Trempealeau County UW-Extension Agent Steve Okonek displays a chart depicting Liebig’s law of minimums at the Soil Health Field Day on Aug. 14 in Arcadia, Wis. The event was put on by the Elk Creek Watershed Group and UW Discovery Farms, and hosted at Ed and Darin Maliszewski’s farm.
PHOTO BY DANIELLE NAUMAN
Trempealeau County UW-Extension Agent Steve Okonek displays a chart depicting Liebig’s law of minimums at the Soil Health Field Day on Aug. 14 in Arcadia, Wis. The event was put on by the Elk Creek Watershed Group and UW Discovery Farms, and hosted at Ed and Darin Maliszewski’s farm. PHOTO BY DANIELLE NAUMAN
    ARCADIA, Wis. – UW-Discovery Farms and the farmer-led Elk Creek Watershed Group teamed up to host their fifth annual Soil Health Field Day Aug. 14 at Maliszewski Dairy, operated by Ed and Darin Maliszewski, near Arcadia, Wis.
    Steve Okonek, Trempealeau County UW-Extension Agent, began his presentation on the importance pH plays in plant growth and nutrient absorption.
    “One of the things you hear about cover cropping is that you can reduce inputs,” Okonek said. “That is probably true, but we need to have a good foundation of soil fertility going into a cover crop situation. There are some really good things that cover crops can do for soil health, but it’s not the silver bullet that is going to solve everything.”
    Okonek brought up Liebig’s law of the minimum, which states that growth is not dictated by the total amount of resources available to a crop, but by the scarcest resource, or the limiting factor.
    “Liebig was a soil scientist from a few centuries ago,” Okonek said. “He came up with this concept of a barrel, that you can only fill the barrel as full as the lowest stave. So if we are low on calcium or low on potassium, we are only going to produce a crop up to where that limiting mineral becomes limiting. We can only produce up to the limiting factor. ”
    The availability of nutrients to a plant is influenced by pH, Okonek said.
    “Necessary minerals are readily available to plants between a pH of 6 and 7,” Okonek said. “We don’t get any toxic levels or tie-up. If we get extremely high pH, over 8, we can start tying up phosphorous into the calcium portion of the soils.”
    Okonek referred to the soils found out in the central Dakotas and in eastern Wisconsin as being high-calcium soils.
    “On the eastern side of Wisconsin we can have some high calcium soils because they were former lakebed soils,” Okonek said. “Brown County and some of those areas will have a pH naturally at 7.5. They haven’t added lime, they’ve farmed those soils for 150 to 200 years, and they just stay at 7.5 because there are a lot of dead snails and clams in there that they are working off of.”
    In juxtaposition, Okonek said soil in western Wisconsin typically suffers from low pH, requiring the application of lime, typically dolomitic lime, to raise the soil pH.
    “What makes our soil acid?” Okonek asked. “Part of it is the nitrogen cycle. There are different nitrogen sources that get the blame for causing acid soils.”
    Okonek said anything that contains hydrogen, which is ammonia, will contribute slightly more to soil acidification than other nitrogen sources, such as manure.
    “As we add anything that contributes to the nitrogen cycle, even legume nitrogen, will cause acidification of soil,” Okonek said. “We create ammonia in the soil just through the natural processes as we turn over organic matter, such as corn stalks, soil bacteria, soil fungi and everything like that.”
    Okonek explained that the nitrogen cycle is a dynamic cycle.
    “If we apply anhydrous ammonia, NH3 grabs a hydrogen from the water molecules to become NH4,” Okonek said. “Then it is in the soil and the bacteria work on that and it becomes nitrate and spins off the hydrogen ions, which cling to the soil, causing the acidity.”    
    Continuing in the cycle, Okonek said the nitrate can either become nitrite or straight nitrogen gas. It is then volatilized into the air, used by plants or leached from the soil by a heavy rain, particularly on a light soil. The nitrate can also be incorporated into bacteria and other soil organisms and turn around in the cycle as those organisms die, decay and release ammonia.
    “There is some anecdotal evidence that says to apply high calcium lime and good things will happen,” Okonek said. “When we put dolomitic lime and high calcium lime into replicated field trials and look at the data, there is no difference. Then it comes down to economics, and which one can be applied for a reasonable price.”
    Okonek advises farmers to look at the calcium carbonate (CaCO3) when selecting liming materials.
    “It is the carbonate ion that neutralizes the pH. The calcium has no effect on pH,” Okonek said. “In our acid situation, we are dealing with hydrogen. We need that carbonate to take the hydrogen ions off of the soil particles.”
    Okonek said in tropical soil situations, such as in Brazil, aluminum toxicity creates the low pH, requiring the application of gypsum (calcium sulfate). The calcium in gypsum will drive the aluminum off the soil particle, alleviating the aluminum toxicity, but will not adjust the pH of the soil, leaving the soil to remain acid.
    “Around here, if we are applying gypsum, we are not adjusting the pH, we are supplying the soil with calcium and sulfur,” Okonek said. “Gypsum is generally a good sulfur source. Since we’ve been cleaning up our diesel fuel and our smoke stacks from electrical generation, we are getting less sulfur deposition in the rain and having to do some supplementation for sulfur. Gypsum is an economical source for sulfur. Just don’t apply calcium sulfate as a liming material.”
    Less alfalfa being used in cropping rotations, and growing more corn and soybeans, has led to pH problems in the soil becoming more common, Okonek said.
    He also said laboratory evidence points to a general lowering trend in soil pH. Okonek explained that after soil-sampling some fields with poor growth situations, soil scientists are discovering very low pH soils, which can eventually impact both corn and soybean growth.
    “If we want to have good crop growth, whether it is a cover crop, corn or soybeans, we still need to manage pH,” Okonek said. “Just because we are opting away from alfalfa, we cannot neglect the soil pH. It still has to be managed, just at a different level.”