No. 8 Article 10/May 18, 2007

Fertility Management for Corn on Corn

Due to favorable prices encouraged by increased demand for ethanol production and strong export sales, we will likely see more corn this year. The USDA has indicated that for 2007, Illinois farmers intend to plant 12.9 million corn acres. That means 1.6 million, or 14.2%, more acres compared to 2006. Since most of those acres will be planted on previous-year corn, there is a lot of interest in fertility management for continuous corn (CC).

Manage for root growth. The most important point to remember is that CC or corn in a corn-corn-soybean (CCS) rotation is still corn, and as such, fertility management needs to be targeted to provide adequate nutrition for this crop. In addition to providing adequate fertility, it is important to realize that CC is a more stressful environment than corn in rotation. Since the benefits of adequate fertility can be realized with adequate uptake of the nutrients by the root of the growing crop, it is recommended to manage for improving root growth.

When doing CC, choose the most productive fields with good drainage and adequate water-holding capacity, minimize soil compaction, and manage the residue from the previous crop. Applying sufficient fertilizer does not always equate to having the nutrients available. This is especially important at early growth stages in fields with high surface residue, such as those of CC. The large quantity of residue left from last year's corn in conservation tillage, and especially no-tillage, systems can cause cooler soil temperatures and wetter soil conditions that can delay planting, germination, and root development. Under these soil conditions, roots' ability to take up nutrients is decreased due to a smaller volume of the soil being exploited by the root system, a decline in the ability of the crop to actively take up nutrients, and slower movement of nutrients in the soil.

Placing a starter fertilizer close to where the young root will be growing can help lessen the impact of early-season adverse soil conditions and get the crop off to a good start and maintain yield potential. This was especially true for corn planted early this year. At this time most soils are sufficiently dry and warm, so there should not be need to be concerned about young roots being able to access nutrients.

Nitrogen. Application of some extra nitrogen can be needed in CC compared to a corn-soybean (CS) rotation, but that is not always the case. The N rate calculator was designed to aid in the determination of N rates to obtain the maximum return to N (MRTN). Using data from many trials in Illinois and a price ratio of 0.1 (for example, $0.37 per pound of N and $3.70 per bushel of corn), the data indicate the following to provide the MRTN for CC compared to CS: for northern Illinois, add 47 lb N/acre; for southern Illinois, add 14 lb N/acre; for central Illinois, no additional nitrogen is needed. These N-addition values will change only slightly by changing the price ratio.

Additional N needs in a CC compared to a CS rotation result mainly from the fact that corn produces much more residue with lower N content than does soybean. These characteristics of corn residue cause greater N tie-up in the process of decomposition and a slower rate of mineralization. Again, application of some of the additional nitrogen in a starter can be beneficial, not only to provide a jump start to the crop but also to compensate for the greater N immobilization occurring during corn residue's decomposition in contrast to soybean residue.

Phosphorus and potassium. If phosphorus and potassium are at adequate levels, there is no need to make any significant change when going into a CC rotation. If the soil test levels are below recommendations, you are advised to establish a fertilization program that will bring them up to sufficiency ranges. In situations of short tenure of the land, where a build-up approach is not permissible, band application at maintenance levels will provide the best management approach. Since we are talking about maintenance levels in a crop removal fertilization program, let me tell you that it is important to remember that there is a difference in the amount that will be needed to provide maintenance levels between a CC and a CS rotation. A 180-bushel corn crop removes 77 pounds of P2O5 and 50 pounds of K2O. On the other hand, a 50-bushel soybean crop removes 42 pounds of P2O5 and 65 pounds of K2O. This means that a CC rotation will require more P and less K than a CS rotation. Increasing the number of acres in CC will also make time management during the planting season an important consideration. For this reason it is advisable to apply P and K in the fall, to avoid time conflicts during the busy planting season. This time of the year, as well as early fall, is a good time to collect soil samples for P and K analysis.--Fabián Fernández

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