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C.M. Geraldson

A gradient concept was initiated and evaluated at the Gulf Coast Research and Education Center, Bradenton, during the 1960s as the nutritional component in a full-bed mulch system of production. Commercial tomato yields in Florida more than doubled with the shift to the gradient-mulch system. Conventionally, nutrients move to the root in the water by mass flow and thus are a function of water requirement. With the soil as the buffer component, nutrient input may or may not be synchronized with root removal. Movement with the gradient is by diffusion and the nutrient/water input is synchronized with rate of removal by the root. The limited buffer potential of the soil is replaced by the gradient with an unlimited buffer potential. Production in the field or a container has a maximum potential with the gradient procedure but can become limited in the field and a failure in the container with conventional procedure. The gradient requires minimal soil (a framework for the gradient) uses minimal water, creates minimal pollution, requires minimal management and provides a nutritional stability that has an unlimited productivity potential. The N–K banded on the soil bed surface in conjunction with a continuing water supply are the basic parameters of the gradient concept.

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Mary Lamberts and Judy Nothdurft

Southeastern Florida is underlain by the Biscayne Aquifer, an officially designated “drinking water quality aquifer.” This is the sole source of water for the more than 3.5 million residents of metropolitan Miami-Fort Lauderdale. Due to the unique nature of the soils in southern Dade County, Fla., most agricultural wells for both irrigation and mix-load activities have been exempt from casing and capping requirements. Wells associated with U-Pic stands need to be capped if children are allowed in fields. The county's Dept. of Environmental Resources Management (DERM) began a study of mix-load wells in the late 1980s. They concluded that surface materials, including agrichemicals, could drain directly into the aquifer. This was particularly true in vegetable fields because most are on leased land. In the mid 1990s, a program to develop voluntary guidelines to retrofit these mix-load wells was begun. Several growers met with DERM, the Florida Department of Environmental Protection and Extension, to finalize three basic designs. Extension hosted meetings and reviewed the brochure describing the retrofit program. In 1996, one area came under close scrutiny by the U.S. EPA for potential point-source pollution. These growers were made aware of the program and have retrofitted at least 95% of the wells in the most environmentally sensitive area.

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Heidi J. Johnson, Jed B. Colquhoun, and Alvin J. Bussan

There is significant interest from vegetable processors, growers, and consumers in organic sweet corn (Zea mays) production. Organic nitrogen (N) management is particularly challenging in high N consuming crops such as sweet corn because of the low N content and low N to phosphorus (P) ratios of organic soil amendments. Various management programs were compared to determine the optimal combination of soil amendments and green manure crops for organic sweet corn production. Alfalfa (Medicago sativa), rye (Secale cereale), and field pea (Pisum sativum) were used as green manure crops. Composted poultry manure and a high N content organic fertilizer were used as organic amendments. Ammonium nitrate was used in a conventional management program for comparison. Treatments were designed to deliver a full rate of N (150 lb/acre), a half rate of N (75 lb/acre), and to limit the amount of P applied. Phosphorus can become a source of pollution when applied to erodible soils, particularly when soils already contain excessive P. Sweet corn yield in many of the organic programs was highly variable among years while the yield was more consistent in the conventional program. This was attributed to differences in organic N mineralization in both the green manure crops and the amendments. The most stable yield from an organic treatment, among years, was achieved using the commercially available organic N fertilizer. Commercially available amendments were costly, and although organic sweet corn received a premium price in years when organic yields were lower, profit was reduced by the high cost of N management.

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George Hochmuth, Osmar Carrijo, and Ken Shuler

Tomato (Lycopersicon esculentum Mill.) was grown in southeastern Florida on sandy soils that tested very high in Mehlich-1 P to evaluate the yield response to P fertilization. One location was used in 1995–96, another in 1996–97. Prefertilization soil samples contained 290 (location 1) and 63 (location 2) mg·kg–1 Mehlich-1 P. Both soil test results were interpreted as very high in P, and P fertilizer was not recommended for the crop. Fertilizer treatments at both sites were 0, 25, 50, 100, 150, and 200 kg·ha–1 P. Neither total marketable yield nor yield in any fruit size category was affected by P fertilization in either season. Amounts of cull (undersized or misshapened) fruits increased quadratically with P fertilization in the second season. Whole-leaf P concentrations increased linearly or quadratically with P application, depending on sample periods, and were always above sufficiency values. Although many tomato growers apply P fertilizer irrespective of soil test recommendations, our results showed that added P was not needed on soils testing very high in P. Furthermore, withholding P applications to soils with high P concentrations will minimize potential P pollution of surface water and groundwater.

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Deborah M. Shuping and Jeffrey D. Zahner

Water conservation is making journal headlines nationwide because of drought, contamination, pollution, and over development. While the idea of xeriscaping began in the Western United States where landscapes can be truly dry, many water-saving principles apply to the Southeast, where home moisture problems and pest problems associated with moisture are a major problem. A year of drought maybe followed by three years of plentiful rainfall, and conditions are significantly different from the semi-arid regions of the country to which most of the present literature on water conservation is directed.

The purpose of this project was to provide information on water conservation to designers, landscape industry personnel, and homeowners in the Southeast. This was done by compiling recommendations based on research being conducted by professionals in building science, forestry, horticulture, entomology and landscape architecture.

An educational tool addressing the pressing national problem of water conservation with a regional emphasis, this project was designed to help readers increase landscape water efficiency by 30 to 50% while lowering maintenance costs and insuring greater survivability of landscape plants in times of water shortage. Through careful planning and design, economically attractive and aesthetically sound water conserving landscapes can be created.

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Wayne C. Porter and Richard L. Parish

Concerns over ground water, nonpoint pollution, and soil erosion have indicated a need for reduced use of preemergent herbicides and reduced tillage. This study was initiated to determine the feasibility of using postemergent, burndown herbicides under hooded sprayers in the production of southernpeas. Two rates of paraquat, glufosinate, and glyphosate were applied at two application timings. All herbicides controlled rice flatsedge but not goosegrass. Since an untreated strip was left surrounding the drill, complete weed control did not occur in this system. In most cases, delaying application of the herbicides by 2 weeks tended to result in lower yields. However, no differences from a delay in cleaning the hoed check were noted. Plots treated with paraquat at 1.0 pt/A – timing 1 and glufosinate at 7.0 lb a.i./A – timing 2 had yields lower than the hoed check. Based on this study, southernpeas can be grown successfully without the use of a preemergent herbicide by proper timing of a hooded application of a burndown herbicide with proper timing.

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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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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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C. M. Geraldson

The purpose of this study was to evaluate the commerical feasibility of a containerized gradient concept with relevance to water requirement, pollution potential, and production efficiency. Basic components included one-half cu ft of media/plant with 2 plants/rigid plastic container. Phosphorous, liming material and micronutrients were mixed in the media and the N-K was banded on the surface at both ends of the container which was protected by a plastic cover. Intermittent micro-irrigation was used to maintain either a lateral or vertical nutrient/moisture gradient. Variations in the media, the size and shape of the container, and the frequency and time of water applications were included in the evaluations. In the spring of 1991, 65 gallons of water was utilized to produce 22.9 lbs of marketable tomatoes/plant. Leaching was insignificant and the water required on an acre basis was projected as 4.8 acre inches with a 2000 plant population. The results indicate that the containerized gradient concept is potentially feasible as a sustainable production system.

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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.