Effects of irrigation frequency on ryegrass and white clover growth. 1. Experimental results

Abstract

The rising demand for the finite amount of water available for pasture irrigation in New Zealand means increasing interest in irrigation efficiency. The effects of frequency of sprinkler irrigation of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) were investigated near Palmerston North on Manawatu fine sandy loam (Dystric Fluventric Eutrochrept), using replicated plots of 1.5 m2. As values range from 12 to 90 mm for the reported soil water deficit at which stress first reduces pasture growth, with the most common values between 20 and 60 mm, deficits of 20 mm (involving irrigation about every 5 days if no rain fell), 40 mm, and 60 mm were chosen to trigger irrigation. There were replicated plots with and without superphosphate treatments for each irrigation and species treatment, as an interaction between fertility and the optimal trigger deficit was considered possible, and such interactions have rarely been investigated. There were also four non-irrigated plots. Yield was measured and soil water content monitored. Irrigating at a soil water deficit of 20 mm (meaning readily available water was always present in the top 150 mm of soil) rather than 60 mm resulted in significantly more ryegrass and white clover production over the irrigation season. This was particularly so when superphosphate was applied to the ryegrass.