Uniform seeding depth is a critical factor in achieving uniform emergence. Uneven emergence affects crop performance, because competition from larger, early-emerging plants reduces the yield potential of smaller, later-emerging plants. Yields can be reduced by 5% when half the stand suffers from a 7-day delay in emergence and by 12% when half the population experiences a 2-week delay.
- If one of six plants (17%) had an emergence delay equal to two leaf stages (about 12 days), then overall yield reduction was 4%–5%.
- If one of six plants had emergence delays equal to four leaf stages (about 21 days), then overall yield was reduced by 8%.
- The sizes of yield reductions associated with delayed emergence were not significantly affected by the spacing variability of the stand (doubles and misses) within the corn row.
This study emphasized the fact that plants that are neighbouring a plant that is delayed in emergence do not compensate for the lower yield of the plant that is developmentally behind.
It is widely believed that uniform in-row plant spacing is necessary to achieve high corn yields. However, a considerable number of studies challenge the notion that increased variability of in-row plant spacing results in large yield losses.
The relative yields when plants are less than perfectly spaced, those plants that have more space compensate for those that are given less space. A collection of research has further shown:
- Yield losses are about 1% if the stand contains two out of six plants (33%) that are clustered as doubles.
- 2% if three out of six plants (50%) are clustered as triples.
- 5 cm (1 in.) increase in plant stand standard deviation decreased yield by less than 0.08 t/ha (1.3 bu/acre), assuming equal plant populations. These results were consistent with earlier research conducted in Ontario during the late 1970s and in Wisconsin from 1999–2001.
- Bob Nielsen (Purdue University, Indiana) reported that every additional 2.5 cm (1 in.) of standard deviation over 5 cm (2 in.) decreases yields by 160 kg/ha (2.5 bu/acre). This suggests that significant yield losses are associated with plant stand variability.
- Results of a survey of 127 Wisconsin commercial corn fields with an average plant population of 73,500 plants/ha (29,750 plants/acre) suggested that plant spacing standard deviation averaged 8.4 cm (3.33 in.) with 95% of fields having standard deviations that were less than 11.7 cm (4.66 in.).
- Results of 24 research trials conducted along with the Wisconsin plant variability survey concluded that significant yield reductions begin to occur only when corn plant standard deviations exceed 12 cm (4.75 in.).
These results from other jurisdictions support Ontario research findings. They suggest minimal yield impact of uneven plant spacing.
Uniformity and timing of emergence, along with achieving target populations, generally have a greater impact on corn yield than uniformity of corn plant spacing. Planter maintenance and choice of attachments (i.e., coulters and residue row cleaners) should focus on achieving consistent seed placement and the creation of in-row seedbed conditions that ensure rapid uniform emergence.
Pre-planting management may also play a critical role in emergence uniformity. If the field is left too uneven, if residue is bunched, or if surface compaction has not been uniformly alleviated, even the most carefully prepared corn planter may not be able to consistently place seed and create in-row seedbed conditions that ensure rapid uniform emergence.
Relatively small investments in time for planter adjustments, such as installing new opener discs, levelling the planter, properly adjusting seed-firming wheels and proper seed depth placement, can significantly increase yield and returns.
There is no simple formula to aid in replant decisions. When contemplating a replant decision, consider the following:
- original planting date
- target plant population vs. actual
- uniformity of plant size
- possible replanting date
- cost of replanting (seed, fungicides/insecticides, fuel, etc.)
Ontario research data conducted and compiled by the Ontario Corn Committee was used to develop a Replant Decision Aid for producers to use when determining if replant is warranted based on their field situation and costs associated with replanting.
This tool can be found at www.gocorn.net.
Written by Ben Rosser, Corn Specialist
News from the OMAFRA Field Crop Team