Bout With Drought – Part 2
Nitrogen Application Opportunities in Water-Limited Environments
In our previous article, we discussed the importance of moisture early in the growing season in getting the crop off to a fast start. Across much of the Corn Belt, we know water has been a limited resource and each year, getting either too much or too little rainfall is a factor we generally can’t control.
Nutrients need to be available at planting for the plant to utilize at its earliest opportunity, and present in adequate quantities to sustain increased crop growth until the next opportunity for application or to reach availability of previous applications (fall/spring applied anhydrous). As we move through or beyond the sidedress season, reflecting on crop observations made from the tractor cab will lead to better crop management in future seasons.
Starter Nitrogen: A Strong Foundation Starts with Understanding Each Acre’s Behavior
At Advanced Agrilytics, we work with growers to understand several factors including soil wetness index (SWI), organic nitrogen contribution, slope, and their current crop rotation to evaluate opportunities to improve management in all facets of agronomy. Many of our fundamental principles are driven by water movement – quite simply, where water runs from, where it runs to, and in the areas of catchment where it stays saturated. With this in mind, SWI describes where water runs to and from across a field’s surface. The higher the SWI number, the more water that is running to that specific area of a field.
However, it does not tell us if a specific area of a field is truly saturated. Therefore, we have to take into account historical yield data to validate whether an area of high SWI or catchment is at risk of excess moisture over a longer period. This is a critical component when we move toward action steps to ensure the crop is set up to receive appropriate nutrition and possible nutrient protection at the most opportune time.
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Variable Rate 2×2 Applications
After initial environmental understanding, we sometimes recommend and can create a 2×2 recommendation that allows us to spatially evaluate nitrogen needed to get this crop to V6. In the example below, our 2x2x0 product is a 70/30 UAN 28% and ATS mixture. In our trial work, we have found that we have grown a bigger plant (aboveground mass) in the VR 2×2 evenly through all environments, even the water-limited acres. Therefore, we expect to achieve consistent canopy in all environments within that 30- to 45-day timeframe.
The understanding of acre behavior and tendencies is critically important when conditions aren’t favorable. Consider these two scenarios that are common: the stable acre, or the acre that often receives the final water deposition after a rainfall, versus the water-limited acre. The stable acre has adequate moisture, better soil structure and mineralogy, and often grows the best crop. This is because we have an increased rate of diffusion of nutrients, better root mass, and more than likely a greater organic nitrogen contribution, among other things. It tends to grow a viable and thriving crop and does so year after year. But what about the tendencies of the water-limited acre? Most years, at some point our lighter soils on knobs (higher elevation, lower organic matter, etc.) lose moisture. This leads to a decreased rate of diffusion, decreased root mass development, decreased nitrogen uptake, and ultimately a decreased opportunity to get to canopy in a timely manner. As a result, it has the tendency to slow growth and ultimately “burn up” due to sunlight penetrating the soil surface and reflecting upwards to the bottom of our leaves.
In the flat rate check strips comparing a 7-gallon flat rate (same mixture) vs. the 12-gallon flat rate (same mixture), we are clearly achieving canopy in the water-saturated areas. This is because we have a greater ability for diffusion and mass flow. In the more water-limited environments, all those processes for uptake are hindered. Notice the visual plant mass difference between the VR 2×2 plants on a
water-limited acre (12- to 18-gallon range) vs. the flat rate 7-gallon plants on the water-limited acre (photo above).
Why Nutrient Placement Matters – Variable Rate or Not
Historically, these are the areas of this field that become water-limited the quickest. With the help of adequate nutrition, placed specifically where needed, we are getting to canopy prior to that burn-up we’ve previously experienced. On a field that is primarily sand (>7 CEC), these light knobs never stand a chance without adequate and repeated moisture events. With the moisture we had in the soil at planting, this crop got out of the ground and off to an excellent start before we ever thought about calling this a dry year.
While variable rate applications may not be feasible in all situations, applying sufficient nutrients to the crop as close as possible to the root system at planting will mitigate the impact of the drier conditions we have experienced. For most of us in the Corn Belt, planting occurs as soon as we can make a sensible planting pass. This is the only time during the growing season we have absolute assurance that there will be adequate soil moisture for germination and nutrient availability. We need to use this knowledge to our advantage.
Cooler Soil, Consistent Growth
Many look at increased plant size at V6 or a quicker rate of canopy achievement as greater photosynthetic capacity, a greater root system, and perhaps just a healthier plant. While all these are true, some additional benefits are the decreased soil temperature and increased moisture retention when rain is received.
When evaluating the stand, take an infrared thermometer and record the soil and lower stalk temperature in both the lower SWI values (higher ground) and higher SWI environments (lower ground). Where sunlight is reaching the soil surface, temperatures can reach 100°F when the ambient temperature is 90°F. In canopied environments, the soil temperature is closer to ambient and the stalk temperature will be 5° to 10° cooler. While much of this is due to shading, another aspect is retention of rainfall received – rainfall following canopy has not evaporated to the atmosphere, and is thus available for nutrient movement and cooling of the plant (like respiration or sweating for humans). Greater than 60% of moisture accessed by the plant is used for cooling. When mid-June rainfall occurs, a plant canopy protects the received moisture for future utilization.
Proactive Management for Next Season
It isn’t too early to think about spring 2024, especially as we evaluate the evolution of the 2023 crop and its conditions. We have the opportunity to use our 20/20 hindsight vision to make more insightful decisions and adjustments in the year ahead.
As we think back about what we could have done differently so far, consider what your acre’s tendencies have shown you over the years. What is expected of all acres under your current management strategies in a dry spring? Could we have taken advantage of the soil moisture at planting to set up our crop for success, even in a dry year? And how can you make sure the crop has adequate nutrients available at its earliest convenience for uptake?
To learn more about the opportunities that remain in the 2023 growing season and to begin planning for the 2024 crop, connect with an Advanced Agrilytics precision agronomist in your area.