Foliar Application Of Urea Research Articles

The Effect of Foliar Nutrition with Nitrogen, Molybdenum, Sucrose and Benzyladenine on the Nitrogen Metabolism in Carrot Plants

The Effect of Foliar Nutrition with Nitrogen, Molybdenum, Sucrose and Benzyladenine on the Nitrogen Metabolism in Carrot Plants The Kazan F1 carrot was cultivated in years 2004-2005 in open-work containers sized 60×40×20 cm filled in with silt loam and located on the open field under shade providing fabric. The following combinations of experiments were arranged: (1) control - without foliar nutrition, and foliar nutrition with: (2) urea, (3) solution of urea+Mo, (4) urea+Mo+BA (benzyladenine - BA), (5) urea+Mo+BA+sucrose, (6) BA in the concentration of 5 mg·dm-3 and (7) BA in the concentration of 10 mg·dm-3. In combinations 2-5 the following concentrations of components in solution were applied: urea and sucrose each in 20 g·dm-3, molybdenum 1 mg·dm-3, benzyladenine 5 mg·dm-3. Foliar nutrition was applied three times. In leaves sprayed with urea and with solution of urea+Mo as well as urea+Mo+BA, an increased concentration of NO3 - was observed when compared to other sites. Foliar nutrition did not result in any significant changes in content of N-total and dry weight in leaves. Foliar application of urea, as well as the solution of urea+Mo+BA, caused an increase in the activity of nitrate reductase (NR) in leaves when compared to the control. Whereas, after spraying the plants with BA only, a noticeable decline in NR activity was revealed in comparison with the control; interestingly, a higher concentration of BA (10 mg·dm-3) was more effective. Foliar nutrition with urea+Mo+BA+sucrose and spraying with benzyladenine only (independently from the concentration) resulted in a significant decrease of the content of NO3 - in storage roots when compared to other combinations. The highest level of nitrogen uptake by single storage root and leaves of one carrot plant was found after urea+Mo+BA+sucrose nutrition. In case of N uptake by yield of leaves and biological yield of whole carrot plants (roots+leaves) the highest values were observed in combination no. 6.

PHENOLOGY, GROWTH, AND GRAIN YIELD OF MAIZE AS INFLUENCED BY FOLIAR APPLIED UREA AT DIFFERENT GROWTH STAGES

Foliar urea application is considered an important factor affecting phenology, growth, yield, and yield components of maize. A field experiment was conducted to study effects of urea spray on Azam variety of maize (Zea mays L.) in Mardan district of the North West Frontier Province (NWFP) of Pakistan during 2005–06. The 5 × 4 factorial experiment was designed with five urea levels (U0 = control, U1 = 2, U2 = 4, U3 = 6 and U4 = 8% urea) applied to main plots and four application timings (T1 = at V9, T2 = V12, T3 = VT and T4 = R1 stages) assigned to subplots. Days to tasseling, silking, and maturity were delayed significantly when urea was applied at the rate of 6% and when applied at the V12 stage. Earlier tasseling, silking, and maturity were observed in urea control plots and in plots that received urea at the V9 stage. Plant height, leaf area, number of grains per cob and per line as well as (1000) grain weight, and grain and stover yields increased significantly up to the 6% urea level. Maize yield and yield components were higher when urea was applied at the V12 and VT stages than at the V9 and R1 stages. It is concluded that urea spray at the rate of 6% during the V12 stage would improve the grain yield and yield components of maize in the study area and contribute significantly to increased production.

MANEJO INTEGRAL DE HUERTOS DE MANGO ‘ATAULFO’ CON ALTAS DENSIDADES DE PLANTACIÓN

The objective of this study was to evaluate the effect of three integral management treatments on orchards at high densities on vigor, vegetative growth, flowering, yield, season of harvest, and fruit size of ‘Ataulfo’ mango. In a mango ‘Ataulfo’ orchard was selected under irrigation with high plantation density, three different integrated management treatments were applied. Each treatment included pruning (light and moderate) irrigation (application or suspension), fertilization (at specific phenological stage), foliar applications of nitrates or urea (to promote vegetative growth and flowering) and Paclobutrazol applied to the soil. The results showed that the three integral management packages showed benefits in diverse aspects: tree size was reduced; the flowering and yield was about for 30 days earlier than control trees; this performance allow us to get better prices when the harvest was obtained out of normal production time. The yield in the three treatments was higher than the control trees during 2007 and 2008. Cumulative yield of two harvests in the control trees was 75.65 kg·tree-1, while in the packages was among 149.40 and 163.59 kg. The average fruit weight was not affected by the treatment. The best package to be recommended is the number one, because it had the highest cumulative yield and it was the cheapest one.

Effects of foliar application of calcium chloride and urea on quantitative and qualitative characteristics of pomegranate fruits

The effects of urea and calcium chloride and their combinations on qualitative and quantitative characteristics of pomegranate fruits were studied over 2 years. Aqueous solutions of urea at 0%, 0.5%, 1% and 2% and calcium chloride at 0%, 2% and 4% were applied on two branches of pomegranate ( Punica granatum L. cv Malase-Yazdi) at full bloom (FB) and 1 month after full bloom (1MAFB) stages. Urea at concentrations of 1% and 2% significantly increased aril size, fruit length and diameter. Calcium chloride at concentrations of 2% and 4% significantly increased average fruit weight and ascorbic acid (AA) content. Both urea and calcium chloride increased soluble solid content (SSC) at all of the used concentrations. In the first time of spraying, higher level of treatments reduced titratable acidity (TA), but the second time of spraying did not significantly affect the TA.

Foliar Application of Urea and Triazone Nitrogen to Cotton

ABSTRACT Upland cotton (Gossypium hirsutum) requires adequate nitrogen (N) for optimum yields. Foliar applications of urea to supplement soil applied N have been tried for many years across the Cotton Belt, but responses have been highly variable. No published information is available regarding response by irrigated cotton to foliar applied N in subtropical South Texas. This study investigated the response of cotton to foliar applied urea and triazone N over a three-year period near Weslaco, Texas. In all years, foliar applied urea tended to increase seed cotton yield when soil applied N was limiting. In the absence of soil applied N, the increase due to foliar urea was significant in two of the three years (28.7 and 15.7% increases). Foliar applied triazone N was ineffective at increasing seed cotton yields.

Influence of foliar urea on the antioxidant response and fruit color of sweet pepper under limited N supply

AbstractBACKGROUND: Foliar fertilizer methods could provide a rapid and efficient response when uptake by plant roots is limited. This work studies the effect of foliar urea sprays (15 g L−1) at different frequencies on the antioxidant metabolism and fruit quality of sweet pepper fruits under N‐limited nutrient solution (3.5 mmol L−1 NO3−) and fully N‐supplied (12.5 mmol L−1 NO3−) plants.RESULTS: Foliar applications of urea in root N‐limited plants increased the total N concentration in the fruits and no significant differences were found with respect to control fruits (plants fully supplied with N by the roots). Fruit color was significantly affected by the urea sprays, and at the highest frequency (twice a week) the largest overall color difference (ΔE) with respect the non‐sprayed fruits was obtained. Foliar urea increased anthocyanin concentration to control values but flavonoids were only affected at the highest application frequency. N deficiency induced oxidative stress but foliar application of urea altered this response, significantly diminishing catalase and ascorbate peroxidase activity.CONCLUSION: Sweet pepper fruits showed a significant and positive response to foliar fertilization on the studied parameters, compensating to a major extent the reduction of N by the roots. In addition to the environmental issues in reducing N contamination, fully monitored automatically sprayed foliar fertilizer could utilize N more efficiently and at lower cost than applying the full recommended rate of other N fertilizers to the nutrient solution, providing flexibility in correcting N nutrition in the plant, and especially the control of nutrient supply independent of the water supply. Copyright © 2008 Society of Chemical Industry

Effect of polybag size and foliar application of urea on cocoa seedling growth

The effects of different polybag sizes and foliar application of urea on the growth of cocoa seedlings in the nursery were studied at the Cocoa Research Institute of Ghana substation at Afosu in the Eastern Region of Ghana between June 2004 and May 2005. Hybrid cocoa seeds were sown in polybags measuring 17.5 cm × 25 cm, 12.5 cm × 25 cm, 12.5 cm × 20 cm, and 12.5 cm × 15 cm filled with top soil. From the four-leaf stage, half of the seedlings in the different polybags received fortnightly foliar application of 2 per cent urea solution, while the other half did not receive foliar application of urea. Each treatment consisted of 50 cocoa seedlings. There were significant differences (P< 0.01) in girth and height between the cocoa seedlings in the different sizes of polybags at 3, 4 and 5 months after sowing. Leaf number and tap root length were also significantly influenced by polybag size at 4 and 5 months after sowing. Generally, seedlings raised in 17.5 cm × 25 cm polybags produced bigger and taller seedlings, more leaves, longer tap root length, and had significantly higher (P< 0.01) total dry matter per seedling than those raised in 12.5 cm × 15 cm polybags. Foliar application of 2 per cent urea improved the growth of cocoa seedlings in all the different polybag sizes. The results suggest that smaller polybag sizes (12.5 cm × 25 cm, 12.5 cm × 20 cm, and 12.5 cm × 15 cm) could be used to nurse cocoa seedlings and transplanted early at 3 months after sowing instead of the recommended practice of nursing in 17.5 cm × 25 cm polybags and transplanting at 5 to 6 months after sowing. More cocoa seedlings raised in smaller polybags could, therefore, be transported per trip for field planting at reduced cost to the farmer.Les effets de différentes dimensions de sac en plastique et d\'application foliaire d\'urée sur la croissance de semis de Cacao dans les pépinières étaient étudiés à Afosu, une sous-station de l\'Institut de Recherche en Cacao du Ghana dans la région de l\'Est du Ghana entre juin 2004 et mai 2005. Les fèves de cacao hybride étaient semées dans les sacs en plastique qui mesuraient 17.5 cm × 25 cm, 12.5 cm × 25 cm, 12.5 cm × 20 cm, et 12.5 cm × 15 cm remplis de couche arable. De la phase de 4-feuille, une demie de semis dans les différents sacs en plastique recevaient tous les quinze jours l\'application foliaire de 2% de solution d\'urée alors que l\'autre demie ne recevaient pas d\'application foliaire d\'urée. Chaque traitement consistait en cinquant de semis de cacao. Il y avaient des différences considérables (P £ 0.01) en circonférence et en taille entre les semis de cacao dans les différentes dimensions de sacs en plastique à 3, 4 et 5 mois après la semaille. Nombre de feuille et la longueur de racine pivotante étaient aussi considérablement influencés par la dimension du sac en plastique à 4 et 5 mois après la semaille. En général les semis élevés dans les sacs en plastique de 17.5 cm × 25 cm produisaient des semis plus gros et plus grands, plus de feuilles, de longueur de racine pivotante plus longue et avaient une totalité de matière sèche par semis considérablement plus élevées (P £ 0.01) que ceux élevés dans les sacs en plastique de 12.5 cm × 15 cm. L\'application foliaire de 2% d\'urée améliorait la croissance de semis de cac ao dans toutes les différentes dimensions de sacs en plastique. Les résultats suggèrent que les sacs en plastique de dimensions plus petites (12.5 cm × 25 cm, 12.5 cm × 20 cm, et 12.5 cm × 15 cm) pourraient être utilisés pour soigner les semis de cacao et repiqués précoces à 3 mois après la semaille plutôt que la pratique actuelle recommandée de soigner dans les sacs en plastique de 17.5 cm × 25 cm et repiquer à 5-6 mois après la semaille. Plus de semis de cacao élevés dans les plus petites sacs en plastique pourraient donc être transporter par trajet pour le repiquage sur le terrain à coût réduit à l\'agriculteur. Ghana Journal of Agricultural Science Vol. 40 (2) 2008: pp. 207-213

Carbon and Nitrogen Reserves in Perennial Strawberry Affect Plant Growth and Yield

Early spring growth of perennial strawberry (Fragaria ×ananassa Duch.) plants is supported by the carbohydrate and nitrogen (N) reserves accumulated from the previous growing season. The limitations of these reserves on the initial spring growth and yield of perennial strawberries have not been studied in detail, particularly the influence of N reserves. Differential N fertigation (0 to 20 mm N) was applied to potted strawberries during the growing season and a supplemental foliar urea application was applied to a portion of the plants in the fall to modify reserve N during dormancy. Plant N content and spring vegetative growth the year after fertigation increased nearly twofold with increasing N fertigation. Photosynthesis per unit leaf area also increased up to 10 mm of fertilizer N and then stabilized through 20 mm. Foliar urea application in fall further increased total plant N content and size, decreased carbohydrate concentration, and also decreased yield in plants with the most total N. Nitrogen fertigation was resumed on a portion of these plants in early spring, but new growth and subsequent yield were unaffected by spring N application. In a second experiment, CO2 enrichment with and without soil and foliar N application in the fall was used to vary carbon (C) and N reserves. CO2 enrichment in fall increased plant size and yield the next July by ≈20%, but total nonstructural carbohydrate and N concentrations were unaffected. Foliar urea application also increased N and C reserves (but not concentration) as well as yield in both enriched and unenriched plants. Although foliar urea in fall decreased carbohydrate concentration, total reserve levels were unaffected because treated plants were larger. In this experiment, spring N increased plant size by ≈50%, but yield was increased only 12%, suggesting that yields are mostly dependent on reserves. Increasing N reserves with a late fall foliar application is one strategy growers can use to efficiently enhance growth and yield in low to moderately fertilized plants.

Urea Foliar Fertilization Affects Onion Weight and Nutrient Content

ABSTRACT Foliar application is used to supply fertilizers to developing crops. This method provides flexibility to the producer in their application. This research was undertaken to investigate effects of foliar application of urea on onion (Allium cepa L.), cv. Salamony, in Syria. Four levels of urea, 0, 2,000, 3,500, and 5,000 mg·L−1, were evaluated. Plants were treated with 16.6 mL/plant of urea three times, at 3-day intervals, starting 26 days after planting. Salamony can positively respond to up to 5,000 mg·L−1 of urea without hazard of leaf burn, and bulb fresh and dry weights increased as urea concentration increased. Nitrogen (N), phosphorus (P), potassium (K), and total cation contents of bulbs were increased, but magnesium (Mg), calcium (Ca), and sodium (Na) contents were not affected by treatment. The 5,000 mg·L−1 treatment proved to be the most effective in increasing bulb fresh and dry weights and increasing mineral uptake.

Plant growth, metabolism and adaptation in relation to stress conditions: Further studies supporting nullification of harmful effects of salinity in lettuce plants by urea treatment

Foliar application of urea to lettuce plants induced pronounced changes in the total amount and in the relative composition of the nitrogen pool. As compared with untreated lettuce plants, urease (UR), nitrate reductase (NR), asparaginase (AS) and glutamine synthetase (GS) activities were, in general, increased with an increase in the concentration of urea. On the other hand, salinization of lettuce plants with NaCl induced a significant decrease in the activities of UR, NR, AS and GS, at vegetative and adult growth stages. In general, treatment of lettuce plants with increasing concentrations of urea fertilizer in combination with each of the levels of salinity resulted in significant increases in all enzyme activities. Treatment with increasing concentrations of urea fertilizer induced significant decreases both in glycine and proline contents below control levels. On the other hand, salinization of lettuce plants with NaCl induced significant pronounced increases in the contents of the two amino acids. Further increments in glycine and proline contents were observed in differently salinized lettuce plants foliary sprayed with increasing concentrations of urea at vegetative and adult growth stages. Salinity solely enhanced the occurrence of novel proteins that were detected neither in the water control nor in the urea-treated plants. Protein banding patterns of lettuce plants treated with urea either alone or in combination with NaCl showed different &lt;I&gt;de novo &lt;/I&gt;protein bands with different molecular weights, induced by urea and/or NaCl at vegetative and adult growth stages.

Effect of foliar urea application on quality, growth, mineral uptake and yield of broccoli (Brassica oleracea L., var. italica)

The objective of this study was to determine the effect of foliar urea applications on quality, growth, mineral content and yield of broccoli under field conditions in 2003, 2004 and 2005. Broccoli cultivars AG 3317 and AG 3324 were treated with foliar urea applications at different concentrations (0.0, 0.4, 0.8 and 1.0%). Foliar applications of urea, especially 0.8 and 1.0% resulted in larger heads, weightier heads and plants as well as higher plants. Conversely, the greatest head and leaf dry matter contents were obtained with no fertilizer-nitrogen application. SPAD chlorophyll readings that were measured in the third year increased with elevated urea concentrations. In regard to the nutrient content, it can be interfered that soil nitrogen fertilization and foliar urea applications increased the content of almost all nutrients in leaves and heads of both broccoli cultivars in three experiment years. Generally, the greatest values were obtained from 1.0% urea application for both cultivars. It results from the study that for optimum yields 0.61 and 0.96% concentrations of urea sprays could be successfully used to obtain better growth and yield in broccoli cultivars AG 3317 and AG 3324, respectively.

Rate of nitrogen application during the growing season alters the response of container-grown rhododendron and azalea to foliar application of urea in the Autumn

SummaryOne-year-old rhododendron (Rhododendron ‘H-1 P.J.M’) and azalea (Rhododendron ‘Cannon’s Double’) plants grown at different nitrogen (N) fertilisation rates were used to assess the influence of soil N applications during the growing season, and foliar applications of urea in the Autumn, on N uptake and accumulation, and plant growth in the following Spring. N uptake efficiency declined linearly during the first growing season with an increasing rate of N fertilisation. For both cultivars, foliar urea application in the Autumn significantly increased plant N content without affecting plant size, regardless of plant N status. Leaves of rhododendron accumulated more N than other plant structures. Plants sprayed with foliar urea in the Autumn had more new growth the following Spring than plants receiving no urea, regardless of whether the plants received fertiliser in the Spring. For azalea, N uptake in the Spring was, in general, not affected by applications of urea during the previous year. For rhododendron, urea application in the Autumn decreased N uptake the following Spring. For both cultivars, increasing N availability during the growing season increased the ratio of above-ground to below-ground dry weight. Our results suggest that combining optimum N applications during the growing season with foliar application of urea in the Autumn can improve N uptake efficiency, increase N storage, and optimise growth in Rhododendron.

Yield of Citrus Trees with Foliar Urea as the Only N Source

In order to evaluate possible reduced nitrate leaching while maintaining yield, `Hamlin' orange and `Flame' grapefruit trees on `Carrizo' or `Swingle Citrumelo' rootstocks were grown from planting using only foliar urea or soil-applied nitrate or ammonium N. An intermediate treatment of foliar and ground N was included also. From the 4th year, yields were recorded for 3 years. As previously reported, canopy growth was greater for the foliar urea treatment for the first 3 years. For 2 of the next 3 bearing years, the grapefruit trees in the foliar urea N treatment produced significantly less yield than the soil-applied treatment and the intermediate treatment was intermediate. The orange trees in the foliar urea treatment produced significantly less fruit than the soil N treatment in only 1 of 3 years, but the yields were numerically less every year. Results for fruit quality and nitrate leaching will be reported also. Foliar urea application alone was more costly and less productive than a soil N program.

Cuticular penetration characteristics of urea in citrus leaves

SummaryRecent interest in reducing nitrate levels in ground water has stimulated a re-examination of the potential use of foliar applications of urea on citrus trees. We examined the penetration characteristics of urea through isolated cuticles in relation to their thickness and surface wax content in citrus (Citrus paradisi Macf.) leaves using a finite dose-diffusion system. Isolated cuticles with the greatest integrity were mounted on diffusion half-cells with the inner morphological surface in contact with citrate buffer solution.14 C-urea in citrate buffer was applied to the outer wax-rich morphological surface and the penetration of urea was monitored by repeated sampling of the receiver solution. Urea penetration through cuticles exhibited an asymptotic curve characterised by an initial lag phase of about 10 min, a quasi-linear phase of maximum penetration rate, averaging 2% of the urea applied h–1, occurred about 40 min after urea application, followed by a plateau phase during which the rate of penetration approached zero at 144 h. Total urea penetration averaged approx. 35% and tended to decrease with increased cuticle weight until the cuticles were 6 months-old. Re-hydration of the urea deposit, with water, stimulated additional penetration of about 1%; however, this was not significant. Epicuticular wax occurred as platelets that increased with leaf age. Dewaxing the cuticles significantly enhanced the maximum penetration rates by 30% of the amount applied h–1 and increased total penetration by 64%. This study provides valuable details on the transport of urea through isolated cuticles which is important in fine-tuning foliar urea fertilisation in citrus trees.

An evaluation of foliar nitrogen and zinc applications to macadamia

The efficiency and effectiveness of foliar nitrogen (N) applications as urea to macadamia leaves were investigated in field experiments at Alstonville, New South Wales. The first experiment (August 2000) evaluated the effect of 1–8% urea solutions on the evidence of leaf burn. A 2% urea solution produced negligible leaf burn (1% leaves with lesions) whereas the incidence of leaf burn increased with urea concentration; 20% of leaves were affected with an 8% urea solution. In the following month, a second experiment was conducted using a 2% urea solution that was painted onto both sides of leaves to measure N uptake efficiency. The urea was enriched with the stable isotope 15N, which allows a direct measure of urea uptake, a common method for tracing plant N uptake. Leaves were sampled after 3 and 6 days, and cellulose acetate was then applied to remove urea adhering to the surface of leaves. Leaves adjacent to urea-treated leaves were also sampled to account for any transport out of treated leaves. The experiment was repeated in September 2001. In 2000, a mean of 31% of the urea was absorbed by the mature leaves and this increased the N content by 2.2%. In 2001, a mean of 38% of the urea was absorbed by the mature leaves and this increased N content by 1.9%. Leaves from part of a large mature macadamia tree were stripped to provide an estimate of leaf biomass. From this, the increase in leaf N uptake for a mature orchard was calculated to be 3.98 kg/ha in 2000 and 4.57 kg/ha in 2001. The efficiency of application and hence leaf N uptake from a commercial spray would be expected to be lower than that of the present study. Commercial foliar urea applications are unlikely to meet the N requirements of a productive macadamia orchard. In a separate study, the efficiency of zinc (Zn) fertiliser as soil (5–20 g Zn/m2 canopy ground area) and foliar applications were examined at a mature commercial orchard near Alstonville on a Ferrosol soil. In August 2001, a 2% solution of zinc sulfate heptahydrate was thoroughly applied to the canopy of trees using a backpack misting machine and mature leaves were sampled 4 weeks later. Non-sprayed control trees were also sampled. Cellulose acetate was applied to sampled leaves to remove foliar-applied Zn adhering to the surface of leaves. The leaf Zn concentrations were increased (P&lt;0.05) from 11 to 52 mg/kg 4 weeks after foliar Zn application. Sprayed leaf Zn concentrations were stable 18 weeks later, and flush leaves that emerged after spray application had similar (P&gt;0.05) Zn concentrations to control leaves 12 months later indicating that little if any remobilisation of Zn had occurred over these periods. Soil Zn application had no effect (P&gt;0.05) on leaf Zn concentrations 1 and 2 years after application. The effectiveness of a commercial foliar Zn application was evaluated in September 2001 using a low set orchard sprayer and a 1% Zn solution. After 4 weeks, leaf Zn concentrations were increased from 12 to 26 mg/kg. Foliar Zn applications can be recommended to increase leaf Zn concentrations in macadamias despite evidence in the literature for only 1% uptake efficiency.

The effect of late-season urea spraying on grain yield and quality of winter wheat cultivars under low and high basal nitrogen fertilization

The late-season foliar application of urea may increase yield and grain quality of wheat ( Triticum aestivum L.). Limited information is available regarding the effect of late urea spraying on the performance of wheat cultivars under various basal N fertilization rates. Field experiments were conducted during 2000 through 2002 to evaluate the responses of six winter wheat cultivars to foliar urea (30 kg N ha −1) treatment around flowering at low (67 kg N ha −1) and high (194 kg N ha −1) basal N fertilization rates. Following urea spraying at low N rate, all cultivars increased grain yields to a similar extent (by an average of 7.8% or 509 kg ha −1) primarily due to an increase in the 1000-kernel weight. No yield response to the late-season urea treatment occurred at high basal N rate where grain yields averaged 24.9% (1680 kg ha −1) higher than those at low N rate. In contrast, late foliar urea application similarly improved grain quality at both low and high N rates by an average of 5 g kg −1 (4.5%) for protein content, 3.2 cm 3 (11.9%) for Zeleny sedimentation, and 20 g kg −1 (8.6%) for wet gluten. These quality increments were consistent in all growing seasons regardless of significant variations in grain yields and protein concentrations across years. However, most cultivars failed to achieve breadmaking standards at low N rate as quality increments associated with the urea treatment were relatively small when compared to those achieved by high basal N rate. Late urea spraying had no effect on the falling number, whereas some cultivars showed small, but significant reduction in the gluten index at both N rates. Cultivars improved the hectolitre weight with the late-season urea treatment only at low N rate. Significant cultivar × urea interactions existed for most quality traits, which were due to the cultivar differences in the magnitude of responses. Thus, late-season urea spraying consistently produced larger yields at low basal N rate, and resulted in cultivar-dependent increases in protein content, Zeleny sedimentation, and wet gluten at both low and high N rates.

(107) Effects of Defoliants (CuEDTA and ZnSO4) and Foliar Urea on Defoliation and Nitrogen Reserves of Almond Nursery Plants

One-year-old field-grown `Nonpareil'/'Nemaguard' and `Nonpareil'/`Lovell' almond nursery trees were used to study the effects of chemical defoliants (CuEDTA and ZnSO4) and foliar applications of urea on defoliation and nitrogen (N) reserves. Although both chemical defoliants significantly promoted earlier defoliation, CuEDTA was more effective than ZnSO4 in promoting early defoliation. Two applications of defoliant had a similar effect as one application on promoting leaf abscission. Foliar applications of urea in addition to defoliant applications (urea + defoliant treatments) generally increased the efficiency of ZnSO4 (1.25% to 2%) and CuEDTA (0.5%) in promoting early defoliation. Although treatments with only defoliants did not consistently lower N reserve levels, trees treated with foliar urea or urea + defoliants had significantly higher nitrogen reserves compared to trees receiving only defoliant treatments. N reserves were comparable in urea + defoliant-treated trees to the levels found in naturally defoliated (control) trees. We conclude that both CuEDTA and ZnSO4 are effective in promoting early defoliation of almond nursery trees. Combining urea with defoliants can effectively promote early defoliation and is important for achieving N reserves similar to naturally defoliated trees.

(329) Postharvest Urea Foliar Sprays Affect Almond and Prune Leaf Nitrogen and Sulfur Dynamics

Urea foliar sprays may be a more efficient and environmentally sound alternative to soil applied fertilizer N in the postharvest period in tree crop production in California. While tree crop sulfur (S) status can interact with tree N status to affect growth, we know of no study assessing tree crop leaf N and S dynamics following fall (postharvest) foliar urea applications. We conducted a field study to measure temporal dynamics of leaf N and leaf S (% dry weight basis) following postharvest urea sprays on prune (Prunusdomestica) and almond (Prunus dulcis). June-budded nursery stock prune (`French' on Myro 29C) and almond (`Price' on Lovell) trees were sprayed to dripping with 6.5% (w/w) and 10% (w/w) standard urea solutions, respectively. Prunes were sprayed on 1 Oct. 2003 and almonds on 18 Nov. 2003. Leaf samples were taken over a 3-week (almond) or 8-week (prune) period, beginning just before treatment. Foliar urea sprays significantly increased prune (23%) and almond (14%) leaf N compared to untreated control within 8 days of application. This affect was transient, as there were no differences in leaf N concentrations between treated and untreated trees at final leaf sampling. Urea sprays did not affect almond leaf S concentration relative to untreated trees. Prune leaf S was significantly reduced compared to untreated trees 8 days after treatment, but only on that sampling date. Remobilization of S from the leaves of control trees of either species was not apparent.

(334) Fruit Set and Yield in Relation to Reserve Nitrogen and Reserve Carbohydrates in `Gala' Apple Trees

Four-year-old `Gala'/M.26 trees were grown under low (2.5 mm), medium (12.5 mm), or high (25 mm) N supply with balanced nutrients in sand culture and the cropload was adjusted to 5 fruit/cm2 trunk cross-sectional area at 10 mm king fruit. After harvesting, half of the trees in each N treatment were sprayed twice with 3% urea a week apart in late September. Before budbreak the following spring, four trees from each treatment combination were destructively sampled for reserve nitrogen and carbohydrate analysis. Foliar urea application significantly increased tree N concentration and concentrations of both free amino acids and proteins, but decreased the concentration of total nonstructural carbohydrates (TNC) at each soil N supply level. When the carbon in free amino acids and proteins are taken into account, trees sprayed with foliar urea had similar levels of total sum of carbon in TNC, free amino acids and proteins. On a whole tree basis, trees sprayed with foliar urea had more N and less TNC. During the second year of the experiment, all the trees received normal N supply. Trees sprayed with foliar urea the previous fall had a significantly larger total leaf area and higher fruit set, fruit number, and total yield than those unsprayed. We conclude that fruit set and early fruit development as well as vegetative growth in spring is mainly determined by reserve nitrogen, not by reserve carbohydrates. Conversion of a portion of TNC to amino acids and proteins leads to better growth and fruiting of apple trees.

Foliar nitrogen applications increase the seed yield and protein content in chickpea (Cicer arietinum L.) subject to terminal drought

The effect of foliar application of isotopically labelled nitrogen (15N-urea) at 4 stages during flowering and podding on the uptake and utilisation of nitrogen by chickpea (Cicer arietinum L.) under conditions of terminal drought was investigated in a glasshouse study. Five treatments were used to investigate the effect of timing of foliar application of urea, equivalent to 30 kg N/ha, on the uptake and utilisation of nitrogen for biomass, yield, seed protein content, and seed size: foliar application at (i) first flower, (ii) 50% flowering, (iii) 50% pod set, and (iv) the end of podding, and (v) an unsprayed control treatment. Terminal drought was induced from pod set onward, resulting in a rapid development of plant water deficits (–0.14 MPa/day) and a decrease in leaf photosynthesis irrespective of the timing of foliar urea application. Foliar applications of urea at first flower and at 50% flowering, before terminal drought was induced, increased yield and seed protein content. The increase in yield resulted from an increase in the number of pods with more than one seed rather than from increased pod number per plant or increased seed size, indicating greater seed survival under terminal drought. Also, the increase in the seed protein content resulted from increased nitrogen availability for seed filling. Foliar application of urea during flowering, before terminal drought was induced, resulted in 20% more biomass at maturity, suggesting that growth prior to the development of water shortage increased the carbon resources for sustained seed filling under conditions of terminal drought. Foliar applications of urea at 50% pod set and at the end of podding did not affect the yield or seed protein content, primarily because the uptake of nitrogen was limited by the leaf senescence that occurred with the development of terminal drought. The results indicate the potential to increase yields of chickpea by application of foliar nitrogen near flowering in environments in which terminal droughts reduce yield.