Influence of Duration of Agroforestry on Physico-Chemical Soil Quality Parameters in Machakos County, Kenya

Abstract

The role of agroforestry in improving soil quality is well appreciated. However, there is debate as to how duration of agroforestry practice affects soil quality especially in the tropical region of Sub Saharan Africa where adoption of the practice is fairly recently. Therefore, objective this study was to investigate the influence of duration of agroforestry on physico-chemical soil quality parameters. The study was conducted using survey research design from a sample of 73 individual farmers, selected using stratified and random sampling. Soils were sampled from adopters and non adopters using soil auger. At least five sub-samples of soils were collected from each of the farmers and the soil mixed to get an integrated soil sample for analysis. The soil were packaged in two-kg khaki papers and taken to the laboratory for further physical attributes (sand, clay, silt and bulk density) and chemical analyses (pH, TN, TP, TOC, C/N and C/P). The exchangeable bases (K, Ca, Mg and Na) as well as micronutrients (Mn, Cu, Fe and Zn) were also analyzed. The results indicated that proportion of sand particles 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 particle decreased with increasing duration of agroforestry adoption while proportion of silt and bulk density showed a significant increase in tandem to stand duration of agroforestry. The TN, TOC and C/P ratio was 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 tree stand and duration of agroforestry. The trend in exchangeable bases and mineral contents in the soil were similar where higher concentrations occurred among adopters and displayed an increase with regard to length of adoption of agroforestry. The current study lends support to assertion that duration of agroforestry positively improves soil quality and therefore urges for mass adoption of the agroforestry practice to enhance increased agricultural productivity.