Crop Emergence and Early Development

Crop Emergence and Crusting

The spring has been challenging in many areas of the province for those wanting to plant corn and soybeans. Cool wet soils and heavy rains have not only made it difficult to get the crop in the ground it has also affected the emergence of crops as well. It is important to check planted fields especially after a significant rainfall to ensure there are no emergence issues.

Soil crusting can be a problem on clay to loam soils. A crust can cause corn to leaf out under ground. In soybeans, a pounding rain or ponding can form a crust which can break the hypocotyl arch of the soybean preventing emergence. In both cases it may be necessary to take some action. Before taking the equipment to the field consider if another rain is forecast as that may help soften the crust. If a number of plants have emerged, do a count of the number of plants emerged, especially in soybeans where full yield potential exists (see table 2-13 in the Agronomy Guide). Remember crust busting operations can result in up to 10% loss of emerged soybeans.

Crop emergence can be aided with some light tillage from a rotary hoe, harrows, coulter cart, planter or seed drill. When setting up to perform this operation do a test strip first and check operation several times as soil moisture and soil types can change across a field. For soybeans, try to perform the tillage operation before the soybeans are at the hypocotyl stage as this is when the greatest loss will occur.

Early Crop Development

The corn plant emerges when 180 crop heat units have accumulated. Each leaf after that takes 75 crop heat units. The soybean plant will emerge in an average of 12 days although that can range from 5 to 21 days depending on variety and climatic conditions. After that it takes about 5 days on average to produce the unifoliate leaves and each trifoliate leaf after that.

Uniformity of Corn Emergence

Uniform seeding depth is a critical factor in achieving uniform emergency. Uneven emergence affects crop performance, because competition from larger, early-emerging plants reduces the yield potential of smaller, later-emerging plants. Research indicates that 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, Corn Yield Response to Plant Spacing and Emergency Variability, shows the results of a University of Guelph study that examined the relative impact of emergence and in-row spacing variability on corn yield. 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.

Source: Lue, Tollenaar, Stewart, Deen, University of Guelph

¹ Expressed as a percent of the uniform spacing and emergence treatment.