Human conversion of soils from natural to agricultural use has led to substantial reductions in the soil carbon sink. Greater soil disturbance, such as that caused by ploughing, can induce rapid respiration and loss of large amounts of soil carbon which would otherwise decompose more slowly. Sensitive land use practice is key to better balancing of the soil carbon sink, and perhaps to reversing recent trends of loss of carbon from soils. Farming practices such as 'no-till' - whereby agricultural land is used without the soil disturbance and carbon loss that comes with ploughing - are becoming more widespread and land use remains a key area of research in studies of anthropogenic greenhouse gas emissions and strategies to reduce them. Lemke and Janzen (Chapter 5, this volume) discuss the impact of no-till farming on emissions or removal of CO2, CH4 and N2O, considering the overall net effect on the earth's climate in both the short and long terms. By doing so, they demonstrate the importance of considering all of these climate-forcing emissions together when assessing the value of no-till agriculture as a climate change mitigation strategy.
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