Dave Franzen

Dr. David Franzen, NDSU Extension soil specialist

CARRINGTON, N.D. – No matter what type of tillage system a farmer uses, the ability for site-specific nutrient management is a growing trend. Gathering this information allows a grower to determine whether fertilizer is needed or not, and at what rate, according to Dave Franzen, North Dakota State University Extension soil specialist.

Franzen spoke at the recent Central Dakota Ag Day in Carrington, N.D., on Dec. 5, and outlined the advantages that can be obtained by using zone soil sampling and mapping in a site-specific nutrient management program. There are two other methods that can be used to obtain this information – grid soil sampling and sensor information, which is usually obtained from a growing crop.

In grid sampling, it takes about one sample per acre grid to characterize a field, and this represents about 50 percent of the nutrient variability in a field, according to Franzen. A soil sample per a 2.5-acre grid only captures about 20 percent of the field’s variability and a 5-acre grid only about 10 percent of the nutrient variability in a field. This method works in areas, such as the “I” states, where there is usually high range rates that require only maintenance fertilizer rates.

However, in North Dakota, lower fertilizer rates have been the rule, resulting in lower range rates for soil nutrients. It has been discovered that the variation in all soil nutrients are related to soil and landscape position, unless part of the field has a historic manure history.

Zone sampling

Zone sampling assumes that fertility patterns exist because of some logical and predicable reason. Zone sampling, according to Franzen, captures about 50 percent of nutrient variability, which gives similar results to a 1-acre grid sampling program.

“The adoption of zone sampling has really made site-specific nutrient application in North Dakota very possible, very productive and profitable,” he said. “One of the big mistakes people make when they go into zone sampling for the first time is they will gravitate to something like a soil map, which is the worst thing you can do.”

Instead, Franzen said you need to use at least two tools and combine their information to develop your soil zones. Those tools should include such things as information from yield monitors, satellite images, optical sensors and electrical conductivity (EC) or magnetic flux (EM) sensors.

Most crop consultants will ask the grower to view the proposed zones before committing to their use for crop management. If that grower has been working a farm for several years, they will usually be able to easily recognize the zones being proposed. Grower input is critical to the successful implementation of zone nutrient management, Franzen noted.

Soil sampling procedures can be accomplished once the management zones are developed. Ideally, most fields can be broken down into 3-5 zones and about 10 soil sample cores will be taken per zone. Franzen stressed yield potential does not factor into the zone recommendations.

“Zone management will be useful in about 98 percent of our fields,” he said. “It will improve the efficiency of fertilizer application, distributing fertilizer to areas that need it and greatly reduce wasteful fertilizer applications.”

In contrast, that using a 2.5-acre grid system will result in a poor map that will result in a less than positive economic return for the effort put into such a system.

More information can be obtained on the following David Franzen websites: https://www.ndsu.edu/soils/personnel/faculty/dr_david_franzen/, https://www.ndsu.edu/fileadmin/soils/pdfs/SF-1176-2.pdf, or https://www.ndsu.edu/fileadmin/soils/pdfs/SF-1176-3.pdf.