Soil nutrient status of smallholder farms in Malawi

A soil sampling exercise was conducted throughout 60% of the smallholder farm sector of Malawi, a small country located at the base of the Great Rift Valley. Soil samples (1,130) were geo-referenced and analyzed for pH, texture, soil organic carbon (C), phosphorus (P), zinc (Zn), potassium (K), and calcium (Ca) status. Descriptive statistics of soil characteristics were used to evaluate soil fertility for two agricultural districts in Northern Malawi, two agricultural districts in Central Malawi, and one agricultural district in Southern Malawi. Generally soils were loamy sands and moderately acid, with "low" to "sufficient" nutrient levels. Over three-quarters of soils sampled had organic C levels which were greater than 0.8%. This indicated that organic C status was adequate in the main to maintain soil structure, although much reduced from the non-cultivated state. The organic C data supported observations of widespread nitrogen (N) deficiency in Malawi. High spatial variability of P and Zn values was noted. However, over 60% of soils had a P status above the critical value of 15 mg kg-1 which was sufficient for smallholder maize production levels. This finding supported efforts to alter the current country-wide fertilizer recommendation of 45 kg ha-1 phosphate. New findings reported here were location specific edaphic problems: i) widespread moderate soil acidity in Central Malawi, ii) natural regions in Central and Southern Malawi which were low in P and Zn, and iii) natural regions in Southern Malawi were very low in organic C. Research requirements were identified. Suggested priorities for technology development were those appropriate to smallholder farmers, such as combined use of small amounts of inorganic and organic fertilizers to address very nutrient deficient soils.