S) due to rill erosion and to validate RUSLE2 model for prediction accuracies. The annual precipitation varied from 699.00 – 896.00mm. and the rainfall erosivity ranged from 351.00 – 485.00 MJmmha^-1hr^-1yr^-1, respectively across the sites. Soil erodibility (0.70 – 0.80) slope length (435.00 – 785.00m), and slope steepness (6 – 9%) cover management factor (0.12 – 0.23) and protection management (0.12) were used as predictor variables in Revised Universal Soil Loss Equation Version 2 (RUSLE2) 2016, across the sites.  Six hectares of overland flow sites consisting of rills were selected randomly at each site for the study.  About 168 soil samples were collected from six sites. The RUSLE2 model annual estimation of soil loss was 260.00 – 447.00 and 150.00 – 495.00 kgha^-1yr^-1, respectively. Annual validation RUSLE2 revealed the r² value of 0.8553. High soil and nutrient (O.M, N, P, K, Ca. Mg, and S) loss were recorded at Piku site with their respective values of 447.00, 3.82, 2.22, 1.95, 2.72, 2.35, 1.49 and1.02 kgha^-1yr^-1. Recommending the management of terraces, mulching, cover crops and vegetation, no – tillage method, buffer zones, contour bonds, check dams, grassed water ways and hillside water ponds to reduce the length of the slope and consequently the soil and nutrient loss.