No. 9 Article 2/June 4, 2010

What Am I Lacking in My Soil Fertility Program?

Most farmers are very pleased with the way planting went this year. Many, though, report that the crop is not looking as good or growing as quickly as they would like, and they are concerned that micronutrients or other fertilizers look to be needed. What is important to remember at this time is that environmental conditions have an important impact on nutrient availability. The fact that nutrients are applied or that they are normally present naturally in the soil does not mean they are necessarily available to plants.

Plants obtain most of their nutrients and water from the soil through their root systems. Any factor that restricts root growth and activity can restrict nutrient availability. This is not because nutrients are not plant-available in the soil, but because the crop's ability to take up those nutrients is restricted. This year different factors or a combination of factors may be at play and restricting nutrient availability. Following are some of the factors that I consider most likely to be contributing to observed deficiencies or slow growth:

In most cases, the deficiencies we are seeing this year relate to growing-season conditions and not to inadequate soil fertility. As conditions improve, much of what you see as nutrient deficiency symptoms will disappear without additional fertilization. However, since growing-season conditions this year accentuate problems that might not be as evident in other years, this is a good opportunity to learn about field conditions or management practices that should be adjusted to prevent or at least lessen problems in the future.

In Illinois, nutrients (besides nitrogen, phosphorus, and potassium) that can most commonly be deficient include these:

The use of micronutrient fertilizers should be limited to areas of known deficiency, and only the deficient nutrient should be applied. An exception would be situations in which farmers already in the highest yield bracket try micronutrients experimentally in fields that are yielding less than would be expected under good management, which includes an adequate N, P, and K fertility program and a favorable pH.

Given the conditions of this growing season, it can be difficult to know exactly what factor or set of factors are causing an observed problem. If you suspect a nutrient deficiency, I suggest collecting plant samples and sending them to a laboratory for nutrient analysis. Critical tissue-nutrient level (below which deficiency occurs) is the concentration needed for a crop to complete its life cycle. These concentrations are largely independent of soil or growing conditions, so the values typically apply across environments and provide a more reliable measurement for micronutrients and secondary nutrients than do soil tests.

When diagnosing a fertility problem through plant analysis, select paired samples of comparable plant parts representing the abnormal and normal plants. After collecting the samples, deliver them immediately to the laboratory. Samples should be air-dried if they cannot be delivered immediately or if they are going to be shipped. Soil factors (fertility status, temperature, and moisture) and plant factors (cultivar and development stage) may complicate the interpretation of plant analysis data. The more information provided concerning a particular field, the more reliable the interpretation will be.--Fabián G. Fernández

Close this window