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Timing is Everything: A Comprehensive Approach to Crop Nutrition

Sep 10, 2018

Grid soil sampling

Grid soil sampling has served as the standard for assessing soil fertility for the last several years. It has allowed growers to invest fertilizer dollars more effectively in comparison to dated alternatives such as composite sampling. Grid soil sampling serves as an excellent base for looking at pH, phosphorus, and in some cases potassium levels. pH and P1 (plant available) phosphorus levels are the two most accurate soil tests conducted. In the case of phosphorus, keeping P1 levels above critical levels but below excessive levels will ensure that maximum yield isn’t limited by phosphorus levels and reduce the environmental impact of off target movement of phosphorus in the soil. Managing phosphorus voluntary and intelligently using grid soil sampling data will help to ensure that farmers can better manage the slippery slope of fertilizing their crops for a yield goal and not a law. Ensuring that soil pH is between 6.0-6.5 is the key to maximizing nutrient availability. Outside of this range certain nutrients become less available causing a yield limitation to the growing crop.

Tissue Testing and Crop Modeling

But what good is having high levels of nutrients in the soil if they aren’t making it into the plant? Soil testing is only the first step in a comprehensive nutrient management program. The grower of tomorrow will use the combination of grid soil sampling, tissue testing, and crop modeling to guide a targeted nutrient application with the goal of feeding his crop, not hitting critical soil test levels. Looking at Winfield United’s eastern cornbelt (IL/IN/OH/MI) tissue testing results from 2012-2017 some patterns stand out in the case of macronutrients.

Corn is running out of nitrogen, sulfur, and potassium late in the season regardless of soil test levels. In the case of nitrogen, we don’t necessarily need to apply MORE of it, we just need to use all of the data available to decide WHEN to apply it to maximize uptake and increase yield. According to Dr. Fred Below’s research at the University of Illinois, over 25% of nitrogen in corn is taken up during the grainfill period (R1 and later).* In soybean, 75% of nitrogen is taken up during this period.* Capturing yield during grainfill is where the majority of our opportunity lies with nitrogen in the eastern United States—late season applications guided by tissue testing and crop modeling data. Leeching, denitrification, and time work against nitrogen applications as soon as they are made. Using the combination of tissue testing and a crop modeling tool such as Winfield United’s Field Forecasting Tool (FFT) will help growers to most accurately invest every dollar they spend on nitrogen with an emphasis on not only yield but ROI as well.

But nitrogen is only a part of the story when it comes to managing nutrition in season. Winfield United eastern cornbelt tissue test results continue to show season long tissue test deficiencies in potassium worsening throughout the reproductive stages of development specifically in soybean but in corn as well. These deficiencies are present in some high K2O potassium testing soils as well, meaning that the plant is not able to take up the nutrient that is present on the soil test. The reason for this is complicated but it involves K2O potassium’s ability to be held tighter to different types of clay. We see the same thing with tightly held positively charged micronutrients such as zinc and manganese. For that reason, some growers in the east have moved to in season applications of dry potash and foliar applications of zinc and manganese which are readily absorbed through the leaf. In addition to nitrogen, leachable nutrients such as sulfur and boron are also being applied inseason in order to better manage timing of uptake by the crop. Winfield United’s FFT is the industry’s only crop model which assesses both nitrogen and potassium stress calibrated to inseason tissue tests providing a data based agronomic and economic recommendation for two major nutrient deficiencies we are seeing late season in both corn and soybean.

Using tissue testing to supplement a grid sampling program is the next step for many growers to move to a crop nutrient program based on timing of application of key nutrients and feeding the crop for maximum ROI. Additionally, using the FFT tool to guide these applications in terms of timing and assessing their value both in terms of overall yield and economics brings real time value to the grower in terms of maximizing his crop nutrition investment in the most targeted way possible. When considering crop nutrient applications for higher yields in the future, using all of the available data to determine when a nutrient application will influence yield will add incremental bushels in the most cost effective way possible.

*Source: Crop Physiology Laboratory, University of Illinois

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