By Delbert Voight
Some fields with poor corn stands are being evaluated for replanting. The Penn State Agronomy Guide has a discussion about the different factors when considering replanting on pages 68-69.
Population Assessment
Once corn germinates, the population in the field can be determined. First take the width at planting (15” or 30” for corn) and convert the row width from inches to feet by dividing by 12. Divide feet by the square feet per acre (43560). This gives you linear feet. Take the number of plants you find per linear foot in the field and multiply by 1,000 to get the plants per acre (ppa).
Here is an example:
Thirty-inch rows divided by 12 is 2.5 feet. 43,560 square feet in an acre divided by 2.5 gives us 17,424 linear feet. One plant in a foot will yield 17,424 plants per acre. If two plants in a foot, then the plant population will be 34,848 plants per acre.
To simplify this you could now take 17,424 and divide by 1000 to get the number of feet you need to represent 1/1000th of an acre. In this case it would be 17.4 feet. In the field, measure 17.4 feet, count the plants, multiply by 1000 and you will have your plants per acre. Do this in several places and take the average of the field.
Stand Evenness
Often, the greatest challenge to assessing whether to replant is the unevenness of the stand. Penn State research suggests that within row unevenness robs 12% of yield, while between rows unevenness only robs 5% of yield. For each inch of deviation university research suggests a 2.5-5 bu/inch loss. This becomes more critical as populations are increased.
Planting Date and Relation to Yield
Planting corn by April 25th is 100%, the 19th of May is 90% and the 29th of May is 80% of yield potential. In the Agronomy Guide, Tables 1.4-8, 1.4-8A and 1.4-8B on page 69 can offer help in making a determination whether one should keep or replant when comparing the plants per acre at harvest by planting date.
Pest Management
Weeds will invade anywhere light is allowed through to the soil, competing with poor stands, so evaluate potential herbicide costs. Important: Review any pesticides that were previously applied and re-crop restrictions.
And Finally:
Check with your dealer to determine the policy for replant support. There could be on-line tools offered by your seed dealer to help assess a stand.
Source:psu.edu