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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 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 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 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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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 J.P. Mitchell

The rate of N mineralization from 35 samples of manure or compost was estimated by both aerobic laboratory incubation and lath house pot studies at Davis, Calif., in 1996–97. Each manure and compost sample was mixed at 2% by dry weight with a 1 loam soil: 1 coarse sand blend. The amended soil blends were moisture equilibrated under 0.025-MPa pressure then incubated aerobically at constant moisture at 25 °C for 3 (1996) or 6 months (1997); subsamples were collected monthly (1996) or bimonthly (1997) for mineral N determination. Four-liter pots were also filled with the amended soil blends and seeded with fescue (Festuca arundinacea). The pots were watered but not fertilized for 16 (1996) or 18 (1997) weeks in a lath house at ambient summer conditions. N mineralization from the pot study was calculated from total fescue biomass N plus mineral N from pot leachate, minus those quantities in pots of the unamended soil blend. N mineralization rate estimates from the two techniques were highly correlated (r 2 = 0.79). Green waste composts typically mineralized <5% of total N, manure composts 5% to10%, and manures (poultry, dairy, and feedlot) 7% to 20%. After 4 months of incubation, N mineralization rate (expressed as percent of total N per month) from the composts and manures was similar to that of the unamended soil blend.

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S. Castro Bustamante and T.K. Hartz

Organic processing tomato (Solanum lycopersicum L.) production is a significant industry in California, yet little nitrogen (N) fertility research is available to guide N management. A total of 37 certified organic processing tomato fields in the Sacramento Valley of California were monitored during the 2012 and 2013 production seasons, with two objectives: 1) to document current N management practices and 2) to investigate the utility of early-season soil and plant N monitoring techniques in predicting seasonal crop N sufficiency. Between ≈3 and 11 weeks after transplanting (WAT) soil mineral N (SMN), leaf N and petiole NO3-N were determined every other week. In 22 fields, whole plant N concentration at ≈11 WAT was determined as a measure of crop N sufficiency. Growers were surveyed regarding N management practices used and fruit yields achieved. Net N mineralization (Nmin) was measured for 20 fields soils by aerobic laboratory incubation. Carbon mineralization (Cmin) in 24 hours following rewetting of air-dried soil and water extractable organic nitrogen (WEON) and carbon (WEOC) were also determined and evaluated as predictors of Nmin. Nitrogen management was primarily based on the application of manure or manure compost in the fall. Organic fertilizers were applied mainly in spring (pre- and post-transplanting). SMN in the top 60 cm at 3 WAT ranged from 6 to 32 mg·kg−1. About 30% of fields were N deficient by 11 WAT. Sensitivity analysis showed that SMN (whether measured from 0 to 30 or 0 to 60 cm) and leaf N at 5 WAT correctly predicted late-season plant N status in >60% of the fields. Nmin in 28 days ranged from 8 to 31 mg·kg−1, representing an average of 2% of total soil N. Correlation between Nmin and Cmin was weak (r = 0.44, P = 0.051) while stronger correlations were observed between Nmin and WEOC, WEON and total soil N (r = 0.63, 0.61 and 0.51, respectively, all P < 0.03). A multiple linear regression model that used 3 WAT SMN (0–30 cm) and WEON as independent variables improved Nmin prediction (adj. R 2 = 0.67). Significant fruit yield increase with sidedress N application of feather meal at 5–6 WAT was observed in 2 of 4 field trials, demonstrating the ability to remedy a soil N limitation identified by early-season N monitoring.

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S.J. Breschini and T.K. Hartz

Trials in nine commercial celery (Apium graveolens L.) fields were conducted between 1997-99 to evaluate grower drip irrigation management practices and their effects on yield and quality. Surface drip irrigation tapes with flow rates higher and lower than the grower-installed tapes were spliced into the field system; as the cooperating growers irrigated and applied N fertigation according to their routine practices these drip tapes delivered either more or less water and N than the field drip system. Total grower water application during the drip-irrigated portion of the season ranged from 85% to 414% of seasonal reference evapotranspiration (ETo). Water volume per irrigation varied among fields from 1.8 to 3.8 cm, with irrigation frequency varying from an average of every other day to once a week. Grower management of drip irrigation was not consistently successful in maintaining soil water tension (SWT) in a desirable range. SWT was often below -30 kPa, and in some cases below -70 kPa. These transient stresses were more often a result of inappropriate irrigation frequency than applied water volume. In four of the fields plots receiving less water than that delivered by the field system produced equivalent marketable yield and quality, indicating a significant potential for water savings. An economically important incidence of petiole pithiness (collapse of parenchyma tissue) was observed in four fields. Infrequent irrigation under high ETo summer conditions, rather than irrigation volume applied, appeared to be the major factor in pith development. N fertigation amount and crop N status appeared to be unrelated to pithiness severity. We conclude that celery drip irrigation management could be substantially improved by maintaining a closer proportionality between irrigation and crop evapotranspiration (ETc), increasing irrigation frequency, and reducing volume per irrigation.