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Fertilizing corn in Minnesota

In Minnesota, corn is grown on more acres than any other crop. Nationally, Minnesota ranks among the top five states in corn production. Average corn yields have improved steadily over the past several decades. In the past, general fertilizer use contributed substantially to yield increases. Today, growers need a total fertilizer management plan that optimizes nutrient efficiency to increase future production and profitability.

Nitrogen guidelines

Minnesota corn growers receive substantial return for money invested in nitrogen (N) fertilizers. For many situations, you cannot achieve the most profitable yield without N fertilizers.

There are many management decisions involved in the use of N fertilizers. The most important is selecting an N rate that will bring the maximum profit with limited effects on the environment. The choice of an appropriate rate of fertilizer N is not easy because of the transient nature of N in soils.

Use the N rate guidelines in Table 1 if corn is grown in rotation with soybean or following corn when NOT irrigated. Corn grown on sandy soils deserves special consideration. If irrigated, the guidelines listed in Table 2 are appropriate when corn is grown in rotation with corn. If corn is grown following soybean on irrigated sandy soils, take a credit of 30 lb of N per acre from the suggestions given in Table 2.

For non-irrigated corn grown on soils with a loamy fine sand texture and less than 3% organic matter, use the guidelines provided in Table 3.

In the past, we considered medium-productivity soils a separate class for management consideration. Today, if soils are medium-productivity and have been more or less responsive to fertilizer N, we suggest adjusting the rate of N based on the acceptable range.

Table 1: Guidelines for use of nitrogen fertilizer for corn grown following corn or soybean when supplemental irrigation is not used

Prior crop N price/Crop value ratio MRTN Acceptable range
Corn -- -- --
0.05 180 lb N/acre 160 to 200 lb N/acre
0.10 155 lb N/acre 145 to 170 lb N/acre
0.15 150 lb N/acre 140 to 155 lb N/acre
0.20 140 lb N/acre 130 to 150 lb N/acre
Soybean -- -- --
0.05 140 lb N/acre 125 to 160 lb N/acre
0.10 120 lb N/acre 105 to 130 lb N/acre
0.15 105 lb N/acre 95 to 115 lb N/acre
0.2 95 lb N/acre 85 to 105 lb N/acre

Table 2: Guidelines for use of N fertilizer for corn following corn when grown on irrigated sandy soils

N price/Crop value ratio MRTN Acceptable range
0.05 235 lb N/acre 210 to 255 lb N/acre
0.10 210 lb N/acre 190 to 225 lb N/acre
0.15 190 lb N/acre 175 to 210 lb N/acre
0.20 180 lb N/acre 165 to 190 lb N/acre

For non-irrigated corn grown on soils with a loamy fine sand texture and less than 3% organic matter, use the guidelines provided in Table 3.

Table 3: Nitrogen guidelines for corn grown on non-irrigated loamy fine sands with less than 3% organic matter

N price/Crop value ratio Corn/Corn Soybean/Corn
0.05 100 lb N/acre 70 lb N/acre
0.10 90 lb N/acre 60 lb N/acre
0.15 80 lb N/acre 50 lb N/acre
0.20 70 lb N/acre 40 lb N/acre

In the past, we considered medium-productivity soils a separate class for management consideration. Today, if soils are medium-productivity and have been more or less responsive to fertilizer N, we suggest adjusting the rate of N based on the acceptable range. 

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Phosphate and Potash Guidelines

When needed, the use of phosphate and/or potash fertilizer can produce profitable increases in corn yields. Soil test categories represent the probability the soil will supply all the needed crop nutrients. Table 8 shows field research data summarizing the expected percent of time for a measurable response to P fertilizer and the percentage of maximum yield produced without applied fertilizer. The chance of a yield response to P and the increase in yield is greatest when soil P tests Very Low and decreases as soil test P increases. Corn yield may still be increased by P at High and Very High soil test, but the net return to P may not be profitable.

Table 8: Corn grain yield response to applied P fertilizer based on soil test category

Bray-P1 or Olsen soil test P category Expected time P fertilizer will increase corn grain yield Expected yield without P fertilizer
Very Low 87% 87%
Low 83% 90%
Medium 27% 98%
High 13% 99%
Very High 7% 99%

Table 9 summarizes guidelines for phosphate fertilizer use. Table 10 lists the guidelines for potash fertilizer use.

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Adjusting for manure use

If you apply manure, reduce the plant nutrients used in your fertilizer program. The nutrient value of manure, however, varies with type of livestock, handling system, and method of application. Old rules are no longer appropriate when calculating the nutrient value of manure. Subtract manure nutrient credits should from the fertilizer guideline.

Using a banded fertilizer

Banded fertilizer at planting is an excellent management tool, especially when soil conditions are cold and wet at planting. Yield increases are not always guaranteed with the use of a starter when soil test values are in the very high range or when recommended rates of broadcast P or K is applied. Account for all nutrients applied in starter fertilizer in the total fertilizer program.

The rate of banded fertilizer application will vary by fertilizer source and soil texture. Application of fertilizer two inches beside and below the seed row presents a very low risk for reduced germination.

CAUTION! Do not apply urea, ammonium thiosulfate (12-0-0-26), potassium thiosulfate or fertilizer containing boron in contact with the seed.

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Daniel Kaiser, Extension nutrient management specialist; Fabian Fernandez, Extension nutrient management specialist; and Jeffrey Coulter, Extension agronomist

Reviewed in 2018

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