No. 12 Article 9/June 12, 2009

Factors That Limit Nutrient Availability

Weather conditions this spring have caused some corn fields to appear nutrient-deficient in some portions of Illinois. Additionally, some farmers are concerned that since phosphorus and potassium applications were skipped this year (no addition of "fresh" phosphorus and potassium), their crops might not have enough, even though soil tests showed adequate levels. It is not unusual for crops in fields or portions of fields to show nutrient deficiencies even though adequate fertility and proper nutrient management plans are followed for phosphorus and potassium.

Under adequate nutrient management practices, these deficiencies are most often temporary and occur during early stages of development. What is important to remember is that in addition to inherent soil properties (parent material; amount of organic matter; depth to bedrock, sand, or gravel; permeability; water-holding capacity; drainage), environmental conditions have an important impact on nutrient availability. The fact that nutrients are applied does not necessarily mean they are available. Plants obtain most of their nutrients and water from the soil through their root systems. Any factor that restricts root growth and activity has the potential to 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.

Keep the following points in mind to avoid excessive concern about the need for additional phosphorus and potassium when a sound nutrient program is already in place.

Diseases and pests can have an important impact on crop-nutrient uptake by competing for nutrients, affecting physiological capacity (such as reduction in photosynthesis rates), and diminishing root parameters through root pruning or tissue death.--Fabián G. Fernández

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