Search Results

You are looking at 61 - 70 of 766 items for :

  • All content x
Clear All
Free access

Michael A. Fidanza and Peter H. Dernoeden

Rhizoctonia blight (RB), incited by Rhizoctonia solani Kühn, is a common disease of cool-season turfgrasses. This 2-year field study was conducted to determine the influence of N source, N application timing, and fungicide treatment on RB severity in `Caravelle' perennial ryegrass (Lolium perenne L.). Ringer Lawn Restore (Ringer), a slow-release N source, was compared to water-soluble urea. Nitrogen was applied according to either a spring (March, May, June, and September) or fall (September, October, November, and May) schedule. Plots received either N only or N plus the fungicide iprodione (3.1 kg a.i./ha applied at 21-day intervals). RB was reduced with fall-applied Ringer compared to spring-applied urea in both years in fungicide-free plots. Nitrogen generally enhanced foliar mycelium growth and RB during the initial infection periods (i.e., late June to late July). By mid- to late August there were extremely high levels of blighting among all fungicide-free treatments. Nitrogen source and N application time had no effect on the level of blighting in iprodione-treated plots. During early disease outbreaks, iprodione did not always prevent foliar mycelium from appearing, but it did protect turf from severe RB. Iprodione reduced blighting, but the level of disease suppression and resulting turfgrass quality provided on the extended spray interval was not acceptable for high-quality golf course fairways. Chemical name used: 3-(3,5-dichlorophenyl)-N-(1-methylethyl)-2,4-dioxo-1-imidazolidine carboxamide (iprodione).

Free access

B.R. Bondada, R Romero-Aranda, J. Syvertsen, and L. Albrigo

Foliar applications of urea-nitrogen are widely used to alleviate N deficiencies in citrus; however, improper applications can cause serious foliar burn and loss of active green leaf area. Light (LM), transmission (TEM), and scanning (SEM) electron microscopy were used to characterize anatomical and ultrastructural details of foliar burn in citrus. LM examination of the burned leaf area showed collapsed adaxial and abaxial epidermal cells and plasmolysis of mesophyll cells that created large intercellular spaces. SEM showed wrinkling of both the adaxial and abaxial epidermal cells. TEM revealed cytoplasmic vacuolation, disruption of cellular membrane, degradation of grana, and appearance of large plastoglobuli, implying loss of physiological activity. In contrast, control leaves had turgid adaxial and abaxial epidermal cells and compact mesophyll cells with few intercellular air spaces.

Free access

Anwar G. Ali and Carol J. Lovatt

This study investigated the effect of irrigation treatments and time of foliar applications of low-biuret urea on yield of 30-yr-old navel orange trees grown under optimal N fertilization. The experiment was carried out at the Agricultural Experiment Station of the University of California, Riverside, using split plot design with 12 replications. The two irrigation treatments were the mainplots and the urea applications were the subplots. Irrigation was withheld from one set of trees from October to March, the other set was irrigated according to commercial practice. Foliar-urea (0.17 kg/tree) was applied in November, December, January, or February.

The results of the first year showed no significant differences between irrigation treatments with regard to total fruit weight or total number of fruit per tree, All trees receiving urea had significantly higher fruit weight and fruit number per tree than the control trees. The specific time of urea application had no significant effect.

With respect to fruit size distribution, the irrigated treatment resulted in a significantly higher number of fruit of size 7.0-8.0 cm (box sizes 88-72). Generally, the non-irrigatd trees had more fruit of size 6.0 cm or less. No interaction between irrigation treatments and foliar urea sprays was observed.

Free access

T. Fujita, K. Kosuge, S. Miyoshi, and S. Shoji

Polyolefin-coated urea commercially called “MEISTER” was invented by T. Fujita and his co-workers. It shows primarily temperature-dependent dissolution and is divided into two groups of dissolution: ordinary (linear) and delayed (sigmoid). The dissolution of MEISTER in the soil is predicted easily with reasonable accuracy by a portable computer using temperature data. Thus, we can select kinds of MEISTER that can release N meeting the plant demand. It has been common knowledge that polymer-coated materials are used mainly on lawns, professional turf, and container-grown ornamental and horticultural plants and to a limited extent, in vegetable production. However, MEISTER is applied not only to high-value crops but also to low-value crops in Japan because this fertilizer can contribute to innovative fertilizer placement and farming systems (described later in this abstract), thereby the total farming cost can be notably reduced. Innovative fertilizer applications; co-situs placement and single basal application Innovative farming systems; paddy rice 1) no-till rice culture by direct-seeding and a single basal co-situs application and 2) no-till transplanting rice culture by single basal fertilization; and upland and horticultural crops 1) multi-cropping by a single basal fertilization and 2) no-till cropping by a single basal co-situs application.

Free access

Kitren Glozer and Joseph A. Grant

While rest-breaking agents have become commonly used in California cherry production, application timing continues to involve a certain amount of uncertainty from year to year. In order to use any chilling model adequately and thereby schedule rest-breaking treatments, both the beginning point of dormancy and the beginning point of chill accumulation must be understood. One method of testing dormancy onset is tree defoliation, which may be used to alter the pattern of budbreak and regrowth in spring. Defoliation is used in many tropical and subtropical fruit-growing regions to promote budbreak and flowering in species that are not adapted to less than adequate chilling conditions. Recent trials in California compared hand defoliation to applications of urea and zinc sulfate to determine effects on budbreak and flowering of sweet cherry, as well as to better identify entry into dormancy. Chemical applications were at concentrations lower than those used to effect complete defoliation. We found that chemical applications tended to advance bloom and that the most effective timings were consistent, based on chill portion accumulation and the Dynamic Model. In one of two years, chemical treatments tended to decrease floral bud death and increase fruit set when compared to hand defoliation and untreated trees.

Full access

Cathy Sabota, Caula Beyl, and Gokul Ghale

This study evaluated whether adding either sucrose or urea to the soak water could enhance production of shiitake mushrooms (Lentinula edodes) on sawdust blocks. For both sucrose and urea experiments, sawdust blocks inoculated with “QR” and “26” strains of L. edodes were placed in the soak water amended with either sucrose or urea at the first soaking only, at the second soaking only, or at all six soakings. Control blocks were soaked in tap water. In Experiment I, blocks were soaked in water containing 0, 20,000, or 40,000 ppm (mg·L–1) sucrose. Strain 26 produced significantly more mushrooms and greater mushroom weight than QR. Addition of sucrose to the soak water resulted in fewer mushrooms harvested and lower yields than controls. There was a significant interaction between the sucrose rate and strain for both mushroom number and biological efficiency (BE). Both strains produced fewer mushrooms and less BE as the concentration of sucrose in the soak water increased; however, QR was less affected by the increasing concentration of sucrose. In Experiment II, sawdust blocks inoculated with QR and 26 strains of shiitake were soaked in water containing 0, 2400, or 3600 ppm (mg·L–1) urea. Strain 26 produced significantly more mushrooms and greater BE than QR. The addition of 2400 ppm of urea to the soak water resulted in more mushrooms per block harvested and a 12% increase in BE over the control. The 2400 ppm rate added at each soak produced more mushrooms and mushroom weight than the control and also produced more mushrooms than any of the blocks in the higher rate of urea (3600 ppm) treatments. Adding 16.9 oz (480 g) of urea per tank to obtain 2400 ppm urea in the soak water results in the minimal increase in cost of about $0.20 per soak (52 sawdust blocks), but potentially increases the value of the mushrooms harvested from each block by $0.75. In an average-sized shiitake mushroom block production facility containing 500 blocks, continuous addition of 2400 ppm urea to the soak water would provide an increased return of about $375 over the entire season.

Free access

R. Romero-Aranda and J.P. Syvertsen

The penetration of foliar-applied urea and salt solutions into citrus leaves was investigated using `Duncan' grapefruit and `Valencia' orange seedlings in a greenhouse, and 8-year-old `Ruby Red' grapefruit trees in field tests during the summer and fall. Net gas exchange rates, Cl, nitrogen, and chlorophyll concentrations of singles leaves were measured during or after the period of foliar applications. Foliar-applied salt treatments increased leaf Cl, and visible burn symptoms were observed when Cl levels reached ≈0.4% of leaf dry weight. After 11 weeks, green areas from salt-treated leaves had similar rates of net CO2 assimilation as control plants. Leaf nitrogen and total chlorophyll increased with repeated sprays. Urea sprayed at 15% caused foliar burn symptoms after two to three applications and increased the amount of leaf abscission. Urea sprayed at 6% increased CO2 assimilation rate ≈50% after three foliar applications in 3 weeks. Nitrogen content and net CO2 assimilation of urea and urea + salt leaves were similar.

Free access

Ronald F. Walden and Robert D. Wright

Rooted cuttings of Ilex crenata Thunb. `Helleri' were grown for 12 weeks in pine bark with two root-zone temperature treatments (unheated or heated to 40C for 6 hours·day–1), two rates of limestone addition (0 or 6 kg·m–3), and three weekly N application rates (200, 400, or 600 mg·liter–1 as urea ammonium nitrate) in a factorial combination. Decreases in shoot and root dry weights due to root-zone heating (69% and 75%, respectively) or limestone addition (41% and 42%, respectively) were not influenced by N application rate. Effects of root-zone heating on medium solution characteristics, which differed in response to limestone addition, were similar for all N application levels. In unlimed pine bark at 400 mg N/liter, the pH and the NH4-N: NO3-N ratio were higher in the heated medium (5.5 and 1.15, respectively) than in the unheated medium (3.9 and 0.64, respectively) after 80 days, suggesting that 6 hours of daily exposure to 40C inhibited nitrification. The higher medium solution pH due to root-zone heating resulted in lower medium solution and shoot tissue Mn concentrations.

Full access

Carol J. Lovatt

The goal of this research was to identify the role essential nutrients play in the physiology of tree crops, and then to apply the nutrient as a foliar fertilizer to stimulate a specific metabolic process at phenological stages when nutrient demand is high. This approach has proven successful. A single winter prebloom foliar application of nitrogen as low-biuret urea [0.16 kg N/tree (0.35 lb N/tree)] to 30-year-old `Washington' navel orange (Citrus sinensis L. Osbeck) trees during flower initiation significantly increased yield and fruit number per tree for each of 3 consecutive years (P ≤ 0.05). The number of commercially valuable largesize fruit also increased significantly with yield increases (r 2 = 0.88). Sodium tetraborate applied foliarly to `Hass' avocado (Persea americana Mill.) trees at the cauliflower stage of inflorescence development (elongation of inflorescence secondary axes, pollen and ovule development) increased the number of pollen tubes reaching the ovule, ovule viability and cumulative yield (P ≤ 0.05). Additional examples are presented.

Free access

Lailiang Cheng, Shufu Dong, and Leslie H. Fuchigami

Bench-grafted Fuji/M26 trees were fertigated with seven nitrogen concentrations (0, 2.5, 5.0, 7.5, 10, 15, and 20 mm) by using a modified Hoagland solution from 30 June to 1 Sept. In Mid-October, plants in each N treatment were divided into three groups. One group was destructively sampled to determine background tree N status before foliar urea application. The second group was painted with 3% 15N-urea solution twice at weekly interval on both sides of all leaves while the third group was left as controls. All the fallen leaves from both the 15N-treated and control trees were collected during the leaf senescence process and the trees were harvested after natural leaf fall. Nitrogen fertigation resulted in a wide range of tree N status in the fall. The percentage of whole tree N partitioned into the foliage in the fall increased linearly with increasing leaf N content up to 2.2 g·m–2, reaching a plateau of 50% to 55% with further rise in leaf N. 15N uptake and mobilization per unit leaf area and the percentage of 15N mobilized from leaves decreased with increasing leaf N content. Of the 15N mobilized back to the tree, the percentage of 15N partitioned into the root system decreased with increasing tree N status. Foliar 15N-urea application reduced the mobilization of existing N in the leaves regardless of leaf N status. More 15N was mobilized on a leaf area basis than that from existing N in the leaves with the low N trees showing the largest difference. On a whole-tree basis, the increase in the amount of reserve N caused by foliar urea treatment was similar. We conclude that low N trees are more effective in utilizing N from foliar urea than high N trees in the fall.