Sulfur nutrition of maize in four regions of Malawi

Sulfur, though widely deficient in Africa, has received little attention by soil fertility researchers. Shifts to low-S, high-analysis fertilizers, continuous cropping, and higher-yielding varieties may have increased S limitations in maize (Zea mays L.) production. We aimed to characterize maize S nutritional status in farmers' fields in four regions of Malawi and determine maize response to S, Four 42 to 68 km(2) study areas were delineated, two with low-elevation lacustrine soils, and two with highly weathered residual upland soils. Maize plants in 238 farmer fields were sampled for nutrient analysis st 8- to 12-leaf vegetative and tasseling growth stages, Replicated experiments were conducted in two years on a total of 20 farms to determine maize yield responses to S with and without N and/or P. Sampling areas differed significantly in maize S concentrations, S Diagnosis and Recommendation Integrated System (DRIS) indices, and N:S ratios. For earleaves, means were 1.46 g/kg S; S DRIS index, 12.2; and N:S ratio, 11.5. The ratio of N:S in the earleaf was the best predictor of maize yield response to S (R-2 = 0.58), Maize yields showed a N x S interaction such that there were no responses to S unless N was also supplied. With 80 kg/ha N, a significant response to S was shown by maize in ail but one of 20 experiments, A response curve for S showed that 5 to 10 kg/ha of S was optimal, with mean yield responses ranging from 90 to 142 kg grain/kg S.