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Richard F. Smith, Louise E. Jackson, and Tiffany A. Bensen

Lettuce growers in the Salinas Valley are often not able to rotate to other crops due to economic pressure, such as high land rent. Winter-grown cover crops (October to March) provide a short-term rotation from lettuce and have been shown to reduce nitrate leaching by 75%. However, the use of winter-grown cover crops is low due to the extended time these cover crops tie up the ground. As a result, growers are interested in the potential of fall-grown cover crops (September to October) to reduce nitrate leaching through the winter. Fall-grown cover crops are incorporated into the soil prior to the onset of winter rains and leave the soil bare over the winter; however, during fall growth, the cover crop has the potential to capture excess nitrate that may leach during the fallow period, but how much has not been previously measured. A long-term trial was established in Fall 2003 using treatments of Indian mustard (B. juncea) `ISCI 61', White mustard (S. alba) `Ida Gold', Cereal rye (Secale cereale) `Merced', and a no cover crop control. All cover crops contained ≈224 kg·ha-1 N upon incorporation. Anion resin bags were installed 90 cm deep in the soil following incorporation to trap leaching nitrate; they were left in place until planting of the lettuce the following spring. First-year results indicated that the mustard cover crops and `Merced' rye all reduced nitrate leaching to the 90-cm depth by 67% to 82% over the bare fallow treatment. These results indicate that fall-grown cover crops have the potential to reduce nitrate leaching in lettuce production systems in the Salinas Valley.

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Richard Smith, Michael Cahn, Timothy Hartz, Patricia Love, and Barry Farrara

Intensive production of cool-season vegetables has contributed to nitrate pollution of groundwater along the central coast of California. Broccoli (Brassica oleracea L. var. italica), cabbage (Brassica oleracea L. var. capitata), and cauliflower (Brassica oleracea L. var. botrytis) are important crops in this region, but few data are available regarding the nitrogen dynamics of these cole crops under current production practices, and whether those practices are protective of groundwater. Monitoring was conducted in 14 commercial broccoli, 8 cabbage, and 8 cauliflower fields evaluating crop growth, rooting depth, N uptake and partitioning, patterns of soil N availability, and current N fertilization and irrigation practices. Aboveground biomass N at harvest averaged 367, 367, and 319 kg·ha−1 for broccoli, cabbage, and cauliflower, respectively, with mean N fertilization rates of 209, 280, and 256 kg·ha−1. The relatively small fraction of biomass N removed at harvest with cauliflower (23%) and broccoli (31%) resulted in a low partial N balance (PNB) of 30% and 57%, respectively, compared with cabbage (PNB of 70%). Rooting depth increased throughout the growing season, reaching ≈1 m by harvest, with about 70% of roots located in the top 40 cm in all crops. Soil mineral N (SMN; 0- to 30-cm depth) varied among fields, with the early-season median value of 18 mg·kg−1 declining to 5 mg·kg−1 by harvest. Seasonal N application was not correlated with early-season SMN. Irrigation applied, predominately through sprinklers, averaged >200% of estimated crop evapotranspiration. Substantial N mineralization from broccoli residue was observed within 2–3 months following fall incorporation, with potential NO3-N leaching losses exceeding 100 kg·ha−1 in both monitored fields. We conclude that improved irrigation management, adjusting N rates based on residual SMN, and employing a remediation practice such as cover cropping to limit winter NO3-N leaching losses could substantially improve N efficiency in cole crop production.

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Brian J. Pearson, Richard M. Smith, and Jianjun Chen

Hops (Humulus lupulus) is a perennial, herbaceous crop cultivated for its strobiles, or cones, which contain a resinous compound used for flavoring and aroma in food, tea, and beer. The United States is the second largest global producer of hops with greater than 15,000 ha in production. Increased demand for hop products has recently resulted in production of hops in nontraditional production areas (non-Pacific northwest U.S. region). To examine cultivation potential of hops within the southeastern United States, 60 hop rhizomes consisting of four varieties were transplanted into native, deep sand soil (Candler and Tavares-Millhopper soil series) within a protected, open-sided greenhouse and evaluated for growth, strobile yield, and brewing values for a period of 2 years. Plant bine length was recorded weekly for 20 weeks throughout year 1 with mean bine lengths of 609, 498, 229, and 221 cm at harvest for ‘Chinook’, ‘Columbus’, ‘Amalia’ and ‘Neo1’, respectively. Mean harvested strobile dry weight recorded for year 1 was 21.2, 17.9, 9.0, and 8.2 g/plant for ‘Columbus’, ‘Chinook’, ‘Neo1’ and ‘Amalia’, respectively. With the exception of ‘Neo1’, mean strobile mass was lower for all cultivars during year 2 with 16.6, 10.3, 25.8, and 2.6 g/plant for ‘Columbus’, ‘Chinook’, ‘Neo1’ and ‘Amalia’, respectively. Alpha acid concentrations by percentage strobile mass for year 1 were 6.8%, 9.7%, 3.8%, and 4.3% for ‘Columbus’, ‘Chinook’, ‘Amalia’, and ‘Neo1’, respectively. Alpha acids varied year 2 with concentrations of 4.8%, 10.4%, and 5.6% for ‘Columbus’, ‘Chinook’, and ‘Neo1’, respectively. Findings support viability of hop production in the southeastern United States and establish the benchmark for future varietal trialing investigations.

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Nicholas D. Warren, Richard G. Smith, and Rebecca G. Sideman

Living mulch systems allow cover crops to be grown during periods of cash crop production, thereby extending the duration of cover crop growth and associated beneficial agroecosystem services. However, living mulches may also result in agroecosystem disservices such as reduced cash crop yields if the living mulch competes with the crop for limiting resources. We examined whether the effects of an Italian ryegrass [Lolium multiflorum (Lam.) Husnot]–white clover (Trifolium repens L., cv. New Zealand) living mulch on broccoli (Brassica oleracea L. var. italica) yield and yield components were dependent on fertilizer rate in field experiments conducted in Durham, NH, in 2011 (Expt. 1) and 2012 (Expt. 2). Drip-irrigated broccoli was grown under a range of organic fertilizer application rates in beds covered with plastic, with and without a living mulch growing in the uncovered, interbed space. Broccoli yields were similar in the living mulch and bare soil controls under the highest rates of fertilizer application in Expt. 1. In Expt. 2, living mulch reduced broccoli yields from 28% to 63%, depending on fertilizer rate. Differences in leaf SPAD values suggest that yield reductions were attributable, in part, to competition for nitrogen; however, other factors likely played a role in determining living mulch effects. Despite yield reductions, the living mulch reduced the prevalence of hollow stem in broccoli in Expt. 1. Organic fertilizer may have inconsistent effects on broccoli yields in living mulch systems.

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Richard Smith*, Krishna Subbarao, Steve Koike, Steve Fennimore, and Adelia Barber

Growers in the Salinas Valley are not able to rotate away from lettuce to other crops such as broccoli, as often as would be desirable due to economic pressures such as high land rents and lower economic returns for rotational crops. This aggravates problems with key soilborne diseases such as Sclerotinia minor, Lettuce Drop. Mustard cover crops (Brassica juncea and Sinapis alba) are short-season alternative rotational crops that are being examined in the Salinas Valley for the potential that they have to reduce soilborne disease and weeds. Mustard cover crops have been have been shown to suppress various soilborne diseases and there are also indications that they can provide limited control of some weed species. However, no studies have shown the impact of mustard cover crops under field conditions on S. minor. In 2003 we conducted preliminary studies on the incidence of S. minor and weeds following mustard cover crops in comparison with a bare control or an area cover cropped to Merced Rye (Secale cereale). There was a slight, but significant reduction of S. minor infection in one of three trials following mustard cover crops. Mustard cover crops also reduced emergence of Shepherd's Purse (Capsella bursa-pastoris) and Common Purslane (Portulaca oleracea) these studies. Mustard cover crops have distinct nitrogen cycling characteristics. They were shown to reach a peak of release of nitrogen in 30 to 50 days following incorporation into the soil. The levels of nitrogen that are released by mustard cover crops were substantial and could be useful in nitrogen fertilizer programs for subsequent vegetable crops.

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Nicholas D. Warren, Rebecca G. Sideman, and Richard G. Smith

Tomato (Solanum lycopersicum) growers select cultivars based on a range of performance criteria. Currently, however, information regarding tomato cultivar performance in high tunnels is lacking. We conducted a tomato cultivar trial in an 1800-ft2 plastic-covered high tunnel in Durham, NH, with 15 indeterminate cultivars using organic fertilizers and pesticides. Tomatoes were grown in-ground in a randomized complete block design (n = 4) using raised beds with plastic mulch and drip irrigation. Marketable and unmarketable yield, several yield components, and susceptibility to two common diseases, leaf mold (Fulvia fulva) and powdery mildew (Oidium lycopersici or Leveillula taurica), were evaluated over a 3-year period. Differences between cultivars existed in all areas of interest, and year-to-year variation in performance was noteworthy in this experiment. ‘Geronimo’ consistently had among the highest yields, ‘Arbason’ and ‘Massada’ produced many individual fruit, and several cultivars including Rebelski, Massada, and Geronimo showed no signs of disease. Some cultivars such as Conestoga appeared susceptible to several different physiological disorders while others were relatively robust against this type of marketable yield reduction. Because we assessed multiple yield and quality variables and observed apparent trade-offs in several of these, we used radar plots to summarize and communicate the performance of each cultivar in an intuitive and comparable manner. Based on these data, several tomato cultivars appear particularly well suited for high tunnel production in northern New England.

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Richard McAvoy, Mariya Khodakovskaya, William Smith, Degang Zhao, Hong Liu, Hui Duan, and Yi Li

A 920 bp fragment of the ACC oxidase gene promoter from tomato (LEACO1) was used to drive GUS gene expression. The LEACO1 0.92kb fragment contained two stress-responsive short motifs; a 10 bp TCA motif (5'-TCATCTTCTT-3') twice (allowing two substitutions) and an 8 bp element (5'-AA/TTTCAAA-3') once. The TCA motif is found in over 30 stress- and pathogen-inducible genes while the 8 bp element is necessary for ethylene-response in the carnation GST1 and the tomato E4 gene promoters. Previously in chrysanthemum, cytokinin regulation with LEACO1 0.92kb produced dramatic increases in lateral branching and bud initiation. Tobacco plants carrying LEACO1 0.92kb –GUS were used to examine the response of the LEACO1 0.92kb promoter to various hormones and hormone inhibitors. GUS activity in LEACO1 0.92kb –GUS plants was detected in leaves and stems, but not roots. High expression was detected in shoots with the apical bud intact, but GUS activity decreased with the apical bud removed. Applying IAA to the shoot apex after removing the apical bud, restored GUS activity. However, the IAA transport inhibitor TIBA reduced GUS activity in shoots with intact apical buds, and in IAA-treated shoots with excised buds. In shoots with excised apical buds, GUS activity increased when the ethylene precursor ACC was applied, but decreased in intact shoots when the ethylene biosynthesis inhibitor AOA was applied. These data suggest that auxins produced in the apical meristem are capable of regulating LEACO1 0.92kb activity, probably through auxin-induced ethylene biosynthetic pathway activity.

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Howard F. Harrison, Judy A. Thies, Richard L. Fery, and J. Powell Smith

A preliminary screening experiment was conducted to evaluate 47 cowpea [Vigna unguiculata, (L.) Walp.] genotypes for use as a weed-suppressing cover crop. Lines evaluated in this study included forage varieties, PI accessions, experimental breeding lines, and land races of unknown origin. Of these, 11 were selected for further testing on the basis of vigorous growth and weed-suppressing ability. In a field experiment repeated over 4 years, the selected genotypes were not different from the leading cover crop cultivar, `Iron Clay', in biomass production. Vigor ratings, vine growth ratings, and canopy widths of some genotypes exceeded those of `Iron Clay'. Vigor ratings and canopy measurements were efficient selection criteria that could be useful for breeding cover crop cowpea cultivars. All selections except an African cultivar, `Lalita', were highly resistant to southern root knot nematode [Meloidogyne incognita (Kofoid and White) Chitwood], and the genotypes varied in seed size, photoperiod, and response to diseases.

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Howard F. Harrison, Judy A. Thies, Richard L. Fery, and J. Powell Smith

A preliminary screening experiment was conducted to evaluate 47 cowpea [Vigna unguiculata (L.) Walp.] genotypes for use as a weed-suppressing cover crop. Of these, 11 were selected for further testing on the basis of vigorous growth and weed-suppressing ability. In a field experiment repeated over 4 years, the selected genotypes were not different from the leading cover crop cultivar `Iron Clay' in biomass production. Vigor ratings, vine growth ratings, and canopy widths of some genotypes exceeded those of `Iron Clay' Vigor ratings and canopy measurements were efficient selection criteria that could be useful for breeding cover crop cowpea cultivars. All except one selection were highly resistant to southern root knot nematode [Meloidogyne incognita (Kofoid and White) Chitwood], and the selections varied in seed size, photoperiod, and response to foliar diseases.

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Howard F. Harrison Jr., D. Michael Jackson, Judy A. Thies, Richard L. Fery, and J. Powell Smith