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Fluid Journal : Winter 2016
Stewart, two at New Richland in both 2013 and 2014, four at Willmar, five at Janesville, and two at Waseca. Plant populations were generally not affected by broadcast and/or starter fertilizer P rates except for New Richland-14 (2014) where populations were slightly greater (800 plants/A) when broadcast P was not applied (Table 2). Desired seeding rates varied somewhat among locations because two different planters were used in this study. At Gaylord, Steward, Willmar, New Richland-14 and St. Charles approximately 14,500 seeds/A were planted to achieve a final stand of 32,000 to 34,000 plants/A; whereas, at New Richland-13, Janesville, and Waseca, 35,500 seeds/A were planted to obtain a final population of 34,000 to 35,000 plants/A. Final populations were greater than expected/ desired (36,200 plants/A) at Stewart but near desired at other locations. Effects. Treatment effects on total dry weight (mass) of whole corn plants at the V5 stage are presented in Table 3. The main effect of broadcast P application increased V5 plant mass at Willmar and Janesville in 2013 and for all of the 2014 locations. When averaged across broadcast P rates, the mass of small corn plants was increased with starter P application at all locations in 2013 and 2014 (cool and wet springs). In 2013, the greatest mass generally occurred with 5 and 7.5 gal/A rates, the O/gal/A control had the least mass and the 2.5 gal/A rate was intermediate. In 2014, plant mass was greater than the control (0 gal/A rate) with 2.5, 5.0, and 7.5 gal/A rates, but no differences among the 2.5,5.0, and 7.5 gal/A rates were observed. Starter fertilizer application did not affect plant mass at either location in 2012 (a very warm spring). Considerable variability in V5 plant mass was observed at Gaylord. One treatment, 120 Ibs. of broadcast P plus 7.5 gal/A of starter, had unusually lower mass. A few plots at this location were affected by flooding or by water running across the plots early in the growing season, which may have contributed to the variability. We hypothesized that, because the broadcast rate of 120 Ib P 2 0s/A was so much greater than the needs of corn early in the growing season, it may diminish the early growth effects of starter fertilizer P. However, no significant broadcast P x starter P interactions were found in these data. Table 2. Corn plant populations at V5 as affected by broadcast and starter fertilizer Prates. Broadcast 10-34-0 Starter Rate (gallons per acre) Location PRate 0 2.5 5 7.5 Averaget -Ib P ')O)ac- ----------------------------- p I ants pe r a cre---------------------------- Gaylord-12 0 33150 33850 33290 34430 33680 120 33900 33250 32370 35130 33660 Averaget 33520 33550 32830 34780 Stewart-12 0 36640 36900 36100 35650 36320 120 36750 36265 35480 36140 36160 Average 36700 36580 35790 35890 New Rich.-13 0 35730 35650 36150 35650 35790 120 36190 35660 35490 35790 35780 Average 35960 35650 35820 35720 Willmar-13 0 34380 35200 34910 35060 34890 120 34140 34580 35580 34860 34790 Average 34260 34890 35240 34960 Janesville-13 0 35190 35510 36300 35330 35580 120 36240 35870 35390 34830 35580 Average 35720 35690 35840 35080 New Rich.-14 0 33030 32690 32930 33420 33020a 120 31940 32540 32090 32300 32220b Average 32490 32610 32510 32860 St. Charles-14 0 33610 33390 34090 33120 33550 120 33780 33610 33460 33340 33550 Average 33700 33500 33770 33230 Waseca-14 0 no data no data no data no data -- 120 no data no data no data no data -- Average -- -- -- -- tWithin each row or column, small letters following numbers indicate treatment significance at P<0.05. Numbers followed by different letters are significantly different. Winter 2016 The Fluid Journal The lack of significant interactions suggests that both P application methods contribute to greater mass of small corn plants; furthermore, their contributions are an additive effect and one application method did not substitute for the other in these data. P concentrations in V5 plants were increased significantly by broadcast P application at five of eight locations [New Richland (both), Willmar, St. Charles, and Waseca] and concentrations were numerically greater at the Stewart and Janesville locations (Table 4). The greatest increase in plant P concentration with broadcast P application occurred at the New Richland (both) and Waseca locations, which had some of the lowest Olsen P levels. The differences in P concentration, along with increased plant mass, contributed to increased P uptake with broadcast P application at six of eight locations (Table 5). Phosphorus concentration of V5 corn plants was increased significantly (P<0.05) by starter P application only at Stewart in 2012 (Table 4). The lack of significant and consistent differences in P concentration are likely due to greater plant mass with these treatments, which results in dilution of P concentration in the plant. Another factor to consider is the rates of P applied in the starter (10, 20, and 30 Ibs P205/A) were much less than the broadcast rate (120 Ibs. P205/A). At these rates starter P was effective at increasing plant mass but did not significantly increase P concentration like broadcast P did, especially when broadcast P was not applied. Starter application did increase P uptake at all 2013 and 2014 locations, which were dominated by cool and wet conditions. However, starter application did not increase P uptake in 2012, a warm spring. These data showed that both in- furrow and broadcast starter P fertilizer enhanced early growth of corn and increased P uptake, especially in cool and wet springs. Yields. Treatment effects on corn grain yield at each location are summarized in Table 6. When averaged across starter P rates, broadcast P application increased corn yields 7, 9, 25, 12, and 24 bu/A at the Stewart, New Richland-13, Willmar, New Richland-14 and Waseca locations, respectively. Starter P increased corn yields at only two of eight locations (New Richland-13 and Waseca), when averaged across the main effect of 18