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Christopher Worden, George Elliott, Bernard Bible, Karl Guillard and Thomas Morris

A composting facility in New Milford, Conn. (NMF), utilizes food-processing residuals, including spent tea leaves, coffee grounds, cocoa shell and cleanings, wastewater treatment sludge from a food ingredients manufacturing plant, and past-expiration processed vegetable products. Materials are composted in aerated, frequently turned windrows under cover. The range of inputs, combined with time constraints on the composting process, has resulted in a variable, immature compost product with a high rate of microbial activity. Users have expressed concern about potential phytotoxicity or nutrient immobilization from using NMF compost. Therefore, research was conducted to determine the influence of cured and uncured NMF compost amendments on potentially sensitive crops with high nutrient requirements. Arugula (Eruca vesicaria) and green bibb lettuce (Lactuca sativa) were grown on two Connecticut organic farm research sites in 1998 and 1999. Both sites have soils classified as coarse loamy over sandy or sandy-skeletal, mixed, mesic, typic, Dystraudepts. Farms differed in the length of time under organic farm management. One farm has been an organic farm since 1988 and consequently has high soil fertility, while the other was a first-year organic farm in 1998, and had relatively low soil fertility. Three amendment types were applied: cured compost, uncured compost, and organic fertilizer (5N-3P2O5-4K2O). Amendment application rates were estimated to provide a comparable range of plant-available nutrients for the amendments and a control without fertilizer. Compost application rates were 3.4, 6.8, 20.2, 35.8, and 71.7 Mg·ha-1 (dry-weight basis) in 1998 and 11.2, 22.4, 44.8, and 89.6 Mg·ha-1 (dry-weight basis) in 1999. Organic fertilizer application rates were 1.34, 2.68, 5.36, 10.72, and 21.44 Mg·ha-1 in 1998 and 1.34, 2.68, 5.38, and 10.72 Mg·ha-1 in 1999. Soil organic matter and nutrients increased with amendment application rate at both locations. Crop yields increased with amendment rate at the new, lower-fertility farm, but yields did not respond to amendments at the older, higher-fertility farm. Yield differences were minor between the uncured and cured compost treatments at both locations. This indicates that either cured or uncured NMF food-processing residual compost can be successfully used as an organic soil amendment for salad green production.

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Usha R. Palaniswamy, Richard J. McAvoy and Bernard B. Bible

Purslane (Portulaca oleracea L.) is an excellent source of the essential fatty acid α-linolenic acid (LNA) but little is known of the effects of cultural conditions on LNA concentration. Purslane seedlings were grown under an instantaneous photosynthetic photon flux [PPF (400 to 700 nm)] of 299 or 455 μmol·m-2·s-1 for a daily duration of either 8, 12, 16, or 20 hours. Thus, plants were exposed to a daily PPF of 8.6, 12.9, 17.2, or 21.5 mol·m-2·d-1 in the low PPF treatment (299 μmol.m-2.s-1) and 13.1, 19.7, 26.2, or 32.8 mol·m-2·d-1 in the high PPF treatment (455 μmol·m-2·s-1). Plants in all treatments received a 20-hour photoperiod by providing ≈5 μmol·m-2·s-1 from incandescent lamps starting at the end of the photosynthetic light period. At low PPF, purslane grown under a 16 hour PPF duration produced the highest concentrations of total fatty acids (TFA) and LNA per unit leaf dry weight (DW), but at high PPF, concentrations of these compounds were highest under 8 and 12 hour PPF duration. Trend analysis indicated that maximum TFA and LNA concentrations occurred with a daily PPF of 14.1 and 17.2 mol·m-2·d-1, respectively; and in the thylakoids, protein, chlorophyll, and LNA concentrations peaked at a PPF of 21.8, 19.9, and 16.1 mol·m-2·d-1, respectively. LNA as a percentage of TFA was unaffected by treatment. Shoot DW increased with PPF up to the highest PPF exposure of 32.8 mol·m-2·d-1.

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Usha Rani Palaniswamy, Richard J. McAvoy and Bernard B. Bible

Purslane (Portulaca oleracea L.) has been identified as an exceptionally rich source of α-linolenic acid (LNA), an essential fatty acid that is beneficial in reducing the incidence of coronary heart disease and certain cancers. In general, about two thirds of the LNA in terrestrial plants is associated with chloroplasts. A green-leafed unnamed cultivar of purslane and a golden-leafed cultivar `Goldberg' were grown hydroponically in a complete nutrient solution with 14.3 mm nitrogen provided as nitrate (NO3 -) and ammonium (NH4 +) forms to yield NO3 --N: NH4 +-N ratios of 1:0, 0.75:0.25, 0.5:0.5, and 0.25:0.75. Young leaves, harvested 18 days after treatment initiation, were analyzed to determine the fatty acid composition and concentrations, and thylakoid protein and chlorophyll concentrations. Although the leaves of plants grown with a NO3 --N: NH4 +-N ratio of 0.5:0.5 contained 239% and 114% more LNA than plants grown with ratios 1:0 and 0.75:0.25, respectively, they contained only 41% and 26% more chlorophyll. The green-leafed cultivar had higher (39%) chlorophyll concentrations than `Goldberg', but both cultivars had similar LNA concentrations [per g dry weight (DW)]. These results suggest that the LNA concentration in the fatty acid-rich species P. oleracea may not be as closely associated with chlorophyll concentration as reported earlier for other plants. Leaves of plants grown in solutions with 0.25:0.75 NO3 --N: NH4 +-N ratio contained 35% less LNA per g leaf DW than the leaves of plants grown in nutrient solutions with a 0.5:0.5 ratio. Although total DW production was not affected by the NO3 --N: NH 4 +-N ratios in the nutrient solutions, the green-leafed cultivar produced higher fresh weight, leaf area, total DW, and number of shoots than `Goldberg'.

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Usha Rani Palaniswamy, Richard McAvoy, Bernard Bible, Suman Singha and Dennis Hill

A study was initiated to identify cultural conditions that optimize the production of important chemopreventive agents in watercress. Chemopreventatives are chemical compounds that reduce or prevent diseases such as cancer. Watercress (Nasturtium officinale) contains phenylethyl glucosinolate that, on hydrolysis, yields PEITC, and PEITC is one of the most-important anti-carcinogens among the cruciferous chemopreventatives tested. Watercress was grown in closed hydroponic systems containing 200 ppm nitrogen and either 64, 128, and 192 ppm sulfur to yield N:S ratios of 1:0.3, 1:0.6, and 1:0.9. The experiment was laid out as RCBD in the greenhouse with six replications. PEITC levels in leaf and stem tissue was assayed using gas chromatograph. After 36 days in the treatment solutions, watercress grown at a N:S ratio of 1:0.6 produced 90.1% and 65.3% (in repeated experiments) more PEITC than plants grown at a N:S ratio of 1:0.3. Plants grown in nutrient solution with a N:S ratio of 1:0.9 produced 57.4% and 24.2% greater PEITC than those grown with a N:S ratio of 1:0.3. Plants grown in a nutrient solution with a N:S ratio of 1:0.9 produced 17.2% to 24.2% less PEITC than those grown with a N:S ratio of 1:0.6. Leaves contained 54% to 70% more PEITC per unit dry mass than stems, suggesting that the leaf is the major site of synthesis and storage of PEITC.