Abstract:The optimal recommended rates of phosphorus (P) and potassium (K) in the Kilombero valley, Tanzania are outdated. The Objective of the study was to establish optimum rates of P and K for improved rice cultivation in rice fields of Kilombero valley. Two on-farm experiments were carried out in two seasons of January to May 2014 and 2015 at Mkula, Mbasa and Kisawasawa sites in Kilombero district, Tanzania. In the first experiment the treatments were a control for P; adequate levels of N and K plus two rates of phosphorus 10 and 20 kg P /ha. In the second experiment the treatments were a control for K; and two rates of K of either 50 or 100 kg/ha. These three treatments each received adequate levels of N, P and Zn. An absolute control and a control for N treatments were included in both of the experiments. The test crop was rice variety SARO-5. Phosphorus application significantly increased grain yield (GY) by 3.26 and 2.01 t/ha at Mbasa and Mkula, respectively. Also P application increased shoot P concentration from a low level (0.12%) to the adequate range (0.19 -0.24%) at the two sites. Potassium application increased significantly GY by 2.76 and 1.93 t/ha at Mbasa and Mkula, respectively. Also K application increased shoot K concentration from a low range (1.14 -1.34%) to the adequate range (2.63 -2.99%) at the two sites. An application of P and K affected neither shoot K nor P concentrations nor GY at Kisawasawa site. It is recommended that 10 kg P/ha and 50 kg K/ha be used as optimum rate for rice production in P and K deficient soils of Kilombero valley.
Abstract:This study was carried out in Kilombero District, Tanzania with the objective of characterizing the soils in terms of their morphology, genesis, physico-chemical properties and classification. Three pedons KISA-P1, MKU-P1 and MBA-P1 were identified within the Kilombero Valley, dug, described and sampled. Disturbed and undisturbed soil samples were taken from designated pedogenic horizons for physical and chemical analysis in the laboratory. Using both field and laboratory data soils were classified using both USDA Soil Taxonomy and World Reference Base for Soil Resources schemes of classification. Results show that the three pedons were developed under Isohyperthemic temperature and Aquic moisture regimes. All pedons were deep (100 -120 cm). Whereas Pedons KISA-P1 and MBA-P1 had sandy clay loam topsoils overlying sandy clay subsoils, Pedon MKU-P1 had clayey texture throughout its profile depth. All pedons had low chromas of ≤ 3 and redoximorphic features in form of abundant mottles particularly in the subsoils. Topsoils of Pedons KISA-P1 and MBA-P1 had dominantly friable to very friable moist consistence while those of Pedon MKU-P1 had very firm moist consistence. Subsoil moist consistence varied from firm to extremely firm (Pedons KISA-P1 and MKU-P1) and from friable to very firm (Pedon MBA-P1). Structures were dominantly weak to moderate subangular blocky in all studied soils but some horizons were structureless single grained and massive. Soil reaction ranged from extremely acid (topsoil of MBA-P1) to mildly alkaline (subsoil of MKU-P1) with pH values of 4.44 and 6.73 respectively. Topsoil organic carbon and total nitrogen contents in the studied pedons were low (0.66 to 1.4%) and very low to low (0.08 to 0.19%) respectively. CEC soil values were rated as low to medium ranging from 8.4 to 23.8 cmol (+)/kg respectively in Pedon KISA-P1 and Pedon MKU-P1. Percent BS values varied between and within studied pedons and ranged from low < 50% to high > 50%. Studied soils manifested nutrient imbalances in respect of basic cations. On the overall, fertility of the studied soils was rated as low to medium. According to USDA Keys to Soil Taxonomy, Pedons KISA-P1 and MKU-P1 classified as Inceptisols, equivalent to Cambisols in WRB for Soil Resources whereas Pedon MBA-P1 classified as Entisols equivalent to Fluvisols. All three sites were recommended for paddy production.
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