The use of leaf development rate to determine time to irrigate pangola grass

Abstract

The leaf development rate (LDR) of pangola grass (the number of new leaves produced on a shoot per unit of time) growing in swards on Cununurra Clay in the Ord Valley was found to decline linearly with cumulative net pan evaporation (+Ep) and ceased at a +Ep of 201 mm. The LDR of vegetative shoots, which have hairy nodes, was 3-5 times greater than that of reproductive shoots, which have glabrous nodes. Nitrogen increased the LDR of only the reproductive shoots. Vegetative shoots were preferred for measuring the response of pangola grass to moisture stress because of their insensitivity to nitrogen fertilizer level and faster LDR. Moisture availability (M) was calculated for each day as follows: M = 201 -+Ep for +Ep < 201, or otherwise M = 0. In an irrigation trial covering two 3-month periods there was a linear relation between M and dry matter yield within each period, and at each of four N rates. It is suggested that LDR measurements could be used to determine irrigation frequency of pangola grass for any site where pan evaporation is also measured. On Cununurra Clay in the Ord Valley the most frequent irrigation schedule (every 2 weeks) gave the highest dry matter yields.