Phosphorus (P) availability is commonly assumed to limit productivity in many tropical soils, yet there is relatively little information on the phosphorus chemical forms, distribution, and transformations that P undergoes in Ethiopian soils. We used a sequential fractionation scheme to assess phosphorus fractions of acid soils of Southern Ethiopia. The study area called Hagereselam is characterized by high soil acidity, and the availability of P in the study area is relatively low. As crop production in Ethiopia is dominated by low external input practices, native P remains the main contributor to plant P nutrition in many locations. Although the total P concentration is 829.7 mg kg−1, the organic P content was relatively low (58 mg kg−1) and constituted on average less than 7% of the total P. The ratio of organic carbon to organic P was generally greater than 240, suggesting the potential for immobilization of P. The Al + Fe-associated P was the dominant inorganic P pool. The majority of the P occurred in recalcitrant form (568.3 mg kg−1). Readily available, exchangeable phosphate, as extracted by anion-exchange resin membranes, was present in very low concentrations (3.3 mg kg−1); moreover, labile P accounted for less than 2% (9.9 mg kg−1) of the total soil P. Lime was used as a reclamation material for acid soils, and the application of lime significantly affected the different P fractions and was involved in the transformation of P fraction. Organic P forms were significantly lower for higher levels of lime application, suggesting that lime amendment enhanced organic P decomposition. Moreover, application of lime increased Ca-P and decreased Al + Fe–P for acid soils.

Integrated nutrient management, which primarily involves the combined application of organic and inorganic nutrient sources, is one of the simplest approaches to handle declining soil fertility challenges and increase crop productivity and production. Keeping in view this fact, a pot experiment was conducted to evaluate the effects of compost and inorganic nitrogen fertilizer and their mixture on soil properties, growth, and nitrogen uptake of maize on loam and clay textured soils at the Awada Agricultural Research Subcenter. Treatments comprised factorial combinations of five compost rates (0, 5, 10, 15, and 20t·ha⁻¹) and four rates of inorganic nitrogen fertilizer (0, 46, 92, and 138kg·N·ha⁻¹) laid out as a completely randomized design with three replications. Results showed that both the main and interaction effects of compost and mineral N fertilizer rates significantly affected the selected soil chemical properties and yield, and nitrogen concentration of maize. There were significant associations between plant parameters and soil nitrogen contents. The addition of 92kg·ha⁻¹·N+10t·ha⁻¹ compost and 46kg·ha⁻¹·N+10t·ha⁻¹ compost was the best treatments for loam and clay textured soils of the study areas, which improved shoot dry matter by 179.5 and 284.5, compared to the unfertilized pot, respectively. From the results of this experiment, we concluded that the integrated application of compost and mineral nitrogen fertilizer enhanced soil chemical properties and thus improved nitrogen uptake and sustainable production of maize in the study areas.

Some soils in Ethiopia reduce plant productivity due to physical and/or chemical limitations. The morphological, physical and chemical properties of problem soils, including sodic, acidic, and saline soils, around southern Ethiopia were characterized and are described in this chapter. The intention is to characterize the soils and better understand the specific nature of the limitations. Sodic soils of Alage, acid soils of Hagereselam, and saline soils of Zeway areas were sampled to represent the problem soils. The soil properties determined included color, electrical conductivity (EC), structure, consistency, bulk density, texture, pH, organic carbon (OC), total nitrogen, available phosphorus (P) and K, exchangeable bases and available micro-nutrients. The soils had considerable heterogeneity in solum and regolith thickness, horizon depth, structural development in surface soils and subsurface horizons, pH, EC and available nutrients. The classification of these soils was made according to Soil Taxonomy and World Reference Base for Soil Resources systems. The sodic soils of Alage had high pH and sodium (Na) content, and low level of OC, available P, copper (Cu) and zinc (Zn). The epipedon was classified as an ochric and the profile also had variation in clay content down the profile to satisfy the requirements of having an argilic horizon and therefore these soils were classified as Typic Natragids. Soils of Hagereselam had very low available P. Available Cu and Zn contents were found to be at the marginal levels for production of most crops. The Hagereselam profile had an argilic horizon with umbric epipedon and was classified as Typic Paleustults. The saline soils in Zeway area had relatively high amounts of calcium and low OC. The profile was found to have ochric epipedon and these soils are classified as Typic Haplocambids. Application of fertilizer including P, Cu and Zn, and removal of sodium and salts from the soil profile may be means of improving the productivity of these soils. Application of organic amendments including manures and crop residues may also be beneficial in increasing the fertility as well as organic carbon content. Key words: Acidic, saline and sodic soils, reclamation, morphological, physical and chemical soil properties.

The application of phosphogypsum (PG) on sodic soils provides nutrients to the soil, reduces the toxic effect of Na⁺, and improves soil properties. Laboratory experiments were performed to evaluate the effects of PG on the chemical properties of sodic soils. The treatments were arranged in a completely randomized design with five replications. The treatments included 0% GR (control), 50% GR (28.18 g·kg⁻¹), 100% GR (56.37 g·kg⁻¹), 150% GR (84.50 g·kg⁻¹), and 200% GR (112.74 g·kg⁻¹) rates that were thoroughly mixed with soil under incubation, whereas PG was mixed with topsoil before leaching at the same application rates under the leaching experiment. Soil and leachate samples from each pot were collected in 7, 14, 21, 28, and 35 days and subjected to spectrometric analysis. Results indicated that there was a highly significant ( ) effect on soil pH, exchangeable sodium percentage (ESP), available P, exchangeable Na⁺, and Ca⁺² under 35-day incubation compared with control. In a closed incubation system, most of the nutrients were released after 7 days of incubation and inconstantly released after 14 days of incubation. Furthermore, the removal of Na⁺ and SAR increased in initial leachate collection and decreased with the subsequent application of irrigation water (PV). Because of the high contents of Ca⁺² released from PG and the residual effect of H₂SO₄, soil pH and ESP were rapidly reduced compared with control. Post leachate analysis also revealed that available P and extractable S-SO₄⁻² were significantly ( ) increased in soil solutions. However, available P was decreased during incubations compared with the value of post leachate analysis. During a closed incubation, displaced Na⁺ replaces Ca⁺² on exchange sites, resulting in increased Ca-P precipitation. Thus, the combined application of PG and irrigation water in 7 to 14 days would allow chemical reaction with the soils and reduce sodicity problems to crop planting.

Soil salinity/sodicity is becoming a challenge for crop production in Ethiopia’s semi-arid and arid regions. However, more information on soil salinity/sodicity needs to be available around Abaya and Chamo Lakes, South Ethiopia Rift Valley. This study aimed to assess and characterize soil salinity/sodicity and determine salt-affected soils’ morphological, physical, and chemical properties. The representative soil pits that were 60 60 60 cm in size were examined, and samples were taken from 0–20, 20–40, and 40–60 cm depths based on the criteria set for agricultural salt-affected soil studies. The soil properties determined include soil color, structure, consistency, bulk density, particle density, porosity, texture, pH, EC, SAR, ESP, CEC, BS, OC, TN, available P, CaCO₃⁻, exchangeable bases, and soluble ions (Na⁺, Ca²⁺, Mg²⁺, K⁺, Cl⁻, SO₄⁻², NO₃⁻, CO₃⁻², and HCO₃⁻. The soil-analyzed results were rated and interpreted following a guide to standardized analysis methods for soil data. The results of this study reveal that the soils had considerable heterogeneity in soil morphological, physical, and chemical properties. The soils of the study site were highly alkaline and had very high sodium content, very high CEC value, and low levels of organic carbon and exchangeable calcium. The dominant soluble cation was sodium, followed by magnesium, calcium, and potassium in all soil depths of the pits. Similarly, Cl⁻ was dominant among the anions throughout the soil depth, followed by HCO₃⁻, SO₄²⁻, and NO₃⁻. The findings of this study imply that removing sodium and salts from the soil depth may improve the salt-affected soils’ productivity in the study area. Application of organic amendments, including manures and crop residues, may also be beneficial in increasing fertility and organic matter content.