Chapter 2. Impacts of Agriculture upon Soil Quality

Agriculture covers nearly 40% of the surface area of the earth and results in 30% of global greenhouse gas emissions and 70% of global water withdrawal. Soil quality plays a fundamental role in ensuring viable and sustainable agricultural production. The impacts on soil quality associated with agriculture include a decline in soil organic matter, compaction, erosion, soil biodiversity, contamination, soil sealing and soil salinisation. Soil organic matter forms the carbon store which is the fundamental element for living fauna in soils that also controls other chemical and physical processes. Intensive agriculture with heavy machinery and large livestock units has also caused soil compaction which is related to factors such as soil texture, packing density, moisture content and plasticity. Compacted soils are also more prone to erosion due to greater ease of runoff associated with the lack of surface roughness and a reduction in tendency for water to seep through the soil profile. Soil biodiversity acts as the engine that makes soil alive and functional in the many processes that it governs. Soil biodiversity is influenced by a wide range of factors including the physico-chemical environment (e.g. pH, temperature, water); the supply and availability of soil plant-derived inputs; managed inputs and indigenous organic matter; and the soil habitat. The sources of soil contaminants can be from diffuse or point source pollution and can be broadly classified as nutrients, heavy metals or organic pollutants. These soil contaminants can influence soil biodiversity. Soil sealing and salinisation only affect a small component of agricultural land.