Evaluation of Makarikari grasses - potential production, nitrogen content and nitrogen recovery of two cultivars fertilized with urea

Abstract

Makarikari grass (Panicum coloratum var. makarikariense) cvs, 04634 and Bambatsi were fertilized with eight rates of urea (0-900 kg N ha-1 yr-1) under irrigation on a red earth at Toowoomba, and cut either 8-weekly or at full flower. Dry matter (D.M.) production increased linearly with N applications up to 450 kg ha-1 for both cultivars. Due to differences in growth rhythm between cultivars, 04634 produced higher total yields cut at full flower (29500 kg ha-1 yr-1) than at 8-weekly intervals (23100 kg ha-1 yr-1), whereas Bambatsi yielded similarly (23000 kg ha-1 yr-1) for the two cutting frequencies. Lower tissue N concentrations occurred at full flower than in 8-week growth for both cultivars (Q4634 -0.85 per cent to 1.08 per cent; Bambatsi-1.39 per cent to 1.55 per cent at 450 kg N ha-1). The N uptake by 04634 was the same for both cutting frequencies, but lower in Bambatsi cut at full flower. The association between N application rate, tissue N concentration and N uptake is outlined. The maximum efficiencies of both N use for D.M. production and per cent N recovery for 04634 and Bambatsi (55 and 35 kg D.M. per kg N applied; 40 and 60 per cent N recovery, respectively) were comparable with published values for other species. Increasing N application rates decreased the efficiency of D.M. production of both cultivars, decreased the per cent N recovery of Bambatsi, but had no effect on the per cent N recovery of 04634. In an extension of the Bambatsi study, the intrusion of spring ephemerals, mainly Bromus unioloides, did not reduce total D.M. production greatly and distributed it better through the growing season. Productivity of Bambatsi during mid-summer was not affected by prior weed competition in the spring.