Critical phosphorus concentrations for subterranean clover in the high rainfall areas of South‐Western Australia

Abstract

The relationship between yield and phosphorus (P) concentration of dried subterranean clover (Trifolium subterraneum) herbage has been measured in many long‐term field experiments in the greater than 800 mm annual average rainfall areas of south‐western Australia. In the experiments, seven levels of different P fertilizers (single superphosphate, rock phosphates, partially acidulated rock phosphates) were applied to the surface, either annually, or once only to new plots in different years. Yields and P concentration in dried herbage were measured whenever possible in each growing season (April to November near the south coast, May to October near the west coast) for several successive years. Critical P, the P concentration in dried herbage related to 90% of the maximum yield, was calculated. At each harvest, critical P was similar for different fertilizers. However, critical P was different when measured for samples collected at about the same time in different years at the same site or different sites, and it consistently decreased with increasing maturity of clover. Mean critical P (%) with standard errors and the number of observations in parenthesis were: April, 0.63 (0.01, 2); May, 0.56 (0.01, 2); June, 0.49 (0.04, 25); July, 0.44 (0.06, 37); August, 0.34 (0.05, 71); September, 0.32 (0.06, 91); October, 0.25 (0.04, 157); and November, 0.19 (0.01, 5), for a total of 390 observations.

Notes

Present address is AGC Woodward‐Clyde, Level 5, East Point Plaza, 233 Adelaide, Terrace, Perth, Western Australia 6000, Australia.