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Rebecca A. Kraimer, William C. Lindemann, and Esteban A. Herrera

From March through June 1996, 15N-labeled fertilizer was applied to mature pecan trees [Carya illinoinensis (Wangehn.) K. Koch] in a commercial orchard to determine the fate of fertilizer-N in the tree and in the soil directly surrounding the tree. The concentrations of 15N and total N were determined within various tissue components and within the soil profile to a depth of 270 cm. By Nov. 1996, elevated levels of 15N were greatest at depths just above the water table (280 cm), suggesting a substantial loss of fertilizer-N to leaching. Recoveries of 15N from tissue and soil at the end of 1996 were 19.5% and 35.4%, respectively. Harvest removed 4.0% of the fertilizer-N applied, while 6.5% was recycled with leaf and shuck drop. In 1997, with no additional application of labeled fertilizer, the tissue components continued to exhibit 15N enrichment. By the end of the 1997 growing season, 15N levels decreased throughout the soil profile, with the most pronounced reduction at depths immediately above the water table. Estimated recoveries of 15N from pecan tissue (excluding root) and soil at the end of 1997 were 8.4% and 12.5%, respectively. In 1996 and 1997, 15N determinations indicated an accumulation of fertilizer-N in the tissues and a loss of fertilizer-N to the groundwater. Early spring growth, flowering, and embryo development used fertilizer-N applied the previous year, as well as that applied during the current year.

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Natalie Anderson and David H. Byrne

Poor germination in Rosa spp. has hindered breeding programs for years. Several methods exist to increase germination of rose seed. Unfortunately no consensus exists on the best method, or if any one method is best for all rose types. Rose seeds from a R. wichuraiana × Old Blush hybrid were broken into 3 replications with an average of 400 seeds per replication. Seeds were leached at room temperature with tap water for a period of 0, 3, 7, or 14 days. Constant filtration and aeration were supplied. After leaching, seeds were placed on either moist milled sphagnum moss or agar. Seeds were then placed in a cold stratification (≈2.8 °C) treatment for 8 to 12 weeks. Individual seedlings were planted when a root was visible. The combination of no leaching plus the moist milled sphagnum moss treatment significantly increased germination over leaching for 3 or more days and agar.

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Cale A. Bigelow, Daniel C. Bowman, and D. Keith Cassel

sand-based rootzones are specified for golf course putting greens because they resist compaction and maintain drainage, even under heavy traffic. Although sands provide favorable physical properties, nutrient retention is generally poor and soluble nutrients like nitrogen (N) are prone to leaching. Laboratory experiments were conducted to evaluate several inorganic soil amendments (clinoptilolite zeolite (CZ), diatomaceous earth, and two porous ceramics), which varied in cation exchange capacity (CEC), and sphagnum peat for their ability to limit N leaching. Columns (35 cm tall × 7.6 cm diameter) were filled with 30 cm of sand-amendment mixtures (8:2 v/v) and NH4NO3 was applied in solution at a N rate of 50 kg·ha-1. Leaching was initiated immediately using 2.5 pore volumes of distilled water in a continuous pulse. Leachate was collected in 0.1 pore volume aliquots and analyzed for NH4 +-N and NO3 --N. All amendments significantly decreased NH4 + leaching from 27% to 88% which was directly proportional to the CEC of the amendments. By contrast, NO3 - losses were consistently high, and no amendment effectively decreased loss compared to nonamended sand. Two amendments with the highest CECs, CZ and a porous ceramic, were selected to further study the effects of amendment incorporation rate, depth, and incubation time on N leaching. Ammonium but not NO3 - leaching was decreased with increasing amendment rate of both products. At 10% amendment (v/v) addition, only 17% to 33% of applied NH4 + leached from the amended sands. Depth of amendment incorporation significantly affected NH4 + leaching, with uniform distribution through the entire 30 cm tall column being more effective than placement within the upper 2.5 or 15 cm. Allowing the NH4NO3 to incubate for 12 or 24 hours following application generally did not affect the amount leached. These results suggest NH4 +-N leaching is inversely related to CEC of the root-zone mixture and that uniform distribution of these CEC enhancing amendments in the root-zone mixtures reduced N leaching to a greater extent than nonuniform distribution.

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Harvey J. Lang and Timothy R. Pannkuk

New Guinea impatiens `Barbados' (Impatiens ×hawkeri) were fertilized with solutions containing N at 6, 12, or 18 mmol·L-1 delivered from a drip irrigation system with either minimum leaching or standard leaching (0.3 to 0.4 leaching fraction). Irrigation was monitored and controlled by computers using microtensiometers placed in representative pots of each treatment. In two separate experiments, growth index, fresh mass, and dry mass were dependent upon both fertilizer concentration and irrigation treatment. Maximum growth overall was achieved at 12 mmol·L-1 N regardless of irrigation treatment; however, standard-leached plants receiving N at both 6 and 18 mmol·L-1 produced larger plants than did similarly fertilized minimum-leached plants. Leaf scorch, spotting, or marginal necrosis did not occur in any of the treatments. Leaf N, P, and K concentrations were highest in plants treated with N at 18 mmol·L-1, but Ca, Mg, and several micronutrients were highest in plants at 6 mmol·L-1 N. At the end of the cropping period for both experiments, growing medium electrical conductivity (EC) in the uppermost one-third layer of the pot was two to four times as high as that in the bottom two-thirds (root zone) layer. Root-zone EC ranged from 0.6 to 4.0 dS·m-1 and increased as fertilizer concentration increased. Standard leaching had little effect in reducing root-zone EC except in plants fertilized with N at 18 mmol·L-1. All plants continued to perform well and flower after 4 weeks in a simulated interior environment. Minimum-leach drip irrigation used ≈35% less solution than did standard irrigation with leaching, and eliminated N runoff.

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Ian A. Merwin, Tammo S. Steenhuis, and John A. Ray

Non-point source water pollution by agrichemicals is a recognized problem that has been studied in agronomic crop systems, and simulated using computer models or artificial soil columns, but rarely measured at field scale in orchards. For three growing seasons, we monitored the movement of nitrate and pesticide analogs and a widely used fungicide (benomyl) in two apple orchards under four different groundcover management systems (GMSs), including turfgrass, wood-chip mulch, residual pre-emergence herbicides, and post-emergence herbicide treatments. In subsoil lysimeter samplers at one orchard, we observed that nitrate and pesticide analogs leached more rapidly and in higher concentrations under herbicide plots compared with turfgrass plots. At another orchard where subsoil leaching and surface runoff of benomyl and nitrate-N were monitored in replicated GMS plots, we observed higher concentrations of benomyl (up to 30 μg·liter–1) and nitrate-N up to 50 μg·liter–1) leaching under herbicide GMS. The highest benomyl concentrations (375 μg·liter–1) and most frequent runoff of this pesticide were observed in the residual pre-emergence herbicide plots. Yearly weather patterns, irrigation, and development of different soil physical conditions under the four GMSs determined the relative magnitude and frequency of agrichemical leaching and runoff in both orchards. The agrichemicals apparently leached by mass flow in preferential flowpaths such as old root channels and soil cracks, while surface chemical runoff occurred mostly adsorbed on eroding soil sediment. These observations indicate that orchard GMSs can have a significant impact on leaching and runoff of pesticides and nutrients.

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Donald J. Merhaut and Julie P. Newman

Lilies are produced throughout the year in coastal areas of California.

Cultural practices involve daily applications of water and fertilizer, using both controlled release fertilizers (CRF) and liquid fertilizers (LF). However, many production facilities are in proximity to coastal wetlands and are therefore at greater risk of causing nitrogen pollution via runoff and leaching. Due to federal and state regulations, nurseries must present a plan of best management practices (BMPs) to mitigate nutrient runoff and leaching and begin implementing these practices in the next 2 years. In the following studies, we determined the potential for nitrate leaching from four different types of substrates (coir, coir: peat, peat, and native soil). There were four replications of each treatment, with a replication consisting of one crate planted with 25 bulbs. Two cultivars were used in two separate experiments, `Star Fighter' and `Casa Blanca'. Nitrate leaching was determined by placing an ion-exchange resin bag under each crate at the beginning of the study. After plant harvest (14–16 weeks), resin bags were collected and analyzed for nitrate content. Plant tissues were dried and ground and analyzed for nitrogen content. Based on the results of these studies, it appears that the use of coir, peat, and soil may not influence plant growth significantly. Substrate type may mitigate the amount of nitrate leaching through the media. However, the cultivar type may also influence the degree of nitrate mitigation, since leaching results varied between the two cultivars.

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Luther C. Carson and Monica Ozores-Hampton

nutrients in the root zone by physical barriers (coating), reduced solubility, or retaining nutrients in a less leachable form ( Trenkel, 2010 ). There are three subgroups of EEFs with different characteristics for horticultural production systems. Slow

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John W. Pote, Chhandak Basu, Zhongchun Jiang, and W. Michael Sullivan

Leaching-induced N losses have been shown to be minimal under turfgrasses. This is likely due to superior ability of turfgrasses to absorb nitrate. No direct evidence for this theory has been reported. The present study quantified nitrate leaching under miniature turf and nitrate uptake by individual turfgrass plants, and established the relationship between nitrate leaching loss and nitrate uptake rate. Seedlings of six Kentucky bluegrass (Poa pratensis L.) cultivars, `Blacksburg', `Barzan', `Connie', `Dawn', `Eclipse', and `Gnome', were planted individually in polystyrene containers filled with silica sand. The plants were irrigated with tap water or a nutrient solution containing 1 mm nitrate on alternate days and mowed to a 5-cm height once each week for 25 weeks. Nitrate leaching potential was then determined by applying 15 to 52 mL of nutrient solutions containing 7 to 70 mg·L-1 nitrate-N into the containers and collecting leachate. After the leaching experiment, plants were excavated, roots were washed to remove sand, and the plants were grown individually in containers filled with 125 mL of a nutrient solution containing 8.4 mg·L-1 nitrate-N. Nitrate uptake rate was determined by monitoring nitrate depletion at 24-hour intervals. Leachate nitrate-N concentration ranged from 0.5 to 6 mg·L-1 depending on cultivar, initial nitrate-N concentration, irrigation volume, and timing of nitrate-N application. Significant intraspecific difference in nitrate uptake rate on a root length basis was observed. Nitrate uptake rate on a per plant basis was significantly (P ≤ 0.05) and negatively correlated (r = -0.65) with nitrate leaching loss. The results provide strong evidence that superior nitrate uptake ability of turfgrass roots could reduce leaching-induced nitrate-N losses.

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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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Hudson Minshew, John Selker, Delbert Hemphill, and Richard P. Dick

Predicting leaching of residual soil nitrate-nitrogen (NO3-N) in wet climates is important for reducing risks of groundwater contamination and conserving soil N. The goal of this research was to determine the potential to use easily measurable or readily available soilclimatic-plant data that could be put into simple computer models and used to predict NO3 leaching under various management systems. Two computer programs were compared for their potential to predict monthly NO3-N leaching losses in western Oregon vegetable systems with or without cover crops. The models were a statistical multiple linear regression (MLR) model and the commercially available Nitrate Leaching and Economical Analysis Package model (NLEAP 1.13). The best MLR model found using stepwise regression to predict annual leachate NO3-N had four independent variables (log transformed fall soil NO3-N, leachate volume, summer crop N uptake, and N fertilizer rate) (P < 0.001, R 2 = 0.57). Comparisons were made between NLEAP and field data for mass of NO3-N leached between the months of September and May from 1992 to 1997. Predictions with NLEAP showed greater correlation to observed data during high-rainfall years compared to dry or averagerainfall years. The model was found to be sensitive to yield estimates, but vegetation management choices were limiting for vegetable crops and for systems that included a cover crop.