03-27-00: Plant to Stand vs Thin

There are several general "concepts" used to get the desired plant population of established sugarbeet plants. One is to plant many more seeds per acre than the desired number of plants per acre and then thin the emerged plants to the target plant population. An advantage of this system is that thinning can be adjusted to compensate for the actual emergence to end up near the target final plant population. Disadvantages include the cost of extra seed and the cost and management of thinning. A second concept is plant-to-stand. In this case the grower must estimate the anticipated emergence and plant enough seeds per acre to compensate for those seeds that do not emerge or develop into established plants. Primary advantages for this system include lower cost for seed and no cost or management required for thinning. A disadvantage is that unexpected weather or soil conditions can cause emergence to be different than estimated, and the established stand can be higher or lower than preferred.

Both "thinned" and "plant-to-stand" systems have been used for successful sugarbeet production. There are different input costs and different types of management involved for each system.

A third concept that might be considered could be called the "hybrid" system and is often a temptation for growers who are not comfortable with estimating a percent emergence for seed spacing, or who have not had consistent plant emergence. The idea behind this system is to plant "on the heavy side" and if emergence is high then thin, but if emergence is low then not thin. At first glance this sounds like a fail safe approach but closer examination reveals a conceptual problem illustrated by the following example.

Suppose a grower uses 30 inch row spacing and would like to end up with about 35,000 plants/A at the four true leaf stage of growth. Plant-to-stand logic might be to anticipate 65 percent emergence and adjust the planter to a 4 1/4 inch average seed spacing. If emergence is 80 percent (very high), the resulting plant population would be 39,000 plants/A which is still acceptable. If the emergence is 50 percent the plant population would be 25,000 plants/A, a little low but still okay. Between 50 percent and 80 percent emergence the plant population is okay. If emergence is below 50 percent, the plant population will be low and there is nothing the grower can do.

If this same grower decided to plant with the intent of thinning, an average seed spacing of 2 or 2 1/2 inches would be recommended. As long as emergence was above 40 percent, and assuming emergence was somewhat random without long gaps, there would still be enough plants to thin without dropping the final plant population too low. With a 2 inch seed spacing, ideally a plant spacing of 6 inches would give a final plant population of 35,000 plants/A. Depending on which plants emerged, a spacing of 4 inches, 6 inches, or 8 inches down the row, but averaging 6 inches, would result in the correct final population. The important point is that the person or machine doing the thinning has a number of options mathematically and practically, to remove plants and end up with a good plant population and good spacing between individual plants.

Now, let's look at the "hybrid" system and assume the grower decided to plant somewhere between the spacings ordinarily used for plant-to-stand and for plant-to-thin. The grower decides to plant at 3 1/2 inch spacing in 30 inch row width. The grower's logic is if emergence is over 70 percent then the field will be thinned. Lay out a 3 1/2 inch spacing on a long piece of paper. Both the math and the practicality of thinning this spacing to a good spacing between individual plants and to a good plant population, become questionable. Let's assume the grower gets 75 percent emergence with the 3 1/2 inch seed spacing and needs to thin. The person or machine thinning plants that were planted at a 3 1/2 inch seed spacing has far fewer options than with a 2 inch seed spacing to end up with both a tolerable spacing between individual plants and a desired plant population. If every other plant emerged in a 3 1/2 inch seed spacing, then everything would be fine. But emergence is never as predictable as every other one. In some sections of the row, emerged plants will be spaced at 3 1/2 inches, 7 inches, 10 1/2 inches, and some wider. A spacing of 3 1/2 inches is too close for good plant development and good harvest so we want one plant removed whenever there is a spacing of 3 1/2 inches or less. This thinning operation will leave plants at a minimum spacing of 7 inches, with some spacings of 10 1/2 inches and greater. The final plant population after this thinning will likely be less than 20,000 plants/acre, even with very careful thinning.

The "hybrid" system with its "in between" seed spacing presents a problem for thinning if thinning is required. If emergence is very low, there will likely be long gaps within the row, reducing yield and encouraging weed growth. If emergence is high,thinning will be required. But thinning, whether manual, selective machine, or non-selective machine, will be left with few options to remove plants that will result in both the desired plant population and adequate spacing between individual plants. Most growers have found that choosing either an intentional thinning system, or an intentional plant-to-stand system, and applying good management for that particular system, will provide a more acceptable final plant stand than with the "hybrid" system.

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