12 research outputs found
Linking evapotranspiration seasonal cycles to the water balance of headwater catchments with contrasting land uses
Land use affects evapotranspiration rates and is a primary driver of the catchment water balance. The water balance of two catchments in southeastern Australia dominated by either grazed pasture or blue gum (Eucalyptus globulus) plantation was studied, focusing on the patterns of evapotranspiration (ET) throughout the year. Rainfall, streamflow, and groundwater levels measured between 2015 and 2019 were combined to estimate annual ET using a water balance equation. In the pasture, eddy covariance was used to measure ET from the catchment. Sap flow measurements were used to estimate tree transpiration in May 2017–May 2018 and Feb 2019–Feb 2021 in two different plots within the plantation. The tree transpiration rates were added to interception, estimated as a percentage of annual rainfall, to calculate ET from the plantation catchment. ET in the pasture showed strong seasonal cycles with very low ET rates in summer and ET rates in spring that were larger than the transpiration rates in the plantation, where trees transpired consistently throughout the year. The estimated annual ET from the water balance equation was comparable to ET estimated from other measurements. In the pasture, ET on average accounted for 88% of annual rainfall, while ET in the plantation was on average 93% of rainfall, exceeding it in the years with annual rainfall lower than about 500 mm. The difference between the ET rates in the plantation and the pasture was approximately 30–50 mm y−1. The larger ET rates in the plantation were reflected in a gradual decrease in the groundwater storage. The larger ET rates were enough to cause a decrease in groundwater storage in the plantation but not in the pasture, where groundwater levels remained stable
An SMS and Email Weather Warning System for Sheep Producers
Part 2: Information Systems, Information Modelling and SemanticsInternational audienceSheep are vulnerable to hypothermia shortly after birth and shearing. Since the 1970’s sheep weather alerts have been reported at a regional scale by the media up to 24 hours prior to a chill event. The SMS and email weather warning system was designed as an enhanced service to provide sheep producers with advanced warnings of forth-coming chill events, based on local weather forecasts, with personalized chill warnings delivered by SMS and email. A trial was conducted with 30 sheep producers who selected one or more local weather stations and a low, medium or high sensitivity threshold to control the frequency at which messages were sent. Sensitivity thresholds were calculated for each weather station from historical data. Numerical forecast data were sourced from the Bureau of Meteorology, and an email and SMS sent each morning whenever forecast chill exceeded the warning threshold within the 7-day forecast period. Participants were interviewed by telephone after a 2-month trial. The alerts were found to be clear and reasonably accurate, but produced an unexpected high number of false warnings at some sites. The SMS format was well received, and farmers were generally happy to continue the trial. False warnings were attributed to over-prediction of wind speeds at some sites relative to on-ground weather stations, most of which were in northern Victoria
Modelling Waterlogging Impacts on Crop Growth: A Review of Aeration Stress Definition in Crop Models and Sensitivity Analysis of APSIM
Currently, crop physiological responses to waterlogging are considered only in a few crop models and in a limited way. Here, we examine the process bases of seven contemporary models developed to model crop growth in waterlogged conditions. The representation of plant recovery in these models is over-simplified, while plant adaptation or phenotypic plasticity due to waterlogging is often not considered. Aeration stress conceptualisation varies from the use of simple multipliers in equations describing transpiration and biomass to complex linkages of aeration-deficit factors with root growth, transpiration and nitrogen fixation. We recommend further studies investigating more holistic impacts and multiple stresses caused by plant behaviours driven by soils and climate. A sensitivity analysis using one model (a developer version of APSIM) with default parameters showed that waterlogging has the greatest impact on photosynthesis, followed by phenology and leaf expansion, suggesting a need for improved equations linking waterlogging to carbon assimilation. Future studies should compare the ability of multiple models to simulate real and in situ effects of waterlogging stress on crop growth using consistent experimental data for initialisation, calibration and validation. We conclude that future experimental and modelling studies must focus on improving the extent to which soil porosity, texture, organic carbon and nitrogen and plant-available water affect waterlogging stress, physiological plasticity and the ensuing temporal impacts on phenology, growth and yield
Modelling Waterlogging Impacts on Crop Growth: A Review of Aeration Stress Definition in Crop Models and Sensitivity Analysis of APSIM
Currently, crop physiological responses to waterlogging are considered only in a few crop models and in a limited way. Here, we examine the process bases of seven contemporary models developed to model crop growth in waterlogged conditions. The representation of plant recovery in these models is over-simplified, while plant adaptation or phenotypic plasticity due to waterlogging is often not considered. Aeration stress conceptualisation varies from the use of simple multipliers in equations describing transpiration and biomass to complex linkages of aeration-deficit factors with root growth, transpiration and nitrogen fixation. We recommend further studies investigating more holistic impacts and multiple stresses caused by plant behaviours driven by soils and climate. A sensitivity analysis using one model (a developer version of APSIM) with default parameters showed that waterlogging has the greatest impact on photosynthesis, followed by phenology and leaf expansion, suggesting a need for improved equations linking waterlogging to carbon assimilation. Future studies should compare the ability of multiple models to simulate real and in situ effects of waterlogging stress on crop growth using consistent experimental data for initialisation, calibration and validation. We conclude that future experimental and modelling studies must focus on improving the extent to which soil porosity, texture, organic carbon and nitrogen and plant-available water affect waterlogging stress, physiological plasticity and the ensuing temporal impacts on phenology, growth and yield
Integrating crop modelling and production economics to investigate multiple nutrient deficiencies and yield gaps
A method is described for integrating crop modelling and production economics to quantify optimum applications of multiple nutrients and yield gaps. The method is demonstrated for crop production in the high-rainfall zone of southern Australia. Data from a biophysical crop model were used to overcome the persistent problem of inadequate experimental data. The Mitscherlich function was expanded to accommodate four variable inputs – nitrogen, phosphorus, potassium and sulphur – and the expansion path was used to determine the economic optimum application of all four nutrients. Modelling revealed the state-contingent yield potential and the extent to which unrealised yield could be explained by profit-maximising behaviour and riskaversion by growers. If growers and their advisors were guided by the methods described, they would be better equipped to assess crop nutrient demands and limitations, predict yield potential, additional profit and the risks associated with high input systems in a variable climate. If scientists were more aware of the extra profits and the risks involved (as well as the quantitative relationships between inputs and outputs) when thinking about what to produce and how to do so, they would be more circumspect about the net benefits to be obtained from closing yield gaps
Temperature and Temperature Humidity Index Changes during Summer to Autumn in a Temperate Zone May Affect Liveweight Gain and Feed Efficiency in Sheep
Lamb finishing during summer in southern Australia faces the challenges of dry paddock feed of low nutrient value and energy concentration, combined with periods of high temperature that reduce appetite. One potential forage to overcome these challenges is camelina, a brassica with a high lipid concentration. Liveweight gain (LWG) and feed efficiency (FE) of a pelleted diet containing 15% camelina hay (CAM) were compared with an equivalent diet based on oaten hay (STD), a feed commonly used during dry seasons. The experiment was conducted under summer to autumn conditions using 56 maternal Composite (Composite) wether lambs (4 months, 28–38 kg liveweight) and 56 Merino wether yearlings (15 months, 37–43 kg liveweight). Animals were maintained in group pens (8/pen) and weekly average feed intakes per pen and liveweights per pen were determined in a shaded well-ventilated animal house. The LWG and FE for both animal types were significantly lower during weeks 5–8 compared with weeks 1–4. These changes coincided with a higher proportion of daytime maxima exceeding 28 °C (50% vs. 21%) and night-time hours exceeding 22 °C (15% vs. 9%). The experiment indicated that the LWG and FE of sheep fed the CAM diet were less affected by the elevated temperatures than sheep fed the STD diet during weeks 5–8. However, further research under controlled environmental conditions is required to further validate these results
Modelling soil organic carbon 2. Changes under a range of cropping and grazing farming systems in eastern Australia
The level of soil organic carbon (SOC) that is attained under agriculture largely depends upon rates of carbon input and its decomposition under various agronomic practises such as stubble (crop residue) management and fertiliser application. In this study, we used the APSIM-Wheat and APSIM-Agpasture models to simulate changes in SOC in a range of crop and pasture management systems across nine locations in eastern Australia. We explored the extent to which various crop and pasture management options affect changes in SOC from a sub-tropical to a temperate environment. Specifically, we examined how nitrogen fertilisation, stubble management and stocking rate affect SOC and what strategies might be employed by farmers to increase SOC sequestration across eastern Australia. We modelled a continuous cropping regime, a continuously grazed pasture and a mixed cropping and pasture rotation. Under continuous cropping higher nitrogen application and higher amounts of stubble incorporation increased the SOC levels at all locations. At Roma, the northern-most site, there was little additional gain in SOC from increasing N above 70kgNha whereas most other sites showed benefits above 70kgNha. The biggest factor in boosting SOC under cropping was the level of stubble incorporation. At all but one site, continuously grazed pasture generally resulted in SOC increases over the 60years. However, increasing stocking rate decreased the rates of SOC changes at all sites. Crop-pasture rotations show that the impacts of even 4years of pasture is likely to be significant in reducing declining SOC at low nitrogen application during cropping phases. N fertilisation and stubble incorporation reduced the impact of stocking rate by reducing the decline in SOC. The difference in SOC changes between nine sites across eastern Australia was largely described by mean temperature and rainfall but high temperature strongly interacted with management practises (stocking rate, N application and residue incorporation) to reduce the sequestration of C despite favourable rainfall. Our results indicate that a mean annual temperature higher than about 20°C can switch a soil from net sink into a net source of atmospheric CO if other factors affecting soil carbon changes such as stubble incorporation, stocking rate and site rainfall are constant
Modelling soil organic carbon 1. Performance of APSIM crop and pasture modules against long-term experimental data
We used the APSIM model to explore the ability to simulate soil organic carbon (SOC) from three long term agricultural experiments (LTAE) over 24-44years in eastern Australia (Hamilton Victoria, Wagga Wagga New South Wales and Warwick Queensland). The model was initialized for each location soil type using a 20-year spin-up period to reach stable SOC fractions. The model was not tuned to any of the data at each site. The cropping systems model simulated reasonably well the calculated changes in SOC over the 24-44-year period at the three different sites under various agronomic management practices. At Hamilton calculated SOC did not change significantly over 32years and the APSIM-Agpasture model represented this satisfactorily. Root mean square error was 4.9tCha (0-30cm) (5.2%) ranging from 1.5 to 10.9tCha (1.7 to 11.8%) over time. Similarly, over twenty-four years of continuous cropping at Wagga Wagga under a Wheat-Lupin crop rotation using APSIM-Wheat and APSIM-Lupin under stubble retention and zero tillage showed a largely neutral trend over time with RMSE of 3.4tCha (0-30cm) (9.5%) ranging from 1.4 to 7.8tCha (4 to 21%) over time. The SOC was much lower at Wagga Wagga compared to that at Hamilton. Forty-four years of continuous cropping at the Queensland site resulted in significant declines in SOC irrespective of the farming practices applied. However, the rates of decline were different with the least decline achieved from high N application with stubble retention. The modelled changes, using APSIM-Wheat and APSIM-Barley, in SOC matched reasonably well the calculated behaviour with the greatest decline under zero N application with overall RMSE of 4.1tCha (0-30cm) (4.5%) ranging from 1.4 to 8.7tCha (2 to 7%) over time. The biophysical simulation model exemplified by the APSIM model explained well the observed changes in SOC at the various locations without specifically fitting the model to the observed data, despite large variation in the calculated data. This indicates that the SOC model was robust over the moderate to long term period. As such the model is suitable to extrapolate a simulated response beyond these locations under various treatment combinations that should predict realistic SOC stocks within the expected mean error of less than 10% (3 to 6tCha 0-30cm)