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Bioenergy production using woody biomass is a major climate change mitigation strategy but is often considered in terms of competitive effects on water. This paper describes the use of a short-rotation biomass system (Phase Farming with Trees PFT or 'Kamikaze Forestry') to manage water in dryland farming systems where this has accumulated below the root zone and has on and off-site environmental impacts. This excess water can be utilized for growth by deep-rooted, high-density biomass plantations inserted as short rotations into agricultural land. The objective is to promote rapid growth and mining of deep stored water through strategies such as high planting densities, the use of fast-growing species or fertilization each of which increases leaf area. Once the water is used, the trees are harvested and excess water is allowed to build up again in the subsequent cropping phase. Biomass production and water depletion were measured in a five-year rotation of trees inserted into a dryland (367 mm yr−1 mean annual rainfall) cereal farming system in south-western Australia. Both were markedly affected by tree age, planting density, and landscape position on a very minor slope. The greatest biomass production was achieved with high-density (4000 stems ha−1) plantings of Eucalyptus occidentalis and Eucalyptus globulus in lower landscape positions. High-density plots of these species in mid and upper landscape positions succumbed to drought after 3-4 years, but depleted available soil water to depths of >8 m, equivalent to 771 mm of stored available water. These results suggest that biomass yield can be readily manipulated through planting density and site selection. Moreover, biomass production can produce positive water management co-benefits. [ABSTRACT FROM AUTHOR]

When planning sampling in an experiment where soil organic carbon (SOC) content is expected to change, it is necessary to know how many samples will need to be taken to demonstrate a change in Soc and after how long this change will be detectable. Much has been published on the number of samples required to demonstrate the minimum detectable difference in SOC. but less on how long it takes for this change to be detectable. In this paper, a model of SOC dynamics is used to estimate the minimum time taken for a change in total SOC content to become measurable under different carbon inputs, land uses and soil types. For free air carbon dioxide enrichment (FACE), and other experiments in which SOC is expected to increase, relationships between the percentage change in C inputs and the time taken to measure a change in SOC are presented, for two levels of sampling intensity corresponding to the maximum that is practically possible in most experiments (∼100 samples) and that used regularly in field experiments (10-20 samples). In FACE experiments, where C inputs increase by a maximum of about 20-25%, SOC change could be detected with 90% confidence after about 6-10 years if a sampling regime allowing 3% change in background SOC level (probably requiring a very large number of samples) were used, but could not be detected at all if a sampling regime were used that allowed only a 15% change in background SOC to be detected. If increases in C inputs are much below 15%, it might not be possible to detect a change in soil C without an enormous number of samples. Relationships between the change in C inputs and the time taken to measure a change in SOC are robust over a range of soil types and land uses. The results demonstrate how models of SOC dynamics can be used to complement statistical power analyses for planning when, and how intensively, to sample soils during experiments. An advantage of the modelling approach demonstrated here is that estimates of the minimum time taken for a change in soil carbon to become detectable can be made, even before any detailed soil samples are taken, simply from estimates of the likely increase in carbon inputs to the soil (via expected changes in net primary production). [ABSTRACT FROM AUTHOR]

SummaryUnder the Kyoto Protocol, the European Union is committed to a reduction in CO2 emissions to 92% of baseline (1990) levels during the first commitment period (2008–2012). The Kyoto Protocol allows carbon emissions to be offset by demonstrable removal of carbon from the atmosphere. Thus, land-use/land-management change and forestry activities that are shown to reduce atmospheric CO2 levels can be included in the Kyoto targets. These activities include afforestation, reforestation and deforestation (article 3.3 of the Kyoto Protocol) and the improved management of agricultural soils (article 3.4). In this paper, we estimate the carbon mitigation potential of various agricultural land-management strategies and examine the consequences of European policy options on carbon mitigation potential, by examining combinations of changes in agricultural land-use/land-management. We show that no single land-management change in isolation can mitigate all of the carbon needed to meet Europe's climate change commitments, but integrated combinations of land-management strategies show considerable potential for carbon mitigation. Three of the combined scenarios, one of which is an optimal realistic scenario, are by themselves able to meet Europe's emission limitation or reduction commitments. Through combined land-management scenarios, we show that the most important resource for carbon mitigation in agriculture is the surplus arable land. We conclude that in order to fully exploit the potential of arable land for carbon mitigation, policies will need to be implemented to allow surplus arable land to be put into alternative long-term land-use. Of all options examined, bioenergy crops show the greatest potential for carbon mitigation. Bioenergy crop production also shows an indefinite mitigation potential compared to other options where the mitigation potential is finite. We suggest that in order to exploit fully the bioenergy option, the... [ABSTRACT FROM AUTHOR]