Suitability of Universal Soil Loss Erodibility, Inter-rill and Rill Erodibility Models for Selected Tropical Soils

Abstract

The universal soil loss equation (USLE) and water erosion prediction project (WEPP) (inter-rill and rill) erodibility factors are important indicators for land degradation assessment all over the world, which were primarily developed for the United States of America (USA). However, information on suitability of USLE and WEPP for tropical environment is scarce. Therefore, studies were carried out to investigate the suitability of USLE and WEPP for selected tropical soils of Southwestern Nigeria. Four pedons classified based on USDA soil taxonomy as Plinthic Petraquept (Adio series), Kanhaplic Haplaustalf (Oyo series), Typic Plinthustalf (Temidire series) and Typic Haplaustalf (Owutu series) were used for the study. Soil erodibility factor was determined using USLE and WEPP models. Origin-Pro. 8.1 software was employed to compare USLE and WEPP models for conformity and suitability. The results showed perfect agreement (R2= 1.0;P< 0.001) between the two WEPP (inter-rill and rill) erodibility models in all the four soil types investigated. In addition, WEPP models (inter-rill and rill erodibility) significantly (R2= 0.82;P< 0.001) related to USLE (El-Swaify and Dangler, 1977) erodibility model. There was a poor relationship (R2= 0.46;P< 0.06) between USLE (Wischmeier and Mannering, 1968) and the WEPP erodibility factors. The WEPP erodibility models with a perfect relationship with soil properties of the four soil types are more suitable than USLE models for predicting soil erodibility of the identified soil types in tropical environments.

Impacts of soil conservation techniques on soil erodibility on an Alfisol

“…These two factors greatly influence soil erodibility in any soil type [ 5 ]. Oshunsanya and Nwosu [ 2 , 4 ] noted that the lesser the erodibility factor, the lower the ease of erosion to occur. I. garbonensis had the least erodibility factor, which indicates a lesser propensity to erode.…”

“…The erodibility rating as modified by Oshunsanya and Nwosu [ 4 ] will be used to rate the soil erodibility of the soil conservation plots. Table 2 summarizes the soil erodibility ratings for soils in the tropics.…”

“…It denotes the ration of silt to clay in the soil expressed as a percentage. This index is particularly very important in tropical regions for soil erodibility modelling as [ 2 , 4 ] observed that there was a strong significant relationship between the ration of silt t clay to the ease of erosion in four common soil types in Nigeria. …”

“…Nwosu and Okon [ 3 ] reported that about 80% of land degradation in Nigeria is due to soil erosion which had greatly affected environmental sustainability and crop yield to meet the demand of the high population in the country. Oshunsanya and Nwosu [ 4 ] noted that soil erodibility establishes the ease at which a given soil is prone to erosion. Erodibility has become a key parameter that assists policy makers, farmers and researchers on the true need for soil conservation against the menace of soil erosion.…”

“…Soil erosion in sub-Sahara Africa has resulted in an average annual harvest yield reduction of 8.2% and if soil erosion rates remains unabated, the average food production will decrease in the future [ 1 , 7 ]. Despite the great high soil loss and runoffs reported in southwestern Nigeria [ 2 , 4 , 8 ], soil conservation programmes are not readily available in the areas within southwestern and central eastern Nigeria [ [9] , [10] , [11] ]. Soil conservation is dependent on understanding the complex relationship between land, land use, the farmer and the socio-economic-political environment [ 12 ].…”