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Agronomy Guide For Field Crops – Corn – Emergence and Spacing Uniformity, Replant Decisions

Uniformity of Emergence
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. Table 1–15, Corn yield response to plant spacing and emergence variability, shows the relative impact of emergence and in-row spacing variability on corn yield. In summary:
  • 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.
Uniformity of Spacing
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 shown in Table 1–15 indicate that when plants are less than perfectly spaced, those plants that have more space compensate for those that are given less space. Doubles are defined as two plants spaced about 3 cm (1.33 in.) apart situated next to a gap of about 38 cm (15 in.). 
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