Influence of Water Management Farming Practices on Soil Organic Carbon and Nutrients: A Case Study of Rice Farming in Kilombero Valley, Tanzania

Water scarcity and nutrient availability for rice farming have become great matters of concern in the contexts of climate change and land use change globally. Both interact and contribute to crop productivity at the expense of nutrients and future water sustainability. The objective of this study was to understand the on-farm potential response of soil organic carbon (SOC), total nitrogen (TN), and total phosphorous (TP) to water management practices in rice farming within the Kilombero Valley, Tanzania. Soil samples were collected from three villages in the study area at four depths: 0–20, 20–30, 30–40, and 40–50 cm. Four water management regimes, namely: A = traditional flooding (rainfed) without intensification of rice farming; B = traditional flooding (rainfed) involving a system of rice intensification (SRI); C = alternative wetting and drying (AWD) involving SRI for one cropping season; D = abandoned fields (fallow); and E = AWD involving SRI for two cropping seasons, were investigated as regards their impact on SOC, TN, and TP. There were significant (p < 0.05) effects of water management regimes on SOC, TN, and TP. AWD involving SRI for one cropping season indicated a positive effect on SOC and TN across all depths as compared to other practices. We conclude that water management practice that involves AWD with SRI for one cropping season is a plausible approach to maintaining high SOC and TN, with the potential for increasing crop production while minimizing water consumption

Agricultural expansion impacts on wetland ecosystem services from Kilombero Valley, Tanzania

Land use change has major impact on the world’s wetland ecosystems and biodiversity. The motivation behind this change has been to increase agricultural production, often resulting in negative effects on water quality and soil fertility. Tanzania has carried out a large expansion and intensification of agriculture under the Kilimo kwanza (First agriculture) initiative which has triggered the need for better knowledge on land use change effects and associated ecosystem functioning. This thesis considers small-scale irrigation schemes to understand the effects of agriculture expansion and farming practices on nutrients, water quality and ecosystem services (ES) in Kilombero Valley, Tanzania. The study approach is multidisciplinary involving interviews, remote sensing, geographical information system techniques, and in-field soil and water ecological sampling. The major land use change in the valley during the last three decades was transformation from forest, bushland and grassland into cultivated land. The rate of change was faster adjacent to irrigation schemes and most changes occurred downstream irrigation canals, close to the floodplain. Irrigation and fertilization contributed to soil carbon and nitrogen accumulation in crop fields, which both declined in concentration with depth into the soil. However, such management practices and agricultural land expansion had impacts on several ES – especially water quality in streams. Streams surrounded mainly by cultivated land, as well as downstream areas, had lower water quality compared to streams with less settlement, more natural vegetation and upstream areas. Furthermore, when evaluated, macroinvertebrates indices were found to be a good indicator of water quality and a complement to chemical and physical water analysis. Irrigation farming produced more food compared to rainfed farming, and also other ES such as flood regulation, erosion control and several cultural services, depending on the river discharge. The thesis shows the importance to use irrigation/fertilization management to enhance soil fertility and preserve soil structure, but also the need for proper irrigation management to prevent flooding and erosion, conserve natural vegetation, and protect water quality. To enhance nature conservation, preserve biodiversity and secure future supply of ES in the valley, investment in irrigation infrastructures should be done at small-scale to mitigate the large-scale exploitation of Kilombero wetland

Carbon Stocks in the Small Estuarine Mangroves of Geza and Mtimbwani, Tanga, Tanzania

Mangrove forests offer important ecosystem services, including their high capacity for carbon sequestration and stocking. However, they face rapid degradation and loss of ecological resilience particularly at local scales due to human pressure. We conducted inventory of mangrove forests to characterise forest stand structure and estimate carbon stocks in the small estuarine mangroves of Geza and Mtimbwani in Tanga, Tanzania. Forest structure, above-ground carbon (AGC), and below-ground carbon (BGC) were characterised. Soil carbon was estimated to 1 m depth using loss on ignition procedure. Six common mangrove species were identified dominated by Avicennia marina (Forsk.) Vierh. and Rhizophora mucronata Lamarck. Forest stand density and basal area were 1740 stems ha−1 and 17.2 m2 ha−1 for Geza and 2334 stems ha−1 and 30.3 m2 ha−1 for Mtimbwani. Total ecosystem carbon stocks were 414.6 Mg C ha−1 for Geza and 684.9 Mg C ha−1 for Mtimbwani. Soil carbon contributed over 65% of these stocks, decreasing with depth. Mid zones of the mangrove stands had highest carbon stocks. These data demonstrate that studied mangroves are potential for carbon projects and provide the baseline for monitoring, reporting, and verification (MRV) to support the projects

Influence of Water Management Farming Practices on Soil Organic Carbon and Nutrients: A Case Study of Rice Farming in Kilombero Valley, Tanzania

Water scarcity and nutrient availability for rice farming have become great matters of concern in the contexts of climate change and land use change globally. Both interact and contribute to crop productivity at the expense of nutrients and future water sustainability. The objective of this study was to understand the on-farm potential response of soil organic carbon (SOC), total nitrogen (TN), and total phosphorous (TP) to water management practices in rice farming within the Kilombero Valley, Tanzania. Soil samples were collected from three villages in the study area at four depths: 0–20, 20–30, 30–40, and 40–50 cm. Four water management regimes, namely: A = traditional flooding (rainfed) without intensification of rice farming; B = traditional flooding (rainfed) involving a system of rice intensification (SRI); C = alternative wetting and drying (AWD) involving SRI for one cropping season; D = abandoned fields (fallow); and E = AWD involving SRI for two cropping seasons, were investigated as regards their impact on SOC, TN, and TP. There were significant (p < 0.05) effects of water management regimes on SOC, TN, and TP. AWD involving SRI for one cropping season indicated a positive effect on SOC and TN across all depths as compared to other practices. We conclude that water management practice that involves AWD with SRI for one cropping season is a plausible approach to maintaining high SOC and TN, with the potential for increasing crop production while minimizing water consumption

Soil Carbon, Nitrogen and Phosphorus Contents along a Gradient of Agricultural Intensity in the Kilombero Valley, Tanzania

The preservation of soils which provide many important services to society is a pressing global issue. This is particularly the case in countries like Tanzania, which will experience rapid population growth over coming decades. The country is also currently experiencing rapid land-use change and increasing intensification of its agricultural systems to ensure sufficient food production. However, little is known regarding what the long term effects of this land use change will be, especially concerning soil quality. Therefore, we assessed the effect of irrigation and fertilization in agricultural systems, going from low intensity smallholder to high intensity commercial production, on soil organic carbon (SOC), total nitrogen (TN), and total phosphorous (TP) concentrations and stocks. Soil sampling was conducted within Kilombero Plantations Ltd. (KPL), a high intensity commercial farm located in Kilombero, Tanzania, and also on surrounding smallholder farms, capturing a gradient of agricultural intensity. We found that irrigation had a positive effect on SOC concentrations and stocks while fertilization had a negative effect. Rain-fed non-fertilized production had no effect on soil properties when compared to native vegetation. No difference was found in concentrations of TN or TP across the intensity gradient. However, TN stocks were significantly larger in the surface soils (0&ndash;30 cm) of the most intensive production system when compared to native vegetation and smallholder production