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Phosphorus (P) transformations and associated changes in soil chemistry following lime application in acidic soils are very determinant to enhance P use efficiency. Thus, this study was conducted to evaluate the effects of different rates of lime on soil P fractions and chemical properties in acidic Luvisols of southern Ethiopia. The lime rates were 0 t/ha (0%), 3.75 t/ha (50%), 7.5 t/ha (100%), and 11.25 t/ha (150%), and incubated for a month with three replications. The soil P fractions analyzed includes soluble P (P-sol), P associated with iron (Fe-P), aluminum (Al-P), calcium (Ca-P), organic part (Org-P) and residual (Res-P). The result indicated that liming significantly (p < 0.05) improved the release of P-sol, Ca-P, and Res-P, and reduced Fe-P, Al-P, and Org-P. The changes in soil chemical properties were also significant. For instance, increased rate of lime enhanced soil pH from 5.3 to 6.5, reduced exchangeable acidity from 1.47 to 0.15 cmol(+)/kg, and increased available P from 2.74 to 8.72 cmol(+)/kg. Yet, the amount of P-sol was found low for plant needs even at a 150% rate of lime. Thus, working on external P requirement to equilibrate the need for plants followed by crop response validation are suggested. [ABSTRACT FROM AUTHOR]

This study investigated phosphorous (P) sorption characteristics under lime rates, and validated them under field conditions. Soil samples from nitisols and luvisols were taken, mixed with lime(tha−1) at[0,0], [5.25, 3.75], [10.5, 7.5] and [15.75, 11.25], respectively, and incubated for 30 days. It was equilibrated with KH2PO4 at 0, 10, 20, 30, 40, and 50 mgPL−1. The data were tested with Freundlich and Langmuir models. External P requirement (EPR) and changes in chemical properties were evaluated. The field validation on wheat involved rates of P (0, 8.2, 16.4, 24.6, 32.9, and 41.1 kg ha−1) and lime (0, 650, and 1300 kgha−1) in a randomized complete block design with three replications. Freundlich was found the best-fitted model. Freundlich coefficient (Kf) ranged from 212 to 45 mgPkg−1 (nitisols) whereas it was 112.7 to 16.29 mgPkg−1 (luvisols). EPR (kgPha−1) without and the highest lime rate were: nitisols (142.5 and 52.32 kgPha−1) and luvisols (124.84 and 25.94 kgPha−1). Liming reduced EPR by 63.3% (nitisols) and 79.3% (luvisols). Liming increased soil pH from [4.55 to 6.60 in the nitisols, and 5.33 to 6.51 in luvisols]; exchangeable acidity (cmol(+)kg−1) 3.84 to 0.01 nitisols, and 0.72–0.05 luvisols, and available P (mg/kg) 3.2–6.32 nitisol, and 2.74–8.72 luvisols. Furthermore, applying 32.9 kgPha−1 x 1300 kgha−1 lime resulted in grain yield (4345.2 kgha−1) that was 449% more than the untreated crop (791.3 kgha−1). The validation result suggested higher P than blanket P recommendation. It also justifies that excess P or lime alone cannot be a complete solution for P management and increased yield. [ABSTRACT FROM AUTHOR]

Understanding the nutrient dynamics in acid soil is fundamental to carry out proper management. The study was conducted to investigate phosphorus (P) pools and selected properties under different rates of lime for acid nitisols of Farawocha, Southern Ethiopia. Four lime rates incubated for a month in three replications were tested. The lime rates were 0 t/ha (0%), 5.25 t/ha (50%), 10.5 t/ha (100%), and 15.75 t/ha (150%). Lime requirement (LR) for 100% was calculated targeting soil pH of 6.5. Data on the P pools such as soluble P (P-sol) and bounded forms of P with iron (Fe-P), aluminum (Al-P), calcium (Ca-P), organic part (Org-P), residual P (Res-P), and total of P fractions were measured. In addition, changes in soil chemical properties such as pH, exchangeable acidity, calcium (Ca), magnesium (Mg), sulfur (S), iron (Fe), copper (Cu), boron (B), zinc (Zn), and manganese (Mn) were analyzed. The result showed that total P was 357.5 mg/kg. Compared to nontreated soil, liming at a rate of 15.75 t/ha significantly improved P-sol (34.2%, r2 = 0.88), Ca-P (61.6%, r2 = 0.92), and Res-P (195%, r2 = 0.94); however, it reduced Fe-P (58.5%, r2 = −0.83), Al-P (71%, r2 = −0.97), and Org-P (19.1%, r2 = 0.93). Overall, the P-associated fractions in the soil, regardless of the lime rates, were in the order of Org_P > Res_P > Fe_P > Ca_P > Al_P > P-sol. Liming raised soil pH by 2.1 units (4.5 to 6.6) over nonlimed soil, whereas it reduced exchangeable acidity from 4.18 to 0.23 meq/100 g soil. Available P, Ca, Mg, S, Cu, Zn, and B contents were significantly improved with lime application. However, liming reduced Fe and Mn contents. In conclusion, these findings showed that liming facilitated the release of P from various pools, modified pH and exchangeable acidity, and resulted in beneficial changes for most of the soil chemical properties. [ABSTRACT FROM AUTHOR]

Background: 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. Result: Although the total P concentration is 829.7 mg kg, the organic P content was relatively low (58 mg kg) 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). Readily available, exchangeable phosphate, as extracted by anion-exchange resin membranes, was present in very low concentrations (3.3 mg kg); moreover, labile P accounted for less than 2% (9.9 mg kg) of the total soil P. Conclusion: 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. [ABSTRACT FROM AUTHOR]