[1]New Conservation Standards have been approved by USDA/NRCS for gypsum in agricultural soils. The benefits of gypsum use listed in the regulations are:
- Improve soil health by improving physical/chemical properties and increasing infiltration of the soil.
- Improve surface water quality by reducing dissolved phosphorus concentrations in surface runoff and subsurface drainage.
- Improve soil health by ameliorating subsoil aluminum toxicity.
- Improve water quality by reducing the potential for pathogens and other contaminants transport from areas of manure and bio-solids application.
These standards validate what we have been reporting and our customers have been seeing for numerous years. Application rates that they recommend are dependent upon soil tests. If soil test magnesium is greater than 13% they would suggest that gypsum applications 1 or 2 tons per acre will help improve soil physical conditions. If CEC is greater than 15 they would recommend 2 tons/acre of gypsum.
For soils with high phosphorus levels or a high or very high P Index rating they recommend no less than 1 ton/acre be applied on the soil surface to reduce phosphorus runoff from fields.
To reduce phosphorus and pathogen loss from fields after a manure application, broadcast no less than 1 ton/acre of gypsum within 5 days after manure applications or prior to the next runoff event, whichever comes first. Mixing gypsum with manure prior to application is also acceptable.
When exchangeable aluminum below a 12 inch soil depth is greater than 1 meq./100 grams of soil apply gypsum at rates recommended by ARS or land grant university. My past experience with soils in the plains states where aluminum toxicity occurs the roots begin showing toxicity symptoms when the level of aluminum exceeds 20 ppm. This would be equivalent to .22 meq/100 g of soil. My recommendation for these soils would be to apply 1 ton of gypsum, but monitor the magnesium levels since magnesium deficiencies are also common in these soils. Mixtures of lime and gypsum are often considered in these soils for best results.
Soil health will improve with gypsum applications and will continue to improve with time. If subsurface drainage needs to be improved installation of drainage tile in combination with surface applications of gypsum greatly enhance soil health.