Potassium deficiency problems showing up in corn
Any condition that will limit the delivery of nutrients to the root surface will aggravate this situation. This is why many people use starter fertilizer. Providing a high concentration of nutrients close to the plant helps overcome some of these problems created by limited root systems. While we can often see significant differences in growth at the V-4 to V-6 growth stage with starter, many times these differences seem to vanish as the nodal roots develop, and little or no yield benefit is seen.
How tillage systems impact potassium movement in the soil
In no-till soils, bulk density increases, and pore size distribution changes. There are commonly fewer, but bigger pores. With fewer pores, the nutrient diffusion route becomes longer. So if the soil becomes dry, and the big pores begin to empty out, the diffusion issue becomes even more of a problem in no-till than in conventional till.
This year’s problems
This year, plants that got off to a quick start are now at V-6 or V-7. The nodal roots are established and growing well, and the plants look pretty good. But there was a lot of uneven emergence. Where seeds were planted a little shallowly and the ground dried out, those seed may have come up a week later and are a leaf or two behind seed planted into moist soil. These later-emerging plants are smaller, pale yellow, and are showing K deficiency due to the dry conditions. The nodal roots on these plants are just getting started and they haven’t rooted as deeply yet as more developed plants.
In one case this year in Atchison County, small plants in spots of a field were found showing K deficiency and yellowing. These spots were surrounded by bigger corn in most of the field, which was greener and one or two leaves further advanced. The big corn had good roots. On the small corn, the nodal roots were only 2 or 3 inches long and just getting started. This is likely an issue of uneven emergence, along with some soil compaction. The soil test K level was good at 200-300 ppm. But all the reasons mentioned above were interacting to cause trouble. The big corn had a greater root density, so it could take up more nutrients under adverse conditions. With more moisture, the small plants will perk up as the root system develops more fully. There may not be a big yield difference in the end, but there will probably continue to be differences in growth stage and eventual maturity as the season goes on.
We have done some plant analysis on some of these problem fields this spring and most of them are showing the “bad” plants as being deficient in K. The problems are worse where the soil test K levels are low. But there are also problems even where soil test levels are high, caused by problems in delivery of available nutrients to the root surface for uptake.
Hybrid differences are also something to consider. We know that different hybrids will respond differently to nutrient deficiencies (particularly to phosphorus). This is likely related to differences in root growth early in the season. Because of all the conditions mentioned above, root growth habits of different hybrids will be particularly important this year, and relevant for K uptake. However, these differences in early growth do not always translate into yield differences at the end of the season. Certain hybrids may look “bad” early in the season, but provide a big advantage later.