ABSTRACT
The primary function of agricultural soils is for food, feed, fibre and fuel production. Management measures in agricultural soils should therefore focus on improving and/or sustaining this function, in both the short and long term in a sustainable manner. Both agricultural crop production and crop quality are closely linked to soil quality (i.e. soil fertility). This is largely determined by factors including nutrient and water supply, but the soil’s suitability as a growth medium for roots and as a habitat for soil organisms is also important. These factors are all dependant on a multitude of bio-physical, chemical and environmental factors. Nutrient supply is dependent on fertilisation (e.g. synthetic supplies of essential plant nutrients) and decomposition (via mineralisation by soil microbes) of soil organic matter and organic amendments (e.g. animal manure, compost and crop residues) and the buffering capacity of nutrients (Box 4.2). Water supply is determined by weather conditions, irrigation and soil physical properties including soil texture and soil structure (see Box 4.1). Soil organic matter is crucial to both nutrient and water supply in many soils, while a good soil structure can enhance both root growth and the ability of the plants to utilise available nutrients and water in the soil. Soils containing low amounts of soil organic matter require higher inputs of chemicals and irrigation, and the long-term sustainability of high-input farming is now under scrutiny. It is widely hypothesised that the high-input farming typical of much of agriculture (largely reliant on plentiful water supplies and chemical fertilisers whose manufacture uses a lot of energy) will not be sustainable in the long term and that new approaches to farming are now required.
