Question: I am on a strip-till/no-till corn-soybean rotation in north-central Iowa. I've been putting down fertilizer for both crops in the strip-till pass. My most recent soil test shows the pH is getting to the 6.1-6.5 area and I'm concerned with fertilizer availability. With no tillage, lime wouldn't be worked into the soil and even if we decided to do shallow tillage on soybean stubble going to corn, it would not get at the lower soil levels where the fertilizer is placed by the strip-till coulters. My fertilizer dealer tells me that there is pelleted lime available that could be mixed with the dry fertilizer and placed through the air delivery system of the strip-till unit. Any comments or further ideas?
Answer: I would not advise this. When we think about liming a field because of its acidity we’re trying to flush out hydrogen. When we take a pH reading of the soil we are measuring hydrogen. When hydrogen gets high we have to flush it out with limestone. You want to think about hydrogen almost like you would a weed seed. Think about how thick some weeds like Palmer amaranth and waterhemp can get in a field. When you put an herbicide on you need to get it in contact with all those weeds so you get a uniform kill. If you knifed your herbicide on, just because you have the right amount of herbicide on per acre you wouldn’t kill many of those weeds. Where you knifed it on you’d have such a high concentration of herbicide you would have problems. Limestone is the same way. To neutralize acidity you have to put it on like paint. Uniform coverage is key.
Limestone moves through the soil about a half inch a year. It’s not like phosphorus that moves an inch in 20 years. Limestone, the carbonate, which is what you’re applying, will move about a half inch per year in most soils. So, you want to surface apply small amounts, say a 1 ton to 1.5 ton rate, for example, and you want to apply it fairly often, like three times over a six-year period. Bear in mind, this is an estimate—you need to use a soil test to make an accurate prediction.
That limestone will keep moving down through the soil profile as you’re applying it over time. We have guys who have no-tilled for 15 to 20 years and they don’t need to tear it up; they can manage the pH from the top. The problem is if you knife that lime down with a strip-till bar, when it starts to neutralize it will be present in a very high rate in that small area and will tie up your phosphorus and give you some efficiency problems with your fertility. In a high pH soil when we have too much calcium it ties up the phosphorus and gives us fits. If you put pelleted lime down with a strip-till bar you’ll have the same problem. Now, you are correct that where you’re putting fertilizer it is more acidic, especially if you’re putting nitrogen down, but that acidity will flush out or leech out to some extent.
When we worry about pH we worry more about pH from a microbial standpoint, not from a crop standpoint. Corn can handle acidity down into the lower fives without much trouble, but soil microbes can’t. You’re not liming to feed the corn crop, you’re liming to keep the soil pH in the neutral range so the microbes can do their thing. If we were just liming for the corn plant so you could pick up calcium, then you could knife it in the strip. But you’re putting on calcium carbonate to neutralize the soil. You’ve got to think about putting lime on like paint. So, in that essence I wouldn’t put pelleted lime in my strip-till machine and I also wouldn’t spread my lime with a manure spreader.
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Correct acidity to create diverse microbial populations, which decompose residue and release soil nutrients.