BackgroundZone mapping is becoming a valuable tool for farmers. Defining the high and low yield areas of a field can improve how you plant the next year. In North Dakota, field level elevation change is less a factor for yield variability, but soil type can be an important contributor for varying yield levels within a field. Some soils could hold a surplus of nutrients from the previous year(s), and some may retain nutrients better.

Zone sampling is the process of taking a sample of soil and then testing the nutrient content based on yield from previous years. This is done after the field is harvested. In essence you will end up with a zone map of nutrient levels for the next year. Figures 1 and 2 are examples of the tools used to retrieve the samples needed for testing.

 Use of DataLoren Mairs uses Landsat imagery of the current years crops to look for areas of better growth in comparison to the rest of the field. To do this he downloads the text version of the green NDVI imagery, then loads the text file into a software program called MapCalc. MapCalc allows Loren to build an accurate color map of the field, and utilize this map as a guide to direct the soil sampling in the field via GPS. This field map (fig. 3,) shows the darker green areas are growing at a better rate than the red areas. These lower growth red and orange areas would be tested for nutrient levels so that next year he can apply the correct amount of fertilizer to bring those areas up to their maximum yield potential.

 Economic and Environmental BenefitsBy providing a visual guide, the NDVI imagery can reduce the effort and increase the accuracy of soil sampling. The final benefit for all this hard work will be apparent when the farmer uses the final zone map of nutrient levels during the next planting season. The farmer will not have to pay for unnecessary fertilization, and less fertilizer to buy means increased profits. It is also good for the environment, as there is less fertilizer to be washed away into streams and rivers, or to seep into the groundwater.