Growth of lettuce cultivars in beds covered with differing materials

In commercial lettuce growing, the intensive cultivation of the soil results in an increase in weed populations, making it difficult to fully exploit the area and increasing production costs. Under such circumstances, the use of soil covers can minimize this problem. Consequently, the objective of this study was to evaluate the effects of different materials as soil covers on the agronomic performance of three lettuce cultivars. The experiment was arranged in randomized blocks, with treatments set in a subdivided plot scheme. Five types of soil cover (plots) were tested: no cover, black plastic, double white faced plastic, straw mulching and kraft paper and three Lettuce cultivars (subplots): loose-crested leaf group, iceberg lettuce group, with four replicates. Number of leaves per plant, stem length and diameter, head diameter, mass of fresh and total dry matter, fresh matter mass of leaves and stem were evaluated. For the Lisa and Americana lettuce groups, bed soil cover materials were more efficient when compared to the uncovered beds. For economic and environmental reasons, kraft paper is recommended as a bedding cover material for these cultivars. Variation in growth occurred between the lettuce cultivars, independently of the use of bedding cover. This occurred in the sequence: loose leaf > iceberg lettuce> loose-crested leaf group.

Rooting Medium Composition and In Vitro Rooting and Greenhouse Survival of Five Raspberry Cultivars

In vitro rooting and subsequent greenhouse survival of `Autumn Britten', `Boyne', `Comet',`Nova' and `Qualicum' raspberry (Rubus idaeus L.) plantlets were compared following four weeks on a rooting medium with and without activated charcoal, and with 0.1, 0.5, 1.0, 2.0 or 3.0 milligrams per litre IBA. The addition of charcoal significantly increased the percentage of plantlets that produced roots in vitro for the hard-to-root cultivars. Percent rooting in vitro was highest with the three lower levels of IBA. Root number was influenced only by the cultivar, while root diameter and length were affected by all the factors investigated. Greenhouse survival was affected by the cultivar, the presence or absence of charcoal and the IBA level in the in vitro rooting medium, with significant interactions. Provided charcoal was present in the rooting medium, the level of IBA didn`t alter survival. The addition of charcoal to the rooting medium improved greenhouse survival of the three hardest-to-root cultivars. Plug plant stem length; internode length and dry weight were increased by the presence of charcoal in the in vitro rooting medium for all but the easiest to establish cultivar. Chemical names used: 3-indolebutyric acid (IBA).

264 Richards Function Applied to a Daily Additive and Iterative Approach to Model Rose Plant Stem Length Growth

Height data were collected three times weekly between pinch and flowering to represent `Royalty' rose (Rosa hybrida L.) response to 15 unique treatment combinations of irradiation as photosynthetic photon flux (PPF: 50 to 300 μmol·m-2·s-1), day temperature (DT: 12 to 22 °C), and night temperature (NT: 15 to 25 °C) under constant growth chamber conditions. Combinations were determined according to the rotatable central composite design. A previous full quadratic model approach was compared with a revised approach using a nonlinear Richards function derivative form. This allowed a dynamic change of parameter values for each daily growth iteration by computer. The Richards function assumes nonconstant daily growth rates are proportional to current size; Euler integration enabled additive accumulation of these values. Ratios of the growth constant (k) to the theoretical catabolic constant (m = v+1) caused flexible changes in the growth curve, which were compared with the previous quadratic approach.