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  • Author or Editor: Paul V. Nelson x
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Palabora vermiculite having a pH of 9.8 was studied in order to (a) assess the extent of influence the alkaline reaction has upon several crops, and (b) to investigate further, means of correcting the problem where it exists. Four marigold, 3 zinnia, and 1 chrysanthemum cultivars were found to develop normally in this medium without adjustment of pH but the chrysanthemum cultivar ‘Giant Betsy Ross’, which is susceptible to alkaline reaction-induced micronutrient deficiencies, developed symptoms of Fe deficiency. Correction of this problem was accomplished in 2 ways: (a) by incorporation of sphagnum peat moss into the medium, and (b) by a drench with H3PO4 at the rate of 40 meq/100 g dry vermiculite.

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Abstract

A series of experiments was conducted with chrysanthemum cv. Giant Betsy Ross grown in acid-washed quartz sand. The nutrient solution was buffered at pH 7.8 to induce Cu deficiency while Fe, Mn and Zn were supplied in high quantities to avoid simultaneous deficiencies. Nutrient levels in the tissues were monitered by atomic absorption analyses.

The critical range of Cu was established at 6.7 to 7.4 ppm for the first fully expanded leaves of the plant. The deficiency first appeared on the terminal leaves as chlorosis most intensely developed at the leaf blade base. As the leaf became more chlorotic the margin, and particularly the lobes toward the leaf apex, retained a normal green color. Tissues over and adjacent to the vascular tissue did not become as chlorotic as the leaf lamella giving rise to the second symptom which was interveinal chlorosis. At that stage the green pigmentation associated with the vascular tissue occurred in a broader pattern than in Fe deficiency. In the third stage of deficiency veinal chlorosis appeared, followed by necrosis of leaves located immediately below the first fully expanded leaf. There was a concomitant regreening of foliage at the terminal end of the shoot which lasted for a short time. In the final stage the shoot apex died.

Open Access

Abstract

Tests in which tips of outer enclosing leaves of vegetative azalea buds were dipped in 4.2% methyl decanoate emulsion indicated that the pinching agent does not translocate in sufficient quantity to kill the meristem. Direct contact must be achieved. A morphological comparison of the vegetative buds of an azalea cultivar responding poorly, ‘White Gish’, and one responding readily, ‘Coral Bells’, to pinching agents indicated that the former has (1) an abnormally long enclosing sheath of leaves and (2) a greater number of trichomes per unit area of leaf surface within the sheath. Both factors can contribute to a reduction in the movement of pinching agent to the meristematic tissue.

A comparative study of vegetative and reproductive buds of the azalea cultivar, ‘Red Wing’, gives an account of the reduced effectiveness of pinching agents in reproductive buds. In the young reproductive bud a greater number of leaf primordia layers and in the older reproductive bud the presence of a thick cuticle on the outer scales as well as the presence of numerous closely overlapping scales reduces penetration of the pinching agent emulsion.

Open Access

Most soilless container root media have limited ability to retain nutrients. Zeolites are minerals of substantial cation exchange capacity that can be precharged with K, and possibly PO4, and used as a component of soilless media as a slow-release nutrient source. A zeolite clinoptilolite (Cp) was charged with K and PO4 at two concentrations and combined at 20% of the mix with sphagnum peat (60%) and perlite (20%) to evaluate its use as the sole source of these nutrients during production of Dendranthema ×grandiflorum (Ramat.) Kitamura `Sunny Mandalay.' Phosphate, K, Na, and pH were determined on unaltered bulk root medium solutions collected over the course of production, and foliar analyses were determined on tissue collected at the middle and end of the crop. All leachate was collected and analyzed to allow for the creation of K and PO4 budgets. Plants that relied on precharged Cp at the low and high rates to meet their K needs and received a N/P/-K fertilizer had similar dry mass and tissue K concentrations as the control plants that received a complete fertilizer. The use of precharged Cp at the low rate reduced K losses through leaching to 23% of the amount lost from control plants receiving water-soluble fertilizer (WSF). Plants that relied on precharged Cp for their PO4 had a lower dry mass and tissue P levels than those of the complete control treatment. However, PO4 concentrations in the root medium solution were above acceptable levels during the first month of production and should be considered when developing a fertilizer application strategy using Cp precharged with PO4.

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Mineralization of N from nonviable cells of Brevibacterium lactofermentum (Okumura et al.) mixed into soilless substrate in elution columns occurred largely during the first 5 weeks with a peak between 2 and 3 weeks. Over a 12-week period, 73% of the total N was recovered in the eluent. To prolong the period of N release to meet the requirements of a slow-release fertilizer, the bacterium was bonded to kraft lignin, a polyphenolic substance highly resistant to degradation. To retard mineralization further, the bacterium-lignin mixture was reacted with formaldehyde to form amino cross-links within and between protein chains. Bonding to lignin was undesirable because N release occurred during the same period as from the bacteria unbound to lignin and the total amount of N recovered was reduced to only 42%. Cross-linking with formaldehyde was less desirable since N was released mainly during the first 4 weeks with a peak during the first elution (0 time) and the total amount of N released was even lower than for the bacterium-lignin mixture. Additions of urea to the latter reaction did not satisfactorily improve subsequent N mineralization. In a second set of treatments lignin was withheld and the bacterium was reacted with weights of formaldehyde (a.i.) equivalent to 0.1%, 0.5%, 1.0%, 5.0%, and 10.0% of the dry weight of bacterium. Formaldehyde quantities ≤1.0% either had no effect or lowered the mineralization of N without altering time of release. Five percent and 10% formaldehyde successfully reduced release of N during the first 4 weeks and increased it thereafter. The best rate was 5%. In this treatment N was released from week 2 through the end of the test (12 weeks). Peak release occurred at 6 weeks. This resulting N source, while not a stand alone product, does have a slow-release property that could lend itself to use in combination with other slow-release N sources.

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The structure of feather keratin protein was modified in attempts to develop a slow-release N fertilizer of 12 weeks duration or longer by steam hydrolysis to break disulfide bonds, enzymatic hydrolysis with Bacillus licheniformis (Weigmann) to break polypeptide bonds, and steam hydrolysis (autoclaving) to hasten mineralization followed by cross-linking of the protein by a formaldehyde reaction to control the increased rate of mineralization. Release of N in potting substrate within elution columns from ground, but otherwise untreated, raw feathers occurred mainly during the first 5 weeks with a much smaller release occurring from weeks 8 to 12. Steam hydrolysis resulted in an increase of N during the first 5 weeks and a decrease during weeks 8 to 11. Cumulative N release over 11 weeks increased from 12% in raw feathers to 52% for feathers steam hydrolyzed for 90 minutes. This favored an immediately available fertilizer but not a slow-release fertilizer. Microbial hydrolysis with B. licheniformis resulted in a modest reduction of N release during the first 5 weeks and a small increase during weeks 8 to 11. Both shifts, while not desirable for an immediately available fertilizer, enhanced the slow-release fertilizer potential of feathers but not sufficiently to result in a useful product. Steam hydrolyzed feathers cross-linked with quantities of formaldehyde equal to 5% and 10% of the feather weight released less N during the first 5 weeks, more during weeks 6 and 7, and less during weeks 9 to 12 compared to raw feathers. The first two shifts were favorable for a slow-release fertilizer while the third was not.

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An actinomycete designated Streptomyces cn1 with a high proteolytic activity and capacity to degrade feather keratin was isolated and its effectiveness for altering feathers to yield a slow-release N fertilizer was evaluated. The pattern of N release in column elution tests from feathers ground to a particle size ≤1 mm, but otherwise unaltered, was characterized by a first period of release from weeks 2 through 5 with a high peak at week 3 and a second period of release from 14 to 20 weeks. The release of N during the first period was 10.5% and during the second period it was 7.3% for a total of only 17.8% of the N contained in these feathers. Grinding feathers to a finer particle size ≤0.5 mm caused increases in N release during the two periods to 14.7% and 15.8% N, respectively, for a total of 30.5% and second period N release began 5 weeks earlier at week 9. Microbial hydrolysis with Streptomyces cn1 for 1 though 5 days resulted in an adverse reduction in total N released, due in part to drying of feathers after hydrolysis. Hydrolysis of feathers for 7 days resulted in 42.6% of total N released over 20 weeks with 77.0% of this released during weeks 6 through 20. The second period of release began at week 8. Hydrolysis of feathers for 9 days was best for purposes of a slow-release fertilizer. Forty five percent of total N was released over 20 weeks with 89.3% of this released during the second period that began in week 7. Root substrate pH was increased in all treatments where feathers were applied. This would require a reduction in the rate of limestone incorporated into a commercial substrate when feather N is used. Pepsin digestibility and ninhydrin tests provided some insight into the N release mechanism but did not effectively predict N release from the feather products.

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Seven organic materials including 1) the bacterium Brevibacterium lactofermentum (Okumura et al.) in a nonviable state, 2) a mixture of two bacteria, Bacillus licheniformis (Weigmann) and Bacillus subtilis (Ehrenberg), plus the fungus Aspergillus niger (van Tieghem) in a nonviable state, 3) an activated microbial sludge from waste-water treatment, 4) sludge from a poultry manure methane generator, 5) unsteamed bonemeal, 6) aged pine needles, and 7) poultry feathers were evaluated to determine their pattern and term of N release and the possibility of using them as an integral part of root media releasing N at a steady, low rate over 10 to 12 weeks for production of Dendranthema × grandiflorum (Ramat.) Kitamura `Sunny Mandalay'. These were compared to the inorganic slow-release fertilizer micro Osmocote (17N-3.9P-10.8K) and a weekly liquid fertilizer control. All organic sources released N most rapidly during the first 2 weeks, followed by a decline, which ended at 6 to 7 weeks. Brevibacterium lactofermentum, bonemeal, and micro Osmocote treatments resulted in about equal growth, which was similar to growth of a weekly liquid fertilizer control for 9 weeks in the first and for 12 weeks in the second experiment. The period of N release could not be extended through increased application rate of source due to the high initial release rate. It was not possible to lower source application rates to achieve an effective, low soil solution concentration due to the large variation in release rate over time. Efficiency of N use varied among plants grown in media treated with various microorganismal sources and was highest in those treated with B. lactofermentum. Nitrogen release from ground poultry feathers was inadequate, and additions of the viable hydrolyzing bacterium B. licheniformis to feathers failed to increase soil solution N levels. Attempts to retard mineralization of B. lactofermentum by cross-linking proteins contained within the bacterium by means of heat treatment at 116C vs. 82C failed. While anaerobic poultry manure sludge proved to be an inefficient source of N, it provided large amounts of P. Organic sources released primarily ammoniacal N, which raised the medium pH by as much as one unit, necessitating the use of less limestone in the medium formulation.

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Soilless container media have almost no capacity to retain PO4 or K. The nutrient retention of two calcined clays, attapulgite and arcillite, and brick chips, precharged with PO4 and K, was investigated. These could serve as an alternative slow-release fertilizer when incorporated into a soilless medium as a component of the mix. Sorption curves were developed at 25 °C for attapulgite of two particle sizes (0.8 to 1.6 mm and 1.6 to 3.2 mm), arcillite (1.1 to 3.2 mm), screened pieces of brick (1.0 to 3.6 mm), and a medium of 7 sphagnum peat: 3 perlite (v/v) using solutions of KH2PO4 (P at 0 to 20,000 mg.L-1). Curves indicated that PO4 and K sorption were similar for both particle sizes of attapulgite, so only the larger size [1.6 to 3.2 mm (8 to 16 mesh)] was used in greenhouse studies. Materials were evaluated in greenhouse studies by growing 'Sunny Mandalay' chrysanthemum [Dendranthema ×grandiflora Kitam. (syn. Chrysanthemum morifolium Ramat.)]. The precharged materials were tested at 10%, 20%, and 30% by volume of a peat: perlite root medium. Phosphate, K, and pH were determined on unaltered medium solutions collected throughout the cropping cycle and foliar analyses were determined on tissue collected at midcrop and end of the crop. Data indicated that precharged calcined clays retained and released PO4, and to some degree K, over time. Precharged clays did not provide K at levels which met plant needs during the latter half of the cropping cycle, but it was released and used at appreciable levels during the first month of crop production. Growth of plants receiving PO4 solely from precharged attapulgite and arcillite at 20% of the medium volume was not significantly different from that of a commercial control when the leaching fraction was maintained at 0.2. However, release of PO4 from the brick chips was not enough to match plant demand. Phosphate lost through leaching from the precharged clays was reduced by about two-thirds compared to control plants fertilized with P at 46.5 mg.L-1 from water-soluble fertilizer at each watering.

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Many plug seedling growers complain about the inadequacy of substrate testing as a measure of nutritional status because results are too variable. We conducted two experiments to test a model system of sampling substrate at a set time after fertilization. Petunias (Petunia×hybrida Hort. ex Vilm. var. multiflora `Primetime White') were grown in 288-cell plug trays. Six fertilizer regimes were used consisting of a factorial arrangement of three fertilizer cycles (at each, every other, and every third irrigation) and two leaching fractions (0% and 20%). Fertilizer or water was applied at 0900 HR daily, and then 24 hours later in Expt. 1, and 1 hour later in Expt. 2, substrate solutions were sampled and analyzed. Samples taken after waterings were used to assess the dilution and leaching effects of water on substrate nutrient concentrations. In Expt. 2, additional substrate samples were taken at various hours after fertilizing to test the effect of plant depletion of the substrate. Substrate nutrient concentration curves constructed from data drawn at a fixed time after fertilizations, but not after waterings, were logical and could be interpreted. When data from a fixed time after fertilizations and waterings were plotted together, the curves could not be interpreted. Data from samples taken at various hours after fertilization in Expt. 2 revealed large reductions in concentrations, often after only 4 hours. Overall, leaching and dilution effects from watering in combination with the increased time span from fertilizing to sampling resulted in nutrient concentrations that could not be interpreted. Substrate testing can be effective for plug seedling production, but samples need to be taken 1 to 2 hours after fertilizations.

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