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M.A. Maurer, F.S. Davies and D.A. Graetz

A field study was conducted on mature `Redblush' grapefruit trees (Citrus paradisi Macf.) on sour orange (Citrus aurantium L.) rootstock from 1991 to 1993 near Vero Beach, Fla. on poorly drained (flatwoods) soil to determine the effects of reclaimed water on leaf, soil and shallow well-water nutrients. Treatments consisted of a canal water applied based on soil moisture depletion, and reclaimed water applied at 23.1, 30.7 and 36.6 mm/wk. Reclaimed water treatments received supplemental fertilization in addition to the N present in the water. All treatments received about 130 kg/ha/yr N. Leaf tissue N, P, K, Ca, Mg and Na concentrations were similar for all treatments, but B concentrations were significantly higher for the reclaimed water treatments in 1991 and 1993. Soil P and Na concentrations also increased in the reclaimed water treatments. Water samples taken from shallow depth wells showed that reclaimed water treatments had lower levels of NO, compared to the control possibly due to leaching. Reclaimed water contained only trace or undetectable levels of heavy metals.

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S.B. Wilson, P.J. Stoffella and D.A. Graetz

Growth of golden shrimp plant (Pachystachys lutea Nees.) transplants was evaluated in media containing 0%, 25%, 50%, 75%, or 100% compost derived from biosolids and yard trimmings. A commercial coir- or peat-based media was amended with compost. As compost composition in the peat or coir-based media increased from 0% to 100%, carbon/nitrogen ratios decreased; and media stability, nitrogen mobilization, pH, and electrical conductivity increased. Bulk density, particle density, air-filled porosity, container capacity, and total porosity increased as more compost was added to either peat- or coir-based media. Plants grown in media with high volumes of compost (75% or 100%) had less leaf area and lower shoot and root dry weight compared to the controls (no compost). Regardless of percentage of compost composition in either peat or coir-based media, all plants were considered marketable after 8 weeks.

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S.B. Wilson, P.J. Stoffella and D.A. Graetz

Three perennial species, wine sage (Salvia spp. Sell x roenen Schultes `Van Houttei'), blue anise sage (Salvia gauranitica St.-Hil. Ex Benth. `Black and Blue'), and indigo spires salvia (S. longispicata Martius Galeotti × S. farinacea Benth. `Indigo Spires') were transplanted in containers filled with a biosolid-yard waste compost, a commercial peat-based mix, or a mixture of 1 compost: 1 peat-based mix by volume) and grown under ebb-and-flow, drip, or manual irrigation systems. Initial physical, chemical, and elemental analyses of the media indicated that compost alone had higher pH, electrical conductivity (EC), total porosity (TP), bulk density (BD), particle density (PD), N, C, P, Ca, Zn, Cu, Fe, and B; lower initial moisture, Mg and Al; and similar Mn contents than did the 100% peat-based medium. Heavy metal (Cd and Pb) contents of compost did not exceed EPA 503 Rule limits for biosolid usage. After 6 weeks, plants were measured for leaf nutrient content, growth (leaf and stem dry weights, stem lengths), and quality (number of flowers, leaf greenness, and subjective quality ratings). At 6 weeks, plants grown in 50% or 100% compost generally had higher leaf K, P, and Mn; similar N and Ca; and lower Mg, Fe, and Al content than plants grown in the 100% peat-based medium. Plants grown in media amended with compost generally produced similar or slightly smaller plants (stem weight, leaf weight, and stem length) than when grown in peat-based media. Plants irrigated by ebb and flow resulted in higher (`Van Houttei') or similar (`Indigo Spires') dry stem weights than plants irrigated manually or with drip irrigation. Plants grown in compost had leaf SPAD readings (leaf greenness), number of flowers, and visual quality ratings that were generally similar (`Indigo Spires') or slightly reduced (`Van Houttei') than plants grown in peat-based media. However, for each species (except for `Van Houttei' grown in 50% compost using drip irrigation), plants were of marketable quality, regardless of irrigation system or medium. This study suggests that compost may serve as a viable alternative substrate for peat in the production of containerized perennials using ebb-and-flow, manual, or drip irrigation systems.

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John D. Lea-Cox, James P. Syvertsen and Donald A. Graetz

15Nitrogen uptake, allocation, and leaching losses from soil were quantified during spring, for 4-year-old bearing `Redblush' grapefruit (Citrus × paradisi Macf.) trees on rootstocks that impart contrasting growth rates. Nine trees on either the fast-growing `Volkamer' lemon (VL) (C. volkameriana Ten & Pasq.) or nine on the slower-growing sour orange (SO) (C. aurantium L.) rootstocks were established in drainage lysimeters filled with Candler fine sand and fertilized with 30 split applications of N, totaling 76, 140, or 336 g·year-1 per tree. A single application of double-labeled ammonium nitrate (15NH 15 4NO3, 20% enriched) was applied at each rate to replicate trees, in late April. Leaves, fibrous roots, soil, and leachates were intensively sampled from each treatment over the next 29 days, to determine the fate of the 15NH 15 4NO3 application. Newly developing spring leaves and fruit formed dominant competitive sinks for 15N, accounting for between 40% and 70% of the total 15N taken up by the various treatments. Large fruit loads intercepted up to 20% of this 15N, at the expense of spring flush development, to the detriment of overall tree N status in low-N trees. Nitrogen supply at less than the currently recommended yearly rate of 380 g/tree exceeded the requirements of 4-year-old grapefruit trees on SO rootstock; however, larger trees on VL rootstock took up the majority of 15N from this rate over the 29-day period. Nitrogen-use efficiency declined with increasing N rate, irrespective of rootstock. The residual amounts of 15N remaining in the soil profile under SO trees after this time represented a significant N leaching potential from these sandy soils. Therefore, under these conditions, present N recommendations appear adequate for rootstocks that impart relatively fast growth rates to Citrus trees, but seem excessive for trees on slower-growing rootstock species.

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Leah E. Willis, Frederick S. Davies and D.A. Graetz

One-year-old `Hamlin' orange [Citrus sinensis (L.) Osb.] trees on sour orange rootstock (C. aurantium L.) were used to compare various fertigation frequencies and rates with application of granular materials. In Expt. 1, granular fertilizer was applied five times per year or liquid fertilizer was applied five, 10, or 30 times per year at 0.23 kg N/tree per year as an 8N-3.4P-6.6K formulation. In Expt. 2, an additional treatment of granular and liquid material was applied three times per year, but fertilizer rate and formulation were the same as in Expt. 1. Experiment 3 included the same application frequencies as Expt. 1, but with two rates of N (0.11 or 0.06 kg N/tree per year). Soil samples were taken from each treatment 1, 4, and 7 days after fertilization at depths of 0-15, 16-46, and 47-76 cm for nutrient analyses. Trunk diameter, shoot growth, and tree height were similar for all treatments 8 months after planting in Expts. 1 and 2, while trees in Expt. 3 had significantly less growth at the lower rate. Soil NH4-N and NO3-N concentrations for all liquid treatments within 1 week of fertilization were highest for the five times per year treatment at the 0- to 15-cm depth, but nutrient concentrations of all liquid treatments were similar at the other depths. For most dates and depths, NH4-N and NO3-N concentrations were similar for both fertilizer rates.

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Y.C. Li, P.J. Stoffella, A.K. Alva, D.V. Calvert and D.A. Graetz

Compost amendment to agricultural soils has been shown to either reduce disease incidence, conserve soil moisture, control weeds or improve soil fertility. Application of compost can range from 5 to 250 Mt·ha–1 (N content up to 4%). Large application of compost with high N and P levels may result in excessive leaching of nitrate, ammonium, and phosphate into groundwater. It could be a serious concern on the east coast of Florida with its high annual rainfall and shallow water table. In this study, five composts (sugarcane filtercake, biosolids, and mixtures of municipal solid wastes and biosolids) were collected from different facilities throughout Florida. Composts were applied on a surface of 15-cm sandy soil columns at the rate of 100 Mt·ha–1 on the surface basis and leached with deionized water by 300 ml·d–1 for 5 days (equivalent to 34 cm rainfall). The concentrations of NO3-N, NH4-N, and PO4-P in leachates reached as high as 246, 29, and 142 mg·L–1, respectively. The amount of N and P leached following 5-day leaching events accounted for 3.3% to 15.8% of total N and 0.2% to 2.8% of total P as inorganic forms.