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William R. Graves, Sandra R. Anfinson, and Kathryn K. Lappegard

Scotch laburnum [Laburnum alpinum (Mill.) Bercht.], Amur maackia (Maackia amurensis Rupr. & Maxim.), and Chinese wisteria [Wisteria sinensis (Sims) Sweet] were inoculated with compatible rhizobia and treated with leaching fractions (LF) of 0, 0.2, and 0.4 using fertilizer solutions with 3.6 and 10.7 mol N/m3 for 10 weeks. LF did not affect plant dry mass, leaf area, or stem length. Growth was higher among plants provided 10.7 mol N/m3, but only plants provided 3.6 mol N/m3 formed root nodules. We conclude that growth is not reduced by eliminating leaching during the first 10 weeks of seedling development, and that application of 10.7 mol N/m3 prevents nodulation of these species.

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Michael D. Frost, Janet C. Cole, and John M. Dole

Improving the quality of water released from containerized production nurseries and greenhouse operations is an increasing concern in many areas of the United States. The potential pollution threat to our ground and potable water reservoirs via the horticultural industry needs to receive attention from growers and researchers alike. `Orbit Red' geraniums were grown in 3:1 peat:perlite medium with microtube irrigation to study the effect of fertilizer source on geranium growth, micronutrient leaching, and nutrient distribution. Manufacturer's recommended rates of controlled-release (CRF) and water-soluble fertilizers (WSF) were used to fulfill the micronutrient requirement of the plants. Minimal differences in all growth parameters measured between WSF and CRF were determined. A greater percentage of Fe was leached from the WSF than CRF. In contrast, CRF had a greater percentage of Mn leached from the system than WRF during the experiment. Also, regardless of treatment, the upper and middle regions of the growing medium had a higher nutrient concentration than the lower region of medium.

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Blaine R. Hanson, Jan Hopmans, and Jirka Simunek

Injection during the middle one-third or the middle one-half of the irrigation is recommended for fertigation using microirrigation. However, short fertigation events are commonly used by growers. This project investigated the effect of fertigation practices on nitrate availability and leaching. The first phase of the project (completed) determined nitrate distributions in the root zone for four microirrigation systems, three soil types, and five fertigation strategies using the HYDRUS-2D computer simulation model. Fertigation strategies included injecting for short time periods at the beginning, middle, and end of the irrigation cycle, respectively; injecting during the middle 50% of the irrigation cycle, and continuous injection. The second phase (ongoing) is investigating the distribution of nitrate, ammonium, urea, phosphate, and potassium around the drip line for selected Phase 1 scenarios. Phase 1 results showed less nitrate leached from the root zone for a 2-h injection time at the end of a long irrigation event compared to injection at the beginning and middle of a long irrigation event for surface drip irrigation. A more continuous fertigation resulted in a more uniform distribution of nitrate in the soil. The results were less conclusive for subsurface drip lines, due to upward movement of nitrate above the drip line. Little difference in nitrate leaching occurred for short irrigation events, regardless of fertigation strategy. Data analysis of the Phase 2 modeling is under way. The HYDRUS-2D model included partition coefficients for ammonium, phosphate, and potassium, and parameters for hydrolysis (conversion of urea to ammonium), nitrification, and denitrification.

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George L. Hosfield and Clifford W. Beninger

Seed coat color in dry bean (Phaseolus vulgaris L.) is determined by the presence or absence of tannins, flavonoids, and anthocyanins. Black beans contain three main anthocyanins that are responsible for their black seed coat color: delphinidin 3-O-glucoside, petunidin 3-O-glucoside, and malvidin 3-O-glucoside. Leaching of anthocyanins occurs in many black bean genotypes during thermal processing (i.e., blanching and cooking). Black beans that lose their dark color after processing are unacceptable to the industry. Since the marketability of black beans can be adversely affected by thermal processing, an experiment was conducted to ascertain whether pigment leaching was due to qualitative or quantitative changes in anthocyanins during processing. Four black bean genotypes that showed differential leaching of color were investigated. `Harblack' retains most of its black color after processing while `Raven' loses most of its color. `Black Magic' and `Black Jack' are intermediate between `Harblack' and `Raven' in processed color. Bean samples (119 ± 1.5 g) of the four genotypes were thermally processed in 100 x 75-mm tin cans in a pilot laboratory. Seed coats were removed from the cooked beans, freeze-dried, and placed in solutions of formic 10 acid: 65 water: 25 methanol to extract anthocyanins. The extracts were analyzed by HPLC. Although all genotypes retained some color, there were no detectable anthocyanins in seed coats of the cooked beans. In a second experiment, raw beans of each genotype were boiled in distilled water for 15 minutes. All four genotypes lost color during boiling, but `Harblack' retained most of its color and had a five-fold higher concentration of the three anthocyanins than did the other genotypes. `Harblack' may retain color better than other black beans because of physical characteristics of the seed coat.

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Catherine S.M. Ku and David R. Hershey

Single-pinched poinsettias (Euphorbia pulcherrima Willd. ex Klotzsch `V-14 Glory') received 210 mg·L-1 constant N fertigation from Hoagland solution with N sources of 100% NO3-N or 60% NO3-N : 40% NH4-N, P concentrations of 7.8 or 23 mg·L-1, and leaching fractions (LFs) of 0, 0.2, or 0.4. The P fertigation rates did not significantly affect plant growth measurements and N leaching. Shoot dry masses and leaf and bract areas of plants fertigated with 60% NO3-N were 11% to 26% greater than those fertigated with 100% NO3-N. Shoot dry mass at the 0 LF was 27% smaller than those at the 0.4 LF. The total amount of N applied via fertigation was 1.7 g at the 0 LF and 3.3 g at the 0.4 LF. Leachate N concentration ranged from 170 to 850 mg·L-1. Nitrogen recovery was 74% to 91%, and the percentage of fertigation N recovered in leachate ranged from 51% at the 0.2 LF to 74% at the 0.4 LF. With a 0.4 LF and 210 mg·L-1 N fertigation, 15% to 22% of the recovered N was found in the shoots, and 68% to 75% was found in the leachate. Even with a 0.2 LF, >50% of the N recovered was found in the leachate. Premium marketable quality poinsettia were produced with N at 210 mg·L-1 from 60% NO3-N : 40% NH4-N fertigation solution at the 0.4 LF. To reduce N leaching to the environment, good marketable quality poinsettias could be grown at a LF of ≤0.2 with 210 mg·L-1 N fertigation if quality irrigation water is available and if a small reduction in growth is acceptable.

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Jim Syvertsen and M.L. Smith

Effects of nitrogen (N) rate and rootstock on tree growth, fruit yield, evapotranspiration, N uptake, and N leaching were measured over a 2-year period. Four-year-old `Redblush' grapefruit trees on either sour orange (SO), a relatively slow-growing rootstock, or `Volkamer' lemon (VL), a more-vigorous rootstock, were transplanted into 7.9-m3 drainage lysimeter tanks filled with native sand and fertilized at three N rates. N rates averaged from about 14% to 136% of the recommended rate when trees were 5 and 6 years old. More N leached below trees on SO as trees on VL had greater N uptake efficiency. Canopy volume and leaf N concentration increased with N rate, but rootstock had no effect on leaf N. Fruit yield of trees on SO was not affected by N rate, but high N increased water use and yield for larger trees on VL. Canopy growth or yield per volume of water used (water use efficiency) was lowest at low N, but N use efficiency was highest at the low N rates.

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John A. Biernbaum, William R. Argo, Brian Weesies, Allen Weesies, and Karen Haack

A series of experiments was conducted to quantify the rate of nutrient loss from a container medium in a 15-cm-wide (1.3-liter) pot with a container capacity (CC) of 0.7 liter/pot under mist propagation and to determine the effectiveness of reapplying fertilizer to medium at 90% of CC with either top watering or subirrigation. Reducing the volume of water applied per day decreased the rate of nutrient leaching. Based on CC leached (CCL), the rate of nutrient loss was similar for all treatments. Differences in the rate of macronutrient removal from the media were measured, but, by 2 CCL, the concentration of all nutrients tested was below acceptable levels for the saturated media extract. With top watering, reapplying water-soluble fertilizer (WSF) at volumes under 0.2 liter/pot did not affect the nutrient concentration in the lower half of the pot at WSF concentrations up to 86 mol N/m3. Applying up to 0.8 liter/pot did increase nutrient concentrations in the lower half of the pot, but the media nutrient concentrations were lower than that of the applied WSF concentration. Applying WSF with subirrigation was limited by the moisture content of the media prior to the irrigation.

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Glenn R. Wehtje, Charles H. Gilliam, and Ben F. Hajek

Adsorption of 14C-labeled oxadiazon was evaluated in three soilless media and a mineral soil at concentrations between 0.1 and 100 mg·kg-1. Adsorption, which was at least 96%, was not influenced by absorbent type (medium vs. soil) or by oxadiazon concentration. However, desorption was greater in the media than in the soil. After five water extractions, 5.4% of the applied oxadiazon was recovered from media, but only 0.4% was recovered from the soil. In the soil and in two of the media, leaching with water failed to displace oxadiazon 2 cm below the surface to which it had been applied. No oxadiazon was detected below 4 cm in the third medium. Oxadiazon is sufficiently adsorbed to resist leaching-based displacement. Oxadiazon is not likely to enter the environment by escaping from treated containers. Chemical name used: 3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-di-methylethyl)-1,3,4-oxadiazol-2-(3H)-one (oxadiazon).

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Catherine S.M. Ku

Earlier study indicates that greenhouse crop production may be an overlooked point source of P pollution. A potential strategy to reduce P leaching may be to eliminate superphosphate amendment in soilless medium. Single-pinched `Amy' poinsettias (Euphorbia pulcherrima) in 15-cm pots were grown in a soilless medium of 3 peat: 1 perlite: 1 vermiculite (by volume). A treatment combination of preplant, finely ground, single superphosphate (SSP) (0N–8.8P–0K) amendment at 0 or 172 mg/pot and leaching fractions (LFs) of 0 and 0.2 were evaluated in a completely randomized design during a 10.5-week study. Plants received constant liquid fertigation with 7.8 mg P/liter and 210 mg N/liter from modified Hoagland solution #1. The total P applied via fertigation ranged from ≈38 mg at 0 LF to ≈50 mg at 0.2 LF. The leachate P concentration ranged from 4 mg/liter to 38 mg/liter. There was no significant difference in yield due to SSP and LF. Across all treatments, mean fresh mass was 36 g, mean dry mass was 5.9 g, mean leaf area was 980 cm2, and mean bract area was 1900 cm2.

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John D. Lea-Cox and James P. Syvertsen

Eighteen, 4-year-old Grapefruit (Citrus paradisi) cv. `Redblush' trees on either Volkamer lemon (C. volkameriana = VL) or Sour orange (C. aurantium = SO) rootstocks were grown in 7.6 kiloliter drainage lysimeters in a Candler fine sand (Typic Quartzipsamments), and fertilized with nitrogen (N) in 40 split applications at 76, 140 and 336 g N year-1 (= 0.2, 0.4 and 0.9 x the recommended annual rate). Labelled 15N was substituted for the N in a single fertigation at each rate at the time of fruit set the following year, to determine N uptake, allocation and leaching losses. “Nitrogen-uptake and allocation were primarily determined by the sink demand of fruit and vegetative growth, which in turn were strongly influenced by rootstock species. Larger trees on VL required at least 336 g N yr-1 to maintain high growth rates whereas smaller trees on SO of the same age only required 140 g N year-1. Of the 15N applied at the 336 g N rate to the SO trees, 39% still remained in the soil profile after 29 days. With optimally scheduled irrigations, 15N leached below the root zone was less than 3% of that applied after 29 days, regardless of rate. However, 17% of the applied 15N was recovered from a blank (no tree) lysimeter tank. Total 15N recovery ranged from 55-84% of that applied, indicating that a sizeable fraction of the 15N applied may have been lost through denitrification.