Why Apply Lime, Gypsum?

Know Situations to Apply Lime, Gypsum

Russ Quinn
By  Russ Quinn , DTN Staff Reporter
Connect with Russ:
(Progressive Farmer photo by John Pocock)

OMAHA (DTN) -- Jeff Littrell freely admits he does things a little differently. For one, the Rochester, Minnesota, farmer grows some organic production as well as conventional commercial crops.

He's also solved the dilemma of whether to apply lime or gypsum to his fields by saying "yes" to both.

"They work very well together," Littrell told DTN.

Warren Dick, Ohio State University soil scientist, said there has long been some confusion among farmers about when to use limestone on their fields and which conditions are best corrected by gypsum.

"Lime is a mainly a pH adjustment; gypsum, on the other hand, while it has many good qualities, is not," Dick said.

Lime also can be used as a source of calcium and can improve soil structure.

While agricultural limestone is a good source of calcium, it often doesn't break down and release its calcium very quickly, said DTN Contributing Agronomist Dan Davidson. In many cases, the process can take a couple of years after application.

Lime also has purity concerns. Davidson said farmers need to understand and watch the purity of the lime they buy.

"Lower purity lime will mean farmers will have to apply more of it to change pH," Davidson said.

While gypsum isn't effective at neutralizing acid soils or effectively raising pH, it is roughly 200 times more soluble than lime, Dick said. The calcium in gypsum can move through the soil and be accessible to the crop much sooner the calcium in lime can.

Gypsum also is a good source of sulfur, which is often in lower quantities in many soils than modern crops require.

Commercial fertilizers also have lower levels of sulfur than in the past. Because of these factors, applying gypsum is an economic source of sulfur, Dick said. He added that the sulfur in gypsum is already in the sulfate form, the form needed to be taken up by plants.

FARMERS USE BOTH

Littrell said he figured out by using both products that gypsum will not increase soluble calcium but it will affect the deep profile over years. It will also increase sulfates which aids in the protein content of corn and soybeans.

"We add lime with the gypsum when possible which aids in the soluble calcium and keeps it in the upper soil profile," Littrell said. "We combine the two at a 1-to-1 ratio."

Littrell mixes 200 pounds of pelletized lime and 200 pounds of pelletized gypsum. While pelletized product is more expense, he said he would need to apply 1,000 pounds of each in raw, mined material, to achieve the same soil-amending results.

Jan Layman, who farms near Kenton, Ohio, also does custom spreading of both lime and gypsum. Knowing what issues your soils have is the key in using the correct amendment to solve the problem, he said.

"In our area, we have trouble with too high levels of magnesium which leads to crusting and lack of water infiltration," Layman told DTN. "Lime will correct the pH and change the calcium/magnesium ratio."

Layman said a scenario favoring gypsum would be if soil pH ratio is in the correct range and a soil test shows calcium and magnesium ratio to be low. Gypsum will raise the calcium levels to an acceptable range. Calcium binds with the magnesium ions and help to leach it out of the root zone and it also leads to soil particle aggregation which increases the amount of pore space in the soil.

"This allows room for more oxygen and water storage," he said.

Lyman said he is shooting for 75% calcium levels in his soils. His soils are not quite there yet but he is trying to push them there. He is in the early stages of using gypsum on his own farm so he does not have any conclusive results yet.

P RUNOFF SOLUTION?

While all the results are not known, Lyman said some soil studies suggest the increased water infiltration rates soils develop from gypsum could help curb phosphorous (P) runoff into water sources.

This is big news in a state like Ohio where the city of Toledo was forced to stop using public drinking water in 2014 due to algae blooms around water supply intakes from Lake Erie. Excess phosphorus, from runoff of farm fields, is believed to be a key reason for the toxic algae blooms.

Dick, the Ohio State University soil scientist, said there have been many studies on gypsum and P runoff over the last few years. The research has shown that soluble P can be reduced anywhere from 40% to 70% by applying gypsum to the soil, he said.

"I have seen the water in these studies myself," Dick said. "The water is clear and obviously cleaner, as can be in the fields with gypsum applied so it does hold some promise."

Russ Quinn can be reached at russ.quinn@dtn.com

Follow him on Twitter @RussQuinnDTN

(GH/PS/CZ/SK)

Russ Quinn