Measuring salinity

Abstract

Root-zone salinity reduces crop yields. The extent of the reduction depends on the kinds and concentrations of salts existing in the soil solutions across the field. The salts which cause root-zone salinity typically dissociate into sodium, calcium, magnesium, and sometimes potassium cations together with chloride, sulphate, bicarbonate, and carbonate anions. These ions, when dissolved in soil water and concentrated in excess of plant needs, can disrupt crop water uptake and plant metabolism. We easily recognize the existence of salinity when we see white salt crusts on soil surfaces. But, root-zone salinity may also exist in field locations which never show white crusting. Surveying and mapping a field using geo-physical instruments operating on the soil surface can reveal this hidden root-zone salinity. Although measurements with these instruments are affected by soil texture, chemistry, water-content, temperature, and other factors, basic indices can still be calculated by linking survey measurements with detailed salinity values derived from soil cores extracted as part of the survey.