- Potassium (K) is essential for plant growth and function, and it is commonly associated with stalk strength and reduced disease instance.
- Potassium uptake can be limited in soils with adequate K levels due to restricted root development.
- Soil conditions, compaction issues, moisture, pH and a balance of soil fertility levels all play a role in plant stalk strength and disease development.
K is an essential nutrient for plant growth. It plays an important role in functions such as opening and closing leaf stomates, which regulate the amount of water vapor, oxygen and carbon dioxide that can pass through. This, in turn, impacts the movement of water, nutrients and carbohydrates throughout the plant. K is also strongly associated with susceptibility to disease as well as stalk strength.
Factors Affecting K Availability
K deficiency manifests in older corn leaves as yellowing or necrotic tissue along the leaf margin. However, symptoms may not always be the result of soil fertility levels. K is considered an immobile nutrient in the soil, requiring roots to physically intercept available soil K, in comparison to more mobile nutrients like nitrogen. Healthy, unrestricted roots are critical for ensuring K uptake in properly fertilized fields. Limited root growth due to drought, saturated soils, soil compaction, low soil temperature or insect damage can all limit nutrient uptake in soils with sufficient K levels.
Role of K in Disease Susceptibility
Not unlike humans, healthier plants are much more resistant to attack from disease. Although genetic resistance is important for managing disease, ensuring that nutrient levels are adequate helps boost a plant’s natural disease defense. Plant disease can rarely be eliminated or cured by a fertilizer application, but the extent of disease severity may be reduced by the presence of certain nutrients. The ratio of all nutrients both in the soil and in the plant may be as important as the level of any one nutrient. Disease protection as a result of potassium uptake is influenced by the availability of soil potassium and its interaction with other nutrients, as well as by environmental factors.1
K Role in Stalk Strength
K deficiencies can result in weakened stalks and lodging. Although K is fairly immobile in the soil, it is highly mobile inside the plant. Due to this, when a deficiency is sensed, K is moved from older tissue to newer growing leaves which may compromise lower stalk strength. Unfortunately, once symptoms are visible, in-season correction to the problem is difficult since most corn plant K uptake is completed prior to tassel, and it is difficult to quickly deliver to the plant due to limited soil mobility.
Similarly, fungicide also plays an important role in disease management and preserving lower stalk health. Due to joint roles in stalk strength, greater understanding of hybrid response to K fertility and fungicide is needed in order to develop better individual hybrid management plans.
2020 Trials
Golden Harvest® Agronomy in Action research trials were established in 2020 at 8 locations to investigate the ability to improve standability and yield potential of hybrids through K and fungicide management. A late season derecho led to the loss of 2 research locations, leaving 6 harvested locations (Figure 1).
Trials were established using a split-split plot design with fungicide as the main factor and the rate of K as the subfactor, with 4 hybrids nested within K blocks. The design resulted in each hybrid receiving the following 4 individual treatments: additional K, R1 fungicide, additional K with R1 fungicide and untreated. 2 hybrids of adapted relative maturity (RM) with excellent stalk strength and 2 rated with less stalk strength were chosen for each location (Table 1).
A total of 40 lbs/A of potassium (0-0-24, NACHURS K-Fuel®) was applied as a split application, 33% in-furrow at planting followed by the remaining 66% in a 4”x4” placement prior to V3 (Figure 2) to designated plots to mitigate the potential for root injury. Miravis® Neo was applied at the VT-R1 growth stage with a high-clearance sprayer to designated plots. Plant stand counts and push-test ratings were taken prior to harvest to assess stalk quality. Individual plot yield, moisture and test weight data were recorded at the time of harvest.
Results
Growing environments and weather conditions varied across locations. Most locations received less rainfall in 2020 compared to the previous 20-year average rainfall (Table 2). In Bridgewater, SD, and Sac City, IA, the growing season rainfall amounts were less than half of the average rainfall amount from the prior 20-year average. Available crop water is a large factor in nutrient exchange in the root zone and in determining yield potential. The amount of water used by the plant varies based on plant growth stage and growing environment. A typical 200 bushel/A corn crop uses about 20” of water.
Response to Additional K
The primary objective of this trial was to better understand how soil K availability can influence yield potential and stalk integrity. There was no significant yield or stalk quality improvement resulting from additional K observed at any of the locations with the exception of a small yield response at Sac City (Graph 1).
Preexisting high to very high K levels at each location (Table 2) likely resulted in the lack of response from supplemental K.
Response to Fungicide
4 of the 6 trial locations showed a positive yield response to fungicide, ranging from 2.8 to 18 bu/A (Graph 1). Individual hybrid yield responses were similar when averaged across locations showing a response to fungicide (Graphs 2 and 3).
Standability at harvest time was also quantified at each location by artificially applying pressure horizontally to multiple plants within each plot and recording the percentage of plants that lodged. 2 of the locations with the largest yield response, Clay Center, KS, and Clinton, IL also had significantly less artificial lodging as a result of fungicide applications (Graphs 4 and 5). Hybrid standability was improved in some more than others due to fungicide applications. Due to intentional hybrid selection based on differing stalk quality ratings, it was anticipated that hybrids with lower stalk quality ratings would benefit more from fungicide applications. However, both G11A33 and G14R38, 2 of the higher stalk quality ratings, had some of the biggest reductions in lodging from fungicide application (Graphs 4 and 5).
Discussion
Overall, incremental K had no effect on late season standability or yield in these trials. However, fungicide use did improve yield in many cases. Fungicides also improved late-season standability in multiple trials, which in some years may provide more financial benefits than a yield increase. While results from this study were mixed this year given high soil sample K levels and excessively dry conditions, future investigation into the effects of potassium application on stalk strength and yield potential may be warranted. Trials repeated in locations with lower overall soil K levels and increased soil moisture may be better able to demonstrate the importance that maintaining adequate K soil fertility may have for managing hybrid late season standability and maximizing yield potential.
For more information on the role of K and fungicides in your corn fields, contact your local Golden Harvest Seed Advisor.
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References:
1 Huber, D.M. and D.C. Arny. 1985. Interactions of potassium with plant disease. Chapter 20. Potassium in Agriculture. Ed. R.D. Munson. ASA-CSSA-SSSA.