Feeding the future – sustainable agriculture
biodiversity. A measure of the variety of life. It is usually calculated from the number of species of organisms although genera, families, classes and phyla can all be counted too.
biofumigation. The suppression of soil-borne pests and pathogens by the use of plants that contain inhibitory chemicals. The plants can be harvested as rotation crops or ploughed back into the soil as green manure.
biological control. A strategy for the control of pests or disease-causing organisms that relies on the use of other living organisms rather than chemical pesticides.
'living' soil. A healthy soil that contains living organisms. These organisms (biota) are important to the health of soil, and a gram of healthy agricultural soil can contain several million micro-organisms. Productive soil is made up of mineral particles; organic matter in the form of decaying parts of plants and animals and the waste products of living things; and hundreds of millions of micro-organisms and other living things (eg, nematodes, arthropods, worms).
monoculture. The cultivation of a single crop, usually on a large area of land and on a commercial trading basis.
nitrogen cycle. The continuous natural cycle by which nitrogen passes from the atmosphere to soil to organisms and back to the atmosphere.
nitrogen fixation. The process of producing nitrogen compounds by combining nitrogen from the air with other substances. The only organisms that can use nitrogen gas to make organic molecules are a few kinds of bacteria. Most nitrogen-fixing bacteria live in the soil or water, but some species live in nodules on the roots of legumes such as lucerne, peas, beans and clovers.
pesticide treadmill. A situation in which farmers apply a pesticide to control a pest, which then develops resistance. Pest numbers increase, so more frequent applications of pesticide are needed for control. Finally the pesticide performs so poorly that farmers introduce a new pesticide. Over time the cycle (treadmill) is repeated with the new pesticide.
pH. The pH scale is used to measure the strength of acids and bases (or alkalis). The acid strength in the human stomach is about pH 2. Alkalis such as caustic soda and basic household cleaners have a pH of about 12 to 14. Neutral is pH 7, (ie, neither acidic or alkaline). The scale is logarithmic, so pH 4 is ten times as acidic as pH 5 and pH 2 is ten times as acidic as pH 3, and so on. For more information see About soil pH (National Aeronautics and Space Administration, USA).
water table. The top level of water in the ground that occupies spaces in rock or soil and lies above a layer of impermeable (non-porous) rock. When the water table rises above ground level a spring, lake or wetland is formed.
Posted September 2001.