One thing that’s critically important to monitor in no-till farming systems is soil pH, according to Kansas State University agronomist Dave Mengel. “The top few inches of soil may become extremely acidic due to the surface application of nitrogen fertilizer,” said Mengel, who is a soil fertility specialist with K-State Research and Extension.
When the soil pH gets too low for optimal crop production, lime must be applied to reduce the effect of toxic aluminum on plant roots, to maintain good conditions for microbial activity, and to get the best performance from some of the soil-applied herbicides, he said.
Most growers prefer to surface-apply the lime if the ground is to remain in long-term no-till, but questions commonly asked are, how effective will surface-applied lime be, and how long will it take to start increasing the soil pH?
“A general guideline for lime applications in no-till is: half the rate, twice as often,” Mengel said, but it depends on several factors.
He explained that the relative ability of soils to store a particular group of nutrients, the cations, is referred to as cation exchange capacity or CEC.
Soils are composed of a mixture of sand, silt, clay and organic matter. Both the clay and organic matter particles have a net negative charge. Thus, these negatively-charged soil particles will attract and hold positively-charged particles, much like the opposite poles of a magnet attract each other. By the same token, they will repel other negatively-charged particles, as like poles of a magnet repel each other.
“A coarse-textured soil with a low cation exchange capacity does not require a lot of lime to correct soil pH, but may need to be limed frequently. A finer-textured soil with a high CEC requires a large amount of lime to initially correct pH, but it may be several years before another lime application is needed due to its high buffering capacity,” he said.
The frequency of lime applications needed also depends in part on how much nitrogen fertilizer is being applied and the yield level of crops being produced. In general, the higher the nitrogen rates and yield levels, the more frequently lime will be needed. Due to the variation in buffering capacity of soils, lime applications should always be guided by soil tests, added.
“The bottom line is that there are beneficial effects of surface application of limestone to acidic no-till soils even though the immediate effect may only be in the top one to two inches,” Mengel said.