Amelioration of sandy soils in drought stricken areas through use of Ca-bentonite

Soil moisture shortage is a major limiting factor to agricultural production in eastern Africa, in view of increased drought incidences and seasonal rainfall variability. This study evaluated the potential for Ca-bentonite (a 2:1 clay mineral) as a possible amendment for increased moisture retention by sandy soils in drought stricken/prone areas in Uganda. The study was conducted both in the greenhouse at NARL-Kawanda and in the field, Nakasongola district. In the greenhouse (27-30oC), Ca-bentonite was mixed with a sandy soil in proportions of 0, 5, 10, 15 and 20% by weight, replicated three times. The mixtures were watered to field capacity (30% water) then maize (Longe V) planted and left to grow for 5 weeks without any additional water application. Under field conditions, Ca-bentonite was applied on sandy soils in the drought-prone Lwabiyata sub county, Nakasongola district in central Uganda. Treatments included: Ca-bentonite applied at 0, 1.25 and 2.5 t ha-1; DAP at 0, 62.5 and 125 kg ha-1; urea at 0 and 60 kg ha-1; and farmyard manure (FYM) at 0, 1.25 and 2.5 t ha-1, arranged in a randomised block design with three replicates. Under greenhouse conditions, Ca-bentonite application significantly (P<0.05) increased the soil moisture retention, pH, N, P, Ca and Mg content, and subsequently, maize dry matter yield. Averaged over 2 seasons, field application of 2.5 t Ca-bentonite ha-1 increased maize grain yield by 37.6%. Yields were significantly (P<0.05) higher (79.8 to 82.0% above the control) where bentonite (2.5 t ha-1) was combined with DAP (62.5 kgha-1 or FYM (2.5 tha-1). The results suggest that Cabentonite has potential as a soil amendment for moisture conservation, neutralising acidity, and improving N, P, Ca and Mg content in sandy soils, and consequently support crop growth and yield. Thus calcium bentonite presents a possible amelioration for sandy soils of low fertility in drought stressed environments. It is thus a promising technology for climate change adaptation in drought prone areas.Keywords: Climate change adaptation, drought mitigation, moisture stress, soil moisture conservation, soil fertility managemen

Critical soil organic carbon range for optimal crop response to mineral fertiliser nitrogen on a ferralsol.

Published online: 18 January 2016Soil Organic Carbon (SOC) is a major indicator of soil fertility in the tropics and underlies variability in crop response to mineral fertilizers. Critical SOC concentrations that interact positively with N fertilizer for optimal crop yield are less understood. A study was conducted on a Ferralsol in sub-humid Uganda to explore the critical range of SOC concentrations and associated fractions for optimal maize (Zea mays L.) yield response to applied mineral N fertiliser. Maize grain yield response to N rates applied at 0, 25, 50 and 100 kg N ha−1 in 30 fields of low fertility (SOC 1.7%) was assessed. Soil was physically fractionated into sand-sized (63–2000 µm), silt-sized (2–63 µm) and clay-sized (1.2% SOC registered the highest agronomic efficiency (AE) and grain yield. Non-linear regression models predicted critical SOC for optimal yields to be 2.204% at the 50 kg N ha−1 rate. Overall, models predicted 1.9–2.2% SOC as the critical concentration range for high yields. The critical range of SOC concentrations corresponded to 3.5–5.0 g kg−1 sand-sized C and 9–11 g kg−1 for clay-sized C

Climate trends, risks and coping strategies in smallholder farming systems in Uganda

Smallholder farmers in Uganda face a wide range of agricultural production risks. Climate change and variability present new risks and vulnerabilities. Climate related risks such as prolonged dry seasons are becoming more frequent and intense with negative impacts on agricultural livelihoods and food security. This paper examines farmers’ perceptions of climate change, climate-related risks affecting crop and livestock production, including climate-risk management and adaptation strategies. Percieved changes in climate included erratic rainfall onset and cessation (which were either early or late), poor seasonal distribution of rainfall and decreased rainfall. In addition, farmers reported variations in temperatures. Drought, increasing disease and pest incidences, decreasing water sources, lack of pasture, bush fires, hailstorms, changes in crop flowering and fruiting times were the major climate-related risks reported. In order to cope with climate change and climate variability, farmers use a wide range of agricultural technologies and strategies. Mulching, intercropping and planting of food security crops were among the most commonly used practices. Other strategies included water harvesting (mainly for domestic consumption), other soil and water conservation technologies and on-farm diversification. Farmers often use a combination of these technologies and practices to enhance agricultural productivity. Analysis of trends in temperature and rainfall showed an increase in average maximum temperatures, while average annual rainfall showed mixed results, where a general decline was observed in one district and a relatively stable trend in the other district. Farmers’ perception of changing rainfall characteristics and increasing temperatures were consistent with observed historical climatic trends based on meteorological data. Keywords: Agriculture, Climate risks, Livelihoods, Vulnerabilities, Coping strategies, Ugand

Impact of Soil Type, Biology and Temperature on the Survival of Non-Toxigenic Escherichia Coli O157

peer-reviewedThe occurrence of microbial enteropathogens in the environment can represent a serious risk to human health. The fate of enteropathogens introduced into the soil environment is dependent on a wide range of complex interacting environmental factors. While the effect of abiotic factors on enteropathogen survival has been widely examined, the interaction of enteropathogens with the soil microbial community is poorly understood. This study investigated the effect of soil biology and soil type on the survival of a non-toxigenic strain of Escherichia coli O157 under different temperature regimes. Soil microcosms of two soil types, with and without an intact microbial community, were inoculated with the enteropathogen surrogate, and survival was determined over a 64-day period, encompassing a shift from cold to ambient temperatures. In both soil types bacterial numbers decreased in soil with an intact microflora, while in the absence of an intact community E. coli populations increased. This effect was temperature specific, with E. coli populations remaining stable at low temperature, regardless of treatment. Soil type was of importance in survival at both cold and ambient temperatures. This work highlights the signifi cance of the soil microbial community in suppressing enteropathogens in soil, and of investigating die-off in a multi-factorial manner.Teagasc Walsh Fellowship Programm