Conservation agriculture Tanzania_casestudy.pdf - Sokoine ...

Erosion is now considered responsible for silting up both Lakes Eyasi and Manyarawith drastic impact on both terrestrial and aquatic organisms (COPEC 2003).Soil erosion and loss of fertility were identified as major environmental constraintsin both high and low altitudes of Karatu. On some occasions a lack of welldefinedland ownership caused farmers to hesitate to make long-term investmentsin measures to conserve the environment. In addition, continuous cultivation is akey element in degrading cropped fields resulting in compaction, nutrient mining,structural damage and erosion, as the soil surface is left bare (KDC 2001).Land pressure on the high-potential agricultural areas in the uplands eventuallyresulted in increased cultivation of marginal lands (COPEC 2003). Intensive croppingon hill slopes without appropriate soil conservation measures resulted in increased soilerosion and reduced soil moisture capacity, which in turn have led to low agriculturalproductivity. On-site effects of soil erosion include loss of fertile topsoil and largefluctuations in volume of rivers and springs, leaving behind deformed terrain.Degraded land stores less water, which again makes crops vulnerable to water stresseven in a minor drought. Less water stored in upper catchments has a serious negativeeffect on the smooth supply of water in Lakes Manyara and Eyasi (COPEC 2003).Offsite effects of soil erosion on the land catena (land top sequence along the slope)cause pollution of water bodies, sedimentation on the farmlands, and physicaldamage to crops and infrastructure. Currently, there is concern about increasedsedimentation in Lake Manyara, which has significantly reduced the lake’s volume.Sedimentation is caused by chemical pollution from farming activities at the uppercatchment areas. It promotes growth of weeds. Environmental degradation inLake Manyara National Park may affect wildlife. As this park is one of the mostpopular tourist sites in Tanzania, there is a real concern that sedimentation andits associated problems may negatively affect the area’s tourist industry and thelivelihoods of those who depend on it (COPEC 2003).Farmers still rely on extractive forms of land management, which lead to loss inorganic matter, nutrient depletion and soil compaction (pers. comm., assistantDALDO, Karatu). Intensive and regular use of hand hoes for digging, and discand mouldboard ploughs for preparing land have created a hardpan layer. Thesehard soil layers hinder rainwater from percolating into the soil, hence less waterinfiltrates and runoff increases, resulting in surface erosion and gullies. Becausethe soil’s productive capacity has weakened over time as a result of low soil fertility,plough pans and droughts, crop yields have declined. Whereas farmers used to getan average of 15–20 bags 3 of maize per acre 4 , currently they are getting less than5 bags under the same land management (KDC 2001). The low yields have ledto severe food insecurity and poor livelihoods as farmers depended on the sale ofsurplus maize cash. In the past farmers responded to these low yields by opening newfields in more fertile areas but population increase has led to abandoning shiftingcultivation and adopting continuous cultivation (Meindertsman and Kessler 1997).In turn, this continuous cultivation led to nutrient mining and severe soil erosiondue to the depletion of soil organic matter and hardpan settings.3 1 bag of maize weighs 100 kg4 1 acre = 0.405 ha70 Ringo et al.