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  • Author or Editor: Giampaolo Zanin x
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Rosa chinensis Jacq. var. mutabilis plants were grown in a greenhouse to determine whether a hand-held chlorophyll meter (SPAD-meter) is suitable for the plant N status assessment. Therefore, plants were fertilized with increasing levels of N, applied through urea form as top dressing. The doses were: 0, 0.15, 0.3, 0.45, 0.6, and 0.75 g of N per liter of substrate. Periodically during the growing season, plant height and width, fresh and dry weight of different plant organs at 10, 20, and 30 weeks after planting, and their total N, plant P, and K were measured. Furthermore, six times along the growing cycle, the amount of chlorophyll in leaves was estimated using a SPAD-meter and analytically measured by chlorophyll extraction with ethanol and reading through a spectrophotometer. In the same leaves, N concentration was also determined. Treatments with 0.45–0.6 g of N per liter of substrate gave the tallest and widest plant. Plant weight and flower production were also the highest with these doses. The concentration of organic N in plant organs increased along with the N availability in the substrate, which suggests that a “luxury consumption” took place. The SPAD values showed high correlation among chlorophyll and N concentrations. Values that ranged between 35–40 seemed to mean good nutrient status. A high correlation was also found among SPAD values and some of the productive characteristics, which indicates that a SPAD-meter is a suitable tool in the dynamic fertilization of rose.

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Liatris is an ornamental plant cultivated as a garden perennial for more than 70 years. Since the early 1970s, Liatris spicata has gained importance as a cut flower because of its long-lasting flowering and its peculiar downward flowering succession. This species is usually cultivated in beds both outdoors and in greenhouses. However, in order to improve yield and quality production, some research has been carried out on soilless cultivation. In particular, floating systems seem to provide the best performances, although only different nutrient solutions or their concentrations have been studied. In this research, in addition to two different concentrations of Hoagland solution [full-strength (H) and a half-strength (1/2H)], three corm circumferences (8/10, 10/12, and 12+) and three plant densities (36, 48, and 60 plants/m2) were also evaluated. The full-strength solution gave the best performance from both qualitative and quantitative standpoints. This nutrient solution also showed, at the end of the experiment, very high residual nitrate-N, which could induce environmental pollution during disposal. Furthermore, the management of the solution appeared more difficult and time-consuming. All these aspects should be taken into account by growers in making choices. Corm size also affected production. Increasing circumference from 8/10 to 12+ increased marketable stems per plant and their quality traits, but, because of the highest mortality of plants observed with the bigger corms, yield per square meter did not increase over corm size of 10/12. Finally, rising plant density from 36–60 plants/m2, the biomass of the single plant decreased. However, it resulted also in the enhancement of sellable production per square meter.

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Water-holding capacity represents the volume of water retained by a substrate after a saturating irrigation and drainage, and it is often referred to as container capacity. However, water-holding capacity is a time-specific measurement that is limited to the status of the substrate immediately after saturation and drainage. It does not provide information regarding how quickly water is lost from the substrate, the substrate water status over time, or the irrigation frequency required for a substrate under specific conditions. A new procedure was developed that generated a single numeric value that described the wetness of a substrate and in so doing took into account the substrate's water-holding capacity and drying rate. This value was referred to as an E-value. For substrates included in this study, E-values ranged from a low of 6 for parboiled fresh rice hulls (PBH) to a high of 93 for the commercial substrate Metro Mix 360. The procedure was shown to generate E-values that were as would be expected for the evaluated substrates and also ranked the substrates as would have been expected. Over repeated evaluations, the procedure was demonstrated to have a maximum inherent variability of plus or minus one E-value.

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