Nitrogen use efficiency in summer sorghum grown on clay soils

Nitrogen fertilizer inputs dominate the fertilizer budget of grain sorghum growers in northern Australia, so optimizing use efficiency and minimizing losses are a primary agronomic objective. We report results from three experiments in southern Queensland sown on contrasting soil types and with contrasting rotation histories in the 2012-2013 summer season. Experiments were designed to quantify the response of grain sorghum to rates of N fertilizer applied as urea. Labelled 15N fertilizer was applied in microplots to determine the fate of applied N, while nitrous oxide (N2O) emissions were continuously monitored at Kingaroy (grass or legume ley histories) and Kingsthorpe (continuous grain cropping). Nitrous oxide is a useful indicator of gaseous N losses. Crops at all sites responded strongly to fertilizer N applications, with yields of unfertilized treatments ranging from 17% to 52% of N-unlimited potential. Maximum yields ranged from 4500 (Kupunn) to 5450 (Kingaroy) and 8010 (Kingsthorpe) kg/ha. Agronomic efficiency (kg additional grain produced/kg fertilizer N applied) at the optimum N rate on the Vertosol sites was 23 (80 N, Kupunn) to 25 (160N, Kingsthorpe), but 40-42 on the Ferrosols at Kingaroy (70-100N). Cumulative N2O emissions ranged from 0.44% (Kingaroy legume) to 0.93% (Kingsthorpe) and 1.15% (Kingaroy grass) of the optimum fertilizer N rate at each site, with greatest emissions from the Vertosol at Kingsthorpe. The similarity in N2O emissions factors between Kingaroy and Kingsthorpe contrasted markedly with the recovery of applied fertilizer N in plant and soil. Apparent losses of fertilizer N ranged from 0-5% (Ferrosols at Kingaroy) to 40-48% (Vertosols at Kupunn and Kingsthorpe). The greater losses on the Vertosols were attributed to denitrification losses and illustrate the greater risks of N losses in these soils in wet seasonal conditions

Improving the simulation of soil temperature within the EPIC model

International audienceSoil temperature is a key driver of several physical, chemical, and biological processes. The Environmental Policy Integrated Climate (EPIC) is a comprehensive ecosystem model that simulates soil temperature dynamics using a cosine function approach driven by daily air temperature and average annual soil temperature at damping depth,which may erroneously predict lower soil temperatures in winter. A new cosine model and a pseudo-heat-transfer model were therefore developed and implemented for simulating soil temperature. The two methods were evaluated by comparing simulated daily soil temperatures with observed data at 24 study sites. Results showed that the two new methods had similar performance and the better statistical results obtained with these new methods demonstrated the ability to better predict the soil temperature for a wide range of pedoclimatic conditions, land management, and land uses. The main reason for the improved performance was due to a better prediction of soil temperature during the winter period

Multi-metric evaluation of an ensemble of biogeochemical models for the estimation of organic carbon content in long-term bare fallow soils

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