Extension and Ag Research News


NDSU to Study Variable-rate Fertilization

Increasingly, farmers are purchasing equipment capable of applying variable rates of fertilizer.

Producers are invited to participate in a research demonstration project to investigate the effects of variable-rate fertilization on crop yields, according to John Nowatzki, North Dakota State University agricultural machine systems specialist.

“Increasingly, farmers are purchasing equipment capable of applying variable rates of fertilizer, but many farmers are reluctant to incorporate this practice,” Nowatzki says. “It could be because there is little whole-field research available to evaluate its effectiveness. The most obvious reason to use variable-rate fertilization is to decrease input costs per unit of harvested crop.”

Northern Plains crop producers are invited to participate in the program with up to four fields each. Each field will be analyzed separately, but then combined into a single database to evaluate the effectiveness of variable-rate fertilization. Interested individuals can contact Nowatzki by e-mail at john.nowatzki@ndsu.edu or call (701) 231-8213 for more detailed information.

Variable-rate fertilizer application allows crop producers to apply different rates of fertilizer at various locations across fields. The technology needed to do variable-rate fertilization includes an in-cab computer with a field zone application map, fertilizing equipment capable of changing rates during operation and a global positioning system (GPS) receiver.

The in-cab computer uses GPS to monitor its position in the field and communicates electronically with the rate controller on the application equipment to change the fertilizer rate as the equipment moves from one zone to the next.

The number of zones in each field is determined by the variability within each field. More uniform field conditions require fewer zones. Zone soil sampling determines the residual nutrients available for the next crop. This information is used with crop yield goals to select the amount of fertilizer to apply in each management zone.

Zone maps are made using a geographic information system (GIS) computer program to combine field variability information to delineate field areas based on productivity levels.

“Several factors contribute to field variability including topography, soil physical and chemical properties, cropping history, historical cropping patterns and field uses,” Nowatzki says. “A regional project in North Dakota, Montana and Minnesota concluded that a variety of factors can be used to develop zones, but topography, remotely sensed images of previous year’s crops and historical crop yield data revealed the highest correlation to crop productivity.”

For this project, Nowatzki plans to use the Web-based zone mapping tool ZoneMap (http://zonemap.umac.org/) to prepare the field zone and application maps. It was developed and is maintained by the Upper Midwest Aerospace Consortium at the University of North Dakota. ZoneMap allows users to use historical satellite imagery and their own yield and soil test data to delineate zone maps and download fertilizer application maps.

Project participants will be required to soil test each zone separately. The producer will select the crop and yield goal. To compare the crop yield between variable rate and the normal practice of applying one fertilizer rate across the entire field, random sections of each zone will have fertilizer applied based on a composite soil test from all soil samples.

Nowatzki will use the as-applied fertilizer application maps and crop yield monitor data from a GIS computer program to analyze the data.

Participant requirements include supplying the geographic field description, cropping history, planned crop and yield goal for each field; soil sampling and testing of each zone; testing a composite soil sample; doing the variable-rate fertilization; sharing the as-applied map; harvesting the crop with a yield monitor; and sharing the yield data.

NDSU will prepare zone and fertilizer application maps, provide the maps to the producers in their desired digital format and analyze the data at the end of the growing season.

NDSU Agriculture Communication

Source:John Nowatzki, (701) 231-8213, john.nowatzki@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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