Lime-Aluminium- Phosphorus interactions in acid soils of the Kenya highlands

Abstract

Liming and phosphorus (P) applications are common practices for improving crop production in acid soils of the tropics. Although considerable work has been done to establish liming rates for acid soils in many parts of the world, information on the role of the lime-Al-P interactions on P fertility management is minimal. A green house pot experiment was conducted at Waruhiu Farmers Training Centre, Githunguri to evaluate the lime-Al-P interactions in acid soils of the Kenya highlands. Extremely acidic (pH 4.48) and strongly acidic (pH 4.59) soils were used for the study. Four lime (CaO) rates and phosphorus (Ca (H2PO4)2 rates were used. The liming rates were: 0, 2.2, 5.2 and 7.4 tonnes ha-1 for extremely acidic soil and 0, 1.4, 3.2, and 4.5 tonnes ha-1 for the strongly acidic soil. Phosphorus applications rates were: 0, 0.15, 0.30 and 0.59 g P kg-1 soil for the extremely acidic soil and 0, 0.13, 0.26, and 0.51 g P kg-1 for the strongly acidic soils. The experiments were a 42 factorial laid in a randomized complete block design (RCBD) and replicated three times. Data collected included: soil chemical properties and P adsorption. The soils had high exchangeable Al (>2 cmol Al kg-1), Al saturation of (>20% Al) and low P. Lime-Al-P interaction significantly (P≤0.05) increased soil pH, extractable P, reduced exchangeable Al, Al saturation, P adsorption and standard phosphorus requirements (SPR). Use of 7.4 tonnes ha-1 lime in extremely acidic soils and 4.5 tonnes ha-1 lime in strongly acidic soils significantly reduced exchangeable Al and SPR by >70%. Lime positively correlated with soil pH, extractable P, and Langmuir maximal adsorption constant and negatively correlated with SPR and exchangeable Al. It was therefore concluded that lime and P positively interact to reduce Al and P adsorption rates in acid soils in the Kenya highlands.