Browsing by Author "Mtama, J. G."

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Pedology at four representative sites of Southern Highland Zone of Tanzania
(Science Publishing Group, 2018-09-06) Mtama, J. G.; Msanya, B. M.; Lee Burras, C.
To study the soils of Southern Highland Zone of Tanzania, four representative pedons of some landscapes were characterized. Their names and identifiers are Seatondale, Mbimba, Inyala, and Uyole, respectively TzSea 01, TzMb 02, TzIny 03, and TzUy04. The pedons were formed from the weathering of among other materials, colluvial igneous rocks, alluvium, eluvial soils, laterite, lacustrine sands and silts, andesite, pumice, aeolian deposits, and metamorphic rocks including coarse grained and strongly foliated biotite gneisses. Twenty soil samples were taken for laboratory characterization. In addition to classical horizon by horizon descriptions and laboratory analyses, 12 core samples were taken for soil-water retention characterization. The available water holding capacity was rated as very low to low. Pedon descriptions and particle size analysis showed clay eluviation-illuviation was the predominant pedogenic process in all pedons. Soil pH was rated slightly acidic to slightly alkaline. Available P ranged from 0.71 mg/kg at Mbimba to 10.67 mg/kg at Seatondale. Exchangeable bases were variable across and within the profiles; at Uyole and Inyala they were high, while at Seatondale and Mbimba they were low and medium. Values of exchangeable bases showed decreasing trends with profile depths in all sites. C/N ratios ranged between 6 and 18, total nitrogen was rated very low to low in both A and B horizons. CEC soil ranged between 17.2 and 36.4 cmol (+) /kg. Organic carbon ranged from very low to high. The soils apparently developed from extreme and moderate weathering of parent materials. According to the USDA Soil Taxonomy, the pedons classified as Fine, Illitic, Active, Isothermic Typic Hapludult; Fine, Illitic, Active, Isothermic Andic Paleudalf; Fine, Illitic, Active, Isothermic, Mollic Paleudalf; Pumiceous, Mixed, Superactive, Isothermic, Typic Hapludand for Seatondale, Mbimba, Inyala, and Uyole, respectively. The soil depths were deep and very deep. Moisture stress and low levels of some macro-elements highly limited the productivity of the soils.
Pedotransfer functions for cation exchange capacity, available water holding capacity and soil organic carbon for representative soils of Southern Highland Zone of Tanzania
(International Journal of Agriculture and Biological Sciences, 2018-10-31) Mtama, J. G.; Lee Burras, C.; Msanya, B. M.
Pedotransfer functions are useful tools in estimating the not easily measured and expensive soil properties. They are especially valuable in settings such as the SHZT where limited direct soil measurements are available. The objective of this study was to develop a series of pedotransfer functions and then evaluate which ones best estimate cation exchange capacity (CEC), available water holding capacity (AWHC) and soil organic carbon (SOC). Data from 20 horizons of four representative pedons was used to evaluate the most predictive properties. Best fit multiple linear regressions were used to obtain relationships and identify property coefficients. Examples of pedotransfer functions developed for the SHZT are %SOC = 0.1*hue-0.03*value- 0.034chroma (n = 20, r 2 = 0.74), CEC ( meq/100g ) = 0.44*%clay + 9.6%SOC (n=20, r 2 = 0.93), and, AWHC (mm/m) = 14.7%SOC + 0.82%clay + 0.35%silt + 0.51%sand (n=12; r 2 = 0.96). All color attributes are for moist samples. The results of predicted CEC, AWHC, and SOC were compared to those measured in the laboratory using the t-test, and the two methods did not differ significantly; two-sided p-value=0.93. These results indicate the promising potential of using the easily measured soil properties and cheap in fiscal terms to estimate the not easily measured soil properties.