Crops are off to a good start in Daviess County.
Little replant will be necessary as most fields are emerging well despite the second and third week of April being somewhat cooler than usual.
It has been a blessing to enjoy dry field conditions with only a couple of rains temporarily stopping activities. Despite the good start, slugs and seed corn maggots have thinned some soybean fields that were planted early in the month.
Each year, farms face the question of replanting, filling in, or leaving a soybean field alone. In the case of flooding and subsequent stand loss, the decision is easy. In fields of low, sporadic plant population, the decision requires more thought.
First, determine what caused the low plant stand. Wet soils, slugs, insects, poor seedling vigor, incorrect planter settings, soil crusting, or herbicide injury can affect the success of a stand and have been factors in fields I have visited.
Take time to look closely when doing stand counts to determine which of these factors are causing challenges. Evaluate other nearby fields of similar soil type that emerged successfully. Were they a different variety or seed lot? Was tillage or lack of an issue? These questions should be answered first.
Determining stand density is the second key. The two common methods are counting plants in a row or the hula-hoop method for narrow row fields. For 30-inch rows, count the number of plants in 17 feet 5 inches and multiply by 1,000.
For 15-inch rows, count the number of plants in 34 feet 10 inches and multiply by 1,000. An easier way to do this is to count the total plants in the rows on each side of 17 feet 5 inches and multiply by 1,000.
The hula hoop works well for 15 and 7.5-inch row fields. While there are different factors for different diameters, the most common is a 33-inch diameter hoop. Toss it out across the field randomly, count the plants within where it lands and multiply by 7,350.
Research by the University of Kentucky has shown 100% of optimum yield can be achieved with a final plant stand of 100,000 for all planter widths and maturity groups. Purdue research has proven final stands can actually be very low and achieve high yields as a% of normal.
Purdue published findings that final stands of 40,000 achieved 87% in 7.5-inch rows and 88% in 30-inch rows. An important consideration is that in these studies, the plots are small scale and plants are uniformly removed by hand thinning to replicate different final stand scenarios.
These studies would not replicate a field of soybeans where stands are low in certain random areas and normal in other areas. The study does provide information indicating thin stands have yield potential if weeds can be controlled considering poor canopy closure which allows sunlight to reach the soil late in the summer long after soil residual herbicides have depleted.
Over the past several years there has been increasing effort to get soybeans planted earlier as it is known the yield potential of soybeans is reduced after a May 15 planting date.
Several factors must be considered to determine the profitability of planting into thin stand fields; the base yield expectation for the field, an estimate of the yield due to thin stands as compared to normal yield expectation, projected gross income without replanting subtracting for additional herbicide due to thin stands, projected gross income with replanting minus replanting expenses.
Purdue has found there is less than a 50% chance additional weed control will be necessary, except in wet fields with high weed pressure. You then compare the potential net returns of both scenarios to determine which the best option is.
When it comes to filling in a thin stand with a 30-inch row planter, Purdue has found the final stand must be below 66,000 before any increase in yield is found.
The second planting can damage some emerged plants, and the late planting yield potential is lower due to later planting and competition from emerged plants. They have found it is typically better to do nothing than to invest time and money attempting to thicken a thin stand.
Clint Hardy is the agricultural extension agent for the Daviess County Extension Office. He can be reached at 270-685-8480.