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- Author or Editor: A. R. Dixon x
Six-year-old trees were repeatedly conditioned by withholding irrigation until Ψpd (predawn) thresholds of either –0.9 (“mild”) or –1.4 MPa (“moderate”) were attained. After conditioning, trees were exposed to severe drought (Ψpd –2.0 MPa) and then to 10 days of well-watered conditions. Throughout the investigation, osmotic potential (Ψπ), leaf RWC, transpiration, and total water potential (Ψx) were measured. Water stress was quantified by integrating Ψx. Conditioning caused a significant, but modest, degree of osmotic adjustment (0.08 to 0.28 MPa), which persisted after a brief relief from stress and transpiration rates were reduced 35% to 50%. Osmotic adjustment was not significantly enhanced by more than one stress exposure or conditioning beyond the mild threshold of stress. During severe drought, the moderate group maintained less negative Ψx and lower transpiration rates (38%). After prolonged stress relief, Ψx was similar among all treatments and daily transpiration rates and Ψx gradually recovered. Thuja occidentalis appears to rely on increased stomatal resistance more than osmotic adjustment to tolerate drought stress.
A concern with the greenhouse production of horticultural commodities, particularly those grown in the ground, is the difficulty in managing nutrient runoff. Alstroemeria, a heavy-feeding crop that is nearly always grown in soil, were planted into 26.5-L pots with a medium of LECA. Greenhouse experiments were designed to examine flowering stem production, quality, and nutrient flux under nutrient solution reuse (closed system) and with one of three levels of nutrition (EC of 2.1, 1.6 and 1.1 mS/cm). Plants in the closed treatments were set on troughs sloped towards separate 24-L reservoirs. The control was an open drainage system fed at 2.1 mS/cm. The reservoirs were kept at a constant volume with the addition of water after every irrigation; nutrients were added to restore the EC to demand levels. Stems were harvested twice per week and the nutrient content of the reservoirs were analyzed biweekly by ion chromatography. Data were analyzed as an RCBD with four treatments and blocks. Analysis of data from the preliminary experiment (29 May to 3 Aug. 1998) indicated number of stems and cymes were similar among treatments. Stem length, dry weight, and number of florets were depressed below the control only in lowest fed treatment. Nutrient application was reduced markedly, by up to 1000-fold in the closed vs. the open production system.
Nitrogen, as urea, was applied to filbert (Corylus avellena L.) trees at the rates of 0, .68, 1.36, and 2.72 kg N/tree/year from 1971-1977. Nitrogen applications significantly increased leaf N, yield, and tree size. Leaf P levels were reduced by N applications in all years. Soil pH, measured after 7 years of N application, significantly declined as N application rate increased. Leaf Mn levels were increased by N applications in all years, probably due to the decrease in soil pH. Yields were expressed as a quadratic function of N and the standard ranges for leaf N in filbert were categorized as follows: deficiency (visible symptoms present) < 2.0% dry weight; below normal 2.0 − 2.2%; normal 2.2 − 2.4%; above normal > 2.4%.
A microcomputer-based image processing system was used to simplify the large number of visual comparisons required to identify various Corylus spp., cultivars, and clonal accessions using polyacrylamide gel electrophoresis isozyme patterns. Photographs of gels stained for peroxidase, acid phosphatase, and phenol oxidase were digitally captured and selected lanes were enhanced and scanned. The scan data were analyzed to locate bands and normalize their position to that of standards. Such data were plotted and a computer-generated isozyme pattern was displayed. Compressed image data were then stored in a database for subsequent automated isozyme pattern comparisons. Photographic records that were previously used in published reports were reevaluated with the computerized system. Species, cultivars, or clones that were characterized in visual evaluations were similarly characterized using the computer method. Computer evaluations usually identified more bands. Band positions were only rarely different and probably resulted from better normalization relative to standard bands when using the computerized procedure.
The Diagnosis and Recommendation Integrated System (DRIS), which uses nutrient element concentration ratios as indicators of nutrient deficiency, was used to evaluate current sufficiency ranges for hazelnut trees. Reference values that were derived from published and unpublished field data were used to calculate DRIS indices for N, P, K, Ca, Mg, Mn, Fe, Cu, B, and Zn. A nutritional imbalance index (NII) was computed as the sum of DRIS indices irrespective of sign, and a threshold NII value (mean NII + 1 SD), above which severe imbalances are expected, was established. DRIS diagnoses were then compared with the sufficiency range approach to determine if relative deficiencies or excesses associated with severely imbalanced trees would have been routinely detected in 624 mineral analyses of hazelnut leaves. A previously published field trial was also reevaluated. DRIS diagnosis generally agreed with the diagnoses made by the sufficiency range method, especially if sufficiency ranges for some elements were made more narrow. However, some nutrients were never identified by DRIS as a major relative deficiency or excess in any of the trees judged severely imbalanced, based on the sum of DRIS indices. Nitrogen and Mg deficiencies were not detected unless lower NII thresholds were used. Unfortunately, lowering NII thresholds enough to detect N and Mg deficiencies identified some high-yielding trees as severely imbalanced. DRIS will not detect all deficiencies or excesses. Therefore, DRIS is best viewed as a supplement to sufficiency range diagnoses that provides additional information when severe imbalances are detected.
Leaves of red raspberry (Rubus idaeus L. cv. Meeker) were sampled every 2 weeks throughout the growing season at 7 different positions on the cane to determine the time and position of minimum leaf nutrient flux. During the last half of August, the 5th to 12th leaves from the terminal 15 cm of the primocane showed the least variation in nutrient concentrations.