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'

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 sub-tropical sub-humid inland climate of the Condamine region is favourable for growing sub-tropical grass-legume sown pastures in most years. The long-term average rainfall for the region is 672 mm. Weather conditions during the trial period were variable with several extended periods of hot and dry drought conditions; particularly in 2013 and 2014. The modelling and simulation studies were an important tool for overcoming the influences of climate variability on results, as well as reasonable inferences due to the short term duration of the project. The mean observed value of soil carbon (0-30 cm) across all trial sites was 1.13%. Values ranged from 0.63 to 0.88 % carbon (31 to 35 t/ha) on light sandy soils of the Brigalow and Alluvial plains to an average of 1.68 % carbon (52 t/ha) for the black cracking clays of the Basalt uplands with some values up to 2.16%. 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. Use of legume-based sown pastures in the GRASP simulation experiments was estimated to maximise economic returns at all sites. At the optimum grazing pressure the mean gross margin across all sites of legume-based sown pasture was $78.60/ha compared to$44.50/ha and $40.50/ha respectively for sown grass pastures and native pasture. Soil carbon sequestration rates were estimated from simulation modelling to be much higher in the first decade after planting a sown pasture than in later decades. This reflected changes in pasture productivity associated with pasture rundown and the progress of soil carbon levels towards new equilibrium conditions. In 50 year simulations (repeated for four different time periods at each site), the mean carbon sequestration of sown grass pastures for the first decade was 459 kg/ha/year compared with 10, 15 and -36 kg/ha/year over the last three decades. Grass-legume pastures had the highest carbon sequestration rates. They were estimated to sequester an average of 595 kg/ha/year for the first decade after sowing and 113 for the second decade. This was followed by an average of 32 kg/ha/year over the last three decades. 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 • the difference was greater for sown grass-legume pastures. Legume-based sown pastures increased carbon sequestration relative to native pasture by 1411 kg CO2e /ha compared with the much lower increase in methane emissions of 127 kg CO2e /ha. 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. Key messages communicated to producers at a series of field days in March 2015 were: • Degraded crop and grazing lands are improved through establishment of legume-based pastures with bonus payoffs in production, carrying capacity, economic returns, and GHG emissions and sequestration rates. • Sown pastures are usually most productive in the first few years after planting and then gradually decline in productivity (known as 'pasture rundown' ) in the following years because of nutrient limitations mainly nitrogen • Maintaining legumes in pastures increases soil nitrogen, pasture growth and cattle production. • Legumes can help to offset pasture rundown. • While droughts cause significant losses in some years, nitrogen is limiting in most years. • Stocking rates should aim to utilise 25 to 30 % of pasture growth. • Increased pasture production builds soil carbon which improves soil health. The study has highlighted several concepts that include the following: • 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 • Legume contributions of nitrogen to foster additional grass growth were important at all sites to either offset or overcome the effects of pasture rundown. They enable production to plateau at a higher level than grass only pastures, which emphasises the importance of legumes in sown pastures. • Legumes are a relatively minor cost when establishing a sown pasture but they contribute greatly to the profitability of sown pastures. This highlights the value of developing technologies to improve the reliability and resilience of agricultural practices to successfully establish and maintain palatable legume-based sown pastures. Lucerne was demonstrated to be a highly successful legume for pastures on the heavier clay soils of the Condamine region, however, more summer active legumes might give additional benefits in the regions summer dominant rainfall climate. The summer growing legumes, shrubby stylos, particularly Caatinga stylo, desmanthus, Wynn cassia, fine-stem stylo and leucaena are options that should be considered. The sown pastures version of the GRASP model has proved to be a useful tool in several ways. Firstly, it provided a mechanism to integrate information from the trial sites and elsewhere which was then used to interpolate and extrapolate data across sites, time periods and levels of output relevant to industry. Secondly, the simulation results are providing industry with information for discussion that would be otherwise not available, and thirdly GRASP and the sown pastures version of GRASP are providing a platform that may well be useful to other projects. 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. The need for this work to continue is accentuated by the continuing rise of carbon dioxide levels in the atmosphere and resulting effects on rising global temperatures and increased climate variability, and also to clarify issues concerning the storage of carbon in soils as a greenhouse gas abatement strategy

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

Context: New Acland coal mine in south-eastern Queensland is seeking to rehabilitate mined land to pastures that are safe, stable and sustainable for beef production. Little is known of the productivity and sustainability of grazing previously mined land in the Darling Downs study region. Additionally, information is required to specify management guidelines for sustainable grazing of regional land types retired from cultivation. Aims: Identify pasture growth characteristics, rainfall use efficiencies and long-term carrying capacities of subtropical sown pastures established on lands rehabilitated after open-cut coal mining in comparison to sown pastures established on un-mined but previously cultivated lands. Methods: Pasture growth and quality (% nitrogen) were observed using the Swiftsynd methodology in ungrazed exclosures with three sites on rehabilitated lands of the Acland Grazing Trial over a 5-year period (2014–2018), and 13 sites on unmined lands over periods of 2–5 years providing data for modelling pasture growth. Key results: Peak pasture yield (TSDM for autumn harvests) averaged for 2017 and 2018 was greater (P < 0.1) on rehabilitated sites than unmined Poplar Box land type sites (5957 and 2233 kg/ha respectively) but similar to Brigalow Uplands and Mountain Coolibah land type sites (3946 and 3413 kg/ha respectively). Pasture rundown was evident, with pasture N uptake decreasing over 5 years at some sites. Soil mineral N supply (potentially mineralisable N and mineral N) in spring was a useful indicator of N uptake over the following growing season. Simulations using the GRASP pasture growth model for the grazing trial period predicted rainfall use efficiencies of 12.0, 7.0, 9.1 and 4.8 kg/ha.mm rainfall for rehabilitated sites and unmined sites on Brigalow Uplands, Mountain Coolibah and Poplar Box land types respectively. Long-term carrying capacities based on estimates of long-term median pasture growth and 30% utilisation were 4.39, 3.58 and 5.92 ha/adult equivalent respectively for the unmined land types, and 2.45 ha/adult equivalent for the rehabilitated lands. Conclusions: Rehabilitated land can be as productive as unmined but previously cultivated land. Implications: Grazing management plans for sustainable management of mined and unmined lands can be developed using data from the present study. The plans will assist with the transition of rehabilitated lands to commercial agriculture

Sustainability of beef production from brigalow lands after cultivation and mining. 3. Pasture rundown, climate and grazing pressure effects

Context: The Acland Land System overlying the Walloon sandstone coal deposits in southern Queensland is generally marginal for cropping but well suited to grazing, and thus cultivated land is commonly returned to pasture. Rehabilitation of these lands after open-cut coal mining seeks to be safe, stable and self-sustaining to satisfy requirements for ecologically sustainable development. Aims: The present paper evaluates the sustainability and economic viability of beef production on (a) lands retired from cultivation and then rehabilitated with sown pastures after open-cut coal mining at the New Acland mine site, and (b) similar nearby pasture lands that were not mined but were also retired from cultivation. Methods: The GRASP grazing systems model was modified and calibrated with short-term (5-year) grazing trial data (soil, pasture and cattle observations), and then used with long-term (60-year) weather data to estimate effects of land type, pasture rundown, climate and grazing pressure on productivity and economic returns. The productivity of three rehabilitated sites and 15 unmined sites were evaluated, including pastures on six commercial properties. Key results: Estimates of long-term mean annual growth of pastures on unmined lands retired from cultivation on three land types (Mountain Coolibah, Brigalow Uplands and Poplar Box) were 3398, 2817 and 2325 kg/ha respectively. Pasture growth was greater on rehabilitated lands; 3736 kg/ha on the site most typical of rehabilitated lands and a mean of 4959 kg/ha across three sites. Seasonal conditions had large effects on cattle liveweight gain (133–213 kg/head per year during the trial); however, pasture growth was the main driver of beef production and economic returns per hectare. In GRASP, potential nitrogen uptake was used to influence key pasture growth processes and accounted for 64% of variation in observed annual growth. The short-term lift and subsequent rundown in productivity typically associated with sown pastures was estimated to have increased mean annual pasture and cattle productivity during the 2014–2018 trial period by up to 17% and 25% respectively. Estimates of long-term mean annual beef production and economic returns for the unmined lands were less than estimated for rehabilitated lands and were 139 kg/head.year (45 kg/ha.year) and AU$154/adult equivalent. Conclusions: Rehabilitated lands were found to be sustainable for beef production at grazing pressures up to 30% utilisation of annual pasture growth, and comparable with grazing systems on native and sown pastures in good condition. Pastures on unmined lands retired from cultivation had reduced productivity. Implications: Overgrazing is a significant and on-going residual risk to sustainable production. Grazing regimes need to continually adjust for changes in novel landscapes, pasture condition and climate. The methods used in the present study could be applied more generally

Enhancement of the Electron Spin Resonance of Single-Walled Carbon Nanotubes by Oxygen Removal

We have observed a nearly fourfold increase in the electron spin resonance (ESR) signal from an ensemble of single-walled carbon nanotubes (SWCNTs) due to oxygen desorption. By performing temperature-dependent ESR spectroscopy both before and after thermal annealing, we found that the ESR in SWCNTs can be reversibly altered via the molecular oxygen content in the samples. Independent of the presence of adsorbed oxygen, a Curie-law (spin susceptibility $\propto 1/T$) is seen from $\sim$4 K to 300 K, indicating that the probed spins are finite-level species. For both the pre-annealed and post-annealed sample conditions, the ESR linewidth decreased as the temperature was increased, a phenomenon we identify as motional narrowing. From the temperature dependence of the linewidth, we extracted an estimate of the intertube hopping frequency; for both sample conditions, we found this hopping frequency to be $\sim$100 GHz. Since the spin hopping frequency changes only slightly when oxygen is desorbed, we conclude that only the spin susceptibility, not spin transport, is affected by the presence of physisorbed molecular oxygen in SWCNT ensembles. Surprisingly, no linewidth change is observed when the amount of oxygen in the SWCNT sample is altered, contrary to other carbonaceous systems and certain 1D conducting polymers. We hypothesize that physisorbed molecular oxygen acts as an acceptor ($p$-type), compensating the donor-like ($n$-type) defects that are responsible for the ESR signal in bulk SWCNTs.Comment: 14 pages, 7 figure

El Nino southern oscillation based rainfall forecasts in southern Africa. II. daily forecasts could help summer planting decisions in Zimbabwe

Analysis of historical data of daily rainfall for Harare showed that El Nino Southern Oscillation (ENSO) impacts on the timing of break-of-dry season and follow-up rainfall as well as the frequency of rain events during summer (Nov-Mar). The Southern Oscillation Index (SOI) was a useful indicator of the timing and frequency of these events, defined as 40mm of rainfall in 3 days. Median dates for the first and second events were 1 December and 17 December respectively; ENSO contributed to a shift in these dates of about 2 weeks. The percent chance of receiving break-of-season rainfall by 1 December during La Nina years was 67% compared to 30% in El Nino years. Maize is a staple food in Zimbabwe and delaying planting after 1 December can result in lower yields. Communal farmers could benefit from this apparent ENSO signal in Zimbabwe by adjusting crop variety, planting time and fertilizer rate. However, poor spatial coverage of long-term (>80 years) daily rainfall data in Zimbabwe limits widespread application

Needs for applied climate education in agriculture

This paper reports on a purposive survey study aimed at identifying needs for the development, delivery and evaluation of applied climate education for targeted groups, so as to improve knowledge and skills to better manage the variable climate. The survey sample consisted of 80 producers and other industry stakeholders in Australia (including representatives from consulting and agricultural extension, and agricultural education sectors), with a 58% response rate to the survey. The survey included an assessment of (i) knowledge levels of the Southern Oscillation Index (SOI) and sea surface temperature’s (SST’s), (ii) skill/ability in interpreting weather/climate parameters. Results showed that despite many of the respondents having more than twenty years experience in their industry, the only formal climate education or training undertaken by most was a one-day workshop. While over 80% of the applied climate skills listed in the survey were regarded by respondents as essential or important, only 42% of educators, 30% of consultants and 28% of producers rated themselves as competent in applying such skills. Essential skills are deemed as those that would enable respondents or their clients to be better prepared for the next extended wet or dry meteorological event, and improved capability in identifying and capitalising on key decision points from climate information and a seasonal climate outlook. The complex issue of forecast accuracy is a confounding obstacle for many to apply climate information and forecasts in management. Addressing this problem by describing forecast ‘limitations and skill’ can help to overcome this problem. The survey also highlighted specific climatic tactical and strategic information collated from grazing, cropping, and agribusiness enterprises and shows the value of such information from a users perspective