Soil Test Note – No. C001

Dr. Stanley L. Chapman , Extension Soils Specialist

 

 

LIMING AND FERTILIZING CORN IN ARKANSAS

 

The modern concept of corn production requires that soil fertility and available soil moisture be removed as yield limiting factors.

 

Desirable Soil pH and Liming

The desirable soil pH for corn ranges from 5.5 to 7.0.  Lime is generally recommended at soil pH values below 5.8.  However, if rice is in the rotation, lime is not recommended without the benefit of additional information such as irrigation water quality.  Even then, lime is not recommended unless the soil pH is below 5.6.

 

Nitrogen

A rough rule of thumb is that one to two pounds of actual nitrogen (N) is required for each bushel of corn produced.  A normal cultivated soil in Arkansas can be expected to supply about 40 pounds of available N per acre per year from the breakdown of organic matter and carryover fertilizer from the previous crop.  The best yield that should be expected without irrigation is about 100 bushels per acre (bu/A) on clays and 125 bu/A on sandy loams and silt loams.

 

If carryover N is high, it will be indicated with the nitrate-nitrogen test.  For a more reliable indication of N carryover, submit a sub-soil sample along with the topsoil sample.  Take the sub-soil sample to at least 24 inches.  Subtract soil N in excess of 40 pounds per acre (lbs/A) from the total recommended fertilizer N for a particular yield goal.

 

A maximum of 120 pounds per acre of fertilizer N is recommended for non-irrigated corn on loamy soils.  With irrigation the recommended N rate increases in 30 lbs/A increments for each 25 bushels per acre (bu/A) of expected yield increase.

 

The maximum recommended N rate for non-irrigated corn on clay soils is 125 lbs/A.  With irrigation the recommended N rate increases in 50 to 75 lbs/A increments for each 20 bu/A of expected yield increase.

 

Generally, no more than half of the total recommended N should be applied pre-plant.  Nitrogen is normally applied with phosphate and/or potash where they are needed.  The remainder of the n should then be side-dressed or top-dressed when a stand is obtained but before the corn gets “knee high.”  The application of all the recommended N pre-plant could result in salt damage to corn seedlings.  This is more likely with corn planted after May 1.

 

It may be advantageous to apply all of the recommended nitrogen pre-plant where the nitrogen source is anhydrous ammonia or a slow release source.  The major objections to applying all the N pre-plant are:

 

1.       Salt damage to seedlings may result.

2.       Losses may occur from leaching or de-nitrification.

3.       Nitrogen will be wasted if a stand of corn is not obtained and a substitute crop does not need the extra N.

 

 Phosphate and Potash

Apply all recommended P and K pre-plant along with at least 30 pounds of N per acre.  Early planted corn may suffer from phosphorus deficiency symptoms (stunted plants and purpling of leaves) even on soils that have high levels of soil test P.  Where this occurs, as little as 15 pounds per acre of P2O5  side-dressed near the row may be effective in overcoming P deficiency symptoms.  However, a warming period will usually allow corn to recover and seldom are yields reduced by the temporary P deficiency.  Where soil test P is less than 100, recommended P fertilizer rates range from 50 to 100 pounds of  P2O5 per acre.  Potash is recommended for soil test K levels below 275 at rates ranging from 50 to 200 pounds of K2O per acre.

 

 Secondary Elements

The secondary elements – calcium, magnesium, and sulfur – are generally considered adequate in most Arkansas soils.  Calcium is adequate for corn as long as lime needs are met.  Magnesium and/or sulfur deficiencies are possible on sandy, leachable soils low in organic matter.  A low level of available magnesium or sulfur in the top-soil has little meaning unless a sub-soil test is also obtained.  Both elements tend to leach downward and accumulate with the clay in the sub-soil.  Medium to high levels of these elements in the top-soil should be adequate for the corn crop.  Both magnesium and the sulfate form of sulfur are added from irrigation water supplied by most wells.  Generally, 10-20 lbs/A of sulfur is added each year from rainfall and other atmospheric sources.

 

Soil tests for sulfur are not very useful in predicting plant needs.  Most S in soils is in unavailable forms associated with organic matter and clay.  Sulfur is released in small amounts as sulfates at various times throughout the year.  Sulfate-S may be either taken up by plants or leached downward, especially in sandy soils.  For this reason, sulfates usually accumulate in sub-soils that contain more clay then the top-soil.

 

Total nutrient analysis of the leaves is useful in evaluating the S status of plants.  Low levels of s may exist in plants early in the growing season but be adequate later on.  Plant roots may either extend into S-rich sub-soils or soil microbes may release S from organic matter as soils warm up.

 

Common sources of S-containing fertilizers in decreasing order of solubility are ammonium sulfate, potassium magnesium sulfate, gypsum, and elemental S.  A broadcast application of 100-200 lbs/A of any of these materials should be adequate to supply the S needs of corn.

 

When the soil test indicates very low levels of magnesium (generally on very sandy, low CEC soils) 20-40 lbs/A should be recommended.  Common commercial magnesium sources include:

 

1.       Dolomatic lime

2.       Potassium magnesium sulfate

3.       Magnesium oxide

4.       Magnesium chloride

 

Dolmatic lime is the most economical source of Mg where lime is needed.  Fertilizer grade potassium magnesium sulfate is marketed under the major brand name of “K-Mag” and “Sul-Po-Mag.”

 

Micronutrients

Although corn uses small amounts of all micronutrients, deficiencies are not apt to occur under most Arkansas conditions.  Molybdenum should not be deficient in corn under any circumstances in Arkansas.  Iron, manganese, zinc, copper, and boron are also adequate in most soils.  However, low levels and possible deficiencies of some of these could occur on leached, sandy, low CEC soils and on medium textured soils that have a pH above 7.0.

 

Zinc is the micronutrient most likely to be found deficient in corn.  Analysis of plant tissue during the growing season is the best way to assess micronutrient status.  The University of Arkansas Diagnostic Service Laboratory at Fayetteville will analyze plant tissue for a fee.  When recommended, zinc should be applied to the soil at the rate of one lb/A of actual zinc in the chelate from or ten lbs/A of actual zinc in the inorganic form.  Zinc sulfate is a preferred source since it dissolves fairly easily and also supplies sulfur.

 

April, 1995

 

The Arkansas Cooperative Extension Service offers its programs to all eligible persons regardless of race, color, national origin, religion, gender, age, disability, marital or veteran status, or any other legally protected status, and is an Equal Opportunity Employer.

 

 

 


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