Iron pyrites as a sulphur fertilizer in an alkaline soil

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Abstract
Iron pyrites at 2 levels of grinding (14 and 50% < 9 .mu.m) each at 3 rates of application (190, 380 and 760 kg ha-1) was applied to maize (Zea mays) in an alkaline soil, in a glasshouse experiment. Every iron pyrites treatment significantly increased the dry weights of whole tops and cobs over the no S control. The 2 highest rates of the finer material produced yields of whole tops and of cobs, and total S concentrations and quantities in the tops, similar to those in treatments receiving 45 kg S ha-1 (S sufficiency) either as Na2SO4 or sublimed S. The highest rate of the coarser material produced highly significant positive responses in each of these 4 measures. The critical S concentration in standard indicator leaves (0.13%) was surpassed in treatments receiving the highest rate of the coarser material and the 2 highest rates of the finer material. In an incubation experiment, iron pyrites was mixed with the alkaline clay soil and kept at 25.degree. C for 20 days. After allowance for oxidation of the iron pyrites incubated dry without soil, the net oxidation of the sulfide S to sulfate in this soil was 0.98 and 2.39% (both figures highly significant) for the coarser and finer material, respectively.
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