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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.
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.
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.
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).
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.
Abstract
An interlaboratory comparison was made of the variation in elemental concentration of leaf lettuce (Lactuca sativa L. cv. Grand Rapids) plants grown under base-line conditions for 28 days in 5 controlled-environment facilities. Two studies were conducted by each of 5 investigators using a sphagnum peat-vermiculite mix obtained from a common source. Plant tissue from all studies was collected and analyzed at 1 laboratory for 10 essential elements (P, K, Ca, Mg, Fe, Mn, B, Zn, Cu, Mo) and 10 non-essential elements (Al, Si, Ti, Sr, Ba, Na, Pb, V, Li, and Sn) by arc emission spectrography. The 10 essential elements occurred at concentrations adequate for normal lettuce growth. Tissue analysis data showed large differences in elemental concentration among experiments conducted by the same investigator as well as by different investigators suggesting inadvertent contamination of the leaf samples by the rooting media or contamination of the watering system in each controlled-environment facility. These differences, however, had no observable effect on vegetative growth. Based on a nested analysis on variance, 95% of the elements showed significant plant to plant differences in concentration. However, based on an analysis of variance components, the greatest source of variation was found among investigators.