A 2 pine bark : 1 moss peat: 1 sand (by volume) medium (11% volumetric, 20% gravimetric moisture) amended with 4.2 kg m −3 of dolomitic limestone and 3 kg m−3 of 32P-, 35S-superphosphate (8.7% P, 11.7% S) was incubated (25°C) for either 0, 15, or 30 days. Columns (4 × 15 cm) of the medium for each incubation time received 48 ml of deionized water (pH 5.5) in 3 hr on day 1 and 16 ml in 1 hr on days 2-21. Forty-six and 21% of 32P and 35S, respectively, leached on day 1 when the medium was not incubated. Thirty-one percent and 28% of the 32P and 14% and 13% of the 35S leached on day 1 if the medium had been incubated 15 or 30 days, respectively. Eighty-two percent of the 32P and 66% of the 35S amendment leached from the unincubated medium during the 3 week experimental period. A similar leaching experiment, but with superphosphate in absorbent cotton instead of the soilless medium, indicates superphosphate dissolves readily.
Research indicates P and S leach rapidly from soilless media amended with ordinary superphosphate (2). Since these elements are in the form of anions, an amendment with a high anion exchange capacity may reduce their leaching from soilless media. In the following study, an anion exchange resin was used to test this theory.
Ten-month-old seedlings, grown from seed extracted from 22 individual pummelo [Citrus grandis (L.) Osbeck] × trifoliate orange [Poncirus trifoliata (L.) Raf.] citrus hybrid trees that survived -15C freezes near Monticello, Fla., were cold-acclimated in controlled-environment rooms and freeze-tested at -6.7C for 4 h. Freeze damage to open-pollinated progeny was ranked by the number of uninjured seedlings and percentage of leaves killed and wood dieback. Morphological segregation was not associated with differences in freeze survival, and the dominant trifoliate gene was readily evident. Progeny from one tree, identified as 98-71, are considered the most likely candidates for further study in developing cold-hardy citrus trees.
Columns of an incubated (25°C, 11% volumetric moisture for 30 days) 2 milled pine bark : 1 Canadian sphagnum peat : 1 builders’ sand (by volume) medium amended with the equivalent of 270 g P·m−3 from radioactive superphosphate (8.7% P) and the equivalent of 0, 33, 200, or 1200 g Al·m−3 from aluminum acetate (13.2% Al) were leached daily with 16 ml deionized water. Eighty percent of the 32P amendment leached during days one to 21 from the medium not amended with Al, whereas 0.3% leached when amended with 1200 g Al·m−3. Leachate 32P levels ranged from 840, 711, 91, and 2.0 μg·ml−1 on day 1 to 2.3, 3.3, 7.6, and 0.9 μg·ml−1 on day 77 for the medium with Al amendments of 0, 33, 200, and 1200 g·m−3, respectively.
Polyvinyl chloride columns (4 × 15 cm) containing by volume either 2 pine bark : 1 moss peat : 0 sand, 2 pine bark : 0 moss peat : 1 sand, 0 pine bark : 1 moss peat : 1 sand, or 2 pine bark : 1 moss peat : 1 sand amended with 3 kg m-3 of 32P-superphosphate (8.7% P) were leached daily with 16 or 32 ml of deionized water (pH 5.5) in 1 hour. Irrigation rate did not affect 32P leaching nor was there a media rate interaction or difference in the percentage total 32P and dissolved 32P leached. Medium 2:1:1 had the greatest percentage (76%) of 32P leached during the 3-week experimental period, however, 55% of the 32P amendment leached from each medium the 1st week.
Available young hybrid trees of Eremocitrus glauca with ‘Valencia’ orange (Citrus sinensis (L.) Osbeck), Sicilian sour orange (C. aurantium L.), ‘Nagami’ kumquat (Fortunella margarita (Lour.) Swing.), and Koethen sweet orange (C. sinensis) were more cold hardy than the Citrus or kumquat parent in natural and controlled freezes. Eremocitrus may be a useful source of cold hardiness for breeding cold-hardy citrus hybrids.
Leatherleaf fern [Rumohra adiantiformis (G. Forst) Ching] fronds became desiccated rapidly after harvest with water potential decreasing from -0.45 to -1.75 MPa within 30 minutes. Partial closing of stomates 30 minutes after harvest accounted for a decrease in the rate of frond desiccation and frond water potential was -2.26 MPa after 180 minutes. Postharvest frond desiccation to water potentials of -1, -2, and -3 MPa in the field prior to water dip and cold storage resulted in frond curl of 32, 56, and 84%, respectively, when placed in postharvest rooms. Water uptake decreased during the first 4 days in postharvest rooms. Declining frond water potentials suggested reduced rate of water uptake was due to blockage of the xylem. However, no obstructions were observed at cut end of stipe from fern with frond curl or those not exhibiting frond curl. Frond water potentials were lower one hour after harvest than when undergoing normal postharvest senescence. Fronds did not exhibit normal drought-imposed wilt or frond curl during prestorage stress. Desiccation resulted in frond curl in some experiments but had little effect in others. These results indicate that frond curl can be triggered by desiccation stress but other factors are predisposing fronds to this disorder.