Phosphorus content of the soil influences the growth and productivity of Themeda triandra Forssk. and Microlaena stipoides (Labill.) R.Br.

Despite native grasses occupying a large area of land in Australia, there has been limited work on the responses of these species to the addition of phosphorus (P). The main objective of this study was to investigate the effect of the addition of P to create a range of P contents in the soil on the productivity and morphology of two native grasses at two times of harvests. Two contrasting perennial native grasses, namely kangaroo grass (Themeda triandra Forssk. syn. T. australis R. Br. Stapf) and weeping grass [Microlaena stipoides var. stipoides (Labill.) R. Br.] were grown in a glasshouse with the addition of P to create five contents of P in the soil (7, 17, 32, 107 and 307 mg kg–1 soil) using a completely randomised design with four replicates per treatment. Grasses were harvested to 5 cm above the substrate surface, and the number of tillers and leaf area were recorded on Day 84 (harvest 1) and Day 112 (harvest 2) of the experiment. Dry matter production for kangaroo and weeping grass increased with P contents of the soil of 32 mg and ≥107 mg P kg–1 soil, respectively. Increased dry matter production for both species was the result of increased leaf area, tiller number and root growth. These results provide data that help to understand the disappearance sequence of kangaroo grass from more fertile soils and an increase in weeping grass, particularly in soils with greater fertility. Further research is required to determine if these results hold for other grass ecotypes.

Performance of 7 Australian native grasses from the temperate zone under a range of cutting and fertiliser regimes

This glasshouse study aimed to examine the performance of 7 Australian native grasses and their responses to different cutting and fertiliser regimes. The 7 native grasses comprised 2 wallaby grasses (Austrodanthonia bipartita cv. Bunderra and Austrodanthonia setacea, Woodhouse ecotype), 2 weeping grasses (Microlaena stipoides cv. Bremmer and ecotype Coleraine), 1 spear grass (Austrostipa mollis, ecotype Lexton), 1 red-leg grass (Bothriochlora macra, ecotype Hamilton), and 1 kangaroo grass (Themeda triandra, ecotype Yass). For each of the 7 grasses, 64 pots each containing 9 plants were arranged in a 4 cutting intensity × 4 fertiliser level factorial design with 4 replicates. The cutting intensity treatments involved (1) cutting to 2 cm at 3–5-week intervals; (2) cutting to 5 cm at 3–5-week intervals; (3) cutting to 10 cm at 3–5-week intervals; and (4) cutting to 2 cm based on leaf stage. The fertiliser regimes included low, medium, and high fertility treatments by applying various rates of phosphorus, and the treatment with addition of compost tea. Herbage accumulation, shoot and root growth, plant survival and tiller density, nutritive characteristics, and leaf stage were monitored. All grass lines produced the lowest herbage mass when cut to 2 cm above ground at 3–5-week intervals. Cutting to 5 cm or to 2 cm based on leaf stage favoured herbage accumulation of Lexton spear grass, Hamilton red grass, Yass kangaroo grass, and Coleraine weeping grass. Cutting to 10 cm favoured herbage accumulation of Bremmer weeping grass and wallaby grass. Cutting to 10 cm together with high fertiliser application considerably increased herbage accumulation in comparison with treatments with low fertiliser application or with compost tea. Shoot and root biomass were maximised when plants were cut to 10 cm above ground, except Lexton spear grass which had highest root biomass when plants were managed based on leaf stage. Plant survival was dramatically affected by defoliation intensity and varied among species. Plant survival declined when plants were cut to 2 cm above ground for most species. Overall, native grasses were considered to have good nutritive characteristics with crude protein ranging from 17 to 22% and neutral detergent fibre from 48 to 60%. Results from this study indicate that it may be possible to use leaf stage as a determinant for the commencement of grazing native species. Optimum leaf stages that could be used as a grazing management guide were on average 3.4 for wallaby grass, 4.2 for weeping grass, 3 for spear grass, 3.8 for red-leg grass, and 4.4 for kangaroo grass. However, further work is required to better define this for likely seasonal variation between C3 and C4 species.