The soils on which Bulindi ZARDI is located, acric ferralsols are fairly productive and support a crop production under good management. The rest of the zone with exception of Kabarole district with productive soil is classified as unproductive. Soil fertility is maintained by recycling of crop residues traditionally involving grass fallows, mulching and crop rotations. In addition, short (improved) fallow, cover crops and intercropping with leguminous crops, organic manures and hedge rows are practiced for soil conservation. Mineral fertilizers are used by very few farmers that grow tobacco and cotton in the Hoima, Masindi and Kibaale.
Understanding soil fertility problems at farm level
Low soil fertility is not generally perceived by locals as a major constraint to crop productivity. Like elsewhere in Uganda, farmers believe the soil is still fertile- thus the less concern to the soil resource base. However, the evidence of soil erosion (some gullies) and incidence of nutrient deficiency symptoms suggest widespread nutrient exhaustion on different cropping systems on farms.
In addition, nematodes and termites are common soil borne pests that hinder increased crop yields. The causes of low soil fertility are varying between farming systems, between villages and most importantly between farms. The investments on soil fertility maintenance should be based on variations between farms and the differences often relate to the levels of resource endowments. With respect to mapping, individual farmers are concerned in variations at village level rather than aggregated information at district level.
Water stress greatly affects the performance of most crops on dominantly clay (> 45.0% clay) and sandy soils in sub locations of Hoima and Buliisa, respectively. The crops which are often most affected are rice and maize with incidences of wilting. Rainless days for a week in areas with clay soil type result in caking and cracking while for less than a week in sandy soil type cause drying up of soils and consequently significant reduction in crop yields (plate 1). Soil and water conservation (S&WC) technologies which are suitable to landscapes and appropriate to farmer preferences are being indentified through baseline soil surveys. Average yield reduction in different soil types due to drought-prone areas need to be quantified to aid in decision making on appropriate S&WC in localities. With the onset of climate change, the intensity and frequency of droughts and unreliable rainfall are predicted to increase in most areas in the zone. Water harvesting technologies within cropped fields are being introduced through trainings and demonstrations with the help of farmer groups and community based organizations.
Caking and cracking after a short dry spell (left) and rapid drying in sandy soils (right) are major constraints to crop productivity on dominantly clay (Hoima district) and sandy soils (Buliisa district)
Soil surveys conducted on farms revealed nutrient exhaustion to result from monoculture in maize-based systems, runoffs in bare hills in bananas, low retention in-situ of crop residues at harvest and intensive tillage. The most frequently occurring soil fertility problems in the zone are associated with very low available phosphorus, low total nitrogen and high clay fractions. The major limitations of clayey soils are various but significant ones are high phosphorus fixation, potassium and ammonium-nitrogen entrapment. The tendency of the soils to cake when dry tends to affect fertilizer and water use efficiency and has economic implications on fertilizer application and tillage at large. On station, trials to optimize nitrogen and phosphorus resources on such type of soils using cover crops are being conducted. Nutrient loss from erosion is a major constraint in especially perennial cropping systems in areas of Bubdibugyo, Kyenjojo and Kasese districts. Cultivation of fragile lands in these highly populated areas threatens water quality aside loss of fertility. Traditionally, farmers plough or cultivate down slope and construct measures for erosion control such as stone lines and water ways/’bunds’ along the slope. Understanding farmer or local knowledge on soil quality is key efforts in the project aimed at integration of indigenous knowledge in decision support systems for improving soil fertility.
Cultivation down the slope in steep hilly slopes on the banks river Mobuku in Bugoye Sub County in Kasese district
Sustainable management of the soil resource base in the Lake Albertine Crescent
A number of demographic and political changes such as population and land holdings have occurred over time in the zone and have a relationship to soil productivity. In particular, the exploration and production of oil and gas in the zone will affect land tenures and holdings with a bearing on the kind of technologies for land management. The oil developments will also directly impact the soil as one of the components of the environment that acts as a sink of exploration and production wastes. A staff has received specialized training overseas on environmental aspects of oil and gas with aim of building capacity for strategic research to address new environmental issues.
Nsoga oil drilling well near Ngwedo centre (left) and oil demarcation line though farmers’ fields in Avogere in Ngwedo Sub County (right), Buliisa.
The available soil information in the country is outdated and besides, it is aggregated at zonal level and cannot be used to make sound decisions on soil fertility management at lower scales. In addition, there is increased recognition on the contribution of indigenous knowledge (ITK) to land evaluation in relation to soil quality and sustainable crop production- an area that has been previously neglected. Baseline studies are being conducted to update the soil data base in relation to soil fertility problems in cropping systems at farm level. Geo-referenced data on soil properties will be used developing soil indices for classification and monitoring soil productivity.
GPS points of a famer’s field taken during assessment of soil status in Ngwedo Sub county, Buliisa district
To appraise ITK on soil quality, field methods for example Soil Test Kits are used for soil assessment to aid farmers’ understanding of the potential constraints at specific locations. Participatory approaches are highly embraced in developing local criteria for soil classification so as to capture knowledge that relates to ethnicity of communities in the case of multi-tribal districts like Kiryadongo and Masindi.
Community based Facilitators assissting in group discussions (left) prior to sketching maps on distribution of soils in their localities 