Illinois Fertilizer
Conference Proceedings
January 28-30, 1991
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Dean E. Wesley1
Key Agricultural Services, Inc., has been using prescription farming techniques for making fertilizer and lime recommendations for 10 years. A computerized color-coded mapping system has been developed to interpret the levels of soil acidity and soil nutrients for selective application of nutrients. Prescription recommendations have proven useful and economical to our clients.
Our experience over the years has shown that a significant number of fields are not uniform in soil test values and that variable rates of fertilizer and lime should be recommended to maximize available input dollars, assure economic yields and minimize possible damage to the environment.
We chose to take a practical, simplified approach to the prescription method by developing a system that was understandable, economical, and at the same time, followed proven recommendations established by long-term experimental results from agriculture experiment stations.
The system that developed was based on a uniform grid sampling pattern of 16 samples per 40-acre field. This grid sampling system allowed us to determine soil differences in the field with a minimum of decision-making by the person taking the soil samples. The sampler does not have to segregate the soil types, wet spots, hillsides, etc., when taking the soil samples because the differences will show in the lab results. This is important, because once. the sampler learns the routine, it will be the same on every farm that he will be working on, making the sample collection more efficient and uniform.
The lab results for each of the soil samples are color-coded and plotted on a scaled map. The fertilizer recommendations are made on the basis of the color code as it appears on the map. The fields are tested every two years to monitor the levels of nutrients. We will know whether the crop removed more or less nutrient than predicted by the previous soil test and will make adjustments to correct the situation before a problem occurs.
The major criticism of this system has been that it is impractical to fertilizer small areas of a field. Our experience has proven otherwise. There usually are uniform trends that occur in the field; very seldom is there a random scattering of widely varying soil test values. The vast majority of the fields will show trends that involve one quarter to one-half of the field. Since the map is plotted to scale, it is easy to approximate the location of these areas and treat them accordingly. Also, an assumption that is often made is that treating one-half of a field will cut the inputs by one half. This is not necessarily true.
Many times, the same amount or even more fertilizer is required by the prescription method than by the conventional whole field method, because average soil test values that are used for the conventional whole field fertilizer recommendations are biased by a few very high soil test values. This results in a major portion of the field being under fertilized.
The prescription method assures environmental responsibility by the grower because the major portion applied will be used by plants and not build to excessive levels in the soil. And in those cases where nutrients are excessive in the soil, the impact on the environment will be minimized by cropping them down to acceptable levels.
Prescription farming is also economically responsible. Applying chemicals only where needed diverts otherwise wasted input expenses into alternative inputs or investments that give a better return to the total farming operation.
In conclusion, we have found prescription fertilizer recommendations to be practical, economical, environmentally responsible and enthusiastically accepted and used by our clients
