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Concerned about rising prices for fuel and fertilizer, crop producers are searching for ways to trim input costs. A switch to a conservation tillage system is one way to do this. There are various conservation tillage systems appropriate for Minnesota. There are many thinking about switching from conventional to conservation tillage systems.

The switch does not necessarily mean that major changes in management practices are needed. There is no need to change practices such as hybrid selection, planting date, and plant population. However, there should be a change in thinking about fertilizer management. Those changes in fertilizer management are described in the paragraphs that follow.

Nitrogen Application

Results of research conducted in the northern Corn Belt, to date, lead to the conclusion that rate of applied nitrogen should not be changed. There is also no strong evidence to suggest a need to change either nitrogen source or time of application as described in the published Best Management Practices. Regarding placement, the most efficient use of nitrogen occurs when the nitrogen fertilizer is not placed in contact with crop residue. This means that in conservation tillage systems, the nitrogen fertilizer should be placed 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 Minnesota. The option chosen by an individual grower, however, should be consistent with Best Management Practices for nitrogen. There are several placement options because nitrogen is mobile in soil s and can move to the root system with soil water.

The Best Management Practices are important guidelines. They are closely tied to the guideline for rates of fertilizer nitrogen to be applied. Those guidelines for the highly productive soils of Minnesota are listed in Table 1.

Table 1. Guidelines for use of nitrogen fertilizer for corn grown on soils considered to be highly productive.

* MRTN = Maximum Return To Nitrogen

Looking ahead, crop producers who use conservation tillage planting systems should give serious consideration on split applications of nitrogen. Results from research trials continue to lead to the conclusion that efficiency of use of fertilizer nitrogen increases as split applications are used.

Since nitrogen is mobile in soils, there are several options for this management practice. In the western part of the state any combination of fall, spring preplant, and sidedress applications are appropriate. In eastern Minnesota, the fall application is not an option. The fall option is also eliminated for corn production on sandy soils.

The application of fertilizer in a band 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 nitrogen 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 nitrogen applied in this band should be limited to less than 50 lb. N per acre. The rate could probably be increased if fertilizer was placed deeper and, thus, further away from the seed. However, this added depth would not be ideal for the phosphate and potash.

Phosphate and Potash Management

In contrast to nitrogen, phosphorus and potassium do not move much in soil. Therefore, placement is more of a concern. There's general agreement that banded applications of phosphate and potash are necessary if a conservation tillage production system is to be successful. This conclusion is based on the results of research conducted in Minnesota and surrounding states.

Rates of phosphate and potash fertilizer that are suggested are adjusted for soil test values for phosphorus (P) and potassium (K). The rates of phosphate suggested for the banded application are listed in Table 2. Currently, these rates are based on expected yield and soil test value for P. These rates are the same as for banded application in conventional tillage systems.

Table 2. Phosphate fertilizer suggestions for banded applications in conservation tillage production systems.

Suggestions for potash use are higher than the rates suggested for banded application in conventional tillage systems. These rate suggestions are listed in Table 3. These rates are based on results of research conducted in Minnesota and surrounding states.

Table 3. Potash suggestions for annual banded application in conservation tillage systems.

Use of phosphate and potash cannot be ignored for the soybean crop in rotation. The soybean crop will respond to banded phosphate if the soil test for P is low (less than 10 ppm, Bray or 8 ppm, Olsen). Likewise a soybean response to banded potash 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 phosphate and/or potash is 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. Application on alternate years assumes that the row will be in the same place each year.

At this time, they are no definite suggestions for the depth of the fertilizer band. In the various research projects, the banded phosphate and/or potash was placed 4 to 5 inches below the soil surface. There is no reason to believe that a deeper placement would be 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. This management tool is encouraged regardless of soil test values for P. This N/P combination usually stimulates early growth of the corn crop. There is no need to plan to place fertilizer in contact with either corn or soybean seed. There is a potential for a negative impact on emergence. Fertilizer in contact with soybean seed has a negative effect on emergence. There are various attachments available that will place fertilizer very close to the seed and this is fine.

Sulfur fertilizers that can be mixed with 10-34-0 should not be placed in contact with the seed if damage to emergence is to be avoided.

*The August 4, 2006 edition of this newsletter described the suggested management practices for use of phosphate and potash fertilizer in conservation tillage production systems. There was a mistake in the heading for Table 3. The original heading was "Potash suggestions for annual banded application in conventional tillage systems." This should be changed to "Potash suggestions for annual banded application in conservation tillage systems." (correction has been made to the above table)

In working with phosphate and potash fertilizer application in any tillage system, it’s important to remember that there can be substantial variability in soil test values for P and K across any landscape. The analytical procedures used in a soil testing laboratory are accurate and are always checked by analyzing standard samples. This laboratory accuracy, however, will not overcome the variability that exists in fields.

In providing guidelines for use of phosphate and potash, it’s necessary to define ranges with specific numbers. For examples, a low level of phosphorus is defined as 6 to 10 ppm (Bray procedure) or 4 to 7 ppm (Olsen procedure).

In addition to the analytical value from the analysis, the decision regarding rate of phosphate and/or potash to any field should be tempered by knowledge of the variability in the field. Use of grid or zone sampling is an excellent way to get some measure of variability. If substantial variability exists, there should be some allowance for some flexibility in rates applied unless variable rate application is used.

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