, 1982 ). Therefore, N deficiency leads to growth limitation in all plant organs, including roots, stems, leaves, flowers, and fruits ( Barker and Pilbeam, 2007 ). Urea is the most commonly used N source for foliar fertilization ( Etehadnejad and
Fruit tree responses to foliar urea sprays are variable. We hypothesized that such variability is a function of leaf age-related changes in urea-N mobility after urea is absorbed. Two experiments were conducted to study the distribution of urea-derived N in shoots and branches of apple (Malus ×domestica Borkh.) trees. Urea labeled with 15N was applied to young expanding leaves in spring and to senescing spur leaves in fall. At the low concentrations used [0.5%, 1%, and 2% (w/v)], very little spring-applied 15N was found in tissues other than the treated leaf. Fall-applied urea-15N, however, was detected in high concentrations in dormant buds and bark of the spurs to which the treated leaves were attached. Almost no N was exported to neighboring tissues. The following spring, there was some redistribution of labeled N to adjacent buds. Foliar urea sprays applied immediately after harvest contributed most to bud N; less urea-N was exported to the buds following later fall applications.
-release fertilizers are relatively expensive, urea (CH 4 N 2 O; 46% N) may be a viable choice of N fertilizers to precharge wood-based substrates, one that is relatively inexpensive and able to overcome N deficit within 24 to 48 h. Urea is hydrolyzed to NH 4 + by the
on pecan scab have been studied since the 1920s; however, most studies have demonstrated little effect of S on pecan scab Fusicladium effusum G. Winter ( Bertrand et al., 1981 ; Waite, 1924 ). Foliar urea sprays are known to enhance fruit
Urea hydrolysis and the fate of ammonium produced were evaluated in bark : peat : sand, peat : vermiculite, and 14 commercial potting media, in cropped and uncropped samples. Urea hydrolysis was much more rapid in pine bark : peat : sand than in peat : vermiculite. Significant variation in urea hydrolysis was observed among the commercial media. Urea hydrolysis was more rapid in cropped than in uncropped media. Substantial net N immobilization was observed in most media. Although nitrification was evident, there was generally very little net nitrate accumulation. Differences in urea hydrolysis and ammonium accumulation were of sufficient magnitude to warrant consideration in fertilizer management.
spreading over leaf surfaces. L-77 improved the efficiency of gibberellin in prolonging the Citrus harvest season ( Greenberg et al., 1987 ). Although Cu fungicides are not routinely mixed with silicone surfactants or urea in spray tank mixes, the behavior
conventional breeding, but also has an adverse impact on economic incomes for breeders. Our study was aimed to induce flowering in juvenile C. chrysantha . We assessed the effects of different combinations of nitrogen fertilizer, urea [CO(NH 2 ) 2 ], and
, 1995 ; Tagliavini et al., 1999 ). Foliar fertilization in fall is an alternative to supplying N to the soil. In some perennial plant species, foliar sprays of urea after terminal bud set can improve N storage without stimulating new growth or delaying
In the article “Urea Hydrolysis in Potting Media”, by George C. Elliott (J. Amer. Soc. Hort. Sci. 111:862–866, November, 1986), Figs. 2 and 3 were reversed. The correct figures and legends are printed below.