Sulfur Nutrition of Maize in Four Regions of Malawi

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Abstract
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 km2 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 at 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 Maize yields showed a N × 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 all 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.