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Fluid Journal : Fluid Journal 1993-1995
1 Fluid Journal Late Spring 1993 Summary: The ability of soybeans to attain high yields from traditional soil fertilization is accepted in most cases. However, many reports have indicated increased yields from supplemental foliar fertilizer applications. Studies spanning 1988 to 1992 show important responses to sprays and fertigations made at reproductive stages are possible. Applications of N, B, Mg, and Mn were made on several cultivars. Yield responses from 6 to 9 bu/A have been attained in most experiments on irrigated, deep, sandy soils in the Coastal Plain of Georgia. Yield increases on loamy soils ranged from 0 to 5 bit/A. Best responses to sprays were attained with 40 lbs of N as low- biuret urea together with 0.4 lb B as sodium borate. The greatest potential for yield response is in soils with low abilities to retain anions such as nitrate and borate and where yield potential is not limited by other factors. Objectives of our studies were to determine if foliar applications ofN,B,Mg,Mnand combinations thereof would result in yield increases if applied during the reproductive stages of soybean growth. Additionally, we intended to determine the conditions for the greatest possible response and also determine the gross physiological reason for increased yield. Sprinkler irrigated field plots were established on either sand or sandy loam soils. Either no fertilizer or combinations of N, B, Mg or Mn were applied from R3 (first pod development) to early R5 (first bean development in pod) stages of growth (Table 1). Positive response Slight leaf burn occurred along the tips when N was applied alone. However, there was no observable bum Dr. Gary Gascho Late-Season Foliar Sprays Boost Soybean Yields Yield increases as high as 9 bu/A achieved in Georgia experiments. ONBMgNNBNMn ONBMgNNBN ++++ ++++ BMgMgB BMgMgB Bonifay Sand + Greenville Sandy Loam + Mg Mg Yield - bu/A 45 40 35 30 Figure 1. Yield effects from 1992 soybean spray treatments. when soluble sodium borate (0.4 lb B/ A) was added to the urea in the N+B treatment. This unexpected observation may have contributed to the increased yields shown in Figure 1. An additional observation was that Mg application, with or without other elements, tended to delay senescence by about two days. Applying N+B, B+Mg and N+B+Mg at the Bonifay site generally resulted in increased branching. The number of pods was greatest when Mg or a combination of N, B, and Mg were applied at the Bonifay sand site and for B application at the Greenville sandy loam site. Total pods per plant exceeded the untreated control when Mg, N+B, N+Mg or B+Mg were applied at the Bonifay site but were not different from the untreated control at the Greenville site. Interaction of cultivar and spray treatment on bean weight at the Bonifay site was not always consistent. But, the N+B application was always among the higher bean weights, regardless of the cultivar, and was the only treatment with bean weights significantly greater than the untreated control. It is important to mention that the two highest yielding treatments (N+B and B+Mg) also had the greatest bean weights. Correlation analysis by cultivar indicated that yield is more closely related to bean weight than other components measured in these studies. Pods on the main sterns and total pods per plant were significantly correlated with yield for four or five cultivars. Branching and pods on branches were less correlated with yields. Conclusions from previous studies indicated that important yield responses resulted, regardless of method of application (Table 2). Fertigation is possible in only a limited number of soybean fields and dribbling is impractical in fields where there are larger soybean plants. Therefore,
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