Effect of Rhizobium Inoculation and Rock Phosphate Fertilizer on Soil Chemical Properties under Selected Green Grams Varieties

The purpose of this study was to determine the effects of Rhizobium and rock phosphate fertilizer application on soil chemical properties in green-gram varieties. The study was carried out at Chuka university horticultural research farm in two seasons (November 2019 - January 2020 and February - April 2020). A factorial experiment of 2 x 2 x 2 was laid out in a randomized complete block design (RCBD). There were three factors; varieties (N26 and KS20), rock phosphate (0 and 30 kg P ha-1) and Rhizobium inoculation (0 and 100 g ha-1) making a total of eight treatments which were replicated three times. Before planting and after harvesting of green-grams, soil pH, fixed-N, total nitrogen (TN), exchangeable cations (EC), available phosphorus (P), total organic carbon (TOC), and exchangeable potassium (K) were sampled and analyzed. Data was analysed using GENSTAT 15th edition (P 0.05). Results from both seasons indicated that combined application of rock phosphate at 30 kg P ha-1 and Rhizobium inoculation at 100 kg ha-1 showed significant (P 0.05) higher increase in soil chemical properties over other treatments. However, treatment R1P1KS20 recorded significantly higher results in soil pH (7.54), TN (0.58%), TOC (3.45%), P (68.20 ppm) and EC (0.95 CmolKg-1), fixed-N (0.50%) and K (1.75 CmolKg-1). On the other hand treatment R0P0N26 recorded significant (P 0.05) lower results in soil pH (5.23), TN (0.04%), TOC (1.86%), P (8.76 ppm), EC (0.21 CmolKg-1) and K (0.58 CmolKg-1). As a result, Rhizobium inoculation in green-grams with rock phosphate is an essential legume nitrogen fixation enhancement strategy. Farmers can use this technology to supplement nitrogen and phosphorus in their crops in a cost-effective way for enhanced soil fertility management. Based on the findings, a sustainable soil fertility management strategy in Tharaka Nithi County should include Rhizobium 100g ha-1 and rock phosphate 30 kg P ha-1, as well as the variety KS20.