Soil microbial biomass changes with application of organic and inorganic in acid soil of Embu County, Central highlands of Kenya

Most studies are focused on fertiliser either organic or inorganic to improve soil fertility, health and crop yields in most of the farming systems worldwide. Although organic and inorganic soil fertility improvements impact indirectly on soil biota, less is addressed regarding the biological component of soil fertility. This includes soil microbial biomass, the active component of the soil organic pool which is responsible for organic matter decomposition thus, affecting soil nutrient content as it is a source and sink of the nutrients C, N, P and S contained in the organic matter. Understanding soil microbial biomass dynamics is particularly critical in the management of acid soils, to reverse declining soil organic matter content and restore soil fertility. Soil acidity contributes for reduced microbial biomass, fertility and crop yields. To evaluate the influence of manure, lime, P fertiliser and their combination on the soil microbial biomass an experiment was conducted in Embu-ATC comprising 8 treatments, including goat manure (10 ton ha-1); Lime (2 ton ha-1), TSP (60 kg P2O5 ha-1); 5 ton ha-1 manure + 2 ton ha-1 Lime; 5 ton ha-1 manure + 30 kg P2O5 ha-1 TSP; 5 ton ha-1 manure + 2 ton ha-1 lime + 30 kg P2O5 ha-1 TSP. The study included manure (0, 5 and 10 ton.ha-1), Lime (0 and 2 ton.ha-1) and P fertiliser (0, 30 and 60 kg P2O5 ha-1). The experiment was laid out, during 2012 short rain (October 2012 to January 2013) and 2013 long rain (March to June 2013) as randomized complete block design (RCBD) with 4 replicates in plots of 4x4.5m. Soil samples were collected at harvest and subjected to microbial biomass analysis. The microbial biomass was analyzed by the chloroform fumigation and extraction method. Data generated was analyzed by use of SAS and LSD was used to separate means at 95% of confidence level. The results showed that at the end of the experiment manure alone increased soil microbial biomass by 175.7%, followed by Lime alone with 145.9% increase, relative to pre-season. The integrated application of manure with lime plus P fertilizer increased 153.1% microbial biomass over the pre-season. Soil pH was strongly and significantly correlated with soil microbial biomass (R2 = 0.74; p = 0.0065) in 2013 LR. Subsequently it was concluded that application of manure and lime is required and recommended for smallholder farmers of the Central Highlands of Kenya (CHK) to promote microorganism’s development and soil fertility.