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- Author or Editor: R. W. Zobel x
Aeroponics, as a method of soilless culture, has been in intermittent use since the 1950's. Early Russian and Italian research suggested that productivity and use of space was optimized with this technique. Prior to the introduction of ultrasonic techniques, aeroponics utilized spray nozzles or spinning disks. In addition to the need for frequent cleaning, the first results in the formation of a boundary layer on the root surface, similar to that formed in hydroponics, which results in nutrient and aeration gradients. The second results in significant physical disturbance to the root system and, except under very controlled conditions, also develops a boundary layer. Ultrasonic fogs avoid these side effects and allow the use of carbon dioxide enrichment of the root zone as well as reduced nutrient concentrations. Initial results with commercially available equipment are very promising. Commercial implementations of ultrasonic aeroponics promise to be far less energy and manpower intensive than any other method of plant culture. Lettuce, corn, tomato, soybean, dry bean, and geraniums have all been cultured with this method.
Plants growing in nature provide a continuous array of biological efficiencies related to mineral nutrition. Nearly all of the temperate and tropical areas of the earth are covered with species adapted to the unique properties of particular soils. These properties may represent the extremes in element availability from very deficient to toxic levels and may be associated with wide ranges in pH.
Root morphological characteristics of ‘Redkote’ and ‘Redkloud’ kidney bean plants (Phaseolus vulgaris L.) were measured during 2 growth stages at 5, 10, 15, and 20 cm within-row spacings under field conditions. Significantly higher total root weight, shoot weight, basal root weight, and stem and hypocotyl diameters of individual plants occurred as within-row spacing increased. Uprooting resistance, taproot weight, and taproot diameter increased as within-row spacing increased up to 15 cm followed by a nonsignificant increase at 20 cm. No differences in adventitious root weight or shoot:root ratios occurred among within-row spacing treatments. ‘Redkote’ root parameters were significantly higher than those of‘Redkloud’, with the exception of adventitious root weight and uprooting resistance. Seed yields were highest for 15 cm spacing although not significantly more than at 5 cm spacing. All parameters with the exception of basal root number were significantly lower during anthesis when compared with full pod fill growth stage.
Number of days to flower (DTF) of 78 bean (Phaseolus vulgaris L.) genotypes was measured in tropical fields at various elevations. The associated 18 mean temperatures varied between 12 and 28C. Daylength was natural 12 or 13 hours of sunlight with or without incandescent light for a total of 18 hours. A statistical analysis with additive main effects and multiplicative interaction effects (AMMI) quantified the effects on the deviation from the DTF grand mean caused by each genotype, plus those caused by each daylength and by each temperature. The more photoperiod-sensitive the genotype (factor 1), the more a longer daylength (factor 2) increased DTF and the more a higher temperature (factor 3) synergistically increased DTF. These three factors interacted to delay the node to flower. An additional control over DTF occurred as the same higher temperature (factor 3) reduced the days required to develop a node (factor 4). Thus, a higher temperature tended to decrease DTF by enhancing the rate of vegetative development, at the same time that it tended to increase DTF by enhancing the photoperiod gene activity. This four-factor interaction resulted in a U-shaped curve of DTF in response to temperature. The smallest DTF on the U-shaped response was interpreted as occurring when the simultaneous effects of temperature toward earlier and later DTF exactly cancelled. At all temperatures below this optimum for flowering, a change of temperature changed DTF predominantly by altering the days required to develop a node. At all temperatures above the optimum, a change of temperature changed DTF predominantly by altering the photoperiod-gene-caused delay of the node to flower. The optimum temperature for flowering was lowered by higher sensitivity of the genotype to photoperiod and also by longer daylength.