Replant decisions are based mainly on a comparison of the yield potential of an existing low stand with that of a full stand at the replant date. This was discussed in the April 22 newsletter. However, the issue of stand uniformity can complicate things. Lack of uniformity may mean variation in plant height, variable distance between plants, or both.
Recent research in the Midwest clearly indicates that uniformity, in terms of both plant size and plant distribution in the row, is important for maximum corn yields with full stands. There is little new information about yield loss caused by uneven plant size or distribution, in addition to that which is due to a low stand. Older studies in Illinois indicated yields were reduced an added 5 percent if there were many 4 to 6 feet gaps in the row and 2 percent if typical gaps were 1 to 3 feet. What if there is considerable variation in plant size? Clearly this will have some effect, though it is likely to be less than when there is a full stand.
Only in extreme cases would lack of uniformity of plant size or plant distribution alone make a replant profitable. Seldom would the yield loss be sufficient to make up for the yield loss of the replant date and the added cost. However, lack of uniformity may tip the decision in favor of replanting in borderline cases. The charts that relate yield with a reduced stand to a full stand are based on studies in which stands were relatively uniform. For example, if the chart says a stand of 14,000 will yield 82 percent of a full 26,000 plant per acre stand, how much should be subtracted if the stand is uneven? Stand gaps and uneven plant heights could easily cut 2 to 5 percent, and maybe up to 10 percent in some cases, from the 82 percent listed. Information that would permit more precise interpretations is needed.