Iron pyrites as a sulphur fertilizer in an alkaline soil

Abstract

Iron pyrites at two levels of grinding (14 and 50 per cent < 9 pm) each at three rates of application (190, 380 and 760 kg ha-l) 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 of cobs over the no sulphur control. The two highest rates of the finer material produced yields of whole tops and of cobs, and total sulphur concentrations and quantities in the tops, similar to those in treatments receiving 45 kg sulphur ha-1 (sulphur sufficiency) either as sodium sulphate or sublimed sulphur. The highest rate of the coarser material produced highly significant positive responses in each of these four measures. The critical sulphur concentration in standard indicator leaves (0.13 per cent) was surpassed in treatments receiving the highest rate of the coarser material and the two highest rates of the finer material. In an incubation experiment, iron pyrites was mixed with the alkaline clay soil and kept at 25¦C for 20 days. After allowance for oxidation of the iron pyrites incubated dry without soil, the net oxidation of the sulphide sulphur to sulphate in this soil was 0.98 and 2.39 per cent (both figures highly significant) for the coarser and finer material respectively.