Anyone who reads this column occasionally knows that I have a “thing” about the importance of soil fertility.
It is one of a short list of items a producer can control that influence the most important part of farm profitability, namely yield. There are several factors that influence the nutrient supply system, but drainage and nutrient concentration work closely to influence the availability of the necessary nutrients that are in the soil.
The chemical reactions involved in nutrient availability and the development of roots are both influenced by drainage and the presence of the all-important element, oxygen, in the soil. Without plenty of oxygen you can apply fertilizers and liming materials correctly and still come up short.
Soil pH is also a critical part of the equation since chemical reactions are greatly influenced by this factor that describes the acidity or alkalinity level of the soil. Chemists regard pH below 7.0 as “acidic” and pH above 7.0 as “alkaline”, but for most field crops we really don’t get too concerned about acidity until pH drops below 6.0.
We rarely worry much about alkaline soils in this region except maybe in those “white land” or “sodic” spots that occur in some fields where old springheads are located and where a lot of dissolved solids like sodium (Na) are left behind as the spring water evaporates. Lime is a very important part of soil fertility not only because it neutralizes or “buffers” soil acidity, but also because it supplies calcium (Ca) and in some cases magnesium (Mg). Some sources of lime even contain small quantities of other useful elements.
By now you are wondering why I went through all that to talk about nutrient deficiencies, but this year two things have occurred together.
First, we had all the early season rain that kept the soil saturated for weeks, limiting the amount of oxygen that could enter the soil. Long term no-till fields with an abundance of porosity from the work of earthworms and old root channels allowed oxygen into the profile, and those few people who were able to do some tillage during that time were able to get some oxygen into the profile as well, even though that method of aeration is temporary.
In addition to soil saturation for most of the period, plants failed to produce normal roots to access the deeper supplies of nutrients. Mycorrhizae were also impaired in their work of helping the plant get nutrients. When you combine these factors, you get a plant that runs out of some of the essential elements needed for good growth and reproduction. Tolerance to disease is also reduced, as can be seen in many fields of cotton, soybeans, and corn as the season draws to a close.
It appears that the main element that is showing up as deficient is potassium, which produces chlorotic soybeans, and cotton that is more susceptible to wilt diseases especially Verticillium. Corn is also showing diseases in areas where soils were saturated for weeks in the form of stalk rots, ear rots, leaf blights and rusts. Many of these conditions are related to the availability of nutrients or at least stress induced by shortages of nutrients. Cool conditions and rainy overcast days and nights have only added to the problem.
As crops begin to mature, we should note their progress and determine whether plant senescence is normal or whether it is induced by nutrient deficiencies and related conditions in the soil. I doubt that we can reverse these problems at this late date, but we can learn more about how to avoid them in the future.