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Monday, October 5, 2015

Fall Nitrogen Applications

Although we are not quite done with the growing season, it is not too early to start making plans for the next growing season.

For some farmers, nitrogen (N) application in the fall is one of the many important decisions to make. Nitrogen is not only a large input in most corn farming operations, but it also represents an important input in terms of the environment. The soil is not a very good place to store N as this nutrient can easily end up in air or water where it can cause environmental degradation. For these reasons, I would like to review important guidelines developed through years of unbiased research in hopes that this will help you make the best decisions for N management.

Where to Apply?
Fall N applications compared to pre-plant or sidedress applications often bear greater risk of N loss that can translate into reduced profitability and environmental concerns. Still, if the decision is made to go ahead with a fall application, N should be applied in the fall only in those soils and environments with the lowest potential for N loss. Places where fall N applications should not be done are soils with high potential for nitrate leaching in the fall or early spring (sandy soils or those with excessive drainage) or soils that are very poorly drained.

What to Apply?
The goal is to use an N source that will stay in the ammonium form as long as possible because once it transforms to nitrate, that is when N becomes susceptible to loss. For fields where a fall application may be appropriate, anhydrous ammonia (NH3) is the best option. This source eliminates the nitrifying bacteria at the point of application, and the activity of nitrifying bacteria within the ammonia retention zone is also inhibited for a couple of weeks because of the temporary high pH that develops as ammonia reacts with soil water to form ammonium. To lengthen the period of bacterial inhibition, it is best to include a nitrification inhibitor with the application of anhydrous ammonia. Nitrification inhibitors, such as N-serve, can protect fall N against loss, but the greatest potential for loss occurs in the spring; by that time the inhibitor is less effective due to its breakdown over time. Nitrogen sources containing nitrate should never be used for fall applications.

When to Apply?
The activity of nitrifying bacteria slows down substantially once soil temperature where anhydrous ammonia is placed (typically at 6-inch depth) is 50°F and getting colder. Using a nitrification inhibitor is no excuse to apply N in warmer soils. In fact, warmer temperatures accelerate the breakdown of the nitrification inhibitor making it less effective. Keep in mind that nitrifying bacteria remain active until 32°F when the soil freezes. For this reason, it is better waiting as long as possible after the soil reaches 50°F and is getting colder.  So, don't go by calendar date but rather keep a close watch on soil temperatures.

Recently the Minnesota Department of Agriculture had a news release explaining when a soil temperature of 50°F is typically reached in Minnesota. The release also provides a useful link to obtain real-time soil temperature from 21 different stations throughout much of the state. However, these values should be used as a reference. It is always best to monitor temperature of individual fields before N application because soil temperature can be influenced by a number of factors such as residue cover, soil color, and drainage.

How to Apply?
Nitrogen volatilization during application is a big concern with anhydrous ammonia not only because of the unpleasant odor but because N that escapes to the atmosphere represents a loss on the investment that will not be recovered by the crop. This often happens when soils are either too dry or too wet because the knife tracks do not fully seal. Increasing the depth of application or reducing application rates can sometimes help with this problem in dry soils, but when the soil is wet, little can be done to minimize loss through volatilization.
Also, apply anhydrous ammonia with caution. Anhydrous ammonia is pressurized  in the nurse tank, and when released it reacts quickly with water. If ammonia comes in contact with your skin, eyes, or mucous membranes, it will cause dehydration and burns, so please use extreme caution when handling it.

How Much to Apply?
 To make the most profitable decision the corn N rate calculator provides the economically optimal N rate at various corn and N prices. The data used for this calculator came from trials where N loss was minimal, but it does not account for carryover N that might not have been used by the previous crop. Also, if you applied manure or the soil has high potential for N mineralization (as in the case of a field coming off of alfalfa), you will need to adjust the values derived from the calculator to reflect what will be available next year.

Once you know how much N you need, remember that you don’t have to apply the entire amount in the fall. If you don’t like taking risks, but a fall application makes sense, then apply some N in the fall and the rest in the spring. A small portion of the total N requirement applied in the fall can provide all the N the corn crop will need to get started in the spring. Applying the remainder closer to when the crop will need the most N can increase N use efficiency because there is less chance for leaching or denitrification.

For more detailed information on how to manage N please read "Fertilizer Guidelines for Agronomic Crops in Minnesota"  and the "Best Management Practices for Nitrogen" publication series 

Monday, September 28, 2015

Sauk Centre Hay Auction Summary Sept 17 2015

I am listing links to view my summary information from the September 17 Sauk Centre Hay auction and other hay markets and crop news.
It was very difficult to make dry hay in some parts of Minnesota through the summer months; and difficult to combine and bale straw for small grain in some areas. It could be helpful to check for signs of moisture issues on hay and straw this year. As with other commodities, moisture can make a difference when buying "by-the-ton."

1. September 17, 2015 Summary - All loads sold, grouped and averaged based on bale and hay or bedding type.

2. History of selected lots - averages for recent years, and each sale so far this year, Grass Hay 5-9% Protein, Straw

3. Graph of Medium Square Groups from RFV 101-200. The Red Line is for the last year. For June through September, the black vertical line represents range in prices.

Monday, September 21, 2015

Updated forecasts indicate high corn yields, but stalk rots create harvest concerns

by Jeff Coulter, Extension Corn Specialist

Much of the corn in Minnesota is rapidly approaching maturity (black layer), with some corn already mature. Updated yield predictions on September 16 by University of Nebraska researchers continue to forecast high corn yields for most of the Corn Belt, including two locations in southern Minnesota:

Thursday, September 17, 2015

Herbicide resistant giant ragweed control: Alternative herbicide options are limited

by Lisa Behnken, Extension Educator, Fritz Breitenbach, IPM Specialist SE Minnesota, Jeff Gunsolus, Extension Agronomist, Weed Science, and Phyllis Bongard, Content Development and Communications Specialist, University of Minnesota

With the increase in herbicide resistant weeds and no new herbicide chemistries on the horizon, what options remain for good weed control? Achieving acceptable weed control is particularly challenging in parts of Minnesota where giant ragweed is resistant to both SOA 2 (ALS inhibitors) and SOA 9 (glyphosate) herbicides.

Monday, September 14, 2015

Agronomic Practices to Optimize the Rotational Benefits from Alfalfa to Corn

Jeff Coulter, Extension Corn Specialist

Corn crops that follow alfalfa usually benefit from reduced or eliminated nitrogen requirement from fertilizer or manure, increased yield potential compared to following other crops, and reduced pest pressure. A recent Extension bulletin describes agronomic practices for alfalfa termination and the two subsequent corn crops that help utilize the benefits of alfalfa:

Thursday, September 10, 2015

Are you happy with your weed control in soybeans this fall?

by Lisa Behnken, Extension Educator, Fritz Breitenbach, IPM Specialist SE Minnesota, Jeff Gunsolus, Extension Agronomist, Weed Science, and Phyllis Bongard, Content Development and Communications Specialist, University of Minnesota

Figure 1. Weed escapes in soybean treated with a single preemergence herbicide application of Outlook and Pursuit on May 5. Photo taken August 6.

With waterhemp becoming more widespread throughout the state and glyphosate resistance increasing, how do your soybeans look this fall? If they look like Figure 1, it may be time to change your weed control strategy.

One strategy for dealing with glyphosate resistant waterhemp is to layer soil residual herbicides. This approach is being evaluated in Rochester, Minnesota and includes a number of residual herbicides in single and two-pass applications. The herbicides in the trial include 1) Dual (s-metolachlor), 2) Outlook (dimethenamid-P), and 3) Warrant (acetochlor). They were selected because of their known effectiveness for controlling waterhemp and their flexibility in application timing. Pursuit (imazethapyr) does not control ​this population of ​waterhemp​ (ALS resistant)​​;​ however, ​it was applied in tank mixes with the pre-emergence herbicides to eliminate other broadleaf weeds.

Tuesday, September 8, 2015

Updated corn yield, maturity, and freeze injury predictions for the Corn Belt

By Jeff Coulter, Extension Corn Specialist

Much of the corn in Minnesota is in the dent stage and silage harvest is underway. Corn in Minnesota generally reaches maturity (black layer) at 55 to 60 days after silking, corresponding to September 15 to 20 for most of Minnesota’s acres this year.
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