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T.K. Hartz

Many factors influence appropriate drip irrigation management, including system design, soil characteristics, crop and growth stage, and environmental conditions. The influences of these factors can be integrated into a practical, efficient scheduling system that determines quantity and timing of drip irrigation. This system combines direct soil moisture measurement with a water budget approach using evapotranspiration estimates and crop coefficients.

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T.K. Hartz and C. Giannini

Windrows of municipal yard and landscape waste at three commercial composting sites in California were sampled at ≈3-week intervals through 12 to 15 weeks of composting to observe changes in physiochemical and biological characteristics of importance to horticulture. Initial C, N, P, and K content averaged 30%, 1.3%, 0.20%, and 0.9%, respectively. Carbon concentration declined rapidly through the first 6 to 9 weeks, while N, P, and K remained relatively stable throughout the sampling period. Few viable weed seeds were found in any compost. A high level of phytotoxicity, as measured by a tomato (Lycopersicon esculentum Mill.) seed bioassay, was observed at only one site; overall, the degree of phytotoxicity declined with compost age. Short-term net N immobilization (in a 2-week aerobic incubation) was observed in nearly all samples, with an overall trend toward decreased immobilization with increased compost age. In a 16-week pot study in which fescue (Festuca arundinacea Shreb.) was grown in compost-amended soil, net N mineralization averaged only 2% to 3% of compost total N content. Neither composting site nor duration of composting significantly affected either N mineralization rate or fescue growth. Growth of vinca (Catharanthus roseus Don.) in a blend of 1 compost : 1 perlite increased with increasing compost age. Overall, at least 9 to 12 weeks of composting were required to minimize the undesirable characteristics of immature compost.

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T.K. Hartz and J. Caprile

Sweet corn (Zea mays L.) cultivars carrying the sh2 mutation show poor seed vigor under stressful field conditions, requiring higher seeding rates to ensure stand establishment. The effects of sodium hypochlorite seed disinfestation, solid matrix priming (SMP), and seed-coating with Gliocladium virens Miller, Giddens & Foster to enhance emergence of sh2 sweet corn in controlled-environment cold stress tests and field trials were investigated. In combination with a chemical fungicide seed treatment (captan, thiram, imazalil, and metalaxyl), SMP significantly improved the percentage and rate of seedling emergence of `Excel' and `Supersweet Jubilee' in a cold stress test (in soil for 7 days at 10C, then 15C until emergence) but was inconsistent under field conditions, improving emergence in only one of four field trials. Sodium hypochlorite disinfestation was ineffective. Compared to a film-coated control, coating seeds with G. virens strain G-6 was highly effective in increasing emergence in two of three cultivars tested in cold stress tests in two soils, while strain G-4 was generally ineffective. In field trials, G-6 treatment significantly increased emergence over that of nontreated seed but was inferior to conventional fungicide treatment and conferred no additional benefit in combination with fungicide treatment. Overall, no seed treatment evaluated was an economically viable alternative for or supplement to chemical fungicide treatment. Chemical names used: cis-N-trichloromethylthio-4-cyclohexene-1,2-dicarboximide (captan); tetramethyl-thiuram disulfide (thiram); 1-[2-(2,4-dichlorophenyl)-2-(2-propenyloxy)ethyl]-1H-imidazole (imazalil); N-(2,6-dimethylphenyl)-N-(methoxyacetyl)-alanine methyl ester (metalaxyl).

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T.K. Hartz and S. Breschini

High rates of N fertilization of cool-season vegetables has contributed to NO3-N pollution of groundwater in the Salinas Valley of central California. Ten field demonstrations were conducted in 1999 to document the utility of presidedress soil NO3-N testing in maximizing N fertilizer efficiency in iceberg lettuce (Lactuca sativa L.). In each demonstration, a plot 36 beds wide × the entire field length was established in a commercial lettuce field. The cooperating growers applied 1 to 3 N sidedressings in these fields. Before each sidedressing the soil NO3-N concentration in the top 30 cm of the plot was determined by an on-farm quick test technique. If NO3-N was >20 mg·kg-1, no N was applied at that sidedressing; for NO3-N <20 mg·kg-1, ≈4 kg N/ha was applied for each milligram per kilogram below the 20 mg·kg-1 threshold. Plot yields, harvested by commercial crews, were compared to the yield of adjacent areas of the field that received the growers' full sidedress N regime. Across fields, seasonal sidedress N application in the PSNT plots averaged N only at 86 kg·ha-1, almost 60% less than the average N (212 kg·ha-1) applied by the growers. Yields in the PSNT plots averaged 1824 boxes/ha, compared with 1829 boxes/ha in the companion field plots. Whole leaf N concentration at heading was above published sufficiency standards in all PSNT plots. Evaluation of heads after 10 days of storage at 5 °C showed that sidedress N application rate did not affect visual quality, decay, or midrib discoloration. We conclude that PSNT can reliably be used to minimize wasteful sidedress N applications in lettuce.

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K.S. Mayberry and T.K. Hartz

Trials were conducted in California to evaluate techniques to extend storage life of netted muskmelons (Cucumis melo L.). The use of polyethylene bags, either as individual melon wraps or as liners for 18-kg commercial cartons, minimized water loss and associated deterioration of the fruit. Individual bags and carton liners were equally effective. A 3-minute dip in 60C water effectively checked surface mold development on wrapped fruits. Lower temperature and/or shorter exposure treatments were less effective. When applied in addition to hot water treatment, imazalil fungicide did not confer significant additional benefit. The combination of polyethylene bags and hot water treatment maintained high quality, marketable fruit for at least 28 days of storage at 3C,

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P.R. Johnstone and T.K. Hartz*

Heavy P fertilization of vegetable crops in the Salinas Valley of California have increased soil P levels, with > 50 mg·kg-1 bicarbonate-extractable P (Pbc) now common. To evaluate the response of lettuce (Lactuca sativa L.) to P fertilization in fields with elevated soil P levels, 12 trials were conducted in commercial fields during 2002-2003. Pbc at the trial sites varied from 53-171 mg·kg-1. In each trial four replicate plots receiving the growers' P application were compared with paired plots in which no P was applied. Leaf P was monitored at cupping stage and at harvest. At harvest mean whole plant mass and % of marketable plants were recorded. The correlation of Pbc to bioavailable P (Pba) was evaluated using 30 representative Salinas Valley soils; Pbc varied among these soils from 15-177 mg·kg-1. Pba was estimated by P adsorption on an anion resin membrane during a 16 h incubation. The effect of temperature on P bioavailability in 6 of these soils was estimated by conducting the Pba incubation at 5, 15 and 25 °C. A significant increase in lettuce yield with P fertilization was achieved at only one trial site, a spring planting where Pbc was 54 mg kg-1 ; at all other sites, including 3 with Pbc < 60 mg kg-1, P application resulted in no agronomic benefit. P application resulted in only a marginal increase in plant P uptake. Pba was highly correlated with Pbc (r = 0.89). Pba increased approximately 40% across soils with each 10 °C increase in soil temperature.

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T.K. Hartz and F.J. Costa

The production of cool-season vegetable crops in California's coastal valleys is characterized by high N input (typically 200–300 kg·ha–1 per crop), with two crops per year the norm. N. removal in harvested biomass seldom exceeds 100 kg·ha–1, suggesting a high degree of inefficiency in N management. A project was conducted on a commercial farm in Santa Maria to document the utility of intensive monitoring of soil and plant N status on improving N management. Eight fields were monitored through successive cropping cycles. Slow-release N fertilizer was applied preplant at 110–250 kg·ha–1 in subplots in each field to provide a reference of known N sufficiency against which to compare field productivity; these reference plots also received the same in-season fertilizer N applied in the balance of the field. N monitoring techniques included: in situ and controlled-environment soil incubation to estimate net N mineralization, soil NO3-N analysis by a “quick test” technique using colormetric test strips, and petiole sap analysis by NO3-N selective electrode. It was consistently demonstrated that, for lettuce, cauliflower, and broccoli, maximum crop productivity was obtained with seasonal N applications 50–100 kg N/ha less than the industry norm and that fertilizer cost savings more than offset the cost of crop and soil monitoring.

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T.K. Hartz and P.R. Johnstone

Limited soil nitrogen (N) availability is a common problem in organic vegetable production that often necessitates in-season fertilization. The rate of net nitrogen mineralization (Nmin) from four organic fertilizers (seabird guano, hydrolyzed fish powder, feather meal, and blood meal) containing between 11.7% and 15.8% N was compared in a laboratory incubation. The fertilizers were mixed with soil from a field under organic management and incubated aerobically at constant moisture at 10, 15, 20, and 25 °C. Nmin was determined on samples extracted after 1, 2, 4, and 8 weeks. Rapid Nmin was observed from all fertilizers at all temperatures; within 2 weeks between 47% and 60% of organic N had been mineralized. Temperature had only modest effects, with 8-week Nmin averaging 56% and 66% across fertilizers at 10 and 25 °C, respectively. Across temperatures, 8-week Nmin averaged 60%, 61%, 62%, and 66% for feather meal, seabird guano, fish powder, and blood meal, respectively. Cost per unit of available N (mineralized N + initial inorganic N) varied widely among fertilizers, with feather meal the least and fish powder the most expensive.

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T.K. Hartz, R. Smith, and M. Gaskell

Limited soil nitrogen (N) availability is a common problem in organic vegetable production that often necessitates additional N fertilization. The increasing use of drip irrigation has created a demand for liquid organic fertilizers that can be applied with irrigation. The N availability of three liquid organic fertilizers was evaluated in an incubation study and a greenhouse bioassay. Phytamin 801 contained fishery wastes and seabird guano, while Phytamin 421 and Biolyzer were formulated from plant materials. The fertilizers ranged from 26 to 60 g·kg−1 N, 8% to 21% of which was associated with particulate matter large enough to potentially be removed by drip irrigation system filtration. The fertilizers were incubated aerobically in two organically managed soils at constant moisture at 15 and 25 °C, and sampled for mineral N concentration after 1, 2, and 4 weeks. In the greenhouse study, these fertilizers and an inorganic fertilizer (ammonium sulfate) were applied to pots of the two organically managed soils with established fescue (Festuca arundinacea) turf; the N content of clippings was compared with that from unfertilized pots after 2 and 4 weeks of growth. Across soils and incubation temperatures, the N availability from Phytamin 801 ranged from 79% to 93% of the initial N content after 1 week, and 83% to 99% after 4 weeks. The plant-based fertilizers had significantly lower N availability, but after 4 weeks, had 48% to 92% of initial N in mineral form. Soil and incubation temperature had modest but significant effects on fertilizer N availability. Nitrification was rapid, with >90% of mineral N in nitrate form after 1 week of incubation at 25 °C, or 2 weeks at 15 °C. N recovery in fescue clippings 4 weeks after application averaged 60%, 38%, and 36% of initial N content for Phytamin 801, Phytamin 421, and Biolyzer, respectively, equivalent to or better than the N recovery from ammonium sulfate.