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Precision Nutrient Management Concepts

University of Minnesota Extension, Stearns County News
February 8, 2017         
Source:  Dan Martens, Extension Educator
University of Minnesota Extension
Stearns, Benton & Morrison Counties

Precision Nutrient Management Concepts
By Dan Martens, University of Minnesota Extension

FOLEY, Minn. (02/08/17)  — Here are a few notes from the Nutrient Management Conference held in St. Cloud on February 7. Keynote Speaker Dr. Raj Khosla, Colorado State University talked about Precision Nutrient Management Zones.

Today many people would think about precision nutrient management related to soil sampling fields in 2.5 acre grids. Based on soil tests and fertilizer guidelines, fertilizer application rates can be programmed for variable rate fertilizer application equipment. This has been around a while and is fairly common. Planters can be equipped for variable rate planting. This equipment is guided by GPS (global positioning systems) that are based on satellite or ground based signal systems.

GPS guided auto-steer is another notable precision ag tool being used more frequently today. If farmers are using equipment that covers 30 feet in a pass, the GPS system will determine a travel path 30 feet from the last pass and follow a path parallel to the previous pass. This improves efficiency by reducing overlaps and skips. This can be even more helpful on spraying equipment where overlaps and skips can be more serious.

Dr. Khosla says precision ag gets attention because of variability in fields. Soils, topography, and other field features change across space and plant and yield response to these conditions vary from year to year. He shared the example of a center pivot irrigated field he works with in Colorado.

With computer yield monitors on combines, they can look at yield in much smaller areas, similar to pixels on a digital camera or digital TV or computer screen. On year on this field, they look at all the yield data for each “pixel” area. The yield mean was 182.5. Only 2% of the pixel areas showed a mean of 182.5. Only 8% were within plus or minus bushels compared to the mean. Only 36% were within a range of plus or minus 10 bushels.

The goal of precision nutrient management is to match inputs to characteristics of the land. In the case of grid sampling, it is not to manage to get the same yield on every 2.5 acre grid. The goal is to optimize the inputs for each grid to get the best rate of return on investment for each grid. Some grid areas have limitations you can’t change easily. He compared this to tailor making gloves so the glove fits best with each finger and the thumb.

Dr. Khosla referred to the 5 R’s - using the Right inputs at the Right time in the Right place in the Right amounts, in the Right manner. Nutrient management zones are created with bare soil images, topographical maps, and adjusted based on the farmers experience with the land. Soil tests and other data are evaluated in these zones. Based this process, they have reduced nitrogen loads on the field by 46% and maintained yield. This year’s yield map is not a good basis for making next year’s nutrient management decisions. Khosla suggested yield maps can be more useful if compiled over about 7 years.

One lesson is that we cannot manage effectively based on broad averages. To gain the advantage, we need to be able to manage based on the inherent capabilities and limitations across the landscape. Dr. Khosla says there will be continued efforts to manage farm inputs more accurately.

Many farmers have worked on managing based on differences they have seen and experienced across the land. New technology provides tools for learning and doing more work on this.


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