In summary after year 1, population plays a role in canopy closure and in canopy humidity levels. The higher populations resulted in quicker canopy closure. The environments where canopy closure was slow the increased population improved yields, however if canopy closure was in early to mid-
July yields were not improved with higher populations. The bushy bean did close the canopy sooner than an in-line bean type. The humidity sensors showed that once the canopy was closed the 160,000 population had higher humidity levels in the canopy compared to the 120,000 populations. However there was not a consistent response to the type of bean causing differences in humidity levels. In some plots the bushy bean had higher humidity levels and other plots it did not seem to be a factor. Higher humidity in the canopy from high populations
can increase the incidence of white mold.
Individual plant yield components were affected by population. Most of the time as population increased the number of nodes and nodes with pods per plant were decreased. The 1st node with pods from the bottom was also higher up the plant, indicating more pod abortion on lower nodes at the higher populations. The number of pods and seeds per plant decreased with
increasing populations. In two out of the three plots the bushy bean reduced individual plant yield components more when pushed to the higher populations compared to the in-line bean. This may be an indicator that the bushy bean will not tolerate as high of populations as the inline bean. However, when evaluating the two VRA prescriptions, there did not seem to be a correlation with Variety A responding to prescription VRA A or Variety B responding to prescription VRA B as originally hypothesized. The VRA A prescription was written based on the
theory that an in-line type variety may need higher plant populations, VRA B was written based on the theory that a bushy type variety may need lower plant populations. There were other environmental factors which led to whether high or low populations were preferred in the field 30 and that was the driving factor if prescription A or B won. Environmental factors such as white mold potential and time to canopy closure may be an important factor in determine a field’s
preference on population. Time to canopy closure may be affected by planting dates and tillage system. Once the environmental factors are taking into consideration for seeding rates, there may be additional fine tuning based on soybean plant type (bushy or in-line).
Overall the VRA planting looks good in comparison to the straight rate planting rates. When comparing the top yields at each plot for both varieties the VRA treatments won six out of six times. When comparing the net dollars per acre at each plot for both varieties the VRA treatments won four out of six times. The average net gain for VRA with all three plots across both varieties was $9.70 per acre greater than the best straight rate treatment.