I have been receiving questions about the productivity of corn fields with stands as low as 10-12,000 plants per acre. Causes of the stand loss in these fields can be attributed to a wide range of factors, including saturated soil conditions and ponding, seedling disease and insect (esp. cutworm) injury, planter adjustment/malfunction, herbicide damage, hail and green snap). The reduced stands are often associated with mid-May plantings and the surviving corn plants are usually at or beyond the V7-8 stage. Despite the magnitude of the stand loss in these May planted fields; they may have the potential to produce yields comparable to June plantings that have much better stands.
Table 1 is from an article by Dr. Bob Nielsen at Purdue University that shows effects of planting date and plant population on final grain yield. It’s based on research conducted by Dr. Emerson Nafziger at the University of Illinois with yield responses to planting date extrapolated beyond May 25. Although the table was used by Dr. Nielsen to discuss recovery from hail damage it may also have application in assessing yield loss in other reduced stand situations.
Let's assume that a farmer planted corn on May 10 and June 4 at a seeding rate sufficient to achieve a harvest population of 30,000 plants per acre. The farmer recently determined that his May stands were reduced to 12,000 to18,000 plants per acre by cutworm and saturated soil conditions, whereas his June stands were nearly 30,000 plant per acre. According to Table 1, the expected yield for the existing stand planted May 10 would be 71-86 percent of the optimum, whereas the expected yield of the June 4 planting would be 75 percent of the optimum. Of course there are other factors to consider…plant spacing may be highly variable in the field with reduced stands and plant development may be uneven. Growers need to be aware that weed pressure is likely to be much greater in such fields because a competitive corn canopy is largely absent. Weed size will need to be monitored closely to ensure that post emergent herbicides can be applied to optimize their efficacy. Another question concerning reduced stands is whether N rates should be cut. Research from OSU and neighboring states indicates that low and high plant populations (ranging from 20,000 to 40,000 plants per acre) show similar yield responses to N.
Nielsen, R.L. 2011.Recovery from hail damage. Corny News Network, Purdue Univ. [Online]. Available here. [URL accessed June 27 2011].