Louise Barton

Soil nitrous oxide and methane fluxes are low from a bioenergy crop (canola) grown in a semi-arid climate.

Understanding nitrous oxide (N2O) and methane (CH4) fluxes from agricultural soils in semi‐arid climates is necessary to fully assess greenhouse gas emissions from bioenergy cropping systems, and to improve our knowledge of global terrestrial gaseous exchange. Canola is grown globally as a feedstock for biodiesel production, however, resulting soil greenhouse gas fluxes are rarely reported for semi‐arid climates. We measured soil N2O and CH4 fluxes from a rain‐fed canola crop in a semi‐arid region of south‐western Australia for 1 year on a subdaily basis. The site included N fertilized (75 kg N ha−1 yr−1) and nonfertilized plots. Daily N2O fluxes were low (−1.5 to 4.7 g N2O‐N ha−1 day−1) and culminated in an annual loss of 128 g N2O‐N ha−1 (standard error, 12 g N2O‐N ha−1) from N fertilized soil and 80 g N2O‐N ha−1 (standard error, 11 g N2O‐N ha−1) from nonfertilized soil. Daily CH4 fluxes were also low (−10.3 to 11.9 g CH4‐C ha−1 day−1), and did not differ with treatments, with an average annual net emission of 6.7 g CH4–C ha−1 (standard error, 20 g CH4–C ha−1). Greatest daily N2O fluxes occurred when the soil was fallow, and following a series of summer rainfall events. Summer rainfall increased soil water contents and available N, and occurred when soil temperatures were >25 °C, and when there was no active plant growth to compete with soil microorganisms for mineralized N; conditions known to promote N2O production. The proportion of N fertilizer emitted as N2O, after correction for emissions from the no N fertilizer treatment, was 0.06%; 17 times lower than IPCC default value for the application of synthetic N fertilizers to land (1.0%). Soil greenhouse gas fluxes from bioenergy crop production in semi‐arid regions are likely to have less influence on the net global warming potential of biofuel production than in temperate climates.

Nutrient leaching and changes in soil characteristics of four contrasting soils irrigated with secondary-treated municipal wastewater for four years

Land treatment is the preferred option for the disposal of wastewater in New Zealand. We applied secondary-treated municipal wastewater to 4 contrasting soils (a Gley, Pumice, Recent, and Allophanic Soil) at the rate of 50 mm per week, for 4 years. Amounts of N and P in applied wastewater, leachates, and removed in herbage were measured every 1–4 weeks, and a range of soil chemical, biochemical and physical characteristics measured by destructive sampling after 2 and 4 years. After 4 years, leaching losses amounted to 290–307 kg N on the Gley and Recent Soils, representing approximately 22% of the N applied. Leaching losses from the Allophanic and Pumice Soils were 44 and 69 kg N/ha, respectively, representing <5% of that applied. More than half of the N leached was in organic forms. Leaching losses of P were <5 kg P/ha on the Pumice and Allophanic Soils (< 1% of that applied), 41 kg P/ha from the Recent Soil and 65 kg P/ha from the Gley Soil (8% and 13% of that applied, respectively). After 4 years, the total C and microbial C content in the A horizon of the irrigated Recent Soil were, respectively, 47% and 44% less than non-irrigated cores. All irrigated soils showed a rise in pH of up to 1 unit, and all had a marked increase in the exchangeable Na+ which reached 4–22% ESP. After 4 years, the saturated and near saturated hydraulic conductivity of the Gley Soil had declined from 567 and 40 mm/h to 56 and 3 mm/h, respectively. Allophanic and Pumice Soils are to be preferred over the Recent and Gley Soils for effective treatment of wastewater and to minimise the loss of nutrients to the wider environment.

Biodiesel production in a semiarid environment: a life cycle assessment approach.

While the use of biodiesel appears to be a promising alternative to petroleum fuel, the replacement of fossil fuel by biofuel may not bring about the intended climate cooling because of the increased soil N2O emissions due to N-fertilizer applications. Using a life cycle assessment approach, we assessed the influence of soil nitrous oxide (N2O) emissions on the life cycle global warming potential of the production and combustion of biodiesel from canola oil produced in a semiarid climate. Utilizing locally measured soil N2O emissions, rather than the Intergovernmental Panel on Climate Change (IPCC) default values, decreased greenhouse gas (GHG) emissions from the production and combustion of 1 GJ biodiesel from 63 to 37 carbon dioxide equivalents (CO2-e)/GJ. GHG were 1.1 to 2.1 times lower than those from petroleum or petroleum-based diesel depending on which soil N2O emission factors were included in the analysis. The advantages of utilizing biodiesel rapidly declined when blended with petroleum diesel. Mitigation strategies that decrease emissions from the production and application of N fertilizers may further decrease the life cycle GHG emissions in the production and combustion of biodiesel.

Simulating response of N2O emissions to fertiliser N application and climatic variability from a rain-fed and wheat-cropped soil in Western Australia

BACKGROUND Besides land management and soil properties, nitrous oxide (N(2)O) emissions from the soil may be responsive to climatic variation. In this study the Water and Nitrogen Management Model (WNMM) was calibrated and validated to simulate N(2)O emissions from a rain-fed and wheat-cropped system on a sandy duplex soil at Cunderdin, Western Australia, from May 2005 to May 2007, then it was deployed to simulate N(2)O emissions for seven scenarios of fertiliser N application under various climatic conditions (1970-2006). RESULTS The WNMM satisfactorily simulated crop growth, soil water content and mineral N contents of the surface soil (0-10 cm), soil temperatures at depths and N(2)O emissions from the soil compared with field observations in two fertiliser treatments during calibration and validation. About 70% of total N(2)O emissions were estimated as nitrification-induced. The scenario analysis indicated that the WNMM-simulated annual N(2)O emissions for this rain-fed and wheat-cropped system were significantly correlated with annual average minimum air temperature (r = 0.21), annual pan evaporation (r = 0.20) and fertiliser N application rate (r = 0.80). Both annual rainfall and wheat yield had weak and negative correlations with annual N(2)O emissions. Multiple linear regression models for estimating annual N(2)O emissions were developed to account for the impacts of climatic variation (including temperature and rainfall), fertiliser N application and crop yield for this rain-fed and wheat-cropped system in Western Australia, which explained 64-74% of yearly variations of the WNMM-estimated annual N(2) O emissions. CONCLUSION The WNMM was tested and capable of simulating N(2) O emissions from the rain-fed and wheat-cropped system. The inclusion of climatic variables as predictors in multiple linear regression models improved their accuracy in predicting inter-annual N(2)O emissions.

Evaluation of a soil moisture sensor to reduce water and nutrient leaching in turfgrass (Cynodon dactylon cv. Wintergreen)

This study evaluated water application rates, leaching and quality of couch grass (Cynodon dactylon cv. Wintergreen) under a soil moisture sensor-controlled irrigation system, compared with plots under conventional irrigation scheduling as recommended for domestic lawns in Perth, Western Australia by the State’s water supplier. The cumulative volume of water applied during summer to the field plots of turfgrass with the sensor-controlled system was 25% less than that applied to plots with conventional irrigation scheduling. During 154 days over summer and autumn, about 4% of the applied water drained from lysimeters in sensor-controlled plots, and about 16% drained from lysimeters in plots with conventional irrigation scheduling. Even though losses of mineral nitrogen via leaching were extremely small (representing only 1.1% of the total nitrogen applied to conventionally irrigated plots), losses were significantly lower in the sensor-controlled plots. Total clippings produced were 18% lower in sensor-controlled plots. Turfgrass colour in sensor-controlled plots was reduced during summer, but colour remained acceptable under both treatments. The soil moisture sensor-controlled irrigation system enabled automatic implementation of irrigation events to match turfgrass water requirements.

Granular wetting agents ameliorate water repellency in turfgrass of contrasting soil organic matter content

The effectiveness of four granular wetting agents to decrease water repellency in sandy soils of contrasting organic matter (OM) content and influences on kikuyugrass [Pennisetum clandestinum (Holst. Ex Chiov)] grown as turfgrass, were evaluated. A laboratory test assessed the wettability of two non-wetting soils (low OM, 4.7%; high OM, 17%) after treatment with granular soil wetting agents, with four being selected for field experimentation. A field experiment included two turfgrass ages (established from 20 week or 20 year old turfgrass in 2005; the latter included a 50 mm ‘mat’ layer and thus had high OM content in the surface soil), four granular soil wetting agents (plus a ‘nil’ as control), and five replicates. Surface soil (0–25 mm) water repellency, measured using the molarity of ethanol droplet test (MED), ranged from 0.4 M to 4.3 M during the irrigation season, and repellency was more severe in the soil with high OM (32%) content than low OM (8.6%) content. Soil wetting agents decreased the development of soil water repellency to varying extents, and maintained turfgrass quality; with improvement related to the amount of active ingredient applied. We recommend utilising an effective soil wetting agent, in combination with practices that limit the accumulation of soil OM, to decrease the severity and incidence of soil water repellency in turfgrass grown on sandy soils.