Sustainability of beef production from brigalow lands after cultivation and mining. 2. Acland Grazing Trial pasture and cattle performance

Abstract

Context. Agricultural land used for open-cut coal mining in Queensland is required by law to be returned to a safe, stable and self-sustaining state for agriculture.Aims. The aim of this research was to identify whether rehabilitated pastures on post-mine soil at a site near Acland could viably support cattle production.Methods. Five years of field data from Botanal pasture assessments, pasture quality, cattle liveweights and faecal observations, plus supplementary cattle liver data, were used to compare pasture and cattle performance from mined and unmined previously cultivated brigalow land. Subtropical pasture species were sown in 2007 (Rehab1, 22 ha), 2010 (Rehab 2, 32 ha) and 2012 (Rehab3, 22 ha) in three rehabilitated paddocks and in 2012 in an unmined (Control, 21 ha) paddock. The paddocks were grazed for 117-190 days of each year by Angus cattle.Key results. Mean total standing dry matter in grazed pasture over the five trial years was consistently higher in Rehab 2 (5656 kg/ha) than in the other paddocks. Rehab 1 (3965 kg/ha) and Rehab 3 (3609 kg/ha) performed at an intermediate level and the Control paddock produced less pasture (2871 kg/ha). Grass leaf crude protein was higher in Rehab 2 than in the other paddocks and declined significantly (P < 0.001) across all paddocks as pasture aged. Pasture species remained perennial, palatable and productive in all paddocks; however, pasture yield, quality and composition trends over time suggested that pasture rundown occurred across all paddocks. The mean liveweight gain (LWG) per head when grazing the trial paddocks (trial LWG) was higher (P < 0.05) in the Rehab 2 cohort than the other paddock cohorts in Years 3 and 5, and trial LWG in the Control cohort was not significantly (P > 0.05) different from one or more of the rehabilitated paddock cohorts each year. Cattle production per hectare during the trial grazing periods was also consistently highest in Rehab 2 (5-year mean trial LWG 131 kg/ha) compared with the other paddocks (67-80 kg/ha). Conclusion.The rehabilitated pastures in use by the mine were considered at least as productive as the surrounding unmined brigalow landscape.Implications. The Acland rehabilitation process was considered successful in establishing pastures that were able to viably support cattle production.

Sustainability of beef production from brigalow lands after cultivation and mining. 1. Sown pasture growth and carrying capacity

“…5, showing potentially available soil N, supports this theory. Cattle production (mean cumulative liveweight gain) from Rehab 2 was also higher (P < 0.05) than from Rehab 3 and Rehab 1, which were similar (Melland et al 2021). Soil mineral N supply helps explain the differences in the uptake of N among sites and the consequent productivity, and has potential as a predictor of N uptake in these pastures.…”

“…Three sites on commercial beef properties (Colliery Park and Roundview) were measured for 3 years (2013)(2014)(2015) and 13 sites were associated with the Acland coal mine as follows: (1) five sites adjacent to the mine were in paddocks used for the Acland Grazing Trial and were measured each year for the 5-year period 2014-2018, and (2) eight sites known as the benchmark sites (BMK) were on unmined lands within 7 km of the mine and were measured for 2 years (2017)(2018). Data from the Swiftsynd observations together with additional soil, pasture and cattle data associated with the grazing trial and BMK sites (Bennett et al 2021;Melland et al 2021) were then used to calibrate the GRASP model (McKeon et al 2010;Clewett et al 2021), assess the effects of climate and derive estimates of long-term (60-year) mean annual pasture growth, RUE and LTCC.…”

“…Despite a general positive relationship between soil mineral N supply and N yields in pasture across a 2.5-fold range of soil N fertility levels (Fig. 6), the soil N indicator was not sensitive enough to reflect declines within individual paddocks over time in observed pasture TSDM and N uptake (Bennett et al 2021;Melland et al 2021). Rehab 2 had the highest mineral N supply, highest N yields in pasture and, also, higher cattle production (Clewett et al 2021;Melland et al 2021).…”

“…6), the soil N indicator was not sensitive enough to reflect declines within individual paddocks over time in observed pasture TSDM and N uptake (Bennett et al 2021;Melland et al 2021). Rehab 2 had the highest mineral N supply, highest N yields in pasture and, also, higher cattle production (Clewett et al 2021;Melland et al 2021). This indicated, first, that rehabilitated mining land can be as productive as unmined land and, second, that Rehab 2 soil is likely to be composed of inherently higher-fertility soil than are other sites, as described above.…”

“…The research reported here is integral to the Acland Grazing Trial (Bennett et al 2021;Clewett et al 2021;Melland et al 2021) established in 2013. The aim was to assess the sustainability and economic viability of beef cattle production from lands that were rehabilitated after open-cut coal mining, compared with surrounding unmined lands (Newsome et al 2014).…”