Abstract

The potato is one of the most important food and cash crops in Malawi, but current yields are low and the fertilizer recommendations rely on outdated soil fertility information. To understand the influence of soil factors in limiting current potato production, the mineralogical and physicochemical soil characteristics of 26 farms in the central highlands of Malawi were evaluated. Cluster analysis with clay, crystalline iron oxide, and total carbon content revealed three clusters with two corresponding to Ferralsols and one to Regosols, which are known to exist in the area. In the three clusters, the soil was generally acidic with low exchangeable acidity and aluminium (Al; < 0.7 cmolc kg-1); thus, Al toxicity was not a concern because the soil solution Al would be very low to negatively affect plant growth. Inorganic nitrogen was adequate, while available phosphate and exchangeable potassium (K) were variable within each cluster. However, a deficiency in exchangeable calcium (Ca; < 3.6 cmolc kg-1) and magnesium (Mg; < 1.2 cmolc kg-1) indicated that low base cation concentration was the problem and the potential yield-limiting factor. Soil management, not soil type, appeared to determine soil nutrient conditions based on the current soil Ca and Mg deficiencies and variable K nutrient status. There is a need for updating the current fertilizer recommendations by incorporating K, Ca, and Mg and promoting soil amendment interventions using locally available animal manure and plant ash.

Key words: acid soil; fertilizer; Ferralsols, Regosols, Solanum tuberosum L., aluminium toxicity, calcium; magnesium.