Effects of Liming on Acid Ferrasols for Sustainable Crop Production in Uganda – A Review

Ferralsols are the predominant soil type covering about 70% of the total land area of Uganda; they are mostly found in the Central and Western regions of the country. Ferralsols are highly weathered, acidic and have inherently low nutrient reserves. Degradation of these soils has led to reduced agricultural production and productivity. Despite the increased human population and the importance of Agriculture to the majority of the households in Uganda, little or no research has been carried out on Acid Ferralsols to improve food security and sustain livelihoods. Besides, the country’s research programs have not prioritized the use and management of soil fertility management strategies such as liming. Crop yields on these soils are often far less than those on research stations. This review paper focuses on the extent and effects, causes, challenges and opportunities associated with liming Acid Ferralsols and the effects on soil properties and crop yield. Many studies have shown that detrimental effects of acid soils can be ameliorated through liming, thus improving on the physio-chemical properties to improve crop production and yield. More research is anticipated to develop lime requirements for acid Ferralsols so as to meet the growing food demand in Uganda

Linkages between Soil Acidity, Soil Plant Nutrients and Land Use on Ferralsols in Central Uganda

A study to examine the linkages between soil acidity, soil plant nutrients and land use on Ferralsols was carried out on smallholder farms in Central Uganda. The objective of the study was to assess the effect of soil pH on soil plant nutrient availability under the current land use. The study was carried out in Mpigi, Masaka, Wakiso, Mukono and Mubende districts representing Central Uganda. Soil samples were randomly collected from Coffee, Banana, soybean, common bean, maize and virgin fields in the five districts and the pH and plant nutrient analyzed accordingly. The analysis of variance (ANOVA) showed significant difference (p<0.01) on soil nitrogen, Calcium (p< 0.05) and Magnesium (p< 0.05). When treatment was assessed, the study showed significant difference (p< 0.01) on potassium. Besides, the study also showed high concentrations of Manganese (Mn) and Iron (Fe) in addition to very high sand and low silt and clay contents. The current land use for coffee production in Masaka district recorded the lowest soil pH (4.4) followed by annual fields (pH 4.60) in Mpigi. The highest soil pH (5.7) was recorded in banana fields in Mubende. The study also recorded very low to low N, P and K. Generally, the study observed rapid soil fertility decline in smallholder farms in the region

Amelioration of Soil Acidity in Ferralsols of Central Uganda

Soil acidity is one of the major constraints limiting crop productivity in Central Uganda. Thus, the ideal soil pH for crop production ranges from 5.5 to 6.8, but in Central Uganda, crops are believed to be cultivated in soils with pH below these ranges. Given the adverse effects of soil acidity to agricultural production, appropriate measures such as the use of lime could be an option to improve the productive capacity. Henceforward, soils were sampled from farmers’ fields in Mpigi, Mubende and Wakiso Districts representing Central Uganda to evaluate rates of CaCO3 and corncob biochar in a greenhouse incubation study. Afterwards, 2 kg of soil was weighed, placed in a plastic container and thoroughly mixed with 0, 1, 3 and 5 g equivalent to 0, 1, 3 and 5 tons/ha CaCO3 and corncob biochar. Soils were arranged in a Complete Randomized Design (CRD) and moistened with 500 ml of water to bring it to about field capacity and pH determination done for a period of three (3) months until equilibration. The analysis of variance (ANOVA) showed significant effect (P<0.001) on soil pH when CaCO3 and corncob biochar were applied with the three districts recording a near neutral pH of 6.7. After pH equilibration in the greenhouse, rates of CaCO3 and corncob biochar that raised the soil pH in each medium were used to calculate the lime rates i.e., 0, 120, 360 and 600 g applied in the fields. In a Complete Randomized Design (CRD) consisting of four replications, soybean varieties were applied as the main plots while rates of CaCO3 and corncob biochar were applied as the sub plots. The analysis of variance (ANOVA) showed that CaCO3 had significant effect (p<0.001) on soil pH with Mpigi recording the highest soil pH (6.7) followed by Mubende (pH 6.6). Rates of CaCO3 and corncob biochar also showed significant effect (p<0.001) on soybean grain yield compared to 0 g CaCO3 and corncob biochar. Application of 600 g of corncob biochar showed significant effect (p<0.001) on soil pH in the different study locations. Besides, increased in CaCO3 rate to 600 g recorded the highest (7137.5 kg ha-1) soybean grain yield in Wakiso District while 600 g of corncob biochar recorded the highest (5637.5 kg ha-1) soybean grain yield in Mpigi District thus signifying the potential effect of CaCO3 and corncob biochar in Acid Ferralsols. &nbsp

Enhancing the Phytoremediation of Hydrocarbon-Contaminated Soils in the Sudd Wetlands, South Sudan, Using Organic Manure

Phytoremediation of hydrocarbon-contaminated soils is a challenging process. In an effort to enhance phytoremediation, soil was artificially contaminated with known concentration of light crude oil containing Total petroleum hydrocarbon (TPH) at a concentration of 75 gkg−1 soil. The contaminated soil was subjected to phytoremediation trial using four plant species (Oryza longistaminata, Sorghum arundinaceum, Tithonia diversifolia, and Hyparrhenia rufa) plus no plant used as control for natural attenuation. These phytoremediators were amended with concentrations (0, 5 and 10 gkg−1 soil) of organic manure (cow dung). Results at 120 days after planting, showed that application of manure at concentrations of 5 and 10 gkg−1 soil combined with an efficient phytoremediator can significantly enhance reduction of TPH compared to natural attenuation or use of either manure or a phytoremediator alone (p0.05). Therefore, the study concludes that use of phytoremediators and manure 5 gkg−1 soil could promote the restoration of TPH contaminated-soils in the Sudd region of South Sudan

Precision of farmer-based fertility ratings and soil organic carbon for crop production on a Ferralsol

Simple and affordable soil fertility ratings are essential, particularly for the resource-constrained farmers in sub-Saharan Africa (SSA), in planning and implementing prudent interventions. A study was conducted on Ferralsols in Uganda to evaluate farmer-based soil fertility assessment techniques, hereafter referred to as farmers' field experiences (FFE), for ease of use and precision, against more formal scientific quantitative ratings using soil organic carbon (SQR-SOC). A total of 30 fields were investigated and rated using both techniques, as low, medium and high in terms of soil fertility – with maize as the test crop. Both soil fertility rating techniques were fairly precise in delineating soil fertility classes, though the FFE was inefficient in distinguishing fields > 1.2 % SOC with medium and high fertility. Soil organic carbon, silt and clay were exceptionally influential, accounting for the highest percentage in grain yield of 50 % in the topsoil (0–15 cm) and 67 % for the mean concentrations from 0 to 15 and 15 to 30 cm. Each unit increase in SOC concentration resulted in 966 to 1223 kg ha⁻¹ yield gain. The FFE technique was effective in identifying low-fertility fields, and this was coherent with the fields categorized as low (SOC < 1.2 %). Beyond this level, its precision can be remarkably increased when supplemented with the SQR-SOC technique