Substances released from plant root system in drops or small quantities of carbohydrates, organic acids, vitamins and many other substances essential for life of soil micro-organisms.

The amount of roots

The part of the soil that can be penetrated by plant roots.

The precipitation discharged into stream channels from an area. The water that flows off the surface of the land without sinking into the soil is called surface runoff. Water that enters the soil before reaching surface streams is called groundwater runoff or seepage flow from groundwater.

Expression used to indicate that there are intricate interactions between soil properties i.e. diagnostic features (intrinsic and dynamic ones), environment (climate, weather, slope, etc.) and management (the analogue from crop production is G (genotype) x E x M), acknowledging that soil functions are never uniquely determined by just one of these three factors.

A non-sodic soil (see sodic soil) containing sufficient soluble salt to adversely affect the growth of most crop plants. The lower limit of electrical conductivity in the saturation extract of such soils is conventionally set at 4 dS m-1(at 25

Salt-affected soils with a high exchangeable sodium percentage (ESP) greater than 15%, pH usually less than 8.5; in general these soils are not suitable for agriculture.

Accumulation of soluble salts (more soluble than gypsum) in the upper soil layers (saline soil = soil containing enough soluble salts to negatively affect most crop plants, commonly 4000

Soil that has been adversely affected by the presence of soluble salts, with or without high amounts of exchangeable sodium. See also saline soil, saline-sodic soil, and sodic soil.

Soil particles being 0.06-2.0 mm in diameter with low specific area OR a soil textural class with 65% or more sand and less than 8% clay. Unlike clays, sandy soils do not shrink and swell on drying and wetting and, unless artificially compacted, are rapidly permeable. (NB: USDA classification uses 0.05 instead of 0.06).