SOIL-WATER BASICS & SOIL HEALTH


infiltration and water retention in the long run. For example, cover cropping or compost application may help mitigate some of the negative impacts of tillage.


What role does gypsum play?


Gypsum is often seen as the go-to solution to improve infiltration, but how does it work? The chemical makeup of gypsum is calcium sulfate. When gypsum is added to the soil, it slowly dissolves, thereby releasing calcium and sulfate in the soil solution. Calcium holds clay particles together, a process referred to as flocculation. The opposite of flocculation is dispersion, a process that destroys soil structure by pushing clay particles apart.


Dispersion is caused by high concentrations of cations with a low charge and large hydrated radius, such as sodium. Dispersion can manifest itself in the top quarter inch of the soil and go unnoticed in typical soil testing. Dispersion can be reversed by adding gypsum, followed by leaching the sodium down below the root zone.


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COMPLETELY ELIMINATING TILLAGE MAY NOT BE POSSIBLE … BUT STRATEGICALLY PLANNING TILLAGE INTENSITY CAN HELP MAINTAIN OR BUILD A LEVEL OF SOIL STRUCTURE THAT SUPPORTS IMPROVED INFILTRATION AND WATER RETENTION IN THE LONG RUN.


Gypsum can also improve infiltration when irrigation water has extremely low salinity or has a high sodium content. In normal soils that contain plenty of calcium, poor soil structure is typically a result of compaction or the loss of organic matter, rather than due to dispersion. In those cases, soil conservation practices such as cover cropping, compost application and reducing tillage intensity are recommended to address the issue.


Charlotte Decock, PhD 


Franklin Gaudi, EdD, CCA, CAIS, CIC, CID, is a  Center at Cal Poly State University.


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