Corn Silage Nutrient Management

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By O.J. Barber, Pioneer Agronomist

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 silage growers also need to 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 also can impact soil fertility levels, which makes regular monitoring key to understanding soil nutrient levels. As we proceed through the fall harvest, there are some things to keep in mind as you prepare for the 2016 crop.

Soil testing informs efficient use of resources. 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 two to three years, at the same time of year and using the same methodology. Without this consistent testing, growers lack trend information that indicates if you are maintaining, depleting or building up a given nutrient.

I also recommend soil sampling be done in the fall after harvest, for the simple reason that it gives you more time to make any necessary pH or nutrient adjustments. Sampling also can 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.

There is no substitute for muddy boots. 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 (P) 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 be on the lookout for while walking fields.

Tissue testing fills in important details. 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 endeavors.

Manure for soil amendment: advantages and disadvantages. One of the advantages of being a dairy producer growing corn for silage is the ready supply of manure you can use to enhance soil fertility. In addition to being an excellent source of the key nutrients a corn crop needs — nitrogen, phosphorus, potassium, sulfur and micros — manure also provides a significant amount of valuable organic matter and improves the water holding capacity of the soil. Based upon manure application history, yield goal and soil test results, growers also may need to add commercial fertilizer to supplement manure applications on low testing soils — but manure is a great tool for corn silage growers to reduce production costs from fertilizer inputs.

It is important to apply manure in a way that is responsible and will allow the benefits to be realized: It should be spread and incorporated uniformly across the field and while field conditions are acceptable for equipment traffic without causing soil compaction. If high rates of manure are applied over time, there is the risk of overloading fields with nutrients (especially P), possibly violating regulations, along with the buildup of salts that can cause many issues with crop production.

Test manure to know for sure. Because of the significant variability in nutrient levels of manure — which is influenced heavily by the production system, handling, storage and environment — testing manure before it is applied goes hand in hand with strong soil and tissue testing programs. Growers should test manure before applying to determine appropriate application rates, and should test regularly to ensure that the nutrient concentration of the supply they are using has not shifted significantly.

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 silage yields next season.

This article was originally published in the Aug. 25, 2015, issue of Progressive Forage Grower, and is reproduced with permission.