Soil Sampling Update

It isn’t too late to submit your fields for testing if you would still like to get that done this fall. With the hot, dry conditions we have delayed sampling due to fire risk but plan to continue soil sampling once we get some moisture and temperatures drop.
 

Fall Applied Nitrogen Fertilizer

Although fall fertilizer can be about nitrogen, phosphorus, or potassium, most commonly we are most concerned about the nitrogen portion. I work with farms that apply 100% of their nitrogen needs for spring wheat and durum in the fall, which has made their spring seeding go much more efficiently. All the same rules apply to fall application techniques as they do spring when it comes to nitrogen. Whether it’s anhydrous ammonia or urea, my approach is to make sure we are incorporating at least 2” deep. This is to make sure you are trapping all gasses in the soil.

It sounds silly to be saying that for urea, but as it slowly interacts with the soil, urea can temporarily become NH3 (anhydrous ammonia) before it interacts with water in the soil and becomes NH4 (ammonium) which is stable in the soil and does not leach. The exception for urea is if we receive rain to incorporate the prills into the soil after application. It certainly feels like a stretch this year with as dry as it is, but if rain is in the forecast, urea can be applied on the surface and be incorporated by rainfall. Nitrogen stabilizers can be applied to urea, like the Excelis Maxx product that Horizon Resources carries, to delay nitrogen loss via volatilization for up to two weeks which buys you some time in dry conditions.

Keeping nitrogen in the stable form of NH4 is the goal of fall applications, and that has everything to do with soil temperature. Both anhydrous ammonia and urea will quickly convert to NH4 in the soil, which does not gas off or leach, and that is what we want. If applied too early in the fall when soil temperatures are consistently above 50 degrees you will jeopardize keeping your nitrogen as NH4. Above 50 degrees, the soil bacteria Nitrosomonas and Nitrobacter are active and they are responsible for the conversion of ammonia (NH4) to nitrate (NO3). Nitrate is the ultimate fate of all applied nitrogen which is not taken up by the crop. It has a polar charge the same as the soil which is what makes it prone to leaching. Nitrogen stabilizers can help reduce N losses via this pathway as well.

All my rambling can be summarized as this; preventing your nitrogen from being converted into nitrate nitrogen is the entire goal going into freeze up, if you do that you are successful. So here is my recommendation for you this fall if fall applied nitrogen is in your plans. Use NDAWN’s website and look at their average weekly soil temperature readings; once soil temperatures on average stay below 50 degrees for a minimum of one week, its safe to apply nitrogen.

Kyle Okke, Crop Consultant, CCA

 

Late Fall Residual Herbicides

Late fall is when we want to be thinking about making applications for next seasons’ weed control with a residual herbicide. Timing that application correctly is key. Many of the products we are applying during this time are broken down by soil microbes, so by following the same rules as fall applied nitrogen you can avoid loss of the active ingredient(s). The general rule of thumb is to wait until the average soil temperature stays below 50 degrees for a minimum of 1 week and stop before the soil freezes solid. Average soil temps over the last week have been between 55 and 60 degrees in NW ND. Although the immediate forecast is warm, soil temps are now reaching that 50 degree mark (NDAWN map below - 4” depth bare soil temperature at 10 am on 10/7/24) so you may want to consider an application in the near future.


 
Keep in mind that fall applied residual herbicides are not meant to replace spring applications of pre-emergent residual herbicides. The fall application controls the earliest growth in the spring, keeping weed size and population to a minimum. This sets a clean slate for spring burndown and the additional residuals that extend weed control further into the cropping season. As weed control is rarely 100%, this layered approach is how we can keep fields clean in the age of glyphosate resistant weeds. A study conducted by weed scientist Caleb Dalley at the NDSU extension experiment station in Hettinger illustrates how effective a fall residual program can be:

Fall and spring herbicide applications for weed control in dry peas
 
Below are some of the common products applied in the fall and their uses.

Flumioxazin (Valor, Panther, Generics) Group 14 MOA
Crops: Spring Wheat, Durum, Lentil, Field Pea, Chickpea, Soybean
 
This has been the most popular fall residual for good reason, it binds tightly to clay and soil organic matter staying in the seed germination zone longer than other options with the same MOA. It also has great activity on Narrow Leaf Hawksbeard, performs well on Kochia, and has activity of a suite of other broadleaf weeds.

Sulfentrazone (Spartan, Authority, Generics) Group 14 MOA
Crops: Spring Wheat, Durum, Field Pea, Chickpea
Used widely in the spring, BUT Sulfentrazone can be a fall applied option. It does not bind to soil like Flumioxazin does and is fairly water soluble so it will leach out of the root zone if late fall rains or heavy snow were to occur. BUT in the advent of drier winters, Sulfentrazone has performed extremely well on kochia, wild buckwheat, and many broadleaf weeds.

Pyroxasulfone (Zidua, Anthem Flex) Group 15 MOA
Crops: Spring Wheat, Lentil, Field Pea, Chickpea, Soybean
This is another option that is getting more limelight for a fall application. But this active ingredient’s strong suit is not kochia. It is primarily a residual grass herbicide that has excellent activity on wild oats and foxtails. It holds tightly to clay and organic matter like Flumioxazin, which makes this a great fall applied option for fields that may have tough to control grasses.

Kyle Okke, Crop Consultant, CCA

 

Herbicide Resistant Weed Survey

Free testing sponsored by the North Dakota Soybean Council for herbicide resistant Kochia or pigweed is still available. If you have had difficulty controlling kochia in your lentils or peas, it could be due to resistance to the common group 14 herbicides that we use in these crops, along with resistance to glyphosate and group 2 herbicides. I tested several fields this summer and identified kochia populations that are resistant to group 14 herbicides. NDSU Extension scientists have previously identified group 14 resistance in the counties indicated in the map below.

 
The testing is conducted by the National Agricultural Genotyping Center in Fargo and they can test kochia or pigweed for group 2, 9 and 14 resistance using a DNA based approach. This is an improvement from the previous method which was to test populations manually using saved seed. Free testing is limited to four plants per farm, which can be from the same field or separate fields. Additional tests cost $195 per plant.

You can submit samples on your own following instructions provided by the NAGC, or reach out to us and we can conduct the sampling on your behalf. The important thing is to submit each plant separately, and not to mix leaves from different plants. Feel free to reach out with any questions.

Dr. Audrey Kalil, Agronomist/Outreach Coordinator

 

Managing Pea and Lentil Root Rot with Rotation

We know our neighbors to the North have been battling root rot in pea and lentil for many years, and the truth is that we have probably been losing yield to these pathogens for longer than we have thought. Aphanomyces is the most damaging root rot pathogen and its spores can last in the soil for more than ten years. There are regions in the world that have stopped growing peas entirely because the pathogen levels in their fields were too high. The new soil DNA test available for Aphanomyces makes it easier than ever to find out if this pathogen is present in your fields and gives us the ability to make adjustments before the pathogen population becomes unmanageable.
It is still possible to achieve acceptable yields in fields where root rot is present, but it is important to adjust your crop rotation.

Research conducted by Dr. Michael Wunsch, Plant Pathologist at the NDSU Carrington REC, found that a six year rotation was necessary to reduce root rot and increase yield in fields with root rot pressure (graphs below). By going from a two (peas/wheat) to six (peas/wheat/barley/canola/wheat/corn) year rotation he observed an increase in yield of 11 bu./ac and a 18% reduction in root rot severity. There was no increase in yield in the three year rotation (peas/wheat/wheat) compared to the two year rotation.

Three different four year rotations were compared to the two year rotation. The only rotation that was statistically better than the two year rotation was the four year rotation which incorporated flax (peas/wheat/flax/wheat). It isn’t clear at this point why flax has a beneficial impact, where four year rotations with three years of wheat, or that include canola do not.

While it would be great to think that we won’t ever have problems with root rot, that just isn’t the case. In a field at the Hettinger REC where there was no history of peas, Dr. Wunsch found that root rot increased after the 4th time peas were grown. With the long history of these crops in our areas, it is likely that Aphanomyces and Fusarium root rot pathogens are widespread. Luckily, we are in an area where we can grow a diversity of crops and have the option to extend our crop rotation and reduce losses to root rot. By combining longer rotations with an effective seed applied fungicide and planting early, we can get ahead of the game and keep these high value crops in the rotation for years to come.

Dr. Audrey Kalil, Agronomist/Outreach Coordinator