Inhibition of nitrification by nitrapyrin, carbon disulphide and trithiocarbonate

We have studied the behaviour of the nitrification inhibitors nitrapyrin (2‐chloro‐6‐trichloromethyl pyridine) and carbon disulphide (CS2), and of trithiocarbonate ion (CS32−). Solutions of Na2CS3 in water or aqueous NH3 are stable but when added to soil they decompose with evolution of CS2, which in laboratory tests was complete within hours. In field experiments each material was injected simultaneously with aqueous NH3 or aqueous urea. Nitrapyrin was held strongly on soil near the centre of the injected band of fertiliser N. It became fully effective only approximately two months after injecting grassland in November (1974 and 1975) with 375 kg N/ha, but approximately one month after injecting winter wheat with 100 kg N/ha in March (1976). In contrast CS2 itself, or CS2 generated by CS32−, diffused rapidly from the injected band and markedly inhibited nitrification for up to three months after injecting grassland and up to one month after injecting winter wheat, but had no effect on nitrification later. The main practical implication of the work is that liquid fertilisers supplying NH4‐N may, if mixed with a trithiocarbonate, be injected into grassland in autumn, without risk of substantial nitrate leaching during winter. This extends the period suitable for injection and eases congestion of work normally done in spring.