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Robert R. Coltman and Stacy A. Riede

`Celebrity' tomatoes (Lycopersicon esculentum Mill.) were grown in peat–perlite under greenhouse conditions in two experiments with five levels of K (25, 50, 100, 200, and 300 mg·liter–1) in irrigation waters. In both experiments, aqueous petiole sap K concentrations (milligrams K per milliliter) were monitored weekly with colorimetric paper test strips. Variation in petiole sap K concentrations among plants was low among three-plant replicates (cvs of 9% to 11%). Petiole sap K concentrations varied considerably from week to week, but remained relatively constant over time at levels determined by external-feed K concentrations. Petiole sap K levels and marketable-fruit yield increased quadratically with increasing external K concentrations. Maximum yields were produced with 190 to 200 mg K/liter in external-feed solutions. Maximum marketable yields of ≈2.75 kg/plant occurred with =5.9 mg K/ml in petiole sap. Quick petiole sap K tests appear to be suitable for assessing the K status of greenhouse tomatoes.

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Hector Valenzuela, Stacy Riede, and Harry Yamamoto

Portable chlorophyll fluorometers have made it possible to evaluate the photosynthetic efficiency of photosystem 11 for vegetable crops under ambient conditions. A sampling protocol was first established to eliminate variability due to positioning of the fiber optics in relation to the leaf, leaf selection, and natural environmental variability. Fluorescence parameters of the quantum yield of noncyclic electron transport (DF/Fm') and electron transport rate (ETR) were taken from several economically important vegetables under ambient conditions between 11 and 14 h. The objective of the second part of the study was to conduct in situ chlorophyll fluorescence and biomass determinations as affected by salt stress and N deficiency. DF/Fm' and ETR were studied in rhizobium inoculated, noninoculated and inorganic N-fed soybean and differences in fluorescence were related to yield. The influence that salt stress, and several N rates have on fluorescence photochemical quenching (qP) and nonphotochemical quenching (qN), NPQ ([Fm-Fm']/Fm'), DF/Fm' and ETR for hydroponically grown lettuce will also be presented.