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T.K. Hartz, W.E. Bendixen, and L. Wierdsma

The utility of presidedress soil nitrate testing (PSNT) in irrigated lettuce (Lactuca sativa L.) and celery (Apium graveolens L.) production was evaluated in 15 commercial fields in California from 1996 to 1997. Fields were selected in which soil NO3-N (5- to 30-cm depth) was >20 mg·kg–1 at the time the cooperating grower made the first sidedress N application. The grower's N regime was compared with reduced N treatments established by reducing or eliminating one or more sidedress applications. All fields were sprinkler and/or furrow irrigated, with minimal in-season precipitation. Reductions in seasonal N application averaging 143 and 209 kg·ha–1 N in lettuce and celery trials, respectively, had no effect on marketable yield in any field. Crop biomass N at harvest in the lowest N treatment in each field averaged 94% (lettuce) and 88% (celery) of that in plots receiving the full grower N program. Based on controlled-environment aerobic incubation of soil from 30 fields in long-term vegetable rotations, in-season N mineralization averaged 1% to 2% of soil organic N. A soil NO3-N “quick test” procedure utilizing a volumetric extraction of field-moist soil and measurement by nitrate-sensitive colorimetric test strips was evaluated and proved to be a practical on-farm method to estimate soil NO3-N concentration. Lettuce midrib NO3-N concentration at cupping stage was poorly correlated with current soil NO3-N level. We conclude that PSNT can reliably identify fields in which sidedress N application can be delayed or eliminated without affecting crop performance.

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T.K. Hartz, P.R. Johnstone, and J.J. Nunez

Carrot (Daucus carota L.) root cracking and breakage during harvest and handling operations result in serious losses. The environmental and management factors affecting carrot cracking and breakage susceptibility were investigated in a survey of fields and a series of trials conducted in California from 2000–02. Roots, leaves and soil were collected from a total of 31 commercial fields of `Sugar Snax' carrot, and soil texture and plant and soil fertility status were determined. Soil moisture was monitored in 10 fields to determine whether irrigation management was correlated with root cracking susceptibility; in 4 of these fields roots were harvested both before 0800 hr and at 1300 hr on the same day to directly compare the effects of root water status on cracking. The effect of N fertilization on cracking and breakage was investigated in 5 field trials. The relative susceptibility of 10 cultivars to cracking and breakage was also compared. Cracking susceptibility was determined with an impact test, and breakage with a loading test. Roots were selected by size (18 to 24 mm diameter) and cooled to 5 °C before testing. The percentage of roots cracked in the impact test varied from 7% to 75% among survey fields. Initial root water potential was not correlated with cracking incidence. However, after hydrating roots to minimize differences in water potential among fields, cracking incidence was correlated with turgor potential (r = 0.41). Soil sand content and mean air temperature in the 30 days preceding harvest were also correlated with cracking (r = –0.48 and 0.36, respectively), suggesting that cracking susceptibility may be minimized in cool weather and in light-textured soil. Irrigation management in the final 30 days preceding harvest had no consistent effect on root cracking. Time of day of harvest had a small but significant effect, with roots harvested before 0800 hr being more crack-susceptible. N fertilization in excess of that required to maximize root yield significantly increased cracking susceptibility. Cultivars varied widely in cracking susceptibility, with less variation in tissue strength and stiffness. Removal of the periderm dramatically decreased susceptibility to both cracking and breakage.

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P.R. Johnstone, T.K. Hartz, and D.M. May

California melon (Cucumis melo) growers commonly apply calcium (Ca) fertilizers during fruit development to increase fruit firmness and improve storage life. Drip-irrigated field trials were conducted in central California in 2005 and 2006 to evaluate the efficacy of this practice on honeydew (C. melo Inodorus group) and muskmelon (C. melo Reticulatus group). In the 2005 honeydew trial, three weekly applications of 10 lb/acre Ca from calcium nitrate (CN), calcium thiosulfate (CTS), or calcium chloride (CC) were injected into the irrigation system during early melon development. In the 2006 muskmelon trial, two applications of 15 lb/acre Ca from CTS or CC were made early, or two applications of CC late, in melon development. The effect of these Ca fertigation treatments on fruit yield, soluble solids concentration, flesh firmness, and Ca concentration were compared with an untreated control receiving no Ca fertigation. Calcium fertigation had no effect on marketable yield, quality, or Ca concentration of honeydew or muskmelon fruit regardless of application timing or Ca source applied. Loss of firmness during either 2 weeks (honeydew) or 1 week (muskmelon) of postharvest storage was unrelated to Ca fertigation treatment and was not correlated with Ca concentration in fruit tissue. We conclude that under conditions representative of the California melon industry, Ca fertigation at typical application rates is ineffective in improving honeydew or muskmelon yield or fruit quality.

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T.K. Hartz, A. Baameur, and D.B. Holt

The feasibility of field-scale CO2 enrichment of vegetable crops grown under tunnel culture was studied with cucumber (Cucumis saivus L. cv. Dasher II), summer squash (Cucurbita pepo L. cv. Gold Bar), and tomato (Lycopersicon escukntum Mill. cv. Bingo) grown under polyethylene tunnels. The drip irrigation system was used to uniformly deliver a CO2-enriched air stream independent of irrigation. Carbon dioxide was maintained between 700 and 1000 μl·liter-1 during daylight hours. Enrichment began immediately after crop establishment and continued for ≈4 weeks. At the end of the treatment phase, enrichment had significantly increased plant dry weight in the 2 years of tests. This growth advantage continued through harvest, with enriched cucumber, squash, and tomato plots yielding 30%, 20%, and 32% more fruit, respectively, in 1989. In 1990, cucumber and squash yields were increased 20%, and 16%, respectively. As performed, the expense of CO2 enrichment represented less than a 10% increase in total preharvest costs. A similar test was conducted on fall-planted strawberries (Fragaria × ananassa Duch. cvs. Irvine and Chandler). Carbon dioxide enrichment under tunnel culture modestly increased `Irvine' yields but did not affect `Chandler'.

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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 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, 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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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, 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, 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.