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T.K. Hartz

Trials were conducted under California field conditions examining the impact of drip irrigation and nitrogen fertigation regime on in-season NO3-N leaching losses. Six field studies were conducted, 4 on tomato and 2 on pepper. Seasonal fertigation ranged from 0-440 kg N/ha; irrigation was applied 3X per week, with leaching fractions of 10-25% of applied water. NO3-N leaching losses were estimated both by suction lysimetry and the use of buried anion resin traps. A similar pattern was seen in all trials. From transplant establishment until early fruit set soil solution at 0.8 m had relatively high NO3-N concentration (>30 mg/liter), which declined as the season progressed; in the month before harvest soil solution NO3-N at 0.8 m was consistently below 10 mg/liter (tomato) and 15 mg/liter (pepper) in appropriately fertilized plots. Seasonal NO3-N leaching estimates were generally below 25 kg/ha (tomato) and 35 kg/ha (pepper), with only modest differences among fertigation regimes. These results suggest that well managed drip irrigation can minimize in-season NO3-N leaching.

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S.J. Breschini and T.K. Hartz

Trials were conducted in 15 commercial fields in the central coast region of California in 1999 and 2000 to evaluate the use of presidedress soil nitrate testing (PSNT) to determine sidedress N requirements for production of iceberg and romaine lettuce (Lactuca sativa L.). In each field a large plot (0.2-1.2 ha) was established in which sidedress N application was based on presidedress soil NO3-N concentration. Prior to each sidedress N application scheduled by the cooperating growers, a composite soil sample (top 30 cm) was collected and analyzed for NO3-N. No fertilizer was applied in the PSNT plot at that sidedressing if NO3-N was >20 mg·kg-1; if NO3-N was lower than that threshold, only enough N was applied to increase soil available N to ≈20 mg·kg-1. The productivity and N status of PSNT plots were compared to adjacent plots receiving the growers' standard N fertilization. Cooperating growers applied a seasonal average of 257 kg·ha-1 N, including one to three sidedressings containing 194 kg·ha-1 N. Sidedressing based on PSNT decreased total seasonal and sidedress N application by an average of 43% and 57%, respectively. The majority of the N savings achieved with PSNT occurred at the first sidedressing. There was no significant difference between PSNT and grower N management across fields in lettuce yield or postharvest quality, and only small differences in crop N uptake. At harvest, PSNT plots had on average 8 mg·kg-1 lower residual NO3-N in the top 90 cm of soil than the grower fertilization rate plots, indicating a substantial reduction in subsequent NO3-N leaching hazard. We conclude that PSNT is a reliable management tool that can substantially reduce unnecessary N fertilization in lettuce production.

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Don Merhaut and Julie Newman

Four types of media [coir, 1 coir: 1 peat (by volume), peat, and sandy loam soil] were evaluated for their effects on plant growth and nitrate (NO 3) leaching in the production of oriental lilies (Lilium L.) `Starfighter' and `Casa Blanca'. Twenty-five bulbs were planted in perforated plastic crates and placed on the ground in temperature-controlled greenhouses. The potential for NO 3 leaching was determined by placing an ion-exchange resin (IER) bag under each crate at the beginning of the study. After plant harvest (14 to 16 weeks), resin bags were collected and analyzed for NO 3 content. Plant tissues were dried, ground, and analyzed for N content. Results indicated that the use of coir and peat did not significantly influence plant growth (shoot dry weight) relative to the use of sandy loam soil; however, substrate type influenced the amount of NO 3 leached through the media and N accumulation in the shoots for `Starfighter', but not `Casa Blanca'.

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Yingqian Lin, Alexa R. Wilson and Pascal Nzokou

). For example, the incorporation of cover crops has proven to significantly reduce nitrate leaching in rubber tree plantations ( Schroth et al., 2001 ) and in cereal grass-based systems where they are reported to be more efficient in the uptake of

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Richard Smith, Michael Cahn, Timothy Hartz, Patricia Love and Barry Farrara

been recognized as a nitrate leaching hazard ( Bakker et al., 2009b ; Congreves and Van Eerd, 2015 ; Everaarts, 2000 ). Yield-maximizing N fertilization rates for cole crops have been reported to range from <150 to >400 kg·ha −1 ( Bakker et al., 2009

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Jose E. Sanchez, Charles E. Edson, George W. Bird, Mark E. Whalon, Thomas C. Willson, Richard R. Harwood, Kadir Kizilkaya, James E. Nugent, William Klein, Alan Middleton, Theodore L. Loudon, Dale R. Mutch and Joseph Scrimger

Designing and implementing more productive, nutrient-efficient, and environmentally sound orchard management systems requires a better understanding of plant and soil responses to more biologically driven management practices. This study explored the effect of orchard floor and N management on soil organic C and N, populations of nematodes, NO3 leaching, and yields in tart cherry (Prunus cerasus L. `Montmorency') production. A baseline conventional orchard system consisting of an herbicide-treated tree row and a full rate of N fertilizer was compared to two modified-conventional and ten alternative orchard floor and N management systems. Living ground cover and the use of mulch with or without composted manure increased total C and the active C and N pools in the soil. For instance, supplemental mulch or mulch applied using a side-delivery mower increased soil C by >20% above the conventional baseline. The size of the active C pool increased 45% and 60% with the use of the species mix 2 ground cover and compost, respectively. Increases in the active N pool ranged from a low of 25% in the soils using mulch or a ground cover mix to a high of 60% when compost was used. As a result, the ability of these soils to provide N to growing plants was enhanced. Total soil N increased in the treatment using natural weeds as ground cover and the full rate of N fertilizer. It is likely that weeds were able to convert significant amounts of fertilizer N into organic forms. Increasing the active C and N pools stimulates microbial activity, and may favor populations of nonplant parasitic nematodes over plant parasitic species. Using a trunk-to-trunk cover crop mix under the cherry trees reduced NO3 leaching by >90% compared to a conventional, herbicide treated soil, even when N fertilizer was used at full rate. Nitrate leaching also dramatically diminished when N fertilizer was fertigated at a reduced rate or when compost was used as N source. Alternative orchard floor and N management did not reduce yields when compared to the baseline conventional treatment.

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Hagai Yasuor, Alon Ben-Gal, Uri Yermiyahu, Elie Beit-Yannai and Shabtai Cohen

, NO 3 -N leaching was found to be the primary N loss pathway at high N application rates in greenhouse vegetable cropping systems ( Min et al., 2011 ). Nitrate leaching and contamination of groundwater are expected to be even more problematic when

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Youssef Rouphael, Giampaolo Raimondi, Rosanna Caputo and Stefania De Pascale

. 103 17 25 Thompson, R.B. Gallardo, M. Rodríguez, J.S. Sánchez, J.A. Magán, J.J. 2013 Effect of N uptake concentration on nitrate leaching from tomato grown in free-draining soilless culture under Mediterranean conditions Sci. Hort. 150 387 398 Walinga

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Eric B. Brennan

alone would be more than twice the annual harvested area for all vegetables in the Salinas Valley! That is a lot of land, labor, fertilizer, tillage, and potential nitrate leaching and carbon emissions depending on how these vegetables are grown and

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Aaron Heinrich, Richard Smith and Michael Cahn

International, Gaithersburg, MD Bouyoucos, G.J. 1962 Hydrometer method improved for making particle size analysis of soil Agron. J. 54 464 465 Breschini, S.J. Hartz, T.K. 2002 Presidedress soil nitrate testing reduces fertilizer use and nitrate leaching hazard