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Fluid Journal : Winter 2013
8 The Fluid Journal Winter 2013 and 75 percent N soil-Urea+NBPT Foliar (P=0.26639). Measurement of leaf N (Figure 5B) and petiole nitrate (Figure 5C) content indicated no significant interaction or treatment effect. The P-values for the treatment effect were, respectively, 0.4197 and 0.2955 for leaf N and petiole nitrate data. Our basic findings in the growth chamber study were: • Application of only NBPT decreased membrane leakage and MDA • Addition of NBPT-to-foliar-urea decreased urease activity measured at 24 h after application and had no effect in the measurements of GS, GR, protein, photosynthesis, and chlorophyll fluorescence. Our basic findings in the field study were: • Addition of NBPT to foliar urea resulted in a yield increase. • Addition of NBPT to foliar urea application had no significant effect on leaf burn, leaf N, and petiole nitrate content. Summary In one published study, foliar urea application with the urease inhibitor phenylphosphorodiamde (PPD) has been reported to have a negative effect on soybean leaves. This study hypothesized that soybean leaf-tip injury caused by foliar urea application was attributed to ammonia formation from urea hydrolysis; however, they reported that the leaf necrosis was attributed to toxicity of urea rather than of ammonia. On the other hand, a later study with wheat did not observe any negative effect from NBPT with foliar-applied urea. In our study the negative effect of adding the urease inhibitor to foliar urea was not evident. We observed that addition of NBPT to foliar urea was effective in inhibiting leaf urease activity measured at 24 h after application. This mode of action of NBPT is carried by a binding and deactivation of the urease receptor for urea. The efficacy of NBPT in inhibiting urease in the soil is well documented. However, to our knowledge there is no report of NBPT effect on leaf urease activity. Since the addition of NBPT to foliar urea decreased urease activity it was expected that NBPT would result in increased leaf urea content. However, 100 percent N Soil-No Foliar and 75 percent N Soil-Urea+NBPT Foliar (P=0.8831), and between 75 percent N Soil-No Foliar and 75 percent N soil- Urea Foliar (P=0.1901). Comparative analysis of the treatments indicated that 75 percent N Soil-Urea+NBPT Foliar (1997.10±108.25 kg ha-1) exhibited a 20 percent and 12 percent increase in seed-cotton yield compared to the treatments 75 percent N Soil- No Foliar (1660.05±61.52 kg ha-1) and 75 percent N Soil-Urea Foliar (1776.60±62.68 kg ha-1), respectively. In 2010, (Figure 4B), the treatment effect on seed-cotton yield was not significant (P= 0 .0951). Differences were expected between treatments 100 percent N Soil-No Foliar and 75 percent N Soil- No Foliar, but the comparison was not significant (P=0.1106). There was a significant effect (P<.0001) for leaf burn in 2010 (Figure 5A). However, the comparative analysis only indicated that higher values of leaf burn occurred in the plots that received foliar urea application. No significant differences were observed between the treatment 75 percent N Soil-Urea Foliar Figure 4: Effect of foliar treatments on seedcotton yield of field grown . N.S. = not significant (P≤0.05).
Early Spring 2013