Soil fertility status in the communal areas of Zimbabwe in relation to sustainable crop production

Improvement and maintenance of soil fertility is the major constraint to sustainable crop production in the communal areas (CAs) or peasant farming areas of Zimbabwe. This study assessed soil fertility status in CAs at two levels, i.e., regional and village levels. The regional soil fertility assessment was based on soil samples submitted by CA farmers to the Soil Testing Laboratory of the Chemistry and Soil Research Institute (CSRI) for analysis and fertilizer recommendations in 1992-1994. It was assumed that these samples would represent the general soil fertility conditions in the most crop production-based CAs since CSRI soil testing service is the only one normally available for farmers in the CAs. To assess soil fertility status at village level, systematic soil sampling in maize-based fields was conducted in Chinamhora and Mhondoro CAs using mapping units of 1-10 km(2), which would presumably capture some effects of farmer soil management on soil fertility status. The regional assessment revealed that 77% of the soils required lime (pH [CaCl2] < 5.0) far most crops, and problems of potential Al toxicity (pH [CaCl2] < 4.3) and P deficiency in over 40% of the soils. Serious problems were incidences of very low N (82%) and marginal to deficient P (84%) levels. The levels of K and Mg were generally adequate (94%). The village Level assessment showed wide variations in soil properties between fields of less than 2 hectares within distances of about 1 km. This implied high probability of multiple soil fertility problems for crops in the CAs. Compared to previous assessments, the results revealed that there is a general acidification and decline in the nutrient status of CA soils. Soil fertility management effects were implied by the lower incidences of P deficiency in the more heavily fertilized Chinamhora CA, and lower incidences of potential Al toxicity and low K at the regional level than at village level which suggested greater use of acidifying N fertilizers and more depletion of soil K under maize. Acidification and depletion of nutrients may become even greater constraints to crop production in the CAs if the trend continues, especially under maize.