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Jong-Myung Choi and Paul V. Nelson

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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Jong-Myung Choi and Paul V. Nelson

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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Jong-Myung Choi and Paul V. Nelson

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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Chiwon W. Lee, Chun-Ho Pak and Jong-Myung Choi

Correlations between the nutrient solution concentration and tissue content of micronutrients were determined for geranium, marigold and petunia. When nutrient solution contained 0.25, 0.5, 1, 2, 3, 4, 5, 6 mM of boron (B), copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo) and zinc (Zn), the tissue content of each microelement increased linearly with increasing levels of the same micronutrient in the fertilizer. Equations for these correlations were established for the six micronutrients used for each species. Increasing levels of micronutrients did not influence tissue macroelement contents. Increasing levels of one micronutrient had little influence on the accumulation of other micronutrients in the tissue. Plant toxicity symptoms developed when the leaf content of microelements increased to a level 5-10 times that of plants grown with the control (Hoagland) solution.

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Chi Won Lee, Chun Ho Pak and Jong Myung Choi

Micronutrient toxicity symptoms of seed geranium (Pelargonium × hortorum Bailey) `Ringo Scarlet' were experimentally induced by using 9 different concentrations of B, Cu, Fe, Mn, Mo and Zn in the fertilizer solution. Plants of 3-4 true leaf stage grown in peat-lite mix were constantly fed for 5 weeks with nutrient solutions containing 0.25, 0.5, 1, 2, 3, 4, 5, and 6 mM of each micronutrient. The control solution contained 20 uM B, 0.5 uM Cu, 10 uM Fe, 10 uM Mn, 0.5 uM Mo and 4 uM Zn. Visible foliar toxicity symptoms developed when the nutrient solution contained 2, 0.5, 5, 1, 0.25, and 0.5 mM, respectively, of B, Cu, Fe, Mn, Mo, and Zn. Reduction in dry matter yield was evident when 1 mM B, 2 mM Cu, 3 mM Fe, 2 mM Mn, 0.5 mM Mo, and 1 mM Zn were used in the fertilizer solution. Leaf chlorophyll contents decreased as Cu and Mn levels increased. Elevated levels of Fe increased tissue chlorophyll contents.

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Chiwon W. Lee, Jong-Myung Choi and Chun-Ho Pak

Seed geranium (Pelargonium × hortorum) micronutrient toxicity symptoms were induced by applying elevated levels of B, Cu, Fe, Mn, Mo, and Zn in fertilizer solution. Beginning at the 3-4 true leaf stage, seedling plants established in 11-cm (0.67-liter) pots containing peat-lite growing medium were fertilized at each irrigation for 5 weeks with solutions containing 0.25, 0.5, 1, 2, 3, 4, 5, and 6 mm plus the standard concentration of each micronutrient. The standard solution contained 20 μm B, 0.5 μm Cu, 10 μm Fe, 10 μm Mn, 0.5 μm Mo, and 4 μm Zn. All treatment solutions contained a fixed level of macronutrients. Visible foliar toxicity symptoms were produced when the nutrient solution contained 0.5 mm B, 0.5 mm Cu, 5 mm Fe, 1 mm Mn, 0.25 mm Mo, or 0.5 mm Zn. Reduction in dry matter yield was evident when 1 mm B, 2 mm Cu, 3 mm Fe, 2 mm Mn, 0.5 mm Mo, or 1 mm Zn was used in the fertilizer solution. Leaf chlorophyll contents decreased as Cu and Mn levels in the concentration range tested increased. Elevated levels of Fe increased tissue chlorophyll contents. The relationship between the nutrient solution and tissue concentrations of each of the six micronutrients was determined.