Carbon sequestration and nitrogen addition in selected soils of Morogoro, Mbeya and Ruvuma under maize-soybean intercropping and rotations

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Sokoine University of Agriculture


This study was conducted in some selected soils of Morogoro (Magadu) and Mbeya (Uyole) regions of Tanzania to classify and characterize their properties. Two representative pedons (SUARAT-P1 and UYOLE-P1) were dug and described using FAO guidelines clarifying morphological features, physico-chemical properties and genesis. The representative pedons were geo-referenced using Global Positioning System (GPS) receiver. A total of nine (9) genetic soil horizons were identified from both sites and samples from each horizon collected for physical and chemical analyses. Soils from both sites were very deep and topsoil moist colors ranged from hue of 7.5YR to 10YR with chroma of less than 3 in SUARAT-P1 and UYOLE-P1 pedons. Soil structure ranged from strong fine crumbs in topsoils to medium coarse sub-angular blocks in subsoils of SUARAT-P1 while UYOLE-P1 had weak fine sub-angular blocks in topsoils and subsoils. The SUARAT-P1 had sandy clay (SC) texture in topsoil and clay texture in subsoil while UYOLE-P1 was sandy loam (SL) in topsoil and sand clay loam (SCL) in subsoil. Soil reaction were slightly acid to very strongly acid in SUARAT-P1 (pH 6.54 - 4.46) whereas UYOLE-P1 were slightly acid to neutral in the subsoil horizons (pH 6.35 – 7.32). Organic carbon ranged from very low to low (0.12- 0.95%) in SUARAT-P1 from 0-23 cm and medium (1.5%) from surface to 25 cm depth in UYOLE-P1. Nitrogen levels were very low to low (0.05 - 0.12%) in both sites, whereas available P ranged from low (0.30 mg kg - 1 ) to medium (8.55 mg kg -1 ) in both pedons. The figures for soil OC and N will be used as baseline to forecast SOC and N sequestration potential in selected study sites. CEC of SUARAT-P1 was medium ranging from 12.4 to 23.2 cmol(c) kg -1 , whereas UYOLE-P1 was medium to high (15 – 34 cmol(c) kg -1 ). The figures for soil OC and N will be set as baseline for SOC and N sequestration studies in the next chapters. In SUARAT-P1, topsoil BS was high (> 50%) and low (< 50%) in the subsoil while UYOLE-P1 registered high BS throughout its profile depth. As diagnostic horizons for soil classification, the SUARAT-P1 had an ochric epipedon overlying a kandic horizon and classified according to USDA Soil Taxonomy as Typic Kandiustults, while UYOLE-P1 had an ochric epipedon over a cambic horizon and was named as Andic Dystrudepts corresponding respectively to Haplic Lixisols and Eutric Andic Cambisols in the WRB for Soil Resources. The results have indicated that, studied soils are less fertile with possible reconstitution through land and crop management practices which include but not limited to no-tilling or conservation tillage, manuring and proper fertilizer application; residue retention, possible fallowing, liming for potential buffering of soil pH especially at SUARAT-P1 and crop rotation and intercropping with leguminous crops.




Tanzania, Soil morphology, Soil classification, Soil nitrogen, Maize-soybean intercropping