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Timothy K. Broschat

Spathiphyllum Schott. `Mauna Loa Supreme' and areca palm (Chrysalidocarpus lutescens H. Wendl.) were grown for 6 months in 3.5-liter containers using a pine bark–sedge peat–sand container medium or a native sand soil. Plants were fertilized with equivalent amounts of a 21N–3P–12K fertilizer applied weekly as a liquid, monthly as a soluble granular, bimonthly as a lightly coated controlled-release, or every 6 months as a heavily coated controlled-release fertilizer. All leachates were collected and analyzed weekly for NO3-N, PO4-P, and K. Amounts of all three nutrients leached per week varied considerably in response to fertilizer reapplications or high rainfall. Nitrate leaching generally decreased over time, PO4-P leaching increased, and K remained relatively constant. Shoot dry weights of spathiphyllum were equivalent for all fertilization methods, but areca palm shoot dry weights were highest with liquid fertilization and lowest with the soluble granular fertilizer. Nutrient leaching for all three ions was highest for the soluble granules and lowest for the two controlled-release formulations.

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Zhenli He, David. V. Calvert, Peter. J. Stoffella, and Mingkui Zhang

To evaluate effects of canopy and micro-irrigation under trees on accumulation and leaching of phosphorus (P) and heavy metals in agricultural sand soils, the horizontal and vertical variations of soil P and metals in a 408-m2 plot within a grove under grapefruit (Citrus paradisi Macf.) production near Fort Pierce, Fla., was examined. A high horizontal variation of labile soil P and metal concentrations was observed. Across the row, the highest values of pH, EC, water-soluble P, and all metals occurred in the soils under the canopies, and the lowest values occurred in the soils near the water furrow or the midway of the inter-row. Along the grapefruit row, the highest values of many measured variables occurred along the northern side of the citrus tree and close to the emitter. The downward movement of P, Cu, and Zn in the soils was more significant in the soils in open areas (near the water furrow and midway of inter-neighboring trees) than those under the canopies. The differences in labile P and metal spatial distributions in the soils were related to the location of emitter fertigation and differences in rainfall-induced leaching in the field. The results suggest that applying fertilizers to sites under the canopy rather than the spaces between the trees can minimize leaching losses of nutrients.

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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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Kimberly A. Williams and Paul V. Nelson

Soilless container root media have little capacity to retain P, and preplant amendments of triple superphosphate (TSP) and water-soluble fertilizer (WSF) P applications are readily leached from them. A soilless medium modified with Al2(SO4)3 was tested to reduce such P losses. Aluminum sulfate solutions were applied to a 70 sphagnum peat: 30 perlite (v/v) medium to result in 0.32, 0.96, and 1.92 kg Al/m3 and dried at 70C. Adsorption isotherms (25C, 0 to 500 mg P/liter) showed that P retention increased as the rate of Al addition increased. In a greenhouse study, plants of Dendranthema ×grandiflorum (Ramat.) Kitamura `Sunny Mandalay' were grown in Al-modified media and an unmodified medium in factorial combination with P from preplant amendment of 0.1 kg TSP-P/m3, or P applied at each watering as WSF at rates of 5.5 or 21.8 mg P/liter. The two highest rates of Al were excessive and resulted in low pH and excessive soluble Al levels in the root medium solution early in the cropping cycle, which were detrimental to plant growth. When the root medium was modified with 0.32 kg Al/m3, soluble Al levels in medium solution were not significantly different than in the unmodified control. TSP-P that leached was substantially reduced by the addition of Al, yet sufficient P was released throughout the cropping cycle for adequate plant growth. Plants grown in Al-modified medium with 0.1 kg TSP-P/m3 did not differ from control plants in unmodified medium + 0.27 kg TSP-P/m3 and were larger than plants grown in unmodified medium + 0.1 kg TSP-P/m3. Aluminum modification of the root medium substantially reduced P leaching when used with WSF containing P. In addition, growth of plants in unmodified medium fertilized with 5.5 vs. 21.8 mg P/liter was similar.

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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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J.E. Ells, A.E. McSay, P.N. Soltanpour, F.C. Schweissing, M.E. Bartolo, and E.G. Kruse

Water and nitrogen (N) are major inputs in the production of onions in the Arkansas Valley of Colorado. Because nitrates move with irrigation water, the effect of different rates of application of both N fertilizer and water on nitrate leaching were studied simultaneously. After a 2-year field study (1990-1991), it was concluded that >50 t·ha-1 of onions could be obtained without any N fertilizer when >42 ppm of nitrate nitrogen (NO3-N) were initially present in the top 33 cm of soil and up to 112 cm of irrigation water was applied. Total onion yield was not improved by applying more than the calculated irrigation requirement. The 2-m profile of soil under these experiments was found to contain >1400 kg·ha-1 of residual NO3-N prior to fertilizer treatments. When twice the estimated irrigation requirement was applied, >1000 kg·ha-1 of NO3-N was unaccounted for and presumed to have been mostly leached below the 2-m profile and partly denitrified. In both years, the onions were planted on land that had been fallowed the previous season, which does not help explain the presence of the high levels of nitrates found in the soil profile. It was concluded that sound water and N management practices in onion fields are crucial for preservation of water quality.

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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.