Mitigation of carbon using Atriplex nummularia revegetation

The use of abandoned or marginally productive land to mitigate greenhouse gas emissions may avoid competition with food and water production. Atriplex nummularia Lindl. is a perennial shrub commonly established for livestock forage on saline land, however, its potential for carbon mitigation has not been systematically evaluated. Similarly, although revegetation is an allowable activity to mitigate carbon within Article 3.4 of the United Nations Framework Convention on Climate Change's Kyoto Protocol, there is a paucity of information on rates of carbon mitigation in soils and biomass through this mechanism. For six sites where A. nummularia had been established across southern Australia four were used to assess changes in soil carbon storage and four were used to develop biomass carbon sequestration estimates. A generalised allometric equation for above and below ground biomass was developed, with a simple crown volume index explaining 81% of the variation in total biomass. There were no significant differences in soil organic carbon storage to 0.3 m or 2 m depth compared to existing agricultural land-use. Between 2.2 and 8.3 Mg C ha−1 or 0.2–0.6 Mg C ha−1 yr−1 was sequestered in above and below ground biomass and this translates to potential total sequestration of 1.1–3.6 Tg C yr−1 on saline land across Australia. Carbon income and forage grazing may thus provide a means to finance the stabilization of compromised land

Measuring and modeling the water balance of low rainfall cropping systems

In low rainfall cropping systems, understanding the water balance and in particular the storage of soil water in the rooting zone for use by crops, is considered as critical information for devising risk management strategies for grain-based farming. Crop-soil modelling approaches remain a cost-effective option to understand the interactions between rainfall, soil and crop growth from which management options can be derived. The objective of this study was to assess error in the prediction of soil water content at key decision points in the season against continuous, multi-layer soil water measurements made with frequency domain reflectometry (FDR) probes in long-term experiments in the Mallee region of South Australia and New South Wales. Using field estimates of crop lower limit or drained upper limits were found to be more reliable than lab-based estimates despite the fact that plant available water capacity (PAWC) between the methods did not substantially differ. Using the Agricultural Production Systems sIMulator (APSIM) to simulate plant available water over three year rotations, predicted soil water was within 7 mm (PAWC 64 – 99 mm) of the measured data across all sowing events and rotations. Simulated (n=46) wheat grain production resulted in a root mean square error (RMSE) of 492 kg/ha which is only marginally smaller than other field studies deriving soil water limits from less detailed methods. The paper shows that using field derived data of soil water limits and soil specific settings for parameterisation of other properties determining soil evaporation and water redistribution enables the APSIM model to be widely applied to managing climate risk in low rainfall environments

Integrating Agent Models and Dynamical Systems

Abstract. Agent-based modelling approaches are usually based on logical languages, whereas in many areas dynamical system models based on differential equations are used. This paper shows how to model complex agent systems, integrating quantitative, numerical and qualitative, logical aspects, and how to combine logical and mathematical analysis methods.