Sulfur Nutrition of Maize in Four Regions of Malawi

with most of the attention being focused on the socalled fertilizer elements, N, P, and K (Stoorvogel et Sulfur, though widely deficient in Africa, has received little attenal., 1993). Sulfur is a macronutrient that is taken up by tion by soil fertility researchers. Shifts to low-S, high-analysis fertilizers, continuous cropping, and higher-yielding varieties may have in- most grain crops in amounts similar to those of P, creased S limitations in maize (Zea mays L.) production. We aimed namely 10 to 30 kg/ha. However, while P has been the to characterize maize S nutritional status in farmers’ fields in four subject of extensive investigations throughout Africa regions of Malawi and determine maize response to S. Four 42 to 68 (e.g., Buresh et al., 1997 ), much less is known about km 2 study areas were delineated, two with low-elevation lacustrine the S status of African soils and the response to S amendsoils, and two with highly weathered residual upland soils. Maize ments in crop production. Deficiency of S is likely to be plants in 238 farmer fields were sampled for nutrient analysis at 8- to widespread in Africa, especially in the savanna regions, 12-leaf vegetative and tasseling growth stages. Replicated experiments where annual burning results in losses to the atmosphere were conducted in two years on a total of 20 farms to determine as SO2. maize yield responses to S with and without N and/or P. Sampling Some early reports recognized the problem. Jones areas differed significantly in maize S concentrations, S Diagnosis and Recommendation Integrated System (DRIS) indices, and N:S ratios. (1977) reported symptoms of S deficiency on maize and For earleaves, means were 1.46 g/kg S; S DRIS index, 12.2; and N:S groundnut (Arachis hypogaea L.) in parts of Malawi. A ratio, 11.5. The ratio of N:S in the earleaf was the best predictor of few experiments in the early literature reported signifimaize yield response to S (R 2 5 0.58). Maize yields showed a N 3 S cant responses by maize to S, generally in the range of interaction such that there were no responses to S unless N was also 12 to 20% increases in yield (e.g., Allen [1976] in western supplied. With 80 kg/ha N, a significant response to S was shown by Kenya, Grant and Rowell [1976] in Zimbabwe, and maize in all but one of 20 experiments. A response curve for S showed Kang and Osiname [1976] in Nigeria). However, comthat 5 to 10 kg/ha of S was optimal, with mean yield responses ranging paratively little research was conducted to investigate from 90 to 142 kg grain/kg S.