Polymer coatings for early planted corn
With many producers wanting to plant earlier and earlier, the use of polymer coatings has been questioned. Polymer coatings are designed to stay intact until a soil temperature of 55° F is reached, at which time water can penetrate the coating allowing for seed germination. Some have questioned whether coated seed is a "key" factor for early plantings to be successful. Does the addition of this coating help to extend the planting window even earlier? A comparison of polymer-coated and non-coated seed was included for each planting date study highlighted in the article, Corn planting dates.
Both plant population and final yield were measured in the research. At the Iowa State University Northeast Research and Demonstration (R & D) Farm at Nashua, coated seed had greater plant populations across all planting dates. On average, the coated seed had a population of 31,700 plants/acre compared to 30,000 plants/acre with the non-coated. Yet this response cannot be isolated as a direct response to the polymer coating. The polymer coated seed also contained an insecticide (Poncho 250), which the non-coated seed did not; therefore, the data is confounded. Even though plant populations increased from the coated seed, this did not result in higher yields (Table 1). There was no yield effect from the polymer coating, either positive or negative, for any of the planting dates.
Plant populations at the Iowa State University Southeast R & D Farm at Crawfordsville were unaffected by the polymer coating, except for the very last planting date, May 1, which had a higher population with coated seed than non-coated (data not shown). The seed used at this location also had insecticide applied to the polymer coated seed but the non-coated seed did not. Overall, a significant yield reduction occurred across planting dates with coated seed (199 bu/acre) compared to non-coated seed (204 bu/acre). Therefore, no yield advantage occurred with the polymer-coated seed for any of the planting dates (Table 2).
By comparing the two research locations, we can see there is a difference in response based on geography. No yield advantage or disadvantage occurred with the polymer coating at Nashua. Although, the polymer coated seed at Crawfordsville was at a yield disadvantage to the non-coated.
| Planting Date Window |
Coated vs. Non-coated | Yield (Bu/Acre)* |
|---|---|---|
| March 20-April 5 | Coated | 185 ns |
| Non-coated | 187 ns | |
| April 5-April 20 | Coated | 200 ns |
| Non-coated | 196 ns | |
| April 20-May 5 | Coated | 193 ns |
| Non-coated | 198 ns | |
| May 5-May 20 | Coated | 180 ns |
| Non-coated | 185 ns |
Table 1: Northeast Research and Demonstration Farm (Nashua). Polymer x planting date research conducted by Ken Pecinovsky, 2003-2005. *There is no significant (ns) yield difference between coated and non-coated seed within any of the planting dates.
| Planting Date (+ / - 3 days) |
Coated vs. Non-coated |
Yield (Bu/Acre)* |
|---|---|---|
| March 15 | Coated | 207 ns |
| Non-coated | 209 ns | |
| April 1 | Coated | 210 ns |
| Non-coated | 210 ns | |
| April 15 | Coated | 203 ns |
| Non-coated | 206 ns | |
| May 1 | Coated | 178 ns |
| Non-coated | 189 ns |
Table 2: Southeast Research and Demonstration Farm (Crawfordsville). Polymer x planting date research conducted by Kevin Van Dee and Jim Jensen, 2002-2004. *There is no significant (ns) yield difference between coated and non-coated seed within any of the planting dates, yet an overall yield reduction occurs with coated seed (across planting dates).
Research investigating the performance of polymer-coated seed in early plantings also has been conducted at the University of Minnesota (Gesch and Archer). Although some variability existed in product performance across the three years (2000-2002) of research, useful recommendations were developed. Instances in which polymer-coated seed was planted into soil colder than 50° F, and did not emerge before 20 days, typically had greater emergence than non-coated seed. Although when polymer-coated seed was planted at near-average planting dates, it would often have a slower emergence rate than the non-coated seed. Overall, plant stands were generally comparable between polymer-coated seed planted up to 4 to 5 weeks before the average planting date and that of the non-coated seed planted on an average date.
The environment, in which polymer-coated seed is used, is extremely important because the product's performance is temperature driven. Based on research conducted at Iowa State University and University of Minnesota, it appears that polymer-coated seed may increase plant emergence and/or population in soils that are cold for prolonged periods. Yet, a negative impact from the coating may result if used on seed planted near the recommended planting date for your area. Polymer-coated seed will likely not help to extend the planting window for most Iowa producers unless an extremely early planting date is desired or if soils are cold for an unusually long period. Expect to see differential product performance based on the location of the research and take that into consideration when determining whether or not to use the product on your farm or your client's fields.
Reference:
R.W. Gesch and D.W. Archer. 2005. Influence of sowing date on emergence characteristics of maize seed coated with a temperature-activated polymer. Agronomy Journal 97:1543-1550.
Portions of this text, written by Lori Abendroth and Roger Elmore, originally appeared in the Integrated Crop Management extension newsletter on pages 63-64 of the IC-496 (4) - March 13, 2006 issue.
