Plant emergence is upon us. An exciting time of year where we can watch all our planning efforts and hard work come to life. Assessing plant populations and taking plant counts falls to a lower priority for many growers during this busy time, with other crops being sown or herbicide applications already underway. Does plant stand count even matter? What can it tell you?
Why it matters
Plant counts are a measure of seeding success, or in some situations, failures. With expensive seed costs, you’re working hard to ensure every seed emerges. Determining why that seed did not emerge should be a priority. By using seed size, survivability and seeding rate, a target plant population has been established. Post-emergence plant counts determine the seed survivability (plant emergence) for the crop and can be used in future years to help determine seeding rates and target plant populations. Not only are plant counts a cost saving exercise for next season, but they help to determine crop management practices and risk over the growing season.
Source: Canola Calculator. Assessing plant emergence example.
How to do it
Whether you use a hoop, a tape measure, or maybe even a boot length… it doesn’t matter what method you use for plant counts. The important part is taking them. Of course, the math and calculations are going to change by method so find what works best for you.
Justine Cornelsen, BrettYoung’s Agronomic and Regulatory Services Manager, prefers to use a hoop to determine plants per square foot. “The small area is something I can visualize, and the hoop helps keep sites assessed random. If not using a hoop to throw, I find my eyes being drawn to high or low plant population areas that may not best represent the entire field. It’s important to take several plant counts across the field and average the results.” She says. And with all of her experience in the field, we trust her.
Where did they go?
If plant counts are lower than expected, the question becomes WHY? The reason for missing plants can come from a variety of possibilities. Many of the causes for plant losses are out of our control, such as frost, excess moisture, drought, wind damage, and soil crusting. Pre-planning can minimize seed and plant damage from fertilizer toxicity, herbicide carry-over, seedling diseases, insect damage, mechanical seed damage, seeder errors, and seeding depth. If plant losses have occurred, knowing the reason for losses can change management practices in future years to help protect plants and reduce future losses.
What to do about low or high plant populations?
If you have extremely low plant populations, it may trigger the need to reseed. The decision to reseed is complex with the number of plants, growing conditions, and time of year taken into consideration. If managed carefully, low plant population crops can still achieve high yields but the economics for saving the crop and reseeding should be looked at.
Plant populations outside of the “optimal” ranges can still be extremely profitable. They may be managed differently through the growing season or monitored more closely. Active scouting should be frequent in all crops, but especially so in low plant population stands that cannot afford to lose plants to damage.
Low plant population example:
- To preserve yield, the few plants remaining must be protected. Frequent scouting should occur so plants are not lost to insect pests that can be managed through an insecticide.
High plant population example:
- Dense crop canopies make for the perfect environment for fungal pathogens to develop; fungicide applications may be required to protect plants from diseases like sclerotinia.
- High plant stands can alter plant architecture to create smaller weaker stalked plants that could lodge, changing harvest plans.
Optimal plant populations
- Canola: 5 – 8 plants per square foot (217,800 – 348,500 plants per acre)
- Soybean: 3.2 – 3.7 plants per square foot (140,000–160,000 plants per acre)
- Silage Corn: 0.7 – 0.8 plants per square foot (32,000 – 34,000 plants per acre)
- Alfalfa: 25 – 40 plants per square foot on seeding year (1,089,000 – 1,742,000 per acre)
A crop’s yield potential is set at plant emergence. Other than post-emergent fertilizer applications, the rest of the season is just preserving that yield through pest control and harvest management practices.