In class demonstrations, it is almost impossible to maintain the same water: air ratio in growing media. If some treatments result in greater plant growth than others, treatment effects on plant growth are often confounded with the effect of water: air ratio in the growing media. In a laboratory demonstration of nutrient deficiencies symptoms in plants, a controlled water table irrigation system maintained a constant water: air ratio in the growing media regardless of the nutrient deficiency affect on plant growth. The modified capillary mat irrigation system consists of one mat edge extending over the edge of the bench into a narrow trough on the side of the bench. The nutrient solution level in the trough is controlled by a liquid level controller, so it is at a fixed distance below the bench surface. The nutrient solution is drawn upward by capillarity to the bench surface and then moves by capillarity over the bench. The system automatically maintains a constant air: water ratio in the growing media. A standard Hogland solution was modified to demonstrate deficiencies in N, P, K, Mg, Ca, Cu, Fe, and Zn on corn, squash, radish, soybeans, and marigold. Seeds were germinated and grown to maturity in either a 10- or 15-cm pot. Students set up the demonstration, were provided instruction in preparing solutions, regularly observed plant growth, and answered questions at the end of the study about differences in plant growth observed. However, possibly because low concentrations of some minor elements in the capillary mat, Zn deficiency was not observed and other elements, although resulting in poor growth compared to the control, did not show severe deficiency symptoms.
The controlled water-table irrigation (CWT) system was evaluated for vegetable seed germination and transplant growth. The system is a modification of capillary mat irrigation except that the mat along one side extends over the edge of the bench into a narrow trough running along the side of the bench. The nutrient solution level in the trough is controlled by a liquid level controller, so it is at a fixed distance below the bench surface. The nutrient solution is drawn by capillarity from the trough upward to the bench surface and then moves by capillarity to the opposite side of the bench. The system automatically maintains a constant air: water ratio in the growing media. Seeds of broccoli, tomato, and pepper were germinated in a 96-cell plug tray and grown to transplanting stage with the CWT system. A factorial experiment consisted of two growing media combined with CWT treatments of 2 and 4 cm. Excellent germination and high-quality seedlings were produced with all treatments. No differences were observed in growth of seedlings at 2 vs. 4 cm or between the two growing media. The CWT system is capable of maintaining a constant uniform water: air ratio in all plug cells on a commercial growing bench. Nutrient solution does not run off the bench. The CWT potentially is an excellent system for the irrigation of vegetable transplants.
Students in plant science courses have difficulty thoroughly understanding the effect of water stress on net photosynthesis and its consequences—reduced plant growth, productivity, quality, and profit. A laboratory demonstration utilizing a controlled water table irrigation system (CWT) provides a nearly constant plant water potential. Pots are placed on a capillary mat with one end suspended in a trough with nutrient solution. The vertical distance from the solution surface to the pot bottom determines the water potential; the water potential is 0 when the pot bottom is at the same level as the nutrient solution. The greater the vertical distance from solution to the pot bottom, the lower the water potential. For this demonstration, the bench was sloped from 0 to 10 cm above the solution over a distance of 90 cm. Corn, squash, soybean, fescue, and marigold seed were directly sown to either 9- or 15-cm pots and then placed on the CWT sloped bench at five vertical distances above the solution. Weekly, students observed plant growth and at the end of 8 weeks evaluated root and shoot growth. For all species, plant growth was indirectly related to the distance above the nutrient solution. Plants at near 0 water potential were much larger than those grown 8 to 10 cm above the solution.
An analysis of using an air-earth heat exchange for controlling the environment in a greenhouse was conducted. For purpose of the analysis, a small greenhouse (2.75 m wide and 4.25 m long) connected to 30.5 m of 45 cm diameter pipe was assumed. In terms of heating, the air-earth heat exchanges proved to be inadequate except for the very southern parts of the United States, and even in these locations the temperature had to be limited to a relatively cool temperature of 10°C. A similar analysis for summer showed that the air-earth heat exchange could effectively limit the occurrence of high temperatures in a greenhouse throughout the United States.
Two varieties of tall bearded iris, ‘Color Carnival’ and ‘First Violet’, were grown at minimum temperatures above 20° F throughout the fall and winter months. Groups of these plants were transferred periodically to a 65° house where they received either long or short-day treatments. Plants of ‘Color Carnival’ flowered under long days, regardless of the length of the vernalization period; under short days, some flowering occurred if the plants received more than 8 weeks of vernalization. Plants receiving 16 or more weeks of vernalization flowered equally well under long days or short days. Plants of ‘First Violet’ did not flower under flowering did not occur until the plants had long days unless the plants had received 16 or more weeks of vernalization; under short days received 20 or more weeks of vernalization. The longer the plants had been held at the minimum temperature, the shorter the time required for flowering after being transferred to 65°.
A greenhouse environment, heated and cooled with air drawn from a coal mine, was modified to reduce high humidity and dripping condensate. Polyethylene covered chambers, constructed within the mine-air greenhouse, were ventilated with mine-air, heated above mine-air temperature and ventilated with mine-air, or heated above mine-air temperature and ventilated with air drawn from outside the greenhouse. Heating the chambers above mine-air temperature did not reduce relative humidity significantly. However, polyethylene glazing on the chambers protected plants growing within the chambers from condensate dripping from the outer covering of the mineair greenhouse, which reduced the disease potential. Snapdragon and lettuce crops were produced in the chambers from early fall through spring. Snapdragon and lettuce grown in chambers ventilated with mine-air generally were of equal or better quality than plants produced in chambers provided with additional heat and ventilated with either mine-air or air drawn from outside the mine-air greenhouse.
Cytokinins were extracted from whole root tissue of aeroponically cultured Chrysanthemum morifolium Ramat., purified by cation exchange, paper and Sephadex LH-20 column chromatography and bioassayed with tobacco callus. Compounds with chromatographic properties similar to those of zeatin and zeatin riboside were found to be the major cytokinin components of the roots.
Cytokinin activity was indicated in roots of Chrysanthemum morifolium Ramat, cv. Polaris cultured using a nutrient film technique and assayed at 3 stages of plant development: young, actively growing; mature flowering; and senescing with dried flowers.
A capillary mat-mist system was developed to provide near constant media water contents at differing quantities of mist. Media water contents were reduced by increasing the capillary mat height above a constant water table maintained at bench level. Increased tensions from 0 to 10 cm above the water table reduced water content in Oasis, rockwool, and peat-perlite by 35.4%, 27.6%, and 17.4%, respectively. There was no difference in water content for each medium when the mist quantity ranged between 600 and 1800 mL·m-2·h-1, except when the capillary mat was at 9 cm above the water table and mist volume was 300 mL·m-2·h-1. Chrysanthemum cuttings rooted best when water content was highest regardless of media. Using the peat-perlite medium, water content had the greatest impact on rooting when the mist volume was low (600 mL·m-2·h-1). Relative water content of cuttings was lowest during the first 5 days of sticking and both reduced media water content and mist quantity resulted in the lowest internal water status for the cuttings.
The CWT irrigation system consists of a capillary mat placed on a level bench so one side extends over the edge of the bench into a trough containing a nutrient solution maintained at a controlled distance below the bench. The nutrient solution is drawn by capillarity up to and over the bench surface. As plants use the nutrient solution or as water evaporates from the media, it is replaced from the trough. The automatic system maintains a constant air/water ratio in the growing media. Geraniums were grown in a peat based media in 15-cm pots at 0, 2, and 4 cm CWT. In a separate study, the water potential was determined in two media. Water potential was determined at the bottom, middle, and top of the container at 0, 2 and 4 cm CWT every 2.5 hrs during the light period. Geraniums at 0 and 2 cm had the greatest leaf area and dry weight. The 0- and 2-cm treatments were >25% greater than plants at 4 cm CWT. The roots of plants at 0 cm CWT were concentrated at 2–4 cm above the bottom of the container, whereas roots at 2 cm CWT uniformily extended from the center to the bottom. Water potential was about the same in each media within each CWT treatment. The water potential from top to bottom decreased slightly about midafternoon on a sunny day when water demand was the greatest. Media at 0 CWT at the container bottom had 0 water potential; whereas the water potential at 2 and 4 CWT had a lower water potential.