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  • Author or Editor: W. L. Berry x
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Requirements for water, nutrient replenishment and acid (for pH control) were monitored for stands of wheat, soybean, potato, and lettuce grown in a recirculating hydroponic culture using a modified 1/2 Hoagland solution with NO3-N. Water use at full canopy cover for all crops ranged from 4 to 5 L m-2 day-1. When averaged over the entire crop cycle, nutrient stock solution (∼0.9 S m-1) use varied from 0.2 L m-2 day-1 (lettuce: to 0.75 L m-2 day-1 (wheat), while acid use varied from 6 mmol m-2 day-1 (lettuce and soybeans) to over 40 mmol m-2 day-1 (wheat). Water-per unit biomass was highest for soybean and lettuce (0.3 to 0.4 L g DW), and least for wheat and potato (0.15 L g DW). Nutrient replenishment per unit biomass was highest for lettuce, 34 mL g-1 DW, with other crops ranging from 21-26 mL g-1 DW. Acid requirements were highest for wheat, 1.2 mmol g-1 DW, and lowest for potato, 0.7 mmol g-1 DW. On a PAR basis, acid needs were highest for wheat, 0.6 mmol mol-1 photons, with all other crops near 0.4 mmol mol-1. Acid data suggest that wheat nutrient uptake favors anions more strongly than the other species, or that more nitrate loss (e.g., denitrification) may occur during wheat growth.

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Critical levels of nutrients in leaf tissue are influenced by plant metabolism, environment, and nutrient availability. In this study, we measured the elemental concentrations in fully expanded, upper canopy potato (Solunum tuberosum cv. Norland) leaves throughout growth and development in a controlled environment. Plants were grown hydroponically (NFT) in NASA's Biomass Production Chamber using a complete nutrient solution with the electrical conductivity maintained continuously at 0.12 S m-1. Photoperiod and air and root zone temperatures were changed midseason to promote tuberization, while CO2 levels were maintained at 1000 μmol mol-1 throughout growth. During vegetative growth, leaf nutrient concentrations remained relatively constant, except for a decline in Ca. During tuber enlargement and plant maturation, overall nutrient uptake decreased. Concentrations of the less mobile nutrients such as Ca, Mg, and B increased in the leaf tissue during mature growth, but somewhat surprisingly, highly mobile K also increased. Leaf concentrations of P, Zn, and Cu decreased during maturation.

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Wheat, soybean, potato, and lettuce crops were grown in a large (20 m2), closed chamber to test plant production for life support in a Controlled Ecological Life Support System (CELSS). Plant crude protein levels were about 15% in wheat and potato biomass, 20% in soybean biomass, and 27% in lettuce biomass at harvest. Nitrate levels were not assayed, but likely contributed to the protein estimates. Nitric acid (used in hydroponic system pH control) contributed 43% for wheat nitrogen needs, 33% for soybean, 30% for potato, and 27% for lettuce. Lettuce contained the highest percent ash (22%) and wheat the lowest (10%). It was likely that the continuous nutrient supply in the hydroponic systems resulted in high ash values. The percentage of plant macronutrients in the inedible biomass was 7% in lettuce, 50% in soybean and potato, and 80% in wheat. Based on these values, perhaps 50% of the macronutrients needed in a multi-crop system could be removed from the inedible biomass and recycled back into the hydroponic system. Applicable technologies for nutrient recovery would include wet or dry oxidation (ashing), water soaking (leaching), or bioreactor degredation. The mass of reagent-grade salts needed in place of nutrient recycling could equal about 30% of the dry food mass required per person day-1.

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The maintenance of pH in unbuffered nutrient solutions has important consequences for the hydroponic industry and proposed nutrient delivery systems for plants in space. The requirement for charge balance by a model plant system, dwarf wheat (Triticum aestinum cv. Yecora rojo), is largely a function of the uptake ratio of four cation species ( NH 4 + , Ca2+, and Mg2+) and two anion species ( NO 3 and SO 4 2 ) up to anthesis. The change in electrical conductivity (EC) and pH of the nutrient solution over time integrates the overall influx:efflux process of the plants. Solutions with three different NH4:NO3 ratios were sampled at 15-min intervals over a 12-h period at 9, 10, 16, 17, 23, 24, 37, and 38 days after planting. Exhaustion of N in the solution at all stages of ontogeny resulted in a 2- to 3-fold reduction in ΔpH/Δt, despite high plant tissue N and irrespective of the concentration of other charge balance ions in solution. These data, combined with a plant nutrient uptake database (normalized for plant relative growth rate per mole PPF), suggest that a system can be developed to control pH by direct supply of various alternative nutrient stock solutions, rather than by the addition of H+ or OH from acid or base.

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Maintaining pH to optimize nutrient availability in unbuffered nutrient solutions is important for closed spaceflight hydroponic systems and in agriculture. Total nutrient uptake is reflected by electrical conductivity (EC) measurements, while pH reflects the net imbalance of cation and anion absorption. The pH of nitrate-only (0 NH 4 + : 100 NO 3 ) nutrient solutions normally increases, whereas with equimolar (50 NH 4 + : 50 NO 3 ), solutions, pH decreases. However, when solution pH was controlled to 5.8 by a mixed N sources (25 NH 4 + : 75 NO 3 ), plant yields of semi-dwarf wheat (Triticum aestivum cv. `Yecora Rojo') were equal to the control (0 NH 4 + : 100 NO 3 ) system. When nutrient uptake was monitored at 15-min intervals, it was found that NH 4 + and NO 3 were taken up simultaneously. Uptake of NH 4 + was more rapid than NO 3 . The change in pH and EC was primarily a function of the absorption of three ions, namely NH 4 + , NO 3 , and K+. A significant amount of the K+ uptake was highly correlated (P < 0.001) to the presence of NO 3 in solution. When the daily N requirement was supplied as a 25 NH 4 + : 75 NO 3 mixture, comparatively little change in solution pH occurred, with reduced K+ uptake by the plants. Thus, by knowing the daily crop N requirement from the relative growth rate, the pH fluctuations within hydroponic nutrient solutions can be reduced with daily additions of a balanced nutrient solution with a 25 NH 4 + : 75 NO 3 mixture of N.

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Abstract

Asparagus (Asparagus officialis L.) cv. UC 157 planted in desert coarse sand in the fall of 1979 and harvested in the springs of 1981, 1982, and 1983 was irrigated with geothermal water, with 2240 ± 1290 ppm total dissolved solids and ground water 1430 ± 460 ppm total dissolved solids. Yields of 3.1 MT/ha of large spears were obtained with ground water and 0.03 MT/ha with the geothermal-irrigated asparagus. Na and Li were significantly increased in the spears that received geothermal irrigation, and B and Fe were significantly increased in those irrigated with ground water. Toxic accumulation of elements in the spears did not occur when geothermal water was used for irrigation, but yields were reduced.

Open Access

Abstract

Labeled 1,3-dichloropropene (1,3-DCPE) (5.90 × 10−7 moles/ml) or 3-chloroallyl alcohol (3-CAA) (6.12 × 10−7 moles/ml) was administered to tomato seedlings through the roots. Radioactivity in various fractions was determined at various intervals of time. Maximum amounts of 1,3-DCPE and 3-CAA had been absorbed and translocated to the aerial parts of the plants by 4 hr. Gas chromatographic analysis of plant materials showed that the compounds were readily metabolized by the plant. The 1,3-DCPE was metabolized to 3-CAA, part of which was converted to 3-chloroacrylic acid and 3-chloro-1-propanol as confirmed by co-chromatography with standard compounds. No parent 1,3-DCPE was found in the plant after a 72-hr incubation period and 3-CAA was not detected after a 96-hr incubation. In unlabeled experiments, micrographs of cells from control plants showed normal organellar structure. By contrast, the chloroplasts in some leaf cells from plants treated with 3-CAA had undergone slight swelling and partial disruption of the membrane system 6 hr after treatment. At 12 and 24 hr after treatment, both chemicals had disrupted the organellar structure of the chloroplasts and the rough endoplasmic reticulum (RER) of some cells. Although the normal organellar structure was disrupted, the data indicate that the dichloropropenes and 3-CAA do not present plant residue problems, and that concern about the ultimate environmental fate of these compounds may be minimal.

Open Access