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Issue No. 17, Article 4/July 29, 2011

Appearance of Nutrient Deficiencies Is Causing Concern

Weather conditions have been very hot and dry for most of Illinois all last week, with maximum air temperatures in the upper 80s to upper 90s. The only area that received rain before Sunday was the upper northern portion of the state. On Sunday (July 24), most of Illinois received some precipitation, ranging from only a tenth of an inch to slightly more than 1.5 inches (Table 1). Because of the dry conditions, some fields have started to show some nutrient deficiencies, specifically of potassium (K). While I suspect that in most cases the deficiencies will disappear with more rain, they are a matter of concern to some farmers. In certain situations deficiencies have shown up even in fields with high or very high fertility, but typically they have occurred in fields with marginal fertility or that are just above critical soil test levels.

Table 1. Precipitation for various Illinois locations, July 18 to 24.

Station

County

Rain (in.)

July 18

July 19

July 20

July 21

July 22

July 23

July 24

Total

Freeport

Stephenson

0.05

0

0

0.01

2.41

0.48

1.54

4.49

DeKalb

DeKalb

0.09

0

0

0.09

0.41

0.40

1.42

2.41

St. Charles

Kane

0.03

0

0

0.03

1.16

0.86

0.17

2.25

Big Bend Con-servation Area

Whiteside

0

0.14

0

0.20

0.20

1.81

1.41

3.76

Peoria

Tazewell

0

0

0

0

0

0

1.26

1.26

Stelle

Ford

0.02

0

0

0

0

0

1.09

1.11

Kilbourne

Mason

0

0

0

0

0

0

1.21

1.21

Bondville

Champaign

0

0

0

0

0

0

1.26

1.26

Champaign

Champaign

0

0

0

0

0

0

1.13

1.13

Perry

Pike

0

0

0

0

0

0

0

0

Brownstown

Fayette

0

0

0.01

0

0

0

1.28

1.29

Olney

Richland

0

0

0

0

0

0

0.69

0.69

Rend Lake

Jefferson

0

0

0

0

0

0

0.81

0.81

Fairfield

Wayne

0

0

0

0

0

0

0.34

0.34

Carbondale

Jackson

0

0

0

0

0

0

0.53

0.53

Dixon Springs

Pope

0

0

0

0

0

0

0.11

0.11

Springfield

Sangamon

0

0

0

0

0

0

0.56

0.56

Belleville

St. Claire

0

0

0

0

0

0

0.16

0.16

Monmouth

Warren

0

0

0

0.85

0

0

1.06

1.91

Source: http://www.isws.illinois.edu/warm/soiltemp/displaymap.asp.

While very little can be done at this point to correct the problem (besides getting rain in the field), the locations of deficiencies should be noted to determine if something should be done for next year. The cause may simply be that the crop cannot access the nutrients present in the soil, even at adequate levels, because of the lack of moisture, but in some situations action may be warranted to correct the problem for the next crop.

If you are seeing nutrient deficiencies, consider the following points in deciding whether they are worth worrying about and whether any response is appropriate.

  • To state the obvious: adequate soil fertility is critical. If the soil lacks adequate fertility, applying sufficient fertilizer is essential. If severe deficiencies resulted this year from the dry conditions or if the problem does not seem to disappear after some rain, that is a pretty good indication of low fertility in the affected field. Previous soil test information, previous fertilization rates, and yield history for the field along with additional soil testing are the best factors for determining if and how much phosphorus or potassium may be needed. If the fertility of the field is a problem, correcting it before next season should be a priority after harvest. Applying phosphorus or potassium now would be very unlikely to help the current crop because leaving the product on the soil surface would not ensure the nutrient gets into the root system. Also, for some crops and nutrients, the crop has taken up pretty much all it would need already. For example, corn takes up all the potassium it needs by about R1 (silking) or R2 (blister) development stage.
  • Soil water content is critical not only to supply the crop's water needs but to dissolve nutrients and make them available to the plant. Temporary nutrient deficiencies can develop when the surface layer of the soil becomes too dry and the crop's root system is small and shallow. Luckily, this year's soil conditions (unlike last year's) generally were fit for crops to develop extensive roots. Good roots have certainly helped crops draw water from deeper in the soil during the current dry conditions. However, new roots tend to be the most important ones for nutrient uptake, since they are more active than older roots and are growing into "new soil" from which nutrients have not yet been removed; roots don't grow into dry soil, however, and they slow their activity during dry conditions. It is for those reasons that some crops might be starting to show nutrient deficiencies. Sunday's rain should help alleviate those problems.
  • Soil compaction can reduce the volume of soil, including nutrients and water, that can be accessed by the plant by limiting, or even completely restricting, root penetration. If you see patterns of nutrient deficiency following old crop rows or wheel traffic, soil compaction may well be a problem. There is nothing you can do to correct it now, of course, but it would be important to break that compaction after harvest this fall if soil conditions are fit to do tillage.
  • Diseases and pests can have an important impact on a crop's uptake of nutrients by competing for nutrients, affecting physiological capacity (such as reduction in photosynthesis rates), and diminishing root mass and root surface area that is important for nutrient and water uptake. Also, weed competition can be a very large problem for crops, especially when resources such as water and nutrients are limited. Making sure fields are weed-free from early in the season allows the crop to grow without competition and to have all the water and nutrients available to it that are in the soil.

--Fabián G. Fernández

Author:
Fabián Fernández

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