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Fertilizers for Corn 

The guidelines of fertilizer rates given in the following Table are general guidelines for optimum economic corn production.
Fertilizers for Corn Table
These general fertilizer guidelines should be used only when a complete soil test has not been taken as the tables in this section are condensed for simplicity. More information is incorporated into the computerized guideline system than is considered in the general tables here. For example, in the Table the recommended rates of fertilizer application are broken down into five general soil groupings. Within each group, the years since a sod was plowed and the legume content of the sod are used to generalize the nitrogen guidelines at two rates of dairy manure additions. When these guidelines are formulated from a complete soil (and manure) test, they are tailored to the grower’s soil resources. Equations are used to calculate the guidelines for specific soil potentials, previous cropping practices, and the type, consistency, and rate of previous and present manure applications. The possible combinations range in the thousands.

For CAFO planning, see the relevant documents on the official Cornell guidelines for field crops page, accessible via the Cornell Nutrient Management Spear Program website: http://nmsp.cals.cornell.edu/guidelines/ nutrientguide.html.

If the rates are applied as recommended for agronomic response, the losses of fertilizer nutrients into the environment are relatively small and optimum economic production can be achieved.

As mentioned, for nitrogen, guidelines are based on crop history and manure use. Work on the Illinois Soil N Test (ISNT) as a tool for assessment of soil N supply from organic matter for corn over the past six years has shown the test to be 84% accurate in identifying sites that do not need extra fertilizer N due to the soil’s N supply capacity (see http://nmsp.cals.cornell.edu/projects/Nitrogenforcorn.asp). These are sites where fertilizer savings can be made beyond what is recommended in the tables or soil test report based recommendation (i.e. where no N is needed due to high soil N supply even though the Cornell guidelines in the tables in this section state additional N could be needed). This test is most relevant in combination with the late season Corn Stalk Nitrate Test (CSNT) and for 2nd or higher year corn fields with a manure history where sidedressing of fertilizer N might not be needed. For more detailed nitrogen guidelines (Cornell guidelines for CAFO planning) see http://nmsp.cals. cornell.edu/nutrient/guidelines/ and the Nitrogen for Corn website of the Cornell Nutrient Management Spear Program: http://nmsp.cals.cit.cornell.edu/projects/NitrogenforCorn.html.

Note: If soil test results are not available and the previous crops have been adequately fertilized, use the fertilizer rates for medium soil test results. If the previous crops have not been adequately fertilized, for example, hay without topdressing, use fertilizer rates for the low soil test results.

BAND RATES
The fertilizer used as a starter should contain a small amount of nitrogen; most, if not all, of the recommended phosphorus; and possibly some potassium. Thus, a good starter fertilizer might range from a ratio of 1-4-0, 1-3-1, 1-3-3, to 1-1-1, depending on the rate of fertilizer required.

Do not apply more than 80 to 100 pounds per acre of N + K2O in the starter band, for example, 400 pounds per acre of 10-10-10. Do not use large rates of fertilizer containing urea or diammonium phosphate in the fertilizer band (see “Fertilizer Injury”).

EFFICIENT NITROGEN USE
It is necessary to determine as accurately as possible the quantity of nitrogen necessary for optimum economical corn production and to apply only this quantity of nitrogen to prevent over-fertilization.

To determine the quantity of nitrogen that should be furnished by commercial fertilizer, all the nitrogen sources must be considered. Soil organic matter supplies 40 to 80 pounds of nitrogen per acre per year. A good legume or legume-grass sod will supply 100 to 150 pounds per acre, or more, and a good grass or grass-legume sod will supply 75 to 100 pounds per acre in the first year after application. Thus, a legume sod and the soil itself would supply approximately 200 pounds per acre of nitrogen; hence, only a starter would be needed. Recent research is New York confirmed that for both optimum yield and quality a small starter N application (30 lbs N or less per acre) is needed for first year corn following sods in the rotation, independent of timing of sod kill (late fall or spring) or percentage legume in the sod (see Agronomy Fact Sheet #21 at http://nmsp.cals.cornell.edu/publications/factsheets.asp). Since first year corn does not need additional N beyond a small starter application, no soil (eg PSNT or ISNT) or plant analysis (CSNT) tools are needed to determine N rates for first year corn. Dairy manure supplies 2 to 5 pounds of nitrogen per ton, depending on the time and method of application. Consider all sources of nitrogen. Unnecessary fertilizer is too expensive from the standpoint of both profits and the environment. For further information on deriving N credits from manure, see Agronomy Fact Sheet #4 at http://nmsp.cals.cornell.edu/ publications/factsheets.asp.

The optimum economic N rate for corn after soybean can be lowered by 20-30 lbs N/acre. This adjustment should be applied only for the first year of corn following soybean.

 After the rate of nitrogen to be added has been determined, the method of application must be evaluated. Because of the large and diverse losses of nitrogen applied in the spring or fall, sidedressed nitrogen has three important advantages: (1) the profit per acre is higher; (2) the amount of fertilizer required to obtain optimal yields economically is considerably less; and (3) the potential quantity of nitrogen that can be lost from the agricultural segment of the environment is reduced.

Because of the potential for pollution from these losses, band and sidedress nitrogen applications are recommended. Work is ongoing to test the effectiveness of enhanced efficiency fertilizers. Rates of nitrogen up to about 40 to 50 pounds per acre can be applied in the fertilizer band provided the N + K2O application does not exceed 80 to 100 pounds per acre. When rates above 40 pounds per acre are recommended, a small starter rate (10 to 30 pounds per acre) should be used in the fertilizer band, and the remaining nitrogen should be applied at sidedress time.

To prevent volatilization of the nitrogen from the urea source in liquid or dry urea fertilizers, a topdressed application of liquid or dry material should be incorporated into the soil on the same day or effective enhanced efficiency fertilizers (addition of urease inhibitors) should be considered.

NITROGEN STATUS OF THE CORN CROP
One can determine whether the proper rate of nitrogen was used by examining the crop. This hindsight evaluation helps refine nitrogen management. Nitrogen sufficiency in one year does not necessarily imply that N rates should be decreased in the next year, and vice versa. Examine the lower leaves of the cornstalks. If three to five of the lower leaves are dead (or nearly so) by the early dent stage and the upper leaves on the plant remain medium to dark green, the proper rate of nitrogen fertilizer was used. If fewer than three leaves die by early dent and the top leaves remain moderately dark to dark green, too much nitrogen was used and the rate could have been decreased by 20 to 40 pounds per acre. If the leaves die up to or above the ear leaf or the entire plant has a light to very light green color and the leaves near the ear leaf are yellow, too little nitrogen fertilizer was used and the optimal rate was 20 to 40 pounds per acre higher than what was applied (in this evaluation, consider only leaves lost because of nitrogen deficiency and not losses caused by leaf blight or drought). Nitrogen deficiency starts as a V-shaped yellowing of the leaf tip, which proceeds toward the stalk, followed by gradual leaf death. Drought symptoms are almost the same as those of nitrogen deficiency, and drought will make nitrogen deficiency appear to be worse.

If a severe drought occurs late in the season (tasseling to early dent), the above descriptions are not valid. Instead, nitrogen rates even below those recommended would have been adequate because over fertilization does not compensate for lack of water.

The large quantities of N needed for optimal corn production can be supplied by soil organic matter, crop residues, manure, and/or commercial fertilizer. The pre-sidedress soil nitrogen test (PSNT) provides a way to determine if there will be sufficient nitrogen in the soil for maximum economic yields corn. PSNT determines the nitrate content of the top 12 inches of soil when the corn is 6 to 12 inches tall. The soil nitrate content at that time is an indication of the total nitrogen available to the plants for the remainder of the growing season.

If PSNT nitrate results are 25 ppm or above, there is sufficient N in the soil for maximum economic corn yields. If there is less than 21 ppm of soil nitrate, additional sidedress N is needed. When the results are between 21 and 25 ppm N, there is about a 10 percent probability that a yield response would be obtained from additional N. The quantity of N that is needed when the nitrate results are below 25 ppm is determined by computing the N requirements considering the soil, crop, rotation, and manure histories as described for corn, but subtracting any fertilizer N applied preplant or at planting.

For additional information on PSNT, instructions on sampling, soil testing kits, or interpretation of results, see http://nmsp.cals.cornell.edu/guidelines/factsheets/factsheet3.pdf  or contact your local Cornell Cooperative Extension office.

A new tool released for use in New York in 2007 is the Late Season Stalk Nitrate Test (Agronomy Fact Sheet #31 at http://nmsp.cals.cornell.edu/guidelines/factsheets.asp). This end-of-season test can be used to evaluate the N supply during the growing season. It is useful as a management tool as it helps identify if adjustments in N management are needed in future years.

 For corn silage, samples should be collected from one week prior to harvest until one day after harvest (if stubble height is ≥ 14 inches).

The portion of the stalk used for the test is important as the test is calibrated for the nitrates that accumulate in this part of the stalk. First measure up 6 inches from the soil surface and cut the plant. Then measure 8 inches up from this first cut, and make a 2nd cut. These cuts result in an 8 inch sample of stalk taken from between 6 & 14 inches above the ground. Make sure not to touch the soil with the corn stalk segment; contamination with soil will greatly impact test results.

 

 Sample an 8-inch segment of the corn stalk between 6 and 14 inches above the ground.

In a uniform field (≤15 acres in size) fifteen 8-inch segments should be randomly cut and combined to make one sample to be submitted for analysis. Areas differing in management or soil type should be sampled separately. Similarly, fields that are more than 15 acres large should be subdivided into smaller sampling units. Split each stalk into four parts by cutting it lengthwise using a clean kitchen knife and toss out three of the four quarters. This will quicken the drying process and reduce the volume to be submitted to the laboratory.

Samples should be submitted as soon after collection as possible. Samples should be placed in a paper bag (not plastic). This allows for some drying to occur and minimizes growth of mold. To provide the most accurate results, samples should not be stored for more than 1 day before shipment to the laboratory. Samples should be submitted to:

 Cornell Nutrient Analysis Laboratory (CNAL)
G01 Bradfield Hall, Cornell University
Ithaca, NY 14853

 The samples should be submitted with a “Late Season Corn Stalk Nitrate Test Submission Form” downloadable from the CNAL Website (http://cnal.cals.cornell.edu/forms/ documents/CNAL-Form-S-Stalk-Nitrate-Internal.pdf).

Based on research conducted in New York in 2005-2008, current interpretations are:
·         Low = less than 250 ppm N
·         Optimal = 250 to 2000 ppm N
·         Excess = greater than 2000 ppm N

These interpretations may need to be adjusted as additional nitrogen rate studies are added to the database in future years.

Low (deficient)- These fields would likely have benefited from some additional N. At harvest time, leaves are dead to or above the ear leaf and/or the entire plant has a light to very light green color. Drought symptoms are almost the same as N deficiency symptoms so drought will make N deficiency appear to be worse. Reminder: first year corn fields tend to test low (if no manure was applied), even where research has shown that optimum yields were harvested; for these fields, a low test is not a sign of N deficiency.

Optimal (sufficient)- Nitrogen availability in these fields was within the range needed for optimum economic production of corn. In this range, three of the five lower leaves will likely be dead by silage harvest time while the top leaves remain medium to dark green.

Excess - If the sample has more than 2000 ppm N, the corn had access to more N than it needed for optimum yield. Most likely, fewer than three leaves from the bottom will have died and the top leaves remain medium to dark green. If manure and/or N fertilizer were applied, the application(s) supplied more N than the crop needed that growing season.

This test is not meant as a one time measurement; it is most effective when used for multiple years on the same field (or fields with similar histories) in order to determine how the fields respond to the way N is being managed. Crop history, manure history, other N inputs, soil type, and growing conditions all impact whether the stalk nitrate test will show that the crop is deficient, sufficient or excessive in N.

The greatest benefit of this test is that it allows evaluation and fine-tuning of N management for each specific field. It does, however, require multiple years of testing to gain experience with on-farm interpretation. Stalk nitrate tests of 2000 ppm or greater indicate excessive levels of available N during the growing season and if corn stalks test above 2000 ppm for two years or more, consider analyzing a soil sample for the Illinois Soil Nitrogen Test to determine soil N supply potential and evaluate the risk of a yield decline if fertilizer and/or manure application rates are lowered.

Related Links:
Nutrient Management Spear Program
Cornell Nutrient Analysis Lab
Agro-One
Adaptive Nirtogen Management

News Letter Articles:
Effect of Sampling Height and Length on Corn Stalk Nitrate Test Results - March 2010 PDF
Impact of N Fertilizer Sources on Corn Silage Yield and Quality - February 2010  PDF
Evaluation of ISNT-Based Nitrogen Management for Multi-Year Corn Sites - June 2009  PDF
N Sidedress Rates on Corn Following Soybeans- April 2009 PDF
Illinois Soil N Test (ISNT) Usefule Tool for NYS Corn Producers - May 2008 PDF
Adapt-N: A New Tool for Adaptive N Management for Corn - May 2008  PDF
Nitrogen Savings for First Year Corn - February 2007  PDF