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  • Author or Editor: Raymond Wheeler x
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An experiment was conducted to determine the effects of banded phosphorus (P) applications at differing rates in irrigated and nonirrigated pecan (Carya illinoinensis) plots on P movement within the soil, P uptake and movement within pecan trees, and the yield and quality of nuts. On 20 Mar. 2015, P applications of 0 kg·ha−1 (0×), 19.6 kg·ha−1 (1×), 39.2 kg·ha−1 (2×), and 78.5 kg·ha−1 (4×) were administered to bands of triple superphosphate to randomly selected trees in nonirrigated and irrigated plots of a ‘Desirable’ orchard bordered by ‘Elliot’ trees. When P was applied at the 2× and 4× rates, the total soil test P decreased linearly by 35% and 54%, respectively, in nonirrigated plots and by 41% and 59%, respectively, in irrigated plots over the course of the experiment. There was no change in soil test P over time at the 0× rate for either irrigation regimen; however, at the 1× rate, soil test P decreased 44% in the irrigated plot but did not change in the nonirrigated plot. The largest linear decrease of the soil test P from the start of the experiment to the end of the experiment occurred in the top 0 to 7.6 cm. In contrast, soil test P at a depth of 15.2 to 22.9 cm decreased linearly by 23% in the nonirrigated plot, but it did not decrease over time in the irrigated plot. Increasing the P application rate increased foliar P quadratically in the nonirrigated plot, but only the 4× application rate increased foliar P compared with the 0× control. In the irrigated plot, foliar P concentrations decreased linearly from 2015 to 2017, and foliar P concentrations were not influenced by the P application rate. No differences in pecan yield or quality were observed in either irrigated or nonirrigated plots. Overall, P banding may not be the most sustainable way to increase foliar concentrations of P quickly or to maintain concentrations of the nutrient in the long term.

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The development of a crop production system that can be used on the International Space Station, long-duration transit missions, and lunar or Mars habitats, has been a part of NASA's Advanced Life Support (ALS) research efforts. Crops that can be grown under environmental conditions that might be encountered in the open cabin of a space vehicle would be an advantageous choice. The production efficiency of the system would be enhanced by growing these crops in a mixed-crop arrangement. This would also increase the variety of fresh foods available for the crew's dietary supplementation. Three candidate ALS salad crops, radish (Raphanus sativus L. cv. Cherry Bomb II), lettuce (Lactuca sativa L. cv. Flandria), and bunching onion (Allium fistulosum L. cv. Kinka) were grown hydroponically as either monoculture (control) or mixed-crop within a walk-in growth chamber with baseline environments maintained at 22 °C, 50% RH, 17.2 mol·m-2·d-1 light intensity and a 16-h light/8-h dark photoperiod under cool-white fluorescent lamps. Tests were carried out at three different CO2 concentrations: 400, 1200, and 4000 μmol·mol-1. Weekly time-course harvests were taken over 28 days of growth, and fresh mass, dry mass, and harvest index were determined. Results showed that none of the species experienced negative effects when grown together under mixed-crop conditions compared to monoculture growth conditions under the range of environmental conditions tested.

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The effects of using mixed cropping strategies for reducing overall mass and increasing system efficiency was examined as part of NASA's mission to study minimally-processed or “salad” crops as dietary supplements on long-duration space missions. To test interspecific compatibility, radish (Raphanus sativus L. cv. Cherry Bomb II), lettuce (Lactuca sativa L. cv. Flandria), and bunching onion (Allium fistulosum L. cv. Kinka) were grown hydroponically as either monoculture (control) or mixed-crop within a walk-in growth chamber maintained at 25 °C, 50% relative humidity, 300 μmol·m-2·s-1 PPF, and a 16-h light/8-h dark photoperiod under cool-white fluorescent lamps. Weekly time-course harvests were taken over 28 days of growth. Results showed that none of the species showed any negative growth effects when grown together under mixed-crop compared to monoculture growth conditions. However, radish showed significant increases in edible mass when grown under mixed-crop compared to monoculture conditions. The observed increases in growth are likely attributable to increased light interception due to a decreased guard row effect as well as a faster canopy development for radish.

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Production of high tunnel tomatoes and snapdragons was evaluated over a 2-year period at the Wiregrass Experiment Station, in southeastern Alabama. `BHN 640', `Florida 91', `Sunleaper', and `Carolina Gold', were evaluated in early Spring 2004. Results indicated that `BHN 640' outperformed `Florida 91' and `Carolina Gold' in early production of high tunnel grown tomatoes. A late Fall 2005 study examined `BHN 640' and `Florida 91'. Results indicated that `BHN 640' was superior to `Florida 91' in total marketable fruit. Season extension of both spring and fall tomato production were accomplished. A planting date study was completed in the early Spring 2005. The following four planting dates were evaluated: 31 Jan., 17 Feb., 4 Mar., and 25. Mar 2005. Wind damage to the high tunnel caused some mortality; however, the two earliest planting dates (31 Jan. and 17 Feb. 2005) produced over 10 lbs. of marketable tomatoes per plant. These were both superior to the last planting date of 25 Mar 2005. Cut snapdragons were evaluated for suitable colored mulch (red, white, or blue) and varieties for summer (`Opus Yellow', `Opus Rose', `Monaco Red', and `Potomac Early White') and fall (`Apollo Purple', `Apollo Yellow', `Monaco Red', `Monaco Rose', and `Potomac Early Orange') production. Results indicated that inflorescence length was affected by the color of mulch. The red mulch had increased inflorescence length compared to the white in Summer 2005. The Fall 2005 study revealed that white mulch had longer inflorescence length than the red or blue mulch. Some varietal differences were observed. The `Apollo Purple' had longer stem lengths than all other varieties for the fall study. The summer study revealed that `Opus Yellow' had longer inflorescence lengths than all others but stem lengths were all similar.

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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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