Changes in leaf nutrient concentrations of fertilized, grazed grasses in the queensland wet tropics

Abstract

Abstract First fully expanded leaves of pangola grass (Digitaria decumbens) and signal grass (Brachiaria decumbens cv. Basilisk) were plucked at fortnightly intervals for a year from grazed pastures receiving P, K and split applications of N fertilizers on the wet tropical coast of north Queensland. For both grasses, N, P and K in these leaves showed similar patterns of change. Annual mean concentrations and standard deviations (% D.M.) were 2.91 ± 0.81 N, 0.30 ± 0.05 P and 2.00 ± 0.48 K for pangola grass. Corresponding values for signal grass were significantly different (P <0.01) at 2.34 ± 0.56 N, 0.26 ± 0.08 P and 2.29 ± 0.45 K. Good predictive relationships were lacking between concentrations of similar nutrients in both grasses even though significant correlations were obtained. Consequently, separate sampling of the two species will be necessary when developing plant chemical standards for assessing maintenance fertilizer requirements. September‐October or March are suggested sampling times for such a study.