With summer rain becoming more prevalent in the northern ag region, perennial grasses that can provide grazing opportunities over summer and winter have become a viable option for graziers and mixed farmers. This trial aims to determine the response of a Gatton panic/annual ryegrass mix to urea, with and without the addition of Nitrogen (N) and Super Phos Extra fertiliser.
Super Phos Extra is a pasture fertiliser containing 8.4% phosphorus, 10.5% sulfur, 20% calcium, 0.1% copper and 0.1% zinc. The copper and zinc are incorporated at manufacture.
Figure 1. Aerial shot of trial site taken 27 July.
Trial details and results
Location TEBCO FISHING CO (Mt Adams), Yandanooka West Road, Irwin Shire
Rotation 2019 & 2020 Perennial/Annual Pasture
Plot Size 15m x 2.5m
Soil type Grey sand
Table 1. Soil analysis February 2021.
The trial tested multiple N rates alongside one phosphorus (P) rate (Table 1).
Table 2. Treatments and Results.
Low annual pasture density (mostly ryegrass) among the panic grass severely limited the dry matter growth response to N fertiliser (Table 2), even though there were strong visual responses (Figure 2). Lack of rain after mid-August probably also affected biomass accumulation where the spring application of N fertiliser had been applied.
Figure 2. Pasture growth in plot with zero N (left) and plot with 60N (right). Taken 25 August.
The pasture growth response to the N fertiliser was not limited by the soil P (or sulfur) levels. The dry matter response to the increasing rates of N was the same whether or not Super Phos Extra was applied (Figure 3). Herbage samples analysed for nutrient uptake (not shown) indicated that P uptake was adequate without Super Phos Extra applied.Figure 3. Dry matter response of pasture (2nd cut) to increasing N rates, with and without Super Phos Extra.
Applying N improved the important feed quality parameters (Table 3). Protein, digestibility and metabolisable energy (ME) all improved as more N was applied.
Table 3. Applying N improvements on feed.
Note: data are the average of the urea rate results because the Super Phos Extra did not impact the results.
Acknowledgements: Sincere thanks to Jeff Cockman for providing the trial site