A low-input sustainable agricultural system for the production of staked, fresh-market field tomatoes (Lycopersicon esculentum Mill.) is described. The system uses winter annual cover crops to fix N, recycle leftover nutrients, produce biomass, and prevent soil erosion throughout the winter and spring. Yields of tomato plants grown in hairy vetch (Vicia villosa Roth), crimson clover (Trifolium incarnatum L.), and rye (Secale cereale L.) plus hairy vetch mulches were higher than those grown in the conventional black polyethylene (BP) mulch system in 2 of 3 years. Fruit were heavier with the plant mulches than with BP mulch. Eight weeks after transplanting, N levels in tomato leaves were higher with plant than with BP mulch, although the plant mulch plots received only 50% of the N applied to the BP plots. The cover crops had no effect on populations of five phytoparasitic nematode species.

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An ethylene biosynthesis-inducing xylanase (EIX) produced by the fungus Trichoderma viride elicited enhanced ethylene biosynthesis and leakage of potassium and other cellular components when applied to leaf disks of tobacco (Nicotiana tabacum L. cv Xanthi). Suspension-cultured cells of Xanthi tobacco responded to EIX by rapid efflux of potassium, uptake of calcium, alkalization of the medium, inhibition of ethylene biosynthesis, and increased leakage of cellular components. EIX-treated cell suspensions released 1-aminocyclopropane-1-carboxylate (ACC) into the surrounding medium, resulting in a reduction of cellular pools of ACC. The responses of both cell suspensions and leaf disks were inhibited (50-80%) by the preincubation of the tissues with the calcium channel blocker La3". High concentrations of EGTA inhibited the alkalization of the medium by cell suspensions responding to EIX, but EGTA alone caused extensive loss of K' and ACC and inhibited ethylene biosynthesis by tobacco cells. Alterations in membrane function appear to be important in the mode of action of EIX in Xanthi cells.

Cadmium, copper, nickel, and zinc were applied as sulfate salts to samples of surface horizons of three Maryland soils in the greenhouse at rates of metals equivalent to those in 0 to 896 dry metric tons/ha of Washington, D.C., digested sewage sludge. The sludge was also applied at a rate of 224 dry metric tons/ha. Two pH regimes, approximately 5.5 and 6.5, were maintained. Metals were extracted by the DTPA (diethylenetriaminepentaacetic acid buffered at pH 7.3) double acid (0.05N HCl, 0.025N H2SO4) extractants. Correlations were determined between extractable soil metals and metal content of two crops of corn (Zea mays L.) each grown for 30 days, but at times of 1 or 13 mo after making the chemical amendments to the soils.Highly significant associations, r values ranging from 0.658 to 0.998, were obtained between the quantities of Cd, Cu, Ni, and Zn extracted by the two extractants. DTPA tended to extract smaller quantities of all metals and tended to be more indicative of reduced plant Zn and Cu uptake under limed conditions than double acid. Cadmium remained the most extractable after 14 mo by either extractant when expressed as a percent of the applied metal that was extractable. Overall metal extractability on this basis followed the order Cd > Cu > Zn > Ni, independent of soil type or extractant.Sludge‐applied metals were approximately half as extractable as sulfate salt‐applied metals at comparable rates of application, but followed the same order of relative extractability.Plant content ofCd, Cu, and Zn was significantly correlated, at the 1% level, with extractability of the respective metal for both extractants for metal salt‐amended soils. Correlations from the sludged soils were poor and generally not significant. Numerically higher and generally more significant correlations were obtained when the data were separated by lime level into two regression equations compared to a combined regression. The primary cause of this effect was the greater metal content of the plant tissue per unit of extractable metal on the low vs. the high pH soils, except for Cd, producing two distinct regression equations. This relationship was more pronounced with the first crop than with the second.

The ethylene biosynthesis-inducing xylanase (EIX) is known to be a potent elicitor of ethylene biosynthesis and other responses when applied to leaf tissue of Nicotiana tabacum 1. cv Xanthi. In contrast, leaf tissue of the tobacco cultivar Hicks was insensitive to EIX at concentrations 100-fold higher than was needed to elicit responses from Xanthi. Cell-suspension cultures of Xanthi and Hicks showed similar differences in sensitivity to EIX. Equivalent levels of ethylene production were elicited in leaf discs of both cultivars after treatment with CuSO,. The F, and Xanthi backcross progeny of Hicks and Xanthi crosses were all sensitive to EIX, whereas the Fz and Hicks backcross progeny segregated for sensitivity to EIX. Individual plants from the Fz and Hicks backcross that were insensitive to EIX produced only insensitive progeny when they were self-pollinated. Progeny from sensitive plants either segregated for sensitivity to EIX or produced all sensitive progeny (an Fz plant). Sensitivity to EIX is controlled by a single dominant gene, based on chi-square analysis of segregation ratios.

A 3-year experiment was conducted to determine the optimum fertilizer N requirements of fresh-market tomato (Lycopersicon esculentum Mill.) `Sunbeam' grown on a hairy vetch (Vicia villosa Roth.) or black polyethylene mulch. In 1993 and 1994, four rates of fertilizer N (0, 56, 112, and 168 kg·ha-1) as water-soluble NH4NO3 were applied in 14 equal applications through the trickle irrigation system starting 1 week after planting. Four additional rates (224, 280, 336, and 392 kg·ha-1) were applied in 1995 to assess the plant response to supra-optimal levels of N. Hairy vetch produced 3.3–4.5 t·ha-1 of above-ground biomass and a total N content of 126–169 kg·ha-1 in the above-ground biomass. Leaf N content at 7 weeks after transplanting of tomatoes correlated positively with yield from black polyethylene but did not correlate with yield from the hairy vetch plots where leaf N content was optimal at all N rates. Predicted tomato yields were higher for the hairy vetch than for the black polyethylene treatment at all applied N rates in all years. Tomatoes grown in black polyethylene required N at 130 to 144 kg·ha-1 to achieve yields equivalent to those grown following unfertilized hairy vetch. Tomato yield increased in response to applied N in both mulches in all 3 years; optimum N rates of 89 and 190 kg·ha-1 in hairy vetch and black polyethylene, respectively, were predicted by a linear plateau model, and 124 and 295 kg·ha-1 by a quadratic plateau model. The linear plateau model is recommended because it would allow less N to become available for runoff and leaching.

Seedlings of five blueberry progenies were planted in a range of soils, with or without the addition of peat moss, in an outdoor pot study to examine the adaptability of blueberries to upland soil conditions. Blueberry progenies ranged from essentially pure highbush (Vaccinium corymbosum L.) to interspecific hybrids containing varying amounts of evergreen (V. darrowi Camp), lowbush (V. angustifolium Aiton), black highbush (V. atrococcum Heller), and rabbiteye (V. ashei Reade) blueberry germplasm. Growth differences occurred due to soil types with Berryland sand producing the most growth although the effectiveness of peat moss diminshed with time. The three different complete fertilizer sources used had no 1273 1274 KORCAK significant effect on growth over the 3 years. Progenies displayed nutritional differences on the same scale as soils with a progeny containing V. corymbosum, V. darrowi V.atrococcum, and V. ashei growing best over all soils.Manganese was the only element to show consistent soil and progeny differences for leaves, roots and fruit. Levels of Mn and Al were generally higher in leaves and fruit than in the roots.

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