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Fluid Journal : Fluid Journal 1999-2001
2 Fluid Journal Fall 2000 fertilization and symbiotic N fixation. This presentation will discuss results of recent Iowa studies (1994-1996) evaluating soybean response to foliar fertilization with macronutrients during early vegetative stages under a variety of growing conditions. Mixed results Twenty-one trials. Figure 1 shows the mean grain yields for the six 3-18-18 treatments used in 1994 at responsive sites, and across the 21 sites. There were statistically significant responses (P<0.1) at seven sites. At four sites, all fertilization treatments increased yield. At two sites, some treatments increased yield, others decreased yields slightly, and others did not affect yield. The differences between treatments were not consistent across sites and could not be explained satisfactorily. At one site, treatments decreased yield (3.8 bu/A). It must be noted that the results for this site are included in the means for the responsive sites shown in Figure 1, so the mean yield increases were actually higher than those represented in the figure. The yield decreases could not be explained by leaf damage (no treatments caused visible damage), rates, or frequency of application. Fertilization had no statistically significant effects across the 21 sites and the mean effect of all treatments was less than 1 bu/A. The 3-gal/A rate produced higher yields than the other treatments, increasing yield by about 2 bu/A, although this increase was not statistically significant. At responsive sites, this treatment increased yield by an average of 6 bu/A. There was no advantage for the highest single rate (4 gal/A) or the double applications when compared with the single 3-gal/A rate. Seventeen trials. Figure 2 shows the mean grain yields for all sites for the new set of treatments applied in 1995. Five sites showed statistically significant response to treatments, but differences between treatments were inconsistent across trials. All treatments increased yield at one site (a 6-bu/A mean increase). Most treatments, except for the double application of 3-18-18 and the 6-gal/A rate of 10-10-10, increased yield at another site (a 5-bu/A mean increase). At two sites, 3-18-18 increased yield an average of 3 bu/A but the other mixtures either had no effect or decreased yield slightly. At one site all treatments decreased yields (a 4-bu/A mean decrease). Average response across all sites and treatments was essentially zero, although fertilization with 3 gal/A of 3- 18-18 (treatment that produced the highest yields in 1994) increased yields by about 1 bu/A. When means for only the responsive sites were calculated, yield advantage for the 3-gal/A rate of 3- 18-18 was about 5 bu/A. Application of 3-18-18 caused no leaf damage. Although 10-10-10 and 8-0-8 caused slight leaf damage, the only meaningful burning occurred for the 6 Figure 3. Soybean yield response to early foliar fertilization for 10 trails, Mallarino, et al., Iowa State University, 1996. FOLIAR FERTILIZATION OF SOYBEANS - 10 TRIALS IN 1996 ALL TRIALS ONE RESPONSIVE TRIALS SOYBEAN YIELD (bu/acre) 55 50 45 40 35 30 Check 2+2 gal 3-18-18 3 gal 3-18-18 6 gal 10-10-10 3 gal 10-10-10 4.5 gal 8-0-8 Figure 2. Soybean yield response to early foliar fertilization for 17 trails, Mallarino, et al., Iowa State University, 1995. FOLIAR FERTILIZATION OF SOYBEANS - 17 TRIALS IN 1995 ALL TRIALS 5 RESPONSIVE TRIALS SOYBEAN YIELD (bu/acre) 55 50 45 40 35 30 Check 2+2 gal 3-18-18 3 gal 3-18-18 6 gal 10-10-10 3 gal 10-10-10 4.5 gal 8-0-8
Fluid Journal 1996-1998
Fluid Journal 2002-2004