In some cases, a rotary spreader's distribution pattern may not be uniform enough, even after all spreader adjustments have been made. A common recommendation in such cases has been to cut the rate of application in half and cover the field twice at right angles. However, recent research by agricultural engineers at Louisiana State University indicates that cutting the rate in half and cutting the swath width in half while maintaining parallel swaths is more effective than the "right angle" method. The "half width" method is practical mainly for correcting severe pattern problems that remain after all mechanical adjustments to the spreader have been made.
There is always the question of which of the two modes of spreader operation – continuous, back-and-forth mode (Fig. 21) or the circuitous, round-and-round mode (Fig. 22) – gives a more uniform spreader distribution. Researchers at Louisiana State University analyzed the distribution pattern data from 90 spreader test runs involving four spreaders with several products and pattern settings. They found that when the continuous spreader pattern is generally acceptable, there is statistically no advantage to using the more cumbersome circular mode of operation. However, if the basic spreader pattern remains badly skewed after all the spreader adjustments are made, the circular mode may help improve the overlapping pattern. However, the half-rate, half-width method with the continuous mode is probably more effective in such cases. It is also easier to use and requires little additional travel over the turf area.