Liquid phosphorus (23% phosphoric acid) was applied preemergence at 0, 22.4, 44.8, 67.2, or 89.6 kg·ha-1 to 9 fields: 3 commercial blueberry fields having plants with very low (<.111%), 3 low (.111-.125%), and 3 adequate (>.125%) leaf phosphorus concentrations. Years of application ('89,'89+'91,'89 + '91 + '93) were assigned in a split-block RCB design with 4 replications at each location. A linear increase in leaf phosphorus concentration with increasing rates of P application was found in both 1989 and 1991. Differences in response were found among locations. A second application in 1991 was effective in raising leaf P levels at most locations to higher levels than the application in 1989. Also, there were higher levels of leaf P in treatment plots that only received P fertilizer in 1989 compared to controls, indicating a carry over effect.
Timothy K. Broschat
Chinese hibiscus (Hibiscus rosa-chinensis), shooting star (Pseuderanthemum laxiflorum), downy jasmine (Jasminum multiflorum), areca palm (Dypsis lutescens), and `Jetty' spathiphyllum (Spathiphyllum) were grown in containers using Osmocote Plus 15-9-12 (15N-3.9P-10K), which provided phosphorus (two experiments), or resin-coated urea plus sulfur-coated potassium sulfate, which provided no phosphorus (one experiment). Plants were treated with water drenches (controls), drenches with metalaxyl fungicide only, drenches with phosphoric acid (PO4-P), drenches with metalaxyl plus phosphorus from phosphoric acid, drenches with PhytoFos 4-28-10 [4N-12.2P-8.3K, a fertilizer containing phosphorous acid (PO3-P), a known fungicidal compound], or a foliar spray with PhytoFos 4-28-10. Plants receiving soil drenches with equivalent amounts of P from PhytoFos 4-28-10, PO4-P, or PO4-P+metalaxyl generally had the greatest shoot and root dry weights and foliar PO4-P concentrations. There were no differences between the control and metalaxyl-treated plants, indicating that root rot diseases were not a factor. Therefore, responses from PhytoFos 4-28-10 were believed to be due to its nutrient content, rather than its fungicidal properties. Foliar-applied PhytoFos 4-29-10 produced plants that were generally similar in size to control plants or those receiving metalaxyl only drenches. Fertilizers containing PO3-P appear to be about as effective as PO4-P sources when applied to the soil, but are relatively ineffective as a P source when applied as a foliar spray. A distinct positive synergistic response for shoot and root dry weights and foliar PO4-P concentrations was observed for the PO4-P+metalaxyl treatment when no P was applied except as a treatment.
Janusz Prusinski and Anwar A. Khan
. Gifts of (2-chloroethyl) phosphoric acid from Union Carbide Corp., Research Triangle Park, N. C., and of seeds of lettuce cultivars from Ferry Morse Seed Co., Modesto, Calif., and Harris-Moran Seed Co., Rochester, N. Y., are greatly appreciated. The cost
G.H. Neilsen, P. Parchomchuk, W.D. Wolk, and O.L. Lau
Newly planted `Jonagold' and `McIntosh' apple (Malus domestica Borkh.) on M.26 fertigated with Ca(N03)2 showed increased early tree vigor and leaf Ca concentration but decreased leaf Mg and Mn compared to trees fertigated with urea or NH4N03. Fertigation with P increased early tree vigor, leaf and fruit P concentration, and decreased leaf Mn in the first year relative to a single planting hole application of granular P. Increased fruit Ca concentration in `Jonagold' in one year was associated with the use of Ca(N03)2 and fertigation of P. Fruit quality was generally unaffected by the experimental treatments.
Stratification by chilling is the primary factor controlling germination of brodiaea (Triteleia laxa Benth.) seeds. A minimum of 8 weeks of low temperature (3C) was required for maximum germination. Soaking seeds in a solution of 1000 mg ethepho/liter for 20 h reduced the number of weeks at low temperature required for germination. Cormel size was affected by the photoperiod during seedling growth. Long days induced early leaf senescence, and cormels harvested from seedlings grown under long days weighed only half as much as those grown under short days. Chemical name used: 2-chloroethyl phosphoric acid (ethephon).
Azolla (Azolla filiculoides) is a floating fern that maintains a symbiotic relationship with an N-fixing blue-green algae. In many parts of Asia, azolla is used as a green manure in flooded rice cultivation. Taro (Colocasia esculenta) grown under flooded conditions is used to produce a traditional Hawaiian staple, poi. Azolla has been present in Hawaii for many years, but is not used in a controlled way for either nutrient augmentation of production sites or weed suppression. In this experiment, azolla was removed from a stream on the island of Kauai and multiplied in a nursery pond. Phosphoric acid was added to the nursery pond as a nutrient (P = 5 ppm) at 5-day intervals to accelerate azolla growth. Azolla was moved from the nursery pond and added to taro production plots at a seeding rate of 488 kg·m–2. Phosphoric acid was used in production plots to hasten coverage of the water surface by azolla. Ten days after azolla inoculation, production plots were covered and taro seed pieces were planted. Weed dry weights from conventional and azolla covered plots were recorded 91 days after taro planting. Taro corms were harvested 315 days after planting. Weed dry weight in azolla plots was 86% less than conventional plots. Azolla delayed taro maturity, causing a 41% reduction in marketable corm yield.
In one greenhouse and two field experiments, eight or ten pepper (Capsicum annuum L.) cultivars were subjected to low-light stress by use of shade cloth (reducing light by 80%) or to foliar sprays of ethephon at 75 or 150 pi-liter-]. Both low-light stress and ethephon identified `Ace', 'Canape', and. `Belrubi' as less susceptible to flower and flower bud abscission than other cultivars in the first field experiment. In the 2nd year, air mean maxima of 32C caused severe abscission in controls and shaded plants, and complete loss of flowers in those sprayed with ethephon. Abscission of disbudded pedicels was not related to abscission susceptibility of eight cultivars when subjected to shade. While ethephon spray can serve as a satisfactory abscission screening tool under unstressed growing conditions, low-light stress imposed by shading may be used under a wider range of conditions. Chemical name used: 2-chloroethyl phosphoric acid (ethephon).
Robert L. Geneve
Seed dormancy in Eastern redbud (Cercis canadensis var. canadensis L.) can be overcome by seedcoat scarification to allow water imbibition, followed by chilling stratification to permit germination. During chilling stratification, there was an increase in the growth potential of the embryo as indicated by the ability of the isolated embryo to germinate in osmotic solutions. Penetration resistance of the testa also decreased after chilling stratification. The combination of seedcoat alteration and the increase in embryonic growth potential was associated with overcoming dormancy in redbud seed. GA3 or ethephon (50 μm) stimulated germination (28% and 60%, respectively) and increased the growth potential of treated embryos. Chemical names used: gibberellic acid (GA3), (2-chloroethyl) phosphoric acid (ethephon).
John M. Smagula and David Yarborough
Experimental plots in a commercial lowbush blueberry (Vaccinium angustifolium Ait.) field deficient in N and P received preemergent 33.6 and 67.2 kg/ha rates of N (urea), P (23 % phosphoric acid), N+P (DAP), N+P+K (S-10-5) or N+P+K (fish hydrolysate, 2-4-2). A RCB design with eight replications of 12 treatments was used. Fertilizer containing N alone was as effective in raising N leaf concentrations, as those containing N and P. However, leaf phosphorus concentrations were raised more by fertilizer providing N and P than only P. Fish hydrolysate fertilizer was as effective as 5-10-5 in raising leaf N, P and K concentrations in prune and crop year leaf samples.
C.A. Sanchez, M. Lockhart, and P.S. Porter
Five field experiments were conducted from 1986 through 1988 to evaluate the response of radish (Raphanus sativus L.) to rate and source of P (triple superphosphate and phosphoric acid) and to rate of K (KC1) on Histosols. Marketable radish root yields increased with P fertilization when the soil tested <13 mg P/dm3 using a test for water-soluble P. No significant differences were due to P source. Results of leaf tissue analysis suggested that the critical concentration of P in radish leaves was 0.45%. Radish did not respond to K fertilization in any of the five experiments, even though preliminary soil-test K levels ranged from 20 to 102 K/dm3. Histosols used for crop production in Florida rarely test below 20 mg K/dm3; thus, radish rarely would require supplementary K fertilization for optimal yield.