Lime & gypsum-Aren’t they the same?
Educating farmers about pH, sulfur, calcium, lime & gypsum is a big part of what I do. There exists a considerable amount of people who believe that lime & gypsum can be interchanged for each other. Occasionally, this even occurs at the dealer level. A quick overview of each:
Lime, or calcium carbonate (CaCO3), is the naturally occurring mineral used to improve an acid soil. When the soil pH is less than 7, acidity exists as an accumulation of hydrogen (H), and aluminum (Al). Aluminum, which is toxic to plant growth, is soluble when the soil pH is less 5.5. When hydrogen accumulates on the outside of a soil particle, or exchange site, their presence is measured by a pH test.
When lime is applied to an acid soil, the carbonate molecule (from lime) & hydrogen combine. The end products from this reaction are H2O (water) & CO2 (carbon dioxide). Calcium is now attached to the exchange site. Because the carbonate liberates the hydrogen, the soil pH will improve (become less acidic).
Gypsum, or calcium sulfate (CaSO4), is a naturally occurring mineral. It provides calcium & sulfur, both essential nutrients, but does not affect soil pH. It is a neutral salt (pH is ~6.7) & has a salt index, or osmotic potential, of 8. It typically has 20-22% calcium, & 16-18% sulfur. The sulfur is in a plant available, or sulfate (SO4) form. In addition to providing needed nutrients, the calcium in gypsum is soluble, even at a pH that is >7. This can be very helpful in improving soil tilth, reducing soil compaction, & improving aeration.
Do you need lime, gypsum or both? We will continue this discussion in a future blog.