Effects of reforestation on degraded soils in the moist semi deciduous zone of West Africa

Abstract

Reforestation with trees and shrubs may be an effective means of increasing soil organic matter content and for regeneration of degraded lands. A study was conducted on a degraded farmland Chromic Luvisol (UNESCO/FAO) or Udic Rhodustalf (USDA, 1999) in the moist semi deciduous zone of West Africa, near Onwe, located at latitude 06^o 41’ N, longitude 01^o 28’ W, and at an altitude of 305m asl. The objective of the study was to quantify the improvement in soil physicochemical properties of degraded Chromic Luvisol with exotic leguminous tree species compared to grass vegetation in the moist semi-deciduous zone of West Africa. To quantify changes due to reforestation, we measured some physical and chemical properties of soil after 20 years (1989 – 2009) of reforestation with Acacia angustissima (Acacia), Cassia siamea (Cassia), and Leucaena leucocephala (Leucaena) mixed and compared with soils under natural grass vegetation. Experimental design used for soil sampling and for evaluating the soil properties was randomized complete block with three replications. Soil organic matter increased from 1.19% to 2.02% while pH dropped from 5.65 to 4.79 in the reforested soils. Cumulative infiltration, infiltration rate, and gravimetric water content showed significant improvement under reforestation compared with soils under natural vegetation. Total porosity increased from 36.7% in the natural grass cover to 51.3% in the reforested soils. Reforestation resulted in significant reduction in bulk density from 1.67 to 1.26g/cm³. Improvement of soil properties under reforestation indicates that planting of well-adapted and fast-growing exotic tree species can gradually improve soil quality and regenerate degraded lands. Reforestation may be thus recommended as a way of regenerating degraded land.

Keywords: Degraded soil, reforestation, trees, soil organic matter