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Habib Khemira, Timothy L. Righetti, and Anita N. Azarenko

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.

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Sohrab Davarpanah, Ali Tehranifar, Gholamhossein Davarynejad, Mehdi Aran, Javier Abadía, and Reza Khorassani

, 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

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Alexander X. Niemiera, Linda L. Taylor, and Jacob H. Shreckhise

-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

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Lenny Wells, Jason Brock, and Tim Brenneman

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

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Vladimir Orbović, Diann Achor, and James P. Syvertsen

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

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Xiao-Juan Wei, Jinlin Ma, Kai-Xiang Li, Xiao-Jing Liang, and Haiying Liang

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

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Matt A. Rudisill, Bruce P. Bordelon, Ronald F. Turco, and Lori A. Hoagland

’s Selected Seeds, Albion, ME) supplemented with dehydrated alfalfa meal [(3.0N–0.2P–0.8K); Fertrell, Bainbridge, PA]; 2) animal manure (partially composted and dehydrated chicken litter, 3.0N–0.9P–2.5K; Fertrell), 3) urea (46N–0P–0K); and 4) unfertilized

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Guihong Bi and Carolyn F. Scagel

, 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

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Paraskevi A. Londra, Maria Psychoyou, and John D. Valiantzas

Recently, urea–formaldehyde resin foam (UFRF) has been introduced as a synthetic organic soil amendment and is used as a substrate in the propagation and growth of plants in hydroponic systems, soilless cultures, and substrates used in production of

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B.R. Bondada, J.P. Syvertsen, and L.G. Albrigo

Foliar-applied urea nitrogen (N) has potential to become an important component in fertilizer programs for citrus in Florida and other citrus growing areas as it can reduce nitrate leaching into ground water. We evaluated seasonal absorption characteristics of three urea formulations, Triazone-urea, liquid urea, and spray grade urea by citrus leaves that were from 2 weeks to 6 months old. The effect of leaf age on 15N absorption by N-deficient and N-sufficient leaves, together with urea absorption over an eight-week period were studied using greenhouse-grown and field-grown plants. All foliar N applications were based on a recommended rate of 34 kg N/ha in 469 L of water. In the field studies, leaf N was increased similarly by the three urea formulations one week after three weekly applications. Young leaves (0.25 month and 1 month old) absorbed a greater percentage of N than the older leaves (3 month and 6 month old). Epicuticular wax concentration increased and 15N absorption declined with leaf age. Nitrogen deficient leaves (1.80% N) had greater wax concentration and lower N absorption than N sufficient leaves (2.60% N). Four to 8 weeks after urea applications, Triazone-urea sprayed leaves had significantly greater leaf N concentration than leaves sprayed with liquid urea or nonsprayed control leaves. The greenhouse studies revealed that the 15N absorption was greater through abaxial leaf surfaces than through adaxial surfaces regardless of leaf N level and application time. Applying foliar 15N-urea during night (2000 hr to 2200 hr) resulted in greater absorption of 15N than in the morning (0800 hr to 1000 hr) or afternoon (1200 hr to 1400 hr). It is clear that maximum N absorption from foliar urea sprays occurred at night through the abaxial surfaces of young leaves with sufficient N. Triazone-urea acted as a slow-release N source that could be exploited in supplying N over an extended period of time.