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  • Author or Editor: Wade Berry x
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Abstract

Lettuce seedlings were grown in a modified Hoagland’s solution, with 9 treatments ranging from 0.06 to 16.0 mM/liter of H2PO4. In the low P solutions the deficiency symptoms shown by lettuce seedlings consisted of leaves showing a darker green and reduced growth. Tissue levels of soluble PO4–P in these deficient seedlings dropped to a low of 379 ppm PO4–P and a high of 13770 ppm PO4–P for plants well supplied with P. The critical level for the evaluation of the P nutrient status of seedling lettuce plants in the conductive, lamina, and root tissue were respectively: 780, 600, 580 ppm soluble PO4–P on a dry wt basis.

Open Access
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Abstract

Lettuce was grown in a complete nutrient solution, with Zn increased stepwise by a factor of 2 for 8 treatments from 1.6 to 200 μg/liter. Forty-seven days after imbibition the plants were harvested and separated into 6 parts for tissue analysis. The plants in the low Zn solutions were stunted in growth and showed a marginal purpling and a rupture of laticifers on the margins of the mature leaves. The symptoms progressed from an overall chlorosis to an interveinal necrosis; with the dark desiccated areas eventually coalescing to cover most of the leaf. The Zn nutrient status of the lettuce plant was best defined by determining the Zn concentration in the mature petiole (mid-rib). The critical level of Zn in the mature petiole is 9 ppm. Concentration of Zn in this tissue below 9 ppm indicates an unfavorable Zn nutrient status for the vegetative growth of lettuce.

Open Access

Water contributes approximately 90% of the life support consumables in a closed space environment, therefore, regeneration of pure water from waste streams is important for long term space travel. Controlled Ecological Life Support Systems (CELSS) will rely on plants to produce food, oxygen, consume CO2 and purify water. Igepon TC42, Amide coco N-methyl N-2-sulphoethyl sodium salt, is the main ingredient of the soap recommended for showering and hand washing aboard Space Station Freedom. To determine the soap concentration which causes plant toxicity, lettuce seeds were germinated in 0.1 strength modified Hoagland's nutrient solution and a series of increasing concentrations of Igepon. After 5 days, the seedlings were examined and primary root length measured. The dose response curve indicates an Igepon acute toxicity threshold of 0.2 g l-1 Below the threshold concentration the curve is similar to that of the control, but drops linearly upon reaching the toxic threshold. Seedlings exposed to concentrations of soap greater than the toxic threshold exhibited root damage characterized by the browning of cells in bands above the root cap resulting in reduced growth rates. The damaged cells enlarged becoming round in appearance prior to departing from adjacent cells. The underlying cells appeared clear and uniform making up a thinner, more fragile root mass when compared to undamaged root regions.

Free access

Abstract

Lettuce seedlings were grown in a modified Hoagland’s solution at concentrations of 0.03 to 8.0 mM/liter of K. In the low K solutions the lettuce seedlings developed K deficiency symptoms which were atypical in that chlorosis followed by random necrotic lesions were the predominant symptoms while the typical symptom of marginal scorch did not develop. Tissue levels of K in 13 day-old deficient seedlings (thinning stage of development) dropped to a low of 0.3% K. The critical level for the evaluation of the K nutrient status in the conductive, lamina, and root tissue were respectively: 2, 1.8 and 1.3% K on a dry wt basis. Seedling lettuce was reduced in yield (weight) when the concentration of K remaining in the culture solution at harvest time was less than 0.01 mMK and they were unable to reduce the concentration of K below 0.001 mMK.

Open Access

Recycling wastewater containing soaps and detergents for plant growth is highly desirable when fresh water is limited. This is especially true during times of drought and is imperative in some specialized situations such as a regenerative space habitat. To regenerate food, water, and air, the National Aeronautics and Space Administration's Controlled Ecological Life Support System (CELSS) must recycle wastewater commonly known as gray water. The anionic surfactant Igepon is the principal ingredient of many detergent formulations and soaps and is a prime candidate for use in a space habitat. To determine if gray water would have phytotoxic effects on crops grown in a CELSS, `Waldmann's Green' lettuce (Lactuca sativa L.) was grown in nutrient solutions containing varying concentrations of Igepon TC-42. Igepon concentrations of 250 mg·L-1 or higher in nutrient solutions resulted in phytotoxic effects in lettuce. Thus, the toxic threshold of Igepon is <250 mg·L-1. Toxicity symptoms include browning of the roots within 4 hours of exposure to Igepon followed by suppression of root dry mass within 24 hours. Plant death never resulted from exposure to Igepon used in these experiments, although roots were killed. The phytotoxic effect of Igepon was not persistent; plants initially displaying acute toxicity show clear signs of recovery within 3 days of initial exposure. Further, when fresh plants were exposed to these same nutrient solutions 3 days or more following initial Igepon addition, no phytotoxic effect was observed. The elimination of the phytotoxicity was associated with a decrease in fatty acid components in the nutrient solution associated with Igepon. The degradation of phytotoxicity appears to be associated with microbes present on the surface of the roots and not directly due to any plant process or instability of the surfactant.

Free access

Abstract

The use of municipal wastewater for horticultural production on the surface appears to be a very simple concept (2, 10, 12). In its simplest form it is the use of a waste product of one process as the raw material for a second process. However, if the best use of the combination of the 2 systems is to be made, it will be necessary to maximize the sum of the 2 systems rather than of each individual system. These 2 systems, horticulture and municipal wastewater, are interfaced by a number of mutual components which are mineral nutrients, CO2, water and heat. The heat and CO2 can only be taken advantage of under controlled environmental conditions, with a bare minimum being greenhouse conditions, while all horticultural operations can utilize the nutrients and water (5).

Open Access

Abstract

Reclaimed, secondary-treated municipal wastewater after chlorination and ponding is being used as the sole source of water and mineral nutrients in research studies on the hydroponic culture of ornamental and vegetable crops. A feasibility study is in progress to determine if greenhouse crops (e.g. tomatoes, cucumbers, lettuce, and chrysanthemums) can be produced using secondary-treated effluent as a water nutrient source, while at the same time removing sufficient primary nutrients and perhaps trace elements to also function as a tertiary treatment process. The cover photo of tomatoes illustrates the type of production achieved. Secondary-treated municipal wastewater constitutes an attractive alternative source of water and fertilizer nutrients for crop production since the nutrients present in the wastewater are already in a usable form and do not require any additional energy input to make them available to plants. At the same time, the removal of nutrients from waste-water during crop production would reduce the pollution load that inherently remains after secondary treatment. Additionally, when these two processes are combined in the same operation, the heat and carbon dioxide produced as byproducts in treatment processes could be used to enhance crop production. Thus, the combined processes could constitute a more attractive, economic alternative than the sums of the two separate operations.

Open Access

Anionic surfactants are the major class of surfactants used in detergent, laundry and related industries. Hence, they are a major contaminate of both domestic and industrial waste streams. Lettuce (Lactuca sativa cv Waldemann's Green) was grown in nutrient solutions with the addition of the anionic surfactant, Igepon TC-42. The toxic response of lettuce to Igepon was that the roots turned brown and became necrotic within 24 h following exposure. Growth was supressed for approximately 4 days following exposure to concentration greater than 0.35 mM; new roots formed rapidly and growth resumed. When fresh plants were transferred to the solutions containing Igepon 48 h following introduction of the surfactant no signs of toxicity were observed. This would indicate that either the first series of plants absorbed the toxic material or the Igepon was decayed or degraded in the nutrient solution. The rapid recovery of plants from this stress suggests the potential of a wide range of strategies that could be developed for utilizing waste streams containing anionic surfactants.

Free access

Wheat (cv. Yecora Rojo) plants were grown in a closed chamber as part of NASA's Controlled Ecological Life Support System (CELSS) program. Plants were grown using a recirculating hydroponics with EC controlled at 0.12 S m-1 by automatic additions of a nutrient concentrate, and pH was controlled at 5.8 units with automatic additions of nitric acid. Daily CO2 exchange, water uptake, and nutrient uptake were monitored for the entire 20 m2 canopy throughout growth. Nutrient use efficiency (NUE) relative to water and CO2 uptake were determined, where NUE-W was defined as the amount of water taken up per unit of nutrient and NUE-C as the amount of carbon fixed per unit of nutrient. Water uptake remained relatively constant after canopy closure (25 DAP), where CO2 uptake peaked during rapid vegetative growth and then declined gradually with age and gain fill. Nutrient uptake also peaked during vegetative growth but declined sharply after anthesis. Water use efficiency (WUE) was high early in growth and then declined with age due to the decrease in CO2 exchange over time. In contrast NUE-C and NUE-W were low during vegetative growth and the increased nearly 10-fold during grain fill.

Free access