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There are several considerations when applying fertilizer in the fallPosted Monday, October 3, 2011, at 4:13 PM
Harvest is progressing steadily with the continued warm and dry weather opening up fields for the application of fertilizer for next year. Some lime and potash and phosphate have been applied on a limited basis. Soil testing is the best way to determine pH and the nutrient needs of the next crop.
Application of lime where the pH is low will probably provide the best return on money assuming other nutrients are at the recommended levels. Lime aids in making the nutrients in the soil available to the plant.
Low soil pH can often be a deciding factor in micronutrient availability. The soils may not be truly deficient of the nutrient and it may be in the soil, but the pH of the soil keeps it from being readily available to plant growth.
Another common practice in this area is the fall application of nitrogen (N). There are four considerations in deciding how to manage fall applications of N.
What to apply -- For fall applications, the only recommended sources are anhydrous ammonia and ammonium sulfate. Both fertilizers are either in the ammonium form or transforms to the ammonium form quickly and are adsorbed onto exchange sites in soil particles and organic matter and is thus protected from leaching.
Nitrogen sources containing nitrate should not be used since it will not become adsorbed onto exchange sites and can be easily leached from the soil. One of the advantages of anhydrous ammonia is that it kills nitrifying bacteria at the point of application. A nitrification inhibitor will lengthen the period of microbial inhibition and many years of research indicate that nitrification inhibitors can protect fall nitrogen against loss and increase the amount of nitrogen present in the ammonium form the following spring.
When to apply -- Nitrifying bacteria are active until soils freeze (32 degrees F) but their activity is greatly reduced once soil temperatures go below 50 degrees F.
Application needs to be directed by soil temperatures and not by date. The temperature guidelines apply equally for anhydrous ammonia, ammonium sulfate, and manure/organic fertilizers that can be used in the fall.
Where to apply -- Soils with high potential for nitrate leaching in the fall or early spring (sandy soils or those with excessive drainage) should not receive fall nitrogen applications. Northern Missouri should have adequate cold temperatures to prevent nitrogen loss.
How to apply -- Soils that are too dry or too wet can result in ammonia loss to the atmosphere because the knife tracks may not seal properly. If you apply manure, poultry litter or other animal-derived fertilizer, incorporate then into the soil to avoid volatilization.
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As our local University of Missouri Agronomy Extension Specialist, Crook has been writing a column for the print edition Agriculture page for the past three years and we will now be sharing it on our web version. Crook has a bachelor and masters degree in agronomy from University of Missouri and received his doctorate in Agronomy from Kansas State University. He was in soybean variety development research for 22 years for various seed companies and has been Saline County's agronomy specialist for 10 years.