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Corn+Soybean Digest

Fertilizer in Conservation Tillage

Concerned about rising prices for fuel and fertilizer, crop producers are searching for ways to trim input costs. Many producers are thinking about a switch to a conservation tillage system to do this.

The switch does not necessarily require major changes in management practices. There is no need to change practices such as hybrid selection, planting date and plant population. However, there should be a change in fertilizer management.

Research in the northern Corn Belt supports current rates of nitrogen (N) application. There is also no strong evidence to suggest a need to change either N source or time of application as described in the published Best Management Practices (BMP).

The most efficient N placement is avoiding contact between N fertilizer and crop residue. This means that in conservation tillage systems, the N fertilizer should go below the soil surface. There are several options for doing this, and one option has not proven to be more effective than another.

The placement options are not consistent across geographies. The option chosen by an individual grower, however, should be consistent with nitrogen BMP. There are several placement options because N is mobile in soils and can move to the root system with soil water.

The BMPs are important guidelines. They are closely tied to the guideline for rates of fertilizer N to be applied.

Looking ahead, crop producers who use conservation tillage planting systems should give serious consideration to split applications of N. Results from research trials continue to conclude that N efficiency increases with split applications.

Since N is mobile in soils, there are several options for this management practice. In western Minnesota, for example, any combination of fall, spring preplant and sidedress applications are appropriate. In eastern Minnesota and on sandy soils, fall application is not an option.

Banding fertilizer at the time of creating the “strip” in the fall is an important management tool. It seems reasonable to ask if all of the needed N can be applied in this band. There has been limited research to address this question. However, results of research conducted to date suggest that the amount of N applied in this band should be limited to fewer than 50 lbs. N/acre. The rate could probably be increased if fertilizer is placed deeper and, thus, farther away from the seed. However, this added depth would not be ideal for phosphate (P) and potash (K).

In contrast to N, P and K do not move much in soil. Therefore, placement is more of a concern. Applications of P and K are necessary for a conservation tillage production system to be successful, according to research.

Rates of P and K that are suggested (see These rates are based on expected yield and soil test P values and don't differ from conventional tillage systems' banded application.

SUGGESTIONS FOR K USE are higher than the rates suggested for banded application in conventional tillage systems. These rates are based on results of research conducted in Minnesota and surrounding states.

Use of P and K cannot be ignored for the soybean crop in rotation. The soybean crop will respond to banded P if soil test levels are low. Likewise, a soybean response to banded K can be expected if the soil test for K is 100 ppm or less. If the soil test values for these nutrients are low, the rates suggested for corn should be used for the soybean crop.

If P and/or K are needed for both crops in the rotation, it may not be practical to apply the fertilizer each year. For these situations, doubling the appropriate rate and applying on alternate years is satisfactory. Alternating application years assumes that the row remains in the same place each year.

At this time, there are no definite suggestions for the depth of the fertilizer band. In the various research projects, the banded P and/or K was placed 4-5 in. below the soil surface. There is no reason to believe that a deeper placement is more effective.

For all conservation tillage systems, a small amount of a fluid fertilizer (10-34-0 for example) placed in contact with or near the seed would be appropriate regardless of P soil test values. This N/P combination usually stimulates early corn growth. Fertilizer contacting the seed has a negative impact on soybean emergence, and is not necessary for corn. There are various attachments available that will place fertilizer very close to the seed.

Sulfur fertilizers that can be mixed with 10-34-0 should not contact the seed; it has a negative impact on emergence.

Editor's Note: George Rehm is a nutrient management specialist and professor emeritus from the University of Minnesota.

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