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Plot size was 12' wide by 30' long. Soybean varieties used in the study varied by year. Soybean varieties were mid to late 3 in maturity and were selected based on the previous year's variety test results at the Hundley-Whaley Farm. The top variety in the previous year's test was selected for this test and the varieties were:
Variety used in 2000 was Wilcross 2338 RR Variety used in 2001 was Prairie Brand 3550 RR Planting rates were counted to represent 100,000, 150,000 and 200,000 seeds per acre. Row width was 15 and 30". Four 30" rows were planted and seven 15" rows were planted. Planting was accomplished with a John Deere Max-Emerge planter equipped with cone units set to deliver the correct amount of seed to each plot. Each year, the first planting was done into a conventionally prepared seedbed and subsequent plantings were made no-till into a stale seedbed. The plot area selected always produced bulk soybeans the year prior to the test. Weed control, besides the initial tillage, consisted of multiple applications of Roundup Ultra or Roundup Ultra Max @ 0.75 pounds acid equivalent/acre applied as needed to control 4-8" tall weeds. All weeds were adequately controlled by these treatments. Harvest was done with a MF35 plot combine after all soybeans in the study were mature. Weight of threshed soybeans was derived from spring scales (milk scales). Harvest dates did not vary with planting dates. The two center rows of the four rows of 30" wide rows were harvested and the five center rows of the seven 15"wide rows were harvested. Initial harvest data was in pounds per plot. Seed moisture was taken at harvest and yield data was adjusted to 13.5% moisture beans. Calculations for yield were based on the following:
Two 30" wide rows, 30 ft. long = 0.0034435 acres/plot Raw plot harvest data, in pounds per plot, was divided by one of the two numbers above, based on plot row width, to get pounds of soybean production per acre. That number was divided by 60 to secure the reported yield of bushels per acre. Plant counts were taken each year by randomly selecting and counting the established plants in two 30" square areas in each plot. Results: Results for 1999 and 2000 have been reported previously. This report will focus on the results obtained from the 2001 study and it will summarize the three years of research. 2001 Results: The soybean plant population and yield is found in Table 2. The highest yielding treatment (50.5 bu/acre) was a result of the earliest planting date, the narrowest row width and the highest planting rate. The lowest yielding treatment (37.0 bu/acre) was from the last planting date, the narrowest row, and the lowest planting rate.
Figure 2 shows that 2001 soybean yields trended upward as planting rate was increased for the later planted (June 11) soybeans. The curve was steeper with the narrower rows and the lower planting rate had a more adverse affect on the yield of soybeans in the 15" rows than it did on the 30" wide rows. 
Figures 3 and 4 show soybean yields as affected by planting rate and row width for the April 26 and May 22 planting dates. Figure 3 shows that there was little difference in yield between planting rates of 100,000 and 150,000 seeds per acre for the earliest planting date, but there was a highly significant yield response to increasing planting rates to 200,000 for both row widths. Figure 4 shows that the soybean planting rates needed to be at least 150,000 seeds per acre for both the 15" and 30" row widths for maximum production with the mid-May soybean planting. There was no positive yield response to increased planting rates beyond 150,000 for the mid-May planting date. 
Figure 5 shows the effect of planting date and row width on soybean yield. Overall yield for the different planting dates trended down as planting date was delayed. The average yield for the different planting dates was 46.1 bu/acre for the April 26 planting; 43.9 bu/acre for the May 22 planting and 42.4 bu/acre for the June 11 planting. Surprising was the fact that the 15" wide rows were more adversely affected by delayed planting date than the 30" rows. The later the planting, the more difference that existed in soybean yield, with the highest yields being obtained with the wider rows. Three Summary Results: Initial study design and yearly data were analyzed with Gillings' Agriculture Research Manager. The three-year data on plant population and crop yield were analyzed by the SAS statistical analysis program operated by Dr. Steve Norberg, UO&E, Bethany, Missouri. Statistically, the results of plant population and crop yield varied significantly by year. The mean soybean yield for the three year period, averaged over all planting rates and dates of planting, resulted in an 0.84 bushel yield advantage for the 15" wide rows (Figure 5). 
While the difference in soybean yield is relatively small, it was statistically significant at the P = 0.1 level. Statistically, there were no differences in seedling plant count when averaged over all dates of planting, planting rates, row widths and years. The mean count of established plants are found in Table 3.
Figure 7 shows the mean three-year soybean seed yields as affected by planting time and row width when averaged over all planting rates. There was little difference in the early and mid dates of planting for either row width. Late planting did yield significantly less than the earlier two planting dates and the wide rows were adversely affected more than the narrow rows when planting date was delayed. 
Figure 8 illustrates the effect of planting rate on crop seed yield (bu/acre) for all planting dates and row widths over the three years of the experiment. Differences in crop yield, as affected by each plant population, were significant at the 90% confidence level. 
Figure 9 illustrates the effects of planting rate and time of planting on soybean yield. Figure 10 illustrates the effect of planting rate and row width on soybean yield. The highest soybean yield response resulted from the move to 150,000 seeds per acre from 100,000 seeds planted per acre regardless of time of planting or row width. Figure 9 shows that the planting rate of 150,000 seeds per acre produced yields ranging from 97-98% of the 200,000 planting rate whereas the 100,000 seeds per acre planting rate only produced yields that were 88-91% of the 200,000 seeds per acres planting rate. The planting date did not significantly change the percentage yield response from increased planting rates. The planting rate of 150,000 seeds per acre in both 15" & 30" rows produced 97.5% of the yield produced by the 200,000 seeds/acre planting rate, however the 100,000 seeds per acre planting rate in 15" rows only produced 88% of the yield provided by the 200,000 seeds per acre planting rate and this compares to 92% of the full yield when the 100,000 planting rate was planted in 30" rows. 
Figure 11 shows that over the three years there was no difference in soybean yield between the early and mid planting date. The late planting date yielded significantly less than the early and mid planting date. Discussion: This experiment, initiated in 1999, began with problems of weather. It was an unusually wet spring and planned planting dates were delayed for more than 30 days because of soggy fields. We still got in three planting dates, but only the last one was close to the date we had planned to plant. The following two years, 2000 & 2001 resulted in more favorable planting conditions and actual planting was at least close to the planned planting dates. We initiated the experiment with three questions that we hoped to answer. The first was, "Which planting date is best for profitable soybean production?" If we make the assumption that the best yields will also provide the most profitability then the data from the study suggests that there is little difference in early and mid planting dates in profitability. The late planting dates in the study always resulted in the lowest soybean yields and would be assumed to be the least profitable. The second question was, "Does planting rate need to be changed with changes in planting date and row width?" The overall data suggests that the highest planting rate (200,000 seeds/acre) resulted in significantly higher yields than the two lower planting rates. Planting date did affect the need for higher planting rates. The earliest planted soybeans showed a higher positive yield response to increased planting rates than the mid and late planted soybeans. The difference in the planting rate of 100,000 and 150,000 seeds per acre had more of an effect on soybean yield in 15" rows than in 30" rows. Over the three year test period the 150,000 planting rate yielded 4 bu/acre more soybeans per acre in 15" rows than the 100,000 planting rate. There was a 2.3 bu/acre increase in yield between the 100,00 and 150,000 planting rate when the soybeans were planted in 30" rows. Both 15" and 30" wide rows responded to the increase in planting rate between 150,000 and 200,000 seeds per acre at approximately the same magnitude (1 bu/acre). The profitability of increasing planting rate from a rate of 100,000 to a rate of 15,000 seeds per acres can be seen in Table 4. The data would suggest that planting rate of 150,000 seeds per acre was more profitable than a 100,000 seeds per acre planting rate in 15" wide rows with all planting times. Using 150,000 seeds per acre in 30" rows could be considered questionable according to this test. Only one of the three planting times resulted in increased profitability by increasing planting rates from 100,000 to 150,0000 seeds per acres.
This data also suggests that it would not be profitable to use planting rates in excess of 150,000 seeds/acre regardless of planting time or row width. The third and final question was, "Are 15" rowed soybeans more profitable than 30" rowed beans? If so, under what conditions?" The data from this study suggests that the increased yield from 15" wide rows, while significantly higher than yields in 30" rows, did not provide high enough yields to pay for the increased costs associated with the narrower rows. The increased cost to own, maintain and operate a 15" wide-row planter will vary considerably, depending upon size of farm operation, but those costs would likely exceed the value of the single bushel of soybeans per acre increase in production that the data from this study suggests is possible. If only the 1999 and 2000 data were considered, an argument could be made that 15" rows, used to produce late planted soybeans, would be profitable. The 15" rowed soybeans, planted late, had increased yields of 3.7 bu/acre over 30" rowed soybeans for both of those years (refer to Table 5). The negative yield response to 15" rows that was recorded in 2001 is thought to be unusual, nevertheless that was the way the crop did respond in 2001. Statistically, the only significant difference in yield between the 15" and 30" wide rows (for the individual years) was the 3.7 bushels per acre yield difference for late planted soybeans in 2000 (P = 0.1).
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