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Variable-Rate Application of Fertilizer


Economics Technical Note Number MT-8

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Economics Technical Note Number MT-8 (PDF; 45 KB)

February 2007
by Jerry Schaefer, NRCS State Economist

Variable-rate application of fertilizer is a common practice for crop production in many states. The technology was introduced in the 1970s and '80s in some parts of Montana but never was widely adopted. NRCS developed a conservation initiative in 2003 in north-central Montana to encourage producers to evaluate the adoption of this practice on their operations. Improved water quality in surface and ground water would result from adoption of this technology. Improvements in plant health would also occur because nutrients would be applied according to the plant needs across the entire field rather than the average of the field.

Five producers who participated in the conservation initiative were interviewed to determine costs and benefits associated with adoption of the variable-rate application of fertilizer. Producers also provided feedback on ways to improve adoption of the new technology. Information obtained from each producer is summarized by the producer. A summary will follow the producer information.


Five producers were interviewed about their experiences with the new technology of variable-rate application of fertilizer. Experiences and results of each producer were unique.

Some producers showed fertilizer savings while others had no savings in fertilizer cost. Some producers used a realistic yield goal to establish the quantity of fertilizer to apply to the field and then variable-rate applied the fertilizer. Others set a target fertilizer cost per acre and then variable-rate applied the fertilizer. Finally, others wanted the volume of nutrients to be the same for the variable-rate application field as other fields on the farm but have the fertilizer applied at a variable-rate.

Some producers experienced yield increases, while others had no yield change. The yield increases may have occurred in one year and not the next. Other producers had differences in protein levels.

Some summary conclusions were:

  1. There was a learning curve involved for everyone trying the new technology. The quality of product provided by the Technical Service Provider (TSP) varied from good to bad. The entity doing the fertilizer application sometimes experienced problems getting the proper rate applied. In a few instances the fertilizer had to be applied twice to get the correct rate.
  2. When producers applied the variable-rate fertilizer themselves they needed a three-tank system to keep the starter fertilizer application with phosphorus different than applying the nitrogen at a variable rate.
  3. A Global Positioning System (GPS) precision guidance system was required to apply the fertilizer for the different zones developed.
  4. A GPS guidance system for the combine with a yield monitor is needed to see the results of the variable-rate application of fertilizer. The yield monitor results can then be used to refine the zones and determine additional areas for soil testing.

The NRCS conservation initiative in north-central Montana to encourage producers to evaluate the adoption of variable-rate application of fertilizer was a success. Producers in several counties in north-central Montana tried the new application method. Of the five producers interviewed, most planned to continue variable-rate application of fertilizer. The producers' planned to continue to refine the zones and the amount of fertilizer applied. This will result in the best use of the fertilizer and the corresponding yields associated with the fertilizer application. In areas where excess fertilizer was applied, groundwater will be improved due to less leaching of nutrients.