Pasture measurements and bio-economic analyses to assess effects of climate, grazing pressure and pasture rundown on soil carbon and returns from legume-based sown pastures in the Condamine region of Southern Queensland. Final Report on project AOTGR1-137 'Increasing soil carbon in degraded cropping and grazing land'
Technical report
Title | Pasture measurements and bio-economic analyses to assess effects of climate, grazing pressure and pasture rundown on soil carbon and returns from legume-based sown pastures in the Condamine region of Southern Queensland. Final Report on project AOTGR1-137 'Increasing soil carbon in degraded cropping and grazing land' |
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Report Type | Technical report |
Authors | |
Author | Clewett, J. F. |
Institution of Origin | Agroclim Pty Ltd |
Number of Pages | 74 |
Year | 2015 |
Publisher | Agroclim Pty Ltd |
Place of Publication | Toowoomba, Australia |
Abstract | The Condamine catchment has been identified as a key area in Australia where there is potential to build soil carbon. There are approximately 1 million hectares of degraded crop and grazing lands in the region that could be potentially improved through establishment of sown pastures, particularly legume-based pastures that have capacity to add nitrogen, lift productivity and build soil carbon. This document provides a final report on several sub-components for the Condamine Alliance project “Increasing soil carbon in degraded cropping and grazing Land (AOTGR1-137)”. The overall objectives of this project were to measure, assess and communicate the impact and feasibility of practices for increasing soil carbon sequestration in cropping and grazing land in the Condamine catchment. Field studies from July 2012 to March 2015 at nine trial sites tested the value of returning crop land to pasture, renovation of pastures and the use of manure and inorganic fertilizer. As part of the overall project, the objectives addressed in this report focus on bio-economic analyses to assess the value of sown pastures in the Condamine region in terms of their capacity to build soil carbon and provide significant economic benefits to industry. The influence of seasonal conditions, land type and management were considered. This included the effects of grazing pressure, manure, fertilizer and importantly the use of legumes. A sown pastures version of the GRASP grazing systems model was used to estimate the effects of season and management on pasture growth and condition, beef production, economic returns, soil carbon sequestration and green-house gas emissions. Nitrogen available for pasture growth was a key component of the model concerning effects of pasture rundown and the influence of legumes. Potential effects of other nutrient limitations particularly phosphorous were recognised but not included in simulation analyses. Soil tests and pasture measurements of net primary production from exclosures and pasture yield/composition from grazed paddocks at the trial sites were used to calibrate and test the modelling process. The mean annual growth of pastures across all sites, pastures, grazing pressures and climatic conditions was estimated to be 3076 kg/ha. This mean was substantially higher on the more fertile clay soils of the region’s Basalt Uplands (3898 kg/ha) but lower on less fertile loam soils of Alluvial Plains (2648 kg/ha) and the sandstone derived soils of the Brigalow Uplands (2708 kg/ha). The optimum commercial grazing pressure in terms of maximum economic return per hectare was estimated to be 25 to 30% utilisation of pasture growth and this was consistent across all trial sites and land types. Lower utilisation levels were estimated to increase live weight gains per head but this reduced overall economic returns. Higher utilisation levels increased short-term economic gain but were likely to cause detrimental effects on pasture condition if persistently used, and also reduce live weight gains per head. This led to lower gross margins and would ultimately lead to reduced soil carbon. Cattle methane emissions were calculated on the basis of dry matter intake. Estimates from GRASP simulations showed that sown pastures should help to reduce green-house gas emissions because: • the additional mean annual soil carbon sequestered by sown grass pastures (relative to native pasture) was 412 kg CO2e /ha and this was substantially more than the corresponding increase in methane emissions (58 kg CO2e/ha) due to higher stocking rates Nitrous oxide emissions as CO2e were estimated from legumes (due to nitrogen fixation) and from livestock urine and faeces due to increased stocking rate on sown pastures. These estimates were low in comparison to carbon sequestration and were lower than methane emissions. • Pasture rundown is a consistent feature of sown pastures in grazing systems and therefore needs to be taken into account in farm management planning processes and carbon sequestration rate calculations The Condamine Catchment is a highly productive agricultural region and this study has shown that it has the potential to significantly increase soil carbon over a large area with legume-based pastures. The region stands out as an area in Australia to continue work to demonstrate, test the value and seek adoption of sown pastures. Therefore it is recommended that further work be conducted in this field to work with the farming community in planned extension programs to demonstrate the advantages of legume-based pastures for increasing productivity, building soil carbon and improving economic returns. This work should integrate field studies, analyses and communications that emphasise farming practices that help to overcome risks including the risks that are linked with agronomy, grazing management, financial issues and climate variability. |
Keywords | sown pasture productivity, soil carbon, GRASP model, climate impacts, grazing management, Queensland pastures |
ANZSRC Field of Research 2020 | 300205. Agricultural production systems simulation |
300207. Agricultural systems analysis and modelling | |
300499. Crop and pasture production not elsewhere classified | |
Byline Affiliations | Agroclim, Australia |
https://research.usq.edu.au/item/q4xq3/pasture-measurements-and-bio-economic-analyses-to-assess-effects-of-climate-grazing-pressure-and-pasture-rundown-on-soil-carbon-and-returns-from-legume-based-sown-pastures-in-the-condamine-region-of
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