Evaluating The Effectiveness Of Four Selected Methods Of Investigating Soil Erosion Effect On Soil Productivity In Nsukka, Enugu State, Nigeria

ABSTRACT

This study was conducted in 2012 at the University of Nigeria, Nsukka Teaching and

Research Farm (UNN), and Ekwegbe, both in Nsukka agricultural zone; to evaluate the

effectiveness of four selected methods of quantifying erosion effect on soil productivity at

Nsukka, southeastern Nigeria. The four methods were (1) desurfacing technique (DT), (2)

Neill’s (1983) productivity index, (3) modified productivity index (MPI) and (4) Riquier’s

productivity index (RI). Soils were sampled at 0-30, 30-60, and 60-90 cm depth zones at each

location prior to planting and after harvest. Incremental depths (0, 2, and 4 cm) of topsoil

layers were manually removed to simulate erosion at the two sites. Poultry manure (10 t ha-1)

was applied two weeks before planting as a soil amendment. Correlation and regression

analyses revealed that RI was significantly (p < 0.05) correlated (positively) with plant height

at 10 WAP (r = 0.75*), LAI at 14 WAP (r = 0.76*) and pod yield (r = 0.72*) at UNN, and

was ranked first in effectiveness, followed by DT, which had a significant (p < 0.05) negative

correlation with plant height at 6 WAP (r = -0.45*), while PI and MPI were less effective. At

Ekwegbe, DT showed significant (p < 0.05; p < 0.01) negative correlations with plant height

at 10 (r = -0.42*) and 14 WAP (r = -0.66**), and LAI at 14 WAP (r = -0.52**), and was

validated as the most effective index, whereas RI, PI and MPI were less useful. Based on RI,

the soils at UNN and Ekwegbe had productivity index ratings of 15% and 8%, respectively,

placing them in the productivity class IV (poor productivity). Following the application of

poultry manure and tillage, the soils recorded potentiality index ratings of 22% and 13%,

respectively, raising the potentiality class of the UNN sandy clay loam soil to III (average

potentiality), while the Ekwegbe sandy loam soil remained in class IV (poor potentiality).

The computed coefficients of improvement (Ci) were respectively 1.5 and 1.6 for the soils at

UNN and Ekwegbe. The findings indicated that although the current productivity levels of

the soils were poor, there was room for improvement, given necessary management practices.