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Abstract
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.
Highlights
Nitisols are deep, well-drained, red, tropical soils with diffuse horizon boundaries and a clay-rich “nitic” subsurface horizon that has typical “nutty,” polyhedric, blocky structure elements with shiny ped faces, predominantly derived from basic parent rocks by strong weathering, but they are far more fertile than most other red tropical soils [1]
Description of the Study Area. e study was conducted on the Wolaita Sodo University research farm which has been established to develop site-specific technologies. e farm is located in Wolaita Zones of Southern Ethiopia. e farm, for many years, was owned and managed using traditional practices but the productivity was low; soil acidity and inadequate fertilizer application were among many factors causing low productivity
E increasing lime rates (0% to 150%) increased Ca, Mg, and K contents with positive correlation values of 0.99∗∗∗, 0.99∗∗∗, and 0.73∗∗, respectively (Tables 5 and 7), while the exchangeable Na and cation exchange capacity (CEC) showed no significant response for the applied lime. e finding was in agreement with [59] which reported that Na was not affected by the lime application
Summary
Well-drained, red, tropical soils with diffuse horizon boundaries and a clay-rich “nitic” subsurface horizon that has typical “nutty,” polyhedric, blocky structure elements with shiny ped faces, predominantly derived from basic parent rocks by strong weathering, but they are far more fertile than most other red tropical soils [1]. More than half of all the nitisols of tropical Africa are found in the Ethiopian highlands followed by Kenya, Congo, and Cameroon, among the most productive agricultural soils along with Vertisols, Luvisols, and Planosols [2]. Due to strong weathering and oxides of Fe and Al domination, nitisols usually have limited availability of phosphorus through fixation or retention [3, 4]. Phosphorus is the most yield-limiting plant nutrient in many regions of the world [5, 6], tropical Africa [7], and most Ethiopian soils [8, 9]. Even if the total soil P exceeds plant requirements, it is mostly in nonavailable forms for crop uptake [12] and locked in primary minerals, precipitated, adsorbed, or inorganically complexed forms, and only approximately 6% (range of 1.5%–11%) readily available to plants [13].
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