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T.K. Hartz, J.E. DeVay, and C.L. Elmore

Soil solarization, alone and combined with metam sodium (MS), was evaluated as an alternative to methyl bromide and chloropicrin (MBC) fumigation, the standard soil disinfestation technique in the California strawberry (Fragaria ×ananassa Duch.) industry. Tests were conducted in two consecutive annual production cycles in Irvine, Calif., an environment representative of the coastal strawberry production area. Solarization treatments were applied from late July through September for October plantings. Treatments were equally effective in reducing baited populations of Phytophthora cactorum [(Lebert and Cohn) J. Schröt] (1989-90) and P. citricola Sawada (1990-91) when compared to pathogen survival in nontreated soil. Solarization and MBC reduced Verticillium dahliae Kleb inocnlnm in 1989-90, but MBC gave superior control in 1990-91. Solarization significantly controlled annual weeds, but was less effective than MBC. In 1989-90, solarization alone increased strawberry yield 12 % over the yield of nontreated plots; when combined with MS, yield increase was 29%, equivalent to that achieved with MBC fumigation. Treatments were equally effective in increasing yields in the 1990-91 test. Chemical names used: sodium N -methyldithiocarbamate (metam sodium), chloropicrin nitrotrichloromethane (chloropicrin).

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D.W. Burger, T.K. Hartz, and G.W. Forister

Seed germination and crop growth characteristics were determined for Tagetes spp. L. `Lemondrop', marigold; Catharanthus roseus Don. `Little Pinkie', vinca; Petunia hybrida Vilm. `Royalty Cherry', petunia; Dendranthema×grandiflorum (Ramat.) Kitamura `White Diamond', chrysanthemum; Pittosporum tobira Ait. `Wheeleri', sweet mock orange; Photinia ×fraseri Dress., photinia and Juniperus sabina L. `Moon Glow', juniper grown in various size containers containing blends of composted green waste (CGW) and UC Mix. Seed germination, plant height, and stem and root fresh and dry mass were lowest in unamended CGW. For most plants studied, a CGW: UC Mix blend containing at least 25% UC Mix was required for adequate growth and development. Germinating seeds and young seedlings were most adversely affected by unamended CGW. As plants grew and were transplanted into larger containers (10- and 15-cm pots, 530 and 1800 mL), they were better able to grow in media with higher CGW content.

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T.K. Hartz, M. LeStrange, and D.M. May

The response of bell pepper (Capsicum annuum L.) to five rates of N fertigation between 0 and 336 kg N/ha was studied at two drip-irrigated sites [Univ. of California, Davis (UCD) and West Side Field Station, Five Points (WSFS)] in California in 1992. Nitrogen application, in the form of a urea: ammonium nitrate mixture (UN-32), was applied in eight (WSFS) or 10 (UCD) equal weekly increments, beginning after transplant establishment. At both sites, fruit yield and mean fruit size peaked at 252 kg N/ha, with additional N retarding crop productivity. Maximum fruit yield was obtained by fertility treatments that maintained petiole NO3-N concentration >5000 μg·g-1 through the early fruit bulking period. Two techniques for monitoring crop N status, designed for field use, were evaluated. There was a close relationship between the NO3-N concentration of fresh petiole extracts, as measured by a portable, battery-operated nitrate selective electrode, and dry tissue analyzed by conventional laboratory technique (r2 = 0.89). Relative chlorophyll concentration, measured nondestructively by a dual-wavelength leaf absorbance meter, was poorly correlated with whole-leaf N concentration (r2 = 0.55). However, the ratio of such chlorophyll readings for a treatment compared to an in-field reference of known N sufficiency (252 kg·ha-1 treatment) showed promise as a technique for identifying N deficiency.

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T.K. Hartz, J.P. Mitchell, and C. Giannini

Nitrogen and carbon mineralization rates of 19 manure and compost samples were determined in 1996, with an additional 12 samples evaluated in 1997. These organic amendments were mixed with a soil: sand blend at 2% by dry weight and the amended blends were incubated at constant moisture for 12 (1996) or 24 weeks (1997) at 25 °C. Net N mineralization was measured at 4- (1996) or 8-week (1997) intervals, C mineralization at 4-week intervals in 1997. Pots of the amended blends were also seeded with fescue (Festuca arundinacea Shreb.) and watered, but not fertilized, for 17 (1996) or 18 weeks (1997); N phytoavailability was estimated from fescue biomass N and mineral N in pot leachate. An average of 16%, 7%, and 1% of organic N was mineralized in 12 weeks of incubation in 1996, and an average of 15%, 6%, and 2% in 24 weeks of incubation in 1997, in manure, manure compost, and plant residue compost, respectively. Overall, N recovery in the fescue assay averaged 11%, 6%, and 2% of total amendment N for manure, manure compost, and plant residue compost, respectively. Mineralization of manure C averaged 35% of initial C content in 24 weeks, while compost C mineralization averaged only 14%. Within 4 (compost) or 16 weeks (manure), the rate of mineralization of amendment C had declined to a level similar to that of the soil organic C.

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T.K. Hartz, R.F. Smith, and W.L. Schrader

California vegetable growers are adopting drip irrigation at an accelerating pace, which affords the opportunity for more exacting control of nitrogen nutrition. Consequently, the need for quick, accurate, grower-friendly techniques for monitoring nitrogen status in soil and plant material has increased. Three field monitoring techniques were examined in detail: the analysis of soil water samples drawn by soil solution access tubes (SSAT). leaf reflectance as measured by the Minolta SPAD 502 chlorophyll meter, and petiole sap analysis with a Horiba portable nitrate-selective electrode meter. Nitrate concentration in soil solution was highly stratified in drip-irrigated soils, both with regard to location in the field and position with respect to the drip line, making the use of SSAT technology impractical as a tool for routine N fertigation scheduling. Correlation of SSAT nitrate values to any measure of plant N status was poor. Similarly, leaf reflectance correlated poorly with any measure of tissue N in the crops examined. Nitrate content of petiole sap was highly correlated with conventional laboratory analysis of dry petiole tissue over a range of crops and nitrogen levels.

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T.K. Hartz, R. Mullen, M. Cahn, and G. Miyao

Trials were conducted in nine commercial processing tomato fields in California from 1994 to 1995 to assess the effects of potassium fertilization on fruit yield and quality. Sites were selected to represent a range of ammonium acetate extractable soil K levels (91 to 284 mg·kg–1, top 30 cm) and K release rates (K at 1.8 to 8.5 mg·kg–1·d–1). Potassium was applied in furrow or drip irrigation during the fruit bulking stage at seasonal rates from 90 to 135 kg·ha–1. Significant yield increase (4% to 24%) was observed at three of the four sites with extractable soil K <125 mg·kg–1 (K released at <3.1 mg·kg–1·d–1); no yield response was observed at the five sites with greater soil K supply. Fruit color and soluble solids content was unaffected by K fertilization at any site. Additionally, red fruit of two cultivars (`Halley' and `Heinz 8892') were collected from 80 commercial fields in 1995 and evaluated for soluble solids content, color (of a comminuted sample as well as visual ranking of internal and external ripening disorders), and tissue K concentration. Fruit K concentration was poorly correlated with any quality characteristic. We conclude that yield response to K fertilization can be adequately predicted by either soil test method and that K supply plays a relatively minor role in tomato fruit quality under representative field conditions.

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T.K. Hartz, K.S. Mayberry, M.E. McGiffen, M. LeStrange, G. Miyao, and A. Baameur

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T.K. Hartz, G. Miyao, R.J. Mullen, M.D. Cahn, J. Valencia, and K.L. Brittan

A survey of 140 processing tomato (Lycopersicon esculentum Mill.) fields in central California was conducted in 1996-97 to examine the relationship between K nutrition and fruit quality for processing. Quality parameters evaluated were soluble solids (SS), pH, color of a blended juice sample, and the percent of fruit affected by the color disorders yellow shoulder (YS) or internal white tissue (IWT). Juice color and pH were not correlated with soil K availability or plant K status. SS was correlated with both soil exchangeable K and midseason leaf K concentration (r = 0.25 and 0.28, p < 0.01) but the regression relationships suggested that the impact of soil or plant K status on fruit SS was minor. YS and IWT incidence, which varied among fields from 0% to 68% of fruit affected, was negatively correlated with K status of both soil and plant. Soil exchangeable K/√Mg ratio was the measure of soil K availability most closely correlated with percent total color disorders (YS + IWT, r = -0.45, p < 0.01). In field trials conducted to document the relationship between soil K availability and the fruit color disorders, soil application of either K or gypsum (CaSO4, to increase K/√Mg ratio) reduced YS and total color disorders. Multiple foliar K applications were effective in reducing fruit color disorders at only one of two sites. In no field trial did K application improve yield, SS, or juice color.

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T.K. Hartz, C. Giannini, E.M. Miyao, and J.G. Valencia

The effect of transplant production and handling practices on processing tomato growth, yield, and fruit quality were evaluated in five field trials in California. In 1999, processing tomato (Lycopersicon esculentum Mill. cv. Halley) transplants were obtained from a number of commercial transplant producers and taken to the Univ. of California-Davis (UCD) where treatments were imposed for 1 week prior to transplanting. Treatments included N and P fertilization, exposure to lath house or greenhouse temperature, withholding water, and storage in the dark for 2 days to simulate shipment from greenhouse to field. Nine treatments per site were compared in field trials at Yolo, Woodland, and Knights Landing. In 2000, transplants were grown at UCD under varying nutrient regimes, including P fertilization rates ranging from weekly application of 0 to 90 mg·L-1. Two commercial field trials comparing 8 treatments were conducted near Winters and Newman. Although transplant production and handling practices significantly influenced relative growth rate in the 3-4 weeks following transplanting in all 1999 trials, effects on fruit yield were minimal, with only one treatment at Woodland showing significantly lower yield and no treatment differences in crop maturity, fruit soluble solids, or juice color observed at any site. In 2000, plants receiving no weekly P fertilization showed slower growth in the 3 weeks after transplanting, but no treatment differences were observed after 6 weeks. Fruit yield, soluble solids content (°Brix) and juice color were unaffected by transplant treatment. We conclude that transplant production and handling practices tested had minimal differential effect on the subsequent field performance of processing tomato transplants in the Central Valley of California.

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T.K. Hartz, L.J. Kies, A. Baameur, and D.M. May

Application of DCPTA, as a seed treatment and a foliar spray, was evaluated for effects on productivity and fruit quality of processing tomato (Lycopersicon esculentum Mill.) and fresh-market pepper (Capsicum annuum L.). Two field trials for each crop were conducted in California during 1992. No DCPTA treatment was effective in increasing vegetative growth or fresh fruit yield of either crop at any site. Total soluble solids concentration and color of tomato fruits were unaffected by DCPTA, regardless of application method. We conclude that DCPTA is not a useful production aid for field-grown tomato or pepper. Chemical name used: 2-(3,4-dichlorophenoxy) triethylamine (DCPTA).