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Fluid Journal : Fluid Journal 2008-2009
prolonging N2 fixation. Information is needed to determine if field-grown glyphosate-resistant soybeans respond to applied Mn in a manner different from conventional soybeans, and if so, what fertilization practices are best to correct the problem. Currently, there is little information on Mn fertilization of soybeans in Kansas. The objective of this research was to determine if the response of glyphosate-resistant soybeans to applied Mn is different from that of conventional soybeans, and if so, to develop fertilization strategies that will prevent or correct deficiencies leading to improved yield for soybean producers. Mn effects Experiment I. Yield of glyphosate- resistant variety KS 4202 RR was 7 bu/A lower than the conventional variety when no Mn was applied (Figure 1). The application of 2.5 lbs Mn/A improved yield and equaled that of the conventional isoline. Yield of the conventional variety was depressed at the high rate of Mn. Tissue Mn concentration (uppermost expanded trifoliate at full bloom) in the herbicide-resistant variety was less than half of the conventional variety when no Mn was applied (Figure 2). Experiment II. Yield of the glyphosate-resistant soybean variety KS 4202 was maximized by a combination of Mn applied as a starter two inches to the side and two inches below the seed at a planting rate of 0.33 lb Mn/A and a foliar application at the same rate applied at the 4-leaf stage (Table 1). A starter alone application at either 0.3 or 0.6 lb Mn/A did not give results equaling the combination of the starter and foliar treatment. Application of foliar Mn applied at 0.33 lb Mn/A at the V4, V8, and R2 stages of growth gave yields equal to the starter plus one foliar application at the V4 stage. One or two foliar applications were not as effective as the starter plus foliar or the three foliar applications. Higher rates of starter-applied Mn and single foliar applications will be investigated in 2009 in order to determine if timing is critical or if higher rates applied earlier in the growing season may be as effective as lower rates applied more Figure 1. Soybean yield response to applied Mn, Scandia, KS, 2005-2006. Figure 2. Soybean leaf tissue Mn concentration (uppermost expanded trifoliate at full bloom), Scandia KS, 2005-2006. frequently. This research provides evidence that the glyphosate-resistant soybean variety used in this experiment did not accumulate in the same manner as the conventional variety and did not respond to application of Mn in this high-yield environment. Dr. Gordon is professor of agronomy, Kansas State University. Table 1. Foliar applied manganese effects on soybean yield, 2005-2007 Stage of Growth Yield, bu/A Starter (0.33 lb) 65 Starter (0.66 lb) 70 Starter (0.33 lb) + V4 (0.33 lb) 76 V4 (0.33 lb) 67 V4 +V8 (0.33 + 0.3 lb) 73 V4+V8+R2(0.33+0.33+0.33lb) 76 Untreated Check 64 LSD (0.05) 3
Fluid Journal 2005-2007