5 tips for continuous corn nutrient management

Dan Kaiser and Jeff Coulter
University of Minnesota Extension
Probably the biggest challenge when it comes to managing continuous corn is the amount of residue that can be left in the field.

When it comes to nutrient management, continuous corn can present challenges. Research has identified a few things that you should consider when managing continuous corn to maximize yield and profitability.

1. Residue management is key

Probably the biggest challenge when it comes to managing continuous corn is the amount of residue that can be left in the field. Corn residue can be slow to break down and tends to be high in carbon and low in nutrients, like nitrogen (N), which are needed for soil organisms to break the residue down. More N is suggested when corn follows corn compared to corn following soybean to account for less available N from the soil due to N being used for microbial decomposition. The application of N as UAN or sulfur (S) as ATS in the fall has been studied as a means of speeding up residue decomposition, but it has not been found to be effective.

2. Do not starve the crop early in the growing season 

Nitrogen and sulfur are two critical nutrients that can be in short supply in continuous corn early in the growing season. A low rate of N and S should be applied at or before planting in situations where the bulk of the N is applied as a sidedress application. Research has shown that maximum yield can be achieved when 45 lbs N/acre is applied at or before planting, with the remaining N applied at V5 to V10 in wet years. Split-applying S is not needed. In most cases, as little as 10-15 lbs/acre of available S applied as a single application at planting can be enough to maximize yield in continuous corn regardless of the soil type or soil organic matter levels.

3. Should you apply starter fertilizer? It depends

Application of fertilizer with the planter (either on the seed or in a band away from the seed) can benefit corn early in the growing season. Near-seed placement of phosphorus (P) can increase early plant growth and vigor but is generally less important for maximizing yield in situations where soil tests are near optimal levels of P (medium to high soil P tests). We have had some success maintaining high yield potential with surface-banded starter to the side of the row containing N and S fertilizer. Both are mobile and will move quickly to the roots if they are placed on clear soil with the planter. Some growers have opted for applying a low rate of 10-34-0 in-furrow (as little as 2.5 to 3 gallons/acre), while also applying N and S as a surface band. For those that do not have the option to do both, it is more important to pick what will give you the greatest chance for increasing yield.

4. Placement of nutrients in important

This tip does not relate to band versus broadcast but rather to the placement of nutrients in a way so that they will not be intercepted by decomposing corn residue. Row cleaners are important when using surface-banded starter. Placing nitrogen in a manner where the residue will not be in contact with the fertilizer is also important. Surface application of urea without incorporation and high levels of crop residue can result in greater volatilization of urea. Knowing the risks for N loss and how they relate to residue is critical to ensure money spent on fertilizer is well-utilized.

5. Know how nutrients cycle when deciding when to take soil samples 

Careful planning of when and where to take soil samples is critical to ensure accurate soil test results. Since crop nutrients are more likely to be applied ahead of corn, keep in mind that some time is needed between fertilizer application and soil sampling, as recent fertilizer applications can inflate soil test results. It is generally best to sample after the growing season but before your next fertilizer application. Corn residue can also contain substantial quantities of potassium (K) which is slow to leach from the residue. K recycling is important when it comes to K availability and can be significantly limited in dry years. Remember, when taking soil samples from corn residue, it is generally better to wait to allow for some of this K to be cycled. Therefore, if you take soil samples early in the fall, you may see lower K soil test values some years.

Continuous corn can be a viable cropping system with careful planning of how you manage nutrients, along with insects and other pests. When managing crop nutrients, knowing which nutrients may be short and when there are deficiencies is important to ensure nutrients will not be yield-limiting.