Pasture production from a long-term fertiliser trial under irrigation

Abstract

New Zealand pastoral farming has benefited greatly from the application of phosphorus (P) and sulphur (S) fertilisers supplied in the main by superphosphate (SSP). The long-term fertiliser trial at Winchmore, mid-Canterbury, New Zealand was set up in 1952 and has yielded a wealth of data on the effect of fertiliser, grazing by sheep and flood irrigation on pasture production. The trial was initially (1952–1958) designed to measure the effect of no fertiliser and SSP applied each year at 188, 376 and 564 kg ha⁻¹. From 1958 to 1980, SSP applications were stopped to the 564 and one half of the 376 kg SSP y⁻¹. The cessation of fertiliser decreased clover content and increased the proportion of weeds and low-fertility grasses. The decline in production once fertiliser application ceased followed a curvilinear pattern, but never reached the low production of the no fertiliser treatments even after 20 years. In 1980, the residual treatments were changed to compare a reactive phosphate rock (RPR)/S treatment as well as an intermediate (250 kg ha⁻¹) rate of superphosphate. The 0, 188 and 376 kg SSP ha⁻¹ have now been unchanged for 60 years, while the 250 kg SSP or equivalent in RPR/elemental S have remained unchanged for 30 years. The 188 and 250 kg SSP ha⁻¹ y⁻¹ treatments have shown that without any nitrogen fertiliser, ryegrass and clover will persist in irrigated pastures and result in high levels of pasture production (11–12 t ha⁻¹) for up to 60 years.

Keywords:

• long-term
• phosphorus
• sulphur
• pasture production
• pasture quality
• grazing
• irrigated pasture

Acknowledgements

The authors wish to acknowledge the contribution of a considerable number of technical staff, particularly JH Baird, SD McBride, GN Green and BM Stuart, and scientists DS Rickard, BF Quin and ML Nguyen. Thanks to J Carson for farm management, P Johnstone for statistical advice and the New Zealand Fertiliser Manufacturer's Research Association for funding.