Producers are tempted to apply nitrogen (N) in February because it is easy to drive across the field and there is no competition with other farm activities. However, research has shown that this may be a costly operation in lost nutrients and a potential environmental concern (nutrients may leave the field and move into streams and other waterways).
A three year OSU study showed that when N is lost from a pre-greenup application (February), yields will be significantly reduced to where they are only slightly better than areas that receive no N. The outcome was the same regardless of the N source. In this same study, when nitrogen loss occurred on the pre-greenup applications, urea ammonium nitrate (28% solution) did not “burn” into the soil, ammonium sulfate did not “stabilize” into the soil, and urea did not stay put until a rain. All three of the sources moved off the plots with water as the soil thawed out, much like losses from manure on frozen ground. Even though polymer-coated products were not tested in this study, it would be expected that these types of N products would also be lost in a similar fashion under the same conditions.
As with phosphorus, the 4R nutrient management philosophy also applies for N. The right time to topdress spring N on wheat is between greenup and early stem elongation (Feekes Growth Stage 6). Rapid uptake of N by wheat generally does not begin until the latter part of April (early stem elongation). Depending upon the source, the risk of N loss increases for every week that applications are made prior to early stem elongation. Since fields may be unfit for application at early stem elongation, a practical compromise is to topdress N any time fields are suitable for application after initial greenup to early stem elongation. Research has shown that significant yield losses generally do not occur from delayed topdress until about late stem elongation to boot stage (Feekes Growth Stage 8 to 9). Boot stage refers to when the wheat head is fully developed and can be easily seen in the swollen section of the leaf sheath below the flag leaf.
A producer may get away with applying N in February on wheat. However university data has not shown a yield advantage for February applications, but results have shown a major N loss and yield reduction from pre-greenup applications. Why take the risk, just wait until greenup; the wheat does not need most of the N until April and May anyway.
Phosphorus and potassium are both considered immobile nutrients in the soil. This characteristic is important as we consider how the plant takes these nutrients up and how we make fertilizer recommendations. The characteristic is why we can use soil tests to determine plant available concentrations and work with defined soil test “critical levels” that will supply the crops need.
Plants primarily obtain immobile nutrients via diffusion. Diffusion is where a gradient of nutrient concentration is established around the root and the surrounding soil. At the root surface concentrations are low and a higher concentration exist in soil surrounding the root establishing a gradient of low to higher concentration which moves phosphorus or potassium to the root. The zone around the root system where diffusion is taking place is fairly small, measured in millimeter(s).
Through soil testing we measure the ability of the soil to supply these immobile nutrients to the plant we are growing. Once soil test levels reach a critical level, the soil is able to supply the plant needs without additional fertilizer.
Another principal that is important in understanding fertilizer recommendations for phosphorus and potassium is the plant root structure. The root system of our annual plants make up <1% of the soil volume. As discussed, the primary uptake of nutrient is via diffusion which happens close to the root surface. The small overall volume of roots and the small zone around that root system where uptake occur combine to indicate there is not a lot of plant to plant competition for phosphorus and potassium uptake. This is important in that higher yields do not require higher soil test levels and critical levels do not change with increasing yield goals.
To be clear, the root system is very important in the overall nutrient uptake of the plant. For example, in years when we have seen phosphorus deficiency symptoms it has been under conditions in which the root system has been held back. Sidewall compaction, cool wet soils or compaction are generally more likely associated with phosphorus deficiency rather than actual low phosphorus availability.
CEC (Cation Exchange Capacity)
Critical Soil Test Level for K
ppm (pounds per acre)
Equation to determine Critical Level at any CEC
Critical Level for ppm K =75+(2.5xCEC)
Critical levels for phosphorus are defined in the Tristate Fertilizer Recommendations depending on crop. The critical P level for corn and soybean rotations is 15 ppm (30 pounds per acre) or if wheat and alfalfa are included in the rotation 25 ppm (50 pounds per acre).
Critical levels for potassium are defined in the Tri-state Fertilizer Recommendations based on CEC (Cation Exchange Capacity) of the soil.
Bulletin 545, Control of Insect Pests of Field Crops, has been recently revised and updated, and is now available as a series of pdf files at our Agronomic Crops Insects web site, http://entomology.osu.edu/ag. The information available are the entire Bulletin 545 itself, files that are split into the crops that we cover (alfalfa, corn, small grains, and soybean), and finally files for each of the individual pests within the four crops. Thus, the pdf files range from a single page for pests such as slugs to over 30 pages for the bulletin in its entirety. These pdf files can be downloaded as needed.
As you use 545, remember that the pesticide label is the actual and final authority for all information, restrictions, and regulations. This publication should be used only as a guide for registered pesticides, but product labels should always be consulted before application.
The Conservation Tillage & Technology Conference will be held at Ohio Northern University in Ada, Ohio on March 5 & 6, 2013. Registration is now open. The full schedule for the program is available at http://ctc.osu.edu.
The program starts with the General Session at 9:30 Tuesday March 5th. Jerry Hatfield, director of the USDA National Lab for Agriculture and the Environment at Ames, Iowa, will discuss how to thrive in times of extreme weather conditions.
This year’s Conference will devote an entire day to cover crops on Tuesday, starting at 8:00 a.m. The Cover Crop sessions will feature: Mike Plumer, U. of Illinois, Barry Fisher, NRCS Indiana, and Dr. Jerry Hatfield, USDA. Certified Crop Adviser and Certified Livestock Manager recertification credits will be available.
Starting at 11:00, concurrent sessions take over. The Tuesday program includes Corn University; Advanced Scouting Techniques; and Nutrient Management (both days). The sessions will end about 6:00 p.m. Corn University will feature four Extension Specialists including Ohio native Emerson Nafziger, University of Illinois; Bob Nielsen, Purdue; Paul Jasa, U. of Nebraska; and Peter Thomison, Ohio State University.
The topics in the Nutrient Management Sessions at CTC have been selected to provide attendees with information on not only management of nutrients from a water quality perspective but also from that standpoint of improving understanding of fertilizers to improve crop yields and the farm's bottom line. A couple of the presentations include: Tillage and Nutrient Management Systems for Improved Drought Tolerance by Tony Vyn from Purdue University and Manure Injection Research by Robert Meinen with PennState. Cover crops, nitrogen management, valuing micronutrients and soil/tissue sample interpretation are also on the agenda. Certified livestock manager credits will also be offered at select presentations throughout this section.
The Wednesday lineup of concurrent sessions starts at 8:30 and includes: Soybean School; Water Quality; Nutrient Management; and No-till, Soil Quality and Seeding Technology. Those sessions will end about 4:30 p.m.
The Soybean School this year features Extension Specialists Emerson Nafziger, Shawn Conley and Vince Davis (both University of Wisconsin), and three from OSU, including Laura Lindsey our new Soybean and Small Grain Specialist.
Registration is available on-line and further information is also on our website: http://ctc.osu.edu.
Certified Crop Advisers here is an opportunity to attend another Conservation Tillage and Technology Conference, March 5 & 6, 2013, and receive some of your much needed continuing education credits.
· For those looking for Soil and Water CEUs, we anticipate 9 credits available.
· For Nutrient Management we expect 11 credits.
· There are plenty of credits in other areas, especially Crop Management for 23 hours.
The complete list of requested credits is posted on the website: http://ctc.osu.edu.
New this year will be easier tracking for CEUs. The sign in sheet will now contain a QR code so those CCAs with smart phones will be able to scan the QR code to report their CEUs. This means that if they are scanning the QR code, they will not have to fill out the sign-in sheet and their CEUs will be recorded within 24 hours of completing the class. With 4,000 records from past conferences, it took us a while to get through them for posting, so this helps us all. The app can be located by searching on the term: “Certified Crop Adviser” in the Apple or Android app store. A link can also be found here for more information: https://www.certifiedcropadviser.org/continuing-education. Because of the high number of CEUs at this program we are asking all CCAs with a smartphone to use this method for reporting.
- Glen Arnold (Nutrient Management Field Specialist),
- Sam Custer (Darke),
- Rory Lewandowski (Wayne),
- Debbie Brown (Shelby),
- Mike Gastier (Huron),
- Bruce Clevenger (Defiance),
- Steve Prochaska (Agronomy Field Specialist),
- Matt Davis (Northwest ARS Manager),
- Les Ober (Geauga),
- Peter Thomison (Corn Production),
- Eric Richer (Fulton),
- Adam Shepard (Fayette),
- David Dugan (Adams, Brown, Highland)