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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, 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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T. K. Hartz, P. R. Johnstone, and E. M. Miyao

The effect of K fertigation through buried drip irrigation on processing tomato (Lycopersicon esculentum Mill.) was evaluated in two California field trials in 2004, and soil K dynamics was investigated in greenhouse trials. Fertigation trials were conducted in fields with exchangeable soil K of 190 (site 1) and 270 mg·kg-1 (site 2), above the yield response threshold by traditional preplant or sidedress K application established by prior research. Two fertigation strategies were compared to an unfertilized control: continuous fertigation at 100 mg·L-1 K from early fruit set through early fruit color development, and weekly application of 40 kg·ha-1 K over the same period. In both treatments, a total of 200 kg·ha-1 K (from KCl) was applied. K fertigation significantly increased fruit yield at site 2, and improved fruit color at both sites. In the greenhouse experiments, fescue (Festuca arundinacea) was grown for 2 weeks atop columns of eight soils ranging from 120–380 mg·kg-1 exchangeable K; the columns were wetted from the bottom, by capillarity. The fescue roots were separated from the soil by a nylon fabric that prevented root penetration while allowing the penetration of root hairs, creating a two-dimensional root/soil interface. In all soils, fescue K uptake reduced soil exchangeable K only in the top 2 mm of the columns, suggesting that effective K diffusion was very limited. In columns of 200-mm height, applying 100 mg·kg-1 K in the water used to wet the soil had minimal impact on fescue K uptake. In columns of 15-mm height, this method of K application more than doubled fescue K uptake in all soils, suggesting that the effective limit of K movement was between 15-200 mm.

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

Diagnosis and Recommendation Integrated System (DRIS) norms were derived for processing tomato (Lycopersicon esculentum Mill.) from a 1993-94 survey of >100 fields in the Sacramento and San Joaquin Valleys of California. Relative foliar N, P, K, Ca, Mg, and S concentrations were expressed in ratio form, with DRIS norms calculated as the means of fields with fruit yield ≥90 Mg·ha-1. Norms were developed for three growth stages: first bloom, full bloom, and 10% of fruits ripe. Optimum foliar nutrient concentration ranges were calculated by regression analysis from DRIS nutrient indices of high-yield fields. These optimum ranges were in general agreement with existing empirically derived sufficiency ranges for N and P, higher for Ca, Mg, and S, and much lower for K. The relatively low foliar K levels observed were attributed primarily to the strongly determinate growth habit of currently used cultivars. In the fields sampled, yield-limiting nutrient deficiency appeared to be rare.

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T.K. Hartz, E.M. Miyao, and C. Giannini

Three field trials were conducted in central California in 1999 to assess the effects of transplant production and handling practices on yield, crop maturity, and fruit quality of processing tomato (Lycopersicon esculentum Mill.). For each trial, transplants of `Halley' tomato were obtained from a variety of commercial greenhouse transplant growers and subjected to various conditioning treatments during the week prior to planting. These treatments included N and/or P fertilization, varying temperature exposure or degree of water stress, or storage in the dark for 2 days before transplanting to simulate shipment from greenhouse to field. Nine transplant treatments (combinations of transplant source and conditioning treatment) were evaluated in each trial, with five 30 m long single-row plots per treatment arranged in a randomized complete-block design. Plots were mechanically harvested. Despite large differences among treatments in initial transplant characteristics (plant height, root cell volume, macronutrient content), there were no significant treatment differences in fruit yield in two trials; in the third trial, one treatment had significantly lower yield than the highest yielding treatment. In no trial were treatment differences in crop maturity (percent green fruit) or fruit quality (soluble solids content or juice color) significant. Across trials, the only transplant characteristic positively correlated with relative fruit yield (treatment yield/mean yield of that trial) was shoot P concentration, which varied among treatments from 1.3 to 11.7 g·kg–1.

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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, 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, P.R. Johnstone, E.M. Miyao, and R.M. Davis

Mustard (Brassica spp.) cover crop residue has been reported to have significant `biofumigant' action when incorporated into soil, potentially providing disease suppression and yield improvement for the succeeding crop. The effects of growing over-winter mustard cover crops preceding processing tomato (Lycopersicon escultentum Mill.) production were investigated in six field trials in the Sacramento Valley of California from 2002–04. A selection of mustard cover crops were compared to a legume cover crop mix, a fallow-bed treatment (the current grower practice in the region), and in two of the six trials, fumigation treatments using metam sodium. Mustard cover crops removed 115 to 350 kg·ha–1 N from the soil profile, reducing NO3-N leaching potential. Soil populations of Verticillium dahliae Kleb. and Fusarium spp. were unaffected by the cover crops, and there was no evidence of soilborne disease suppression on subsequent tomato crops. Mustard cover crops increased tomato yield in one field, and reduced yield in two fields. In one of two fields, metam sodium fumigation significantly increased tomato yield. We conclude that, while environmental benefits may be achieved, mustard cover cropping offers no immediate agronomic benefit for processing tomato production.

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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).