by Noa Lansing

When producers think of managing soil nutrients in corn production, they likely think first of nitrogen and rightly so as it is the most common yield-limiting nutrient. But nitrogen is just the beginning of the story. Corn growers need to also test for and manage potassium, phosphorus and micronutrients to maximize yields and keep the soil productive over the long term.

As corn growers continue to increase yields, nutrient removal rates also increase, making fertility management a key way to improve profitability each season. Weather extremes such as drought and excessive precipitation can also impact soil fertility levels, which makes regular monitoring key to understanding soil nutrient levels. When we get done with the fall harvest, there are some things each producer should keep in mind to prepare for the 2018 crop.

Growers should have a database of several years’ worth of soil sample results for each field to inform fertilizer decisions. I recommend sampling at least every four years, at the same time of year and using the same methods. Without this consistent testing, growers lack trend information that indicates if they are maintaining, depleting or building up a given nutrient.

I also recommend soil sampling in the fall after harvest, for the simple reason that it gives you more time to make any necessary pH or nutrient adjustments. Sampling can also be done in the spring, but you may be hard pressed to get amendments in place and available before you plant. You may also consider management zone or grid sampling and variable rate applications to maximize the value of fertilizer applications.

In many cases, nutrient deficiencies are visible on the plants during the growing season, so scouting efforts should include a close watch for signs of nutrient deficiency. Purple leaves may indicate a phosphorus deficiency, although some corn hybrids may purple early on even when P levels are adequate. Yellowed leaf margins may indicate a shortage in potash, and V-shaped yellowing down the midrib indicates a nitrogen shortage. Interveinal stripes or white banding on young leaves and shortened internodes are signs of possible zinc deficiency. These are just a few examples of nutrient deficiency symptoms growers should in addition to your regular soil testing program, I often encourage growers to conduct tissue samples when the crop is actively growing. Tissue testing can detect nutrient deficiencies that may not be visible during your regular scouting.

A consistent soil testing program to determine needed inputs, scouting your fields and using manure and fertilizer applications to maintain soil fertility will help you achieve top yields next season.