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Fluid Journal : Winter 2013
9 The Fluid Journal Winter 2013 urea measurement collected at 24 h after treatment application showed no significant differences between the treatments Foliar Urea and Foliar Urea+NBPT. There was a numerical increase in leaf urea content with addition of NBPT, thus it is possible that a statistical difference could be detected if the measurements were done after the 24 h period. The data of urease and urea in cotton indicated that the total hydrolization and assimilation of the foliar applied urea are not completed in the period of 24 h. The data of membrane leakage and MDA had identical results, indicating that application of Foliar NBPT improved the cell membrane integrity of cotton leaves. The treatment Foliar Urea+NBPT showed statistically equal values compared to the Foliar NBTP treatment; however, its values were not significantly different from the Foliar Urea treatment. The process involved in the role of NBPT on cell membrane integrity is not clear; however, since NBPT binds to Ni urease receptor sites, it is possible that NBPT has a Ni chelating effect in the plant. A 1992 study reported that Ni affected the cell plasma membrane properties and ATPase activity of rice plants. Another study reported Ni causing oxidative stress in a variety of plants, thus NBPT in the plant could be resulting in a protective mechanism against Ni. In this experiment, no evidence of a negative effect of urea and/or NBPT was observed in the measurements of GR, GS, protein, photosynthesis and chlorophyll fluorescence. However, it is possible that an effect of NBPT could occur in a measurement collected after the 24 h sampling, since a significant NBPT effect was observed in urease and membrane integrity data. Additional research is needed to address this hypothesis. The yield data of the field experiment showed a significant interaction between treatment and year of the experiment. This indicated that the values of seed-cotton yield responded differently to foliar treatment applications, depending on the year of the experiment. We observed a significant seed-cotton yield increment with addition of NBPT to foliar urea. Addition of NBPT increased yield compared to application of foliar urea alone and it resulted in equivalent seed- Dr. Oosterhuis is Professor of Crop Physiology at the University of Arkansas, and Dr. Kawakami is Research Agronomist in Matto Grosso, Brazil. Figure 5: Effect of foliar treatments on leaf burn (A), leaf N (B), and petiole nitrate (C) of a field grown cotton (2010). N.S . = not significant (P≤0.05). cotton yield to the 100 percent N Soil application treatment. However, data on leaf burn, leaf N, and petiole nitrate content did not show any significant effect of the addition of NBPT to foliar urea application. The significant influence of NBPT on cotton yield could result from the NBPT effect on the inhibition of urease and improvements of cell membrane integrity indicated in the growth chamber study. In conclusion, the use of NBPT to foliar urea application in the growth chamber study decreased urease acridity and showed trends for increasing leaf urea content and improving cell membrane integrity. In the field study, seed-cotton yield improvements were observed with the addition of NBPT to foliar urea.
Early Spring 2013