Nutrient Management

With the current corn prices, many producers are considering trading in the benefits of crop rotation to plant corn on corn while still no-tilling. Following is another in a series of CropWatch articles on critical points to consider and recommendations for making no-till corn on corn more successful.

1. Use soil tests. Use proper soil testing procedures to determine the levels of nutrients in the soil and use realistic yield goals for determining the fertilizer rates. With corn-on-corn production, a deeper soil sample is needed for residue nitrates left over from the previous corn crop (2 foot minimum, 3 or 4 foot sample preferred). Realize that continuous corn yields may be 5-10% lower than for corn following soybeans. A stalk nitrate test at the end of the season can be used to evaluate the efficiency of the nitrogen application rate. 
    
2. Apply nitrogen below the residue and the soil surface. By placing the nitrogen in the soil, volatilization losses are minimized. By reducing contact with residue, less is immobilized by the microbes breaking down the residue. (See EC155 Nutrient Management for Agronomic Crops in Nebraska for further details on potential losses.) Several minimal residue disturbance, in-the-soil placement systems are available for liquid solutions and anhydrous ammonia using knife, coulter or strip-till applicators. There are fewer options for minimum soil disturbance when injecting dry fertilizer.
   
   

   

3. Applying UAN solution. Use a knife or a stream behind a coulter to inject UAN in the soil, beneath the residue. When applying on the surface, use streaming nozzles to minimize residue contact, applying the UAN solution in bands. When surface applying liquid nitrogen or using UAN solution as a herbicide carrier, apply it early preplant when the temperatures are lower and the chances of rainfall for incorporation are higher. A urease inhibitor will reduce volatilization losses if there is a period of time before an incorporating rainfall occurs.
    
4. Applying dry urea. Some airseeders are being used to place dry urea into the soil, below the residue. To reduce losses with surface application, apply urea early in the season when the temperatures are lower and the chances of rainfall for incorporation are higher. If possible, apply urea a day or two before a forecasted rain. Do not apply urea on a wet soil or after rain as the soil is drying because losses will occur. Urease inhibitors, polymer coatings or other special ureas are available to reduce volatilization losses or to provide time released nitrogen.
    
5. Increase the nitrogen rate compared to a corn/soybean rotation. Some call it a corn-on-corn penalty, others call it a legume credit, as nitrogen rates have to be increased by 40 to 50 pounds per acre without the legume benefit. The University of Nebraska–Lincoln nitrogen recommendation for corn assumes corn as the previous crop and gives a legume credit for soybeans (see soilfertility.unl.edu for the "UNL Corn Nitrogen Recommendation Calculator"). Under heavy residue conditions, a little extra nitrogen may be justified early to help correct the carbon/nitrogen ratio of the high carbon content corn residue. This aids residue breakdown by feeding the microbes that decompose the existing residue. This releases the nutrients tied up by the previous crop and returns the extra nitrogen to the system at a time close to when the crop needs it. Tillage will decompose the residue faster by mixing oxygen into the soil system, but the carbon and nitrogen release from the residue will be rapid, far before the crop needs the nutrients. A legume cover crop could reduce some of this nitrogen penalty by providing some biological diversity.
6. Improve nitrogen timing. Avoid fall nitrogen applications on sandy or lighter textured soils to reduce leaching losses. On heavier soils, only anhydrous ammonia should be used as a fall nitrogen source and only after soil temperatures are below 50°F to minimize leaching losses. Above 50°F, a nitrification inhibitor should be used to reduce losses by keeping the nitrogen in the ammonium form longer. Even early spring applications have the risk of loss from denitrification in wet or saturated soils. Split nitrogen applications, some preplant and some sidedressed, or a healthy starter combined with sidedress is much more efficient to provide nitrogen when the crop needs it and where leaching and denitrification are major concerns.
    
7. Provide early "starter" nitrogen. Provide some nitrogen close to the growing plant by the V5 stage of crop growth to avoid stress when the plant is determining potential ear size. Some research shows that at least 30 pounds per acre of nitrate nitrogen should be readily available to the plant at this growth stage. The nitrogen could be applied as a starter close to the seed, either streamed on the surface behind the planter or with a starter attachment about 4 inches to the side of the seed furrow, or applied in a preplant application such as in strip-till or as liquid injected behind a coulter close to the row. Depending on the rate and timing, preplant anhydrous between the rows or surface applied liquid or dry nitrogen may not have enough nitrogen available to the plant at this early growth stage as the effective root zone is quite small at this time. This early nitrogen application is especially important to producers who normally sidedress or use fertigation to apply their nitrogen fertilizer.
    

8. 

   Use an in-furrow pop-up fertilizer. A starter fertilizer, applied in the seed furrow as a pop-up at planting time, will help feed slower growing seedlings. This provides good early growth, especially in cooler soils or under heavy residue; however, depending on the soil test level, it may not increase yields. (See NebGuide G361, Using Starter Fertilizers for Corn, Grain Sorghum and Soybeans) Don't put too much "salt" in the seed furrow. The salt equivalent of the total fertilizer in the furrow for no-till shouldn't exceed 5 pounds on lighter textured soils or 8 pounds on heavy soils. The salt comes from the total pounds of nitrogen (N), potassium (K), and half the sulfur (S) in the starter fertilizer. The phosphorus doesn't add salt — that's why 10-34-0 is commonly used as an in-furrow pop-up. Ammonium thiosulfate shouldn't be used in the furrow because of the high salt content and ammonium toxicity on the germinating seed. If the equivalent salt content of the fertilizer is too high or a higher rate is needed, use a starter attachment to separate the fertilizer from the seed.

    

9. Minimize soil disturbance with starter fertilizer attachments. In-furrow placement eliminates the soil and residue disturbance of the typical starter attachment and saves the cost of the attachment. Another consideration is that the attachment must be designed to handle the residue in no-till and will require additional weight on the planter to achieve proper penetration. The larger diameter, single disk fertilizer openers work much better than old-style double disk starter attachments. Many no-tillers move the starter attachments over to be about 4 inches from the row so that any soil disturbed by the attachment doesn't affect the depth gauge wheels, especially when the soil is wet and sticky. At this distance, the soil between the seed-vee and the fertilizer band is disturbed less, making it less likely to dry out in dry springs and less likely to be lost to erosion by rainfall on sloping soils.

10. Build low testing soils. Do a good job of soil testing to develop nutrient management plans. Continue dry broadcasting to build low phosphorus soils, even in no-till, as the broadcast phosphorus is a surface "band" of fertilizer that works its way down slowly. With residue on the soil surface in no-till conserving soil moisture, there are usually plenty of feeder roots right at the soil surface to pick up the phosphorus. Occasionally knife in phosphorus to create bands of phosphorus below the surface for when the soil surface is dry; this is easily accomlished if you're knifing in nitrogen. Also, sulfur and zinc can be broadcast in no-till to build low testing soils and lime can be surface applied, without incorporation, to correct pH problems over time. Use manure, when available, to build the soil and improve biological activity. If tillage is required by zoning regulations for the manure application, take advantage of this opportunity to incorporate lime and phosphorus. 

Paul Jasa
Extension Engineer
Charles Shapiro
Soils Scientist - Crop Nutrition
Gary Hergert
Extension Soils Specialist