For the third year in a row, the forecast is shaping up to feature a La Niña. There is currently a 75% chance of a La Niña during the Northern Hemisphere winter (December – February) 2022-2023.

Although we don’t often consider field-level impacts during the winter, this potential weather pattern can ultimately impact cover crops and no-till practices now and until the 2023 growing season. The ForGround team has created this resource to help you navigate production-related decisions as you look into the future.

Figure 1 - Typical wintertime La Nina pattern in for North America. Image from NOAA-PMEL.

What is La Niña?

La Niña happens when unusually cold ocean temperatures are observed in the equatorial region of the Pacific Ocean, which is the opposite of the warm phase known as El Niño. To reach a formal La Niña designation, there is considerably more exact criteria to be met, but ultimately, those cool temperatures need to persist for months in a row and be coupled with “commonly associated” atmospheric conditions (ENSO Blog, 2016). The key interest from this designation is how this alters the jet stream patterns and, ultimately, the seasonal weather (Figure 1) for the U.S. This La Niña forecast, coupled with recent trends and conditions, contribute to the final Winter Forecast from NOAA (Figure 2). It is important to point out this forecast is a regional, long-term forecast and there are many other ocean-atmosphere drivers on shorter time scales that will drive variability within the season.

Figure 2- 2022-2023 U.S. Winter Outlook for temperature (left) and precipitation (right) from the Climate Prediction Center released on October 20, 2022.

How will La Niña Shape the Near-Term Forecast?

This article will not dive into the many details and nuances of regional forecasts, but NOAA has provided the chances for above or below normal temperatures and precipitation for the U.S. These indicate increased odds for warm temperatures in south and cool in the North Central/ Northwest U.S. For precipitation, there appears to be very little relief for the drought conditions in the Plains, as there are enhanced chances for drier than normal conditions in the south and wetter than normal in the Pacific Northwest and Great Lakes regions. Soil moisture (see Figure 3) heading into winter is below normal for a majority of the West, Plains, East Coast, and Western Corn Belt, but even normal winter precipitation would not provide much relief. It is important to point out the extended ENSO (El Niño Southern Oscillation) predictions are showing neutral to El Niño conditions by next summer (ENSO Diagnostic Discussion, NOAA) The one thing that is certain about long-term forecasts and models is that they are never certain. There are many variables and there will not be any two years alike; however, these statistical outlooks should at least help us to prepare and plan for potential scenarios on the farm. So, let’s do a little “what if” scenario for key areas of the country with some increased odds for temperatures or precipitation to be above or below normal.

Figure 3- Satellite-based root zone soil moisture for the U.S. at the end of November. Map provided by NASA GRACE.

Region-Specific Recommendations

The ForGround sustainable agronomy team has taken a look at each region to provide specific recommendations for your operation to manage the affects of La Niña.

Northern Plains (Cool/Normal to drier winter signal)

Overall, the key considerations to manage with these potential conditions:

• Winter-kill and limited growth on cover crops (or wheat)
• Low moisture levels this spring for planting
• Extra crop residue
• Delayed weed growth
• Volunteer corn

Figure 4- Annual ryegrass cover crop in early Fall.

The winter does not typically offer much for plant growth or precipitation, so a cool outlook gives us less confidence of generating any extra growth of those cover crops. In fact, if there is less snow and colder temperatures, winter kill could become a real issue. Snow (as much as I hate scooping it) is extremely beneficial to overwintering plants. What will help? Keeping residue standing on those fields will help keep some of the snow on the fields and provide that extra insulation and moisture. As an example, a study in Minnesota over three winters showed the average snow depth during the continuous snow-cover period increased from 6 inches of snow with no standing residue to 22 inches in treatments with residue at the 24 in height (Sharratt, 2002). At a ratio of 15:1, that would equate to about 1 inch of extra moisture on that field.

The decomposition of the residue from the previous crop will likely also be slowed during a cool winter with drier conditions because the rate of breakdown is heavily influenced by temperature and moisture (Al-Kaisi, 2014). These conditions could also increase the amount of volunteer corn you see in the spring, due to lack of rotting. Research has shown a 10-20% decrease in soybean yields with 3,500-5,000 volunteer corn plants per acre (Jhala & Rees, 2018). This requires some extra considerations with crop protection options, especially in corn-on-corn rotation, so have that visit with your crop protection rep.

If conditions do stay dry through winter and into the spring, this may reduce or delay weed germination and growth, depending on species (Calgado, et al. 2009). This delay may not be a bad thing, but worth considering the timing of your first herbicide pass.

South (Warm/Dry Winter signal)

Key considerations:

• Water availability
• Cover crop termination timing

Figure 5 - Drought Outlook for Winter 2022-23 shows expansion in the Central and Southern U.S. Image from NOAA.

There are increased odds for warmer and drier conditions this winter for all areas of the south (west – central – east), which is the typical La Niña pattern. This means a lot of different things for different operations, so this will focus on how this influences water availability. As it sits now, soil moisture seems to be in fairly good shape except for the far west and far east areas of the region, with some pickets of dryness in Texas, but the long-term drought is still lingering. The monsoon rains and precipitation in the Mid-South and Lower Delta allowed some recharge of the upper portions of the soil. The Drought Outlook (Figure 5) shows continuation of long-term drought in most areas with some expansion towards the southeast.

Depending on your location, the expected abnormally warm and dry conditions may have a negative impact on water availability and put pressure on irrigation of crops. As we all know, a well timed rain can be a lifesaver, but this type of pattern puts water stress at a heightened risk.

Field practices and recommendations will vary significantly based on location and crop-type. From a no-till perspective, having that residue may be a blessing, especially if we are not immediately concerned about cool/wet conditions this spring. If you have grown cover crops on your row crop fields, the warm conditions will enhance growth; however, early termination may be needed to reduce water depletion in the profile. For example in Texas, Texas A&M researchers suggested terminating cover crops six weeks prior to planting cotton. You will want to pay close attention to soil-water conditions and cover growth, while consulting local resources to best determine the timing on your farm.

Great Lakes Region (Wet/Cool Winter signal)

Key considerations:

• Cool, wet soil at planting
• Using cover crops to use moisture
• Limited winter field work

Figure 6- Departure from normal precipitation (left) and temperature (right) for the region for the winter of 2008-2009. Maps from the High Plains Regional Climate Center.

The forecast for the Great Lakes region and portions of the Midwest shows a typical La Niña pattern. There have been many La Niña events in recent years, but winter 2008-2009 had regional conditions similar to this forecast (HPRCC), plus it was also a weak La Niña year (NOAA CPC). The caveat to that is winter 2011-2012 was also a La Niña and this region was very warm, so it is important to understand the variations that can take place.

A cool and wet winter in the Great Lakes region may mean a lot of things to different operations, but, the most impactful piece may be cool, wet soils lingering into the spring. These cool and wet soils may limit field work for fertilizer or weed control, and may even delay planting. If you are a no-till farmer and have heavy residue on your field, this may slow your soil temperatures and drying. Soil types will respond differently, but a recent 1-year study in 2018 by Iowa State University showed on May 8th No-Till plots were an average of 3°F cooler and contained 0.14 cm3 more water in top 2 inches than the chisel plow plots (Iowa State University, 2019).

If you have cover crops planted in your no-till fields, this growth in the spring may actually use that soil moisture and allow these fields to dry out a bit quicker (Ohio State University, 2017). According to an article from Michigan State University, cereal rye may use 0.8” of water per week in early April and increase to 1.2” per week in early May. Of course, there are other considerations to be made around herbicides and crop selection that may alter the final decision on cover crop termination timing; however, having that cover crop growing gives you some options.

Resources: ACIS Climate Maps. High Plains Regional Climate Center. https://hprcc.unl.edu/maps.php?maps=ACISClimateMaps Al-Kaisi, M. 2014. Myths and Facts about Crop Residue Break Down. Iowa State University. Retrieved from: https://crops.extension.iastate.edu/cropnews/2014/04/myths-and-facts-about-residue-breakdown Calgado, J., Basch, G., Carvalho, M. 2009. Weed emergence as influenced by soil moisture and air temperature. Journal of Pest Science. 82(1):81-88. February 2009. https://www.researchgate.net/publication/226947514_Weed_emergence_as_influenced_by_soil_moisture_and_air_temperature Cold and Warm Episodes by Season. NOAA Climate Prediction Center. https://origin.cpc.ncep.noaa.gov/products/analysis_monitoring/ensostuff/ONI_v5.php Cover crops play important role in resilient agriculture. January 13, 2022. AgriLife Today. Texas A&M University. https://agrilifetoday.tamu.edu/2022/01/13/cover-crops-play-important-role-in-resilient-agriculture/ El Niño and La Niña Alert System. ENSO Blog – Climate.Gov – January 5, 2016 https://www.climate.gov/news-features/understanding-climate/el-ni%C3%B1o-and-la-ni%C3%B1a-alert-system Groundwater and Soil Moisture Conditions from GRACE-FO Data Assimilation for the Contiguous U.S. and Global Land. https://nasagrace.unl.edu/ Jhala, A., & Rees, J. 2018. Impact of Volunteer Corn on Crop Yields. June 1, 2019. UNL CropWatch. Retrieved from: https://cropwatch.unl.edu/2018/impacts-volunteer-corn-crop-yields Kelley, L. April 19, 2021. Cover crop termination timing to help manage soil moisture. Michigan State University. Retrieved from: https://www.canr.msu.edu/news/cover-crop-termination-timing-to-help-manage-soil-moisture Managing Wet and Cold Soils. February 26, 2019. Iowa State University – Integrated Crop Management. Retrieved from: https://crops.extension.iastate.edu/cropnews/2019/02/managing-wet-and-cold-soils NOAA Climate Prediction Center - https://www.cpc.ncep.noaa.gov/ NOAA- Pacific Marine Environmental Laboratory (PMEL). https://www.pmel.noaa.gov/elNiño/what-is-la-Niña Sharratt, B.S.. 2002. Corn stubble height and residue placement in the northern US Corn Belt: Part I. Soil physical environment during winter. Soil and Tillage Research. Volume 64, Issues 3-4, March 2002, Pages 243-252. https://www.sciencedirect.com/science/article/pii/S0167198701002604 U.S. Winter Outlook: Warmer, drier South with ongoing La Niña - https://www.noaa.gov/news-release/us-winter-outlook-warmer-drier-south-with-ongoing-la-Niña

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