Previous work suggests that some sweet potato (Ipomoea batatas, L.) cultivars can produce high storage root yields on soils without fertilizer N addition. This study was conducted to compare storage root yields, total biomass, N uptake and fibrous root weights of sweet potato cultivars grown on low N level soils with and without N addition. In 1987 and 1988, improved sweet potato cultivars developed at International Institute of Tropical Agriculture (liT A), Ibadan, Nigeria were grown with and without 50 kg N ha-1 in Oxic Paleustalfs with low N and C concentrations. Yields of 21 to 38 Mg ha-1 were produced for four of the five improved cultivars grown in soil without N addition. Total biomass, foliage, fibrous root and storage root weights and N concentration in leaves were not influenced by fertilizer N addition. Up to 158 and 89 kg N ha-1 uptake in total biomass occurred with the + N and -N treatments, respectively. Indigenous soil N levels and fibrous root weights for -N vs. + N treatments could not account for the total N uptake and biomass produced on soils without N addition.

Nitrogenase activity has been found associated with roots of sweet potato (Ipomoea batatas (L.) Lam). The objective of this investigation was to characterize N2-fixing isolates of the genus Azospirillum found in association with roots of different sweet potato cultivars. Five cultivars ('Carver', 'Jewel', 'Rojo Blanco', 'Centennial', 'Southern Queen') were grown in greenhouse pots on Norfolk sandy loam at pH 6.5 for periods of 1 to 3 months. Enrichment cultures of fibrous and storage root samples were grown on N-free semisolid malate medium at 35 °C. Sixteen bacterial isolates with taxonomic characteristics similar to those of Azospirillum were isolated from the five cultivars. Nitrogenase activities of single colonies grown in semisolid media for 30 h ranged from 32 to 472 nmol C2 H4∙culture−1∙h−1. The isolates were characterized by their acidification of carbon sources, ability to reduce nitrate, and morphology.

Peanut plants (Arachis hypogaea L. cv. Georgia Red) were grown hydroponically using a recirculating nutrient film technique. The effect of CO2 enrichment on nutritive composition of hydroponic peanut seeds was examined at two elevated CO2 levels (700 and 1400 ppm) that simulate potential conditions in National Aeronautics and Space Administration (NASA) Controlled Ecological Life-Support Systems (CELSS) and compared to ambient CO2 condition in hydroponics (the control). Plants were harvested at 97 days after planting, and the seeds were air-dried and analyzed for composition. Percentages of crude protein, crude fat, ash, and carbohydrate of hydroponic peanut seeds were around 30%, 30%, 3%, and 30%, respectively. The major amino acids were aspartic acid, glutamic acid, and arginine. The limiting amino acid of peanut, methionine, was 1.2%. Linoleic acid was the major fatty acid, followed by oleic and palmitic acids. The major mineral elements were K, P, Mg, and Ca. The results showed that certain peanut varieties can be grown hydroponically. The composition of the hydroponically grown peanuts is generally similar to reported peanut composition. The nutrient composition was not affected at the elevated CO2 concentrations investigated. Keywords: CELSS; hydroponic; NFT; elevated CO2 levels; peanut

Because sweetpotato [Ipomoea batatas (L.) Lam.] stem cuttings regenerate very easily and quickly, a study of their early growth and development in microgravity could be useful to an understanding of morphological changes that might occur under such conditions for crops that are propagated vegetatively. An experiment was conducted aboard a U.S. Space Shuttle to investigate the impact of microgravity on root growth, distribution of amyloplasts in the root cells, and on the concentration of soluble sugars and starch in the stems of sweetpotatoes. Twelve stem cuttings of ‘Whatley/Loretan’ sweetpotato (5 cm long) with three to four nodes were grown in each of two plant growth units filled with a nutrient agarose medium impregnated with a half-strength Hoagland solution. One plant growth unit was flown on Space Shuttle Columbia for 5 days, whereas the other remained on the ground as a control. The cuttings were received within 2 h postflight and, along with ground controls, processed in ≈45 min. Adventitious roots were counted, measured, and fixed for electron microscopy and stems frozen for starch and sugar assays. Air samples were collected from the headspace of each plant growth unit for postflight determination of carbon dioxide, oxygen, and ethylene levels. All stem cuttings produced adventitious roots and growth was quite vigorous in both ground-based and flight samples and, except for a slight browning of some root tips in the flight samples, all stem cuttings appeared normal. The roots on the flight cuttings tended to grow in random directions. Also, stem cuttings grown in microgravity had more roots and greater total root length than ground-based controls. Amyloplasts in root cap cells of ground-based controls were evenly sedimented toward one end compared with a more random distribution in the flight samples. The concentration of soluble sugars, glucose, fructose, and sucrose and total starch concentration were all substantially greater in the stems of flight samples than those found in the ground-based samples. Carbon dioxide levels were 50% greater and oxygen marginally lower in the flight plants, whereas ethylene levels were similar and averaged less than 10 nL·L−1. Despite the greater accumulation of carbohydrates in the stems, and greater root growth in the flight cuttings, overall results showed minimal differences in cell development between space flight and ground-based tissues. This suggests that the space flight environment did not adversely impact sweetpotato metabolism and that vegetative cuttings should be an acceptable approach for propagating sweetpotato plants for space applications.

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