Absorbability (Q) is a new concenpt which is derived from absorbance of determining nitrate nitrogen in soil by UV spectrophotometry for characterizing the contents of nitrate nitrogen and soluble organic nitrogen in soils.Absorbance indiGates only the concentration of a light-absorbing component in solution rather than the content of this component in sample (e.g.,soil sample).Absorbability may be used as an index of characterizing the content of a light-absorbing component in sample.When a soil is extracted by an extractant,the absorbability (Q) of the soil at a particular wave length is directly proportional to the absorbance (A) and volume (V) of soil extract but inversely proportional to the mass(m) of soil sample and the optical path length (b),
Soil-Q=AV/bm
within a certain range,the values of soil-Q possess additive property.