When you select ground for plots, experts say to find level and uniform ground if possible. That's sometimes easier to do than it sounds. The land used for the Precision Planting and Indiana Prairie Farmer study at the Throckmorton Research farm near Romney, part of the Purdue University research farm system, doesn't appear to be all that different at first glance. However, if you look closer, there are higher and lower areas in the topography.
The way around letting that affect investigating yield differences amongst factors or variables that you are studying is to put all of one factor in a separate experiment on one soil type. That was done in these plots. Depth of planting was investigated at four depths with the location in the block chosen at random in one case. In the other case the amount of downforce on planter units was analyzed in comparisons. The two soil types turned out to be different. This year, due to the season, one block was about 50% or more higher-yielding than the other block.
It won't affect comparing treatments, however, notes Jeff Phillips, Tippecanoe County Extension educator who helps with the plots. That's because all of the depth variables were repeated four times on one soil type, and all of the downforce variables were repeated four times on the same soil type, even though the soil types were different.
Yield for the spoil types was so different that it is plain to see on a yield monitor map of each plot. Colors representing various ranges were selected by the computer, with reddish and brownish plus yellowish areas generally representing lower yields. When both plots were finished, it was obvious that as a whole, the plot where depth was compared was significantly higher-yielding than the average in the plots where downforce was compared.
This year plants on higher ground, even slightly higher, less productive soils with less water-holding capacity, as in this case, paid the price. Yields were lower. Even though these plots all pollinated slightly after the hottest stretch of weather, one was definitely more affected, and the difference can be tied directly to soil type.