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Fluid Journal : Winter 2013
4 The Fluid Journal Winter 2013 Summary: Urea is the most recommended foliar nitrogen (N) source due to its relatively low toxicity, quick absorption and low cost. However, literature reports of yield increases with foliar urea application are inconsistent. The addition of a urease inhibitor may improve the use of foliar urea. Our study consisted of a growth chamber experiment using control, foliar urea, foliar urea + NBPT, and foliar NBPT. It also included a field experiment with: full recommended N soil rate with no foliar N application, a 75 percent N soil rate with no Improves efficiency of foliar fertilization in field and growth room tests. The Fluid Journal • Official Journal of the Fluid Fertilizer Foundation • Winter 2013 • Vol. 21, No. 1, Issue # 79 Drs. Derrick Oosterhuis and Eduardo Kawakami Increasing Yields Using Urea With Urease Inhibitors Foliar N application has been used as a supplement to meet cotton N requirements. Cotton root capacity for absorbing nutrients declines when the plants are developing fruit and, therefore, at this stage it is reasonable to supply N to plants by foliar application. Foliar application of N has the advantages of low cost and rapid response of the plant. It has the disadvantages of possible foliar burn, compatibility problems with other chemicals, and limitations on the amount of nutrient that can be applied. Many studies have been done testing the use of foliar urea in cotton; however, results for yield have been inconsistent. Once in the plant, urea is converted to ammonia by the enzyme urease and ammonia is incorporated to glutamate by the enzyme glutamine synthetase. In the available literature, it is still not clear whether leaf burn resulted from foliar urea application or is caused by toxic accumulation of urea or ammonia. In soybeans, foliar urea leaf burn is mainly associated with urea accumulation. However, to our knowledge, no research has been done in cotton. Use of a urease inhibitor with foliar urea application could be an effective method to help elucidate the fate of urea in cotton leaves. A well known urease inhibitor is N-(n-butyl) thiophosphoric triamide (NBPT) applied in the soil with urea. NBPT has been shown to have a high efficiency for inhibiting urease at low concentration in a wide variety of soils. Our preliminary data indicated that addition of NBPT to foliar urea increased cotton yield, with values significantly higher than urea alone. Furthermore, seed-cotton yield of NBPT + foliar urea treated plots, which received only 75 percent of the full recommended N rate, was statistically equivalent to plots that had 100 percent of the full recommended N rate. Thus, the use of urease inhibitor with foliar urea fertilization could have the potential of enhancing N assimilation in plant leaves, which could help improve foliar N management in crops. Objectives The main objectives of this study were to understand: • Foliar urea assimilation in cotton plants. • How the use of the urease inhibitor NBPT will affect the efficiency of foliar urea application. • Do cotton leaves treated with urea suffer from toxicity of urea or ammonia? With a better understanding of the physiological effects of foliar urea application and the use of a urease inhibitor, we expect to improve foliar N management in crops. Growth Room Methodology Planting. Cotton (Gossypium hirsutum L.) cultivar ST4554B2RF, was planted in 1.5 liter pots filled with soil from a representative cotton growing area in Marianna, AR. Pots were arranged in a large walk-in growth chamber. Temperatures (day/night) were 30/20oC, relative humidity 70 percent. Fertilization rates (P2O5 and K2O) were 45 and 73 kg/ha-1 , calculated using a soil volume of 1 ha and 0.15 m furrow slice. No soil N fertilization was applied in this experiment and pots were watered daily only with double deionized water. foliar application, a 75 percent of recommended N soil rate with two foliar urea applications, and a 75 percent of recommended N soil rate with two foliar urea + NBPT applications. In the growth room study the addition of NBPT to foliar urea inhibited urease activity and exhibited a trend for increased leaf urea content and improved cell membrane integrity. In the field study, the addition of NBPT to foliar urea resulted in an increase in seed-cotton yield. In conclusion, NBPT was effective in inhibiting cotton leaf urease, and in improving nitrogen use efficiency (NUE) and yield in field grown cotton. “Foliar urea increased seed- cotton yield”
Early Spring 2013