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It's a good time to adjust fertilizer for higher yieldsPosted Monday, November 1, 2010, at 3:11 PM
Crop yields have steadily increased over the past years. Average corn yields in the past ten years have increased by about 2.8 bushels per acre for a total of 28 bushels per acre. The average soybean yield in the same period has increased about 0.6 bushels per acre per year for a total of 6.3 bushels per acre. When planning your fertility needs, be sure to consider the higher yield levels and account for nutrient removal and set realistic yield goals.
A soil test is always beneficial in determining fertility plans. The soil test provides information as to what is available from the soil as well as the condition of the soil. The soil test indicates what is needed to meet yield goals and also what is not needed to aid in managing costs. With the cost of fertility and increasing yields, sampling soil every two years may enable you to better manage nutrients and the expenses associated with them. In medium to high yield environments it is important to keep the soil test values for each nutrient in the maintenance zone. The maintenance zone is that level of nutrients at which there is a small probability of a yield response when soil test values are above the maintenance range.
Soil pH greatly affects the availability of all nutrients. At soil pH levels between 5.5 and 7.0, the nutrients as a whole are more available than at pH's outside of this range. A soil pH of 6.5 should be targeted.
As yield levels increase secondary nutrients may become more of an issue. In the past, impurities in fertilizer, usage of manure and natural soil levels provided adequate levels of secondary nutrients. As yields increase the levels of secondary nutrients in the soil may not be sufficient to produce maximum yields.
Boron, calcium, iron, molybdenum, sulfur, manganese and zinc are some of the more important of these nutrients. Some soil types such as sandy soils or other low organic matter soils may not supply adequate sulfur. Tissue testing can be used to determine if deficiencies are occurring.
The most important factor to remember is the balance of nutrients. One nutrient being high cannot compensate for another nutrient that is low. Each nutrient needs to be at levels that provide a balanced diet for the plant to produce maximum yields and the pH needs to be at the correct level so that the nutrients in the soil are available to the plant to provide the balanced nutrition it needs.
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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.