Agroforestry stand age influence physical and chemical soil parameters

The role of agroforestry in improving soil parameters is well known. However, there is debate as to how age of agroforestry practice affects physical and chemical parameters especially in the tropical region of Sub-Saharan Africa where adoption of the practice is fairly recent. To understand those effects, a study was conducted using soil samples taken in farms adopting/non adopting agroforestry practises, selected using a stratified, random sampling strategy. Soil was sampled from adopters and non-adopters using soil auger. At least five sub-samples were collected from each location and the soil mixed to get an integrated soil sample for analysis. The physical (sand, clay, silt and bulk density), chemical properties (pH, total nitrogen [TN], total phosphorus [TP], total organic carbon [TOC], carbon nitrogen ratio [C/N] and carbon to phosphorus ratio [C/P]) were analyzed in the soil. The exchangeable bases (K, Ca, Mg and Na) as well as micronutrients (Mn, Cu, Fe and Zn) were also analyzed. The results indicated that sand was significantly (P < 0.05) higher among non-adopters compared to adopters while silt and bulk density was significantly (P < 0.05) higher among the adopters compared to the non-adopters. Sand levels decreased while silt and bulk density significantly increased with increasing agroforestry stand age. The TN, TOC and C/P ratio were significantly (P < 0.05) higher among adopters and increased consistently with age of adoption, while C/N was higher among non-adopters and decreased with increasing age of agroforestry stand. The trend in exchangeable bases and micro-nutrients in the soil were similar, where higher concentrations occurred among adopters and displayed an increase with regard to age of agroforestry stand. Our results support the hypothesis that age of agroforestry practice affects soil in parameter-specific patterns.