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C.M. Geraldson

The Earth Box is made of recycled plastic and designed to maintain a water table. A nutritional gradient is initiated with N–K fertilizer applied on the surface of the soil or media contained in the box. The box is designed to facilitate the functioning of a nutritional procedure known as the gradient concept. Basically, the concept synchronizes the nutrient/water input with removal, providing stability and nutritional predictability to the ionic composition of the soil solution. Crop response (yields and, especially, quality) with the Earth Box has been most positive, indicative of an optimal nutritional precision. The positive response is also evident in the field—average tomato yields in Florida more than doubled with the inception of the gradient-mulch system (1970s). the gradient as the dominant nutritional component eliminates the soil (type and/or quantity)–plant–season as nutritional variables. The Earth Box with minimal water, minimal pollution, minimal management, and the potential for a minimal unit cost could be the basis of a globally sustainable production system.

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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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L.P. Brandenberger, R.P. Wiedenfeld, and D. Makus

Fertilization programs used commercially for bell peppers (Capsicum annuum) in the subtropical Lower Rio Grande Valley of Texas may vary substantially from recommendations based on research. Therefore, a commercial fertilization program used on a significant fraction of the pepper production in this area was evaluated at two locations. Preplant soil tests showed NO3-N levels were low at one location and very high at the other. Nitrogen application where preplant soil NO3-N was low resulted in a six-fold yield increase (from 197 to 1203 kg·ha–1), and improvements in fruit weight, fruit volume, fruit density, wall thickness, wall strength, and carotenoid and chlorophyll a and b contents. No other nutrient application at either location or N application at the site where preplant soil NO3-N levels were high significantly affected yield by size class, fruit quality characteristics, storage properties, or mineral and organic components. Nitrogen application had the greatest effect on dry-weight accumulation and N uptake during fruit set and maturation when N demand was high. Where N responses were observed, N application increased total dry weight in plant and fruit by 150% and total N uptake by 186%, yet this increase amounted to a N fertilizer uptake efficiency of only 12%. Thus, N should be used judiciously to prevent pollution of drainage and ground waters.

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C.M. Geraldson

The conventional nutritional paradigm has been described as an empirical evaluation of how yield varies with nutrient application and is considered as a trial-and-error procedure. The gradient concept shifts the emphasis from variations in fertilizer application to one specific procedure designed to stabilize the ionic composition of the soil solution; thus providing the potential to enhance productivity beyond the limits of the trial-and-error procedure. By maximizing nutrient movement by diffusion and minimizing movement by mass flow (with the water), movement of nutrients and water to the root can by synchronized with removal by the root. A surface source of soluble nutrients (primarily N–K) in conjunction with a constant water table are the basic parameters. With the shift to a gradient-oriented procedure, commercial tomato yields in Florida (1970s) more than doubled. The Earth Box™, made of recycled plastic (manufactured by Laminations, Inc., Scranton, Pa.) is designed to maintain the parameters for a containerized gradient concept. Tomato yields have averaged 6 to 8 kg/plant (two plants/box). With the addition of side air spaces to the original air space between the media and the water table, the average yield increased by 20% to 30% with a maximum of 11.3 kg/plant (Fall 1996). With minimal water (for transpiration only), minimal management (maintaining the water table), minimal pollution (no leaching), and the associated nutritional stability, the containerized gradient concept has the potential to become a universal sustainable production system for the commercial grower as well as the home gardener.

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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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J.R. Heckman, W.T. Hlubik, D.J. Prostak, and J.W. Paterson

Research was conducted with sweet corn (Zea mays L.) to evaluate the presidedress soil NO3 test (PSNT) originally developed for use on field corn on a wide range of New Jersey soils. Soil NO3-N concentrations reflected differences in N availability due to manure or preplant N application. The relationship between soil NO3-N concentration and relative yield of marketable ears was examined using Cate–Nelson analysis to define the PSNT critical level. Soil NO3-N concentrations >25 mg·kg–1 were associated with relative yields at ≥92%. The success rate for the PSNT critical level was 85% for predicting whether sidedress N was needed. Including NH4-N in the soil analysis did not improve the accuracy of the soil test for predicting whether sidedress N was needed. Although the PSNT is quite accurate in identifying N-sufficient sites, it appears to offer only limited guidance in making N-fertilizer rate predictions. The PSNT is most useful on manured soils, which frequently have sufficient N. The test likely will help decrease the practice of applying “insurance” fertilizer N and the ensuing potential for NO3 pollution of the environment.

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S.B. Sterrett, C.P. Savage Jr., and H.E. Hohlt

Tomatoes (Lycopersicon esculentum Mill.) were grown under plastic culture on a Bojac sandy loam soil in 1991, 1992, and 1994 to determine influence of nitrogen rate at planting and water application scheduling by pan evaporation (PAN) on crop yield and fruit size. Marketable yield and percentage of large fruit was significantly increased in 1991, 1992, and 1994 as irrigation application increased from 0.5 to 1.0 or 1.5 PAN (one application per day). Nitrogen applications exceeding 168 kgha–1 resulted in lower yield and reduced fruit size in 1992. In 1994 (late planting followed by hot, dry growing season), yield was increased with increasing N to 213 kgha–1 with 1.0 PAN, but not influenced by N at 1.5 PAN. Residual soil nitrate concentration was increased with reduced irrigation or increased nitrogen application. Nutrient management plans to address non-point source pollution concerns of EPA will need to reflect crop irrigation needs to maintain yield and fruit size while minimizing nitrate accumulation within the soil profile.

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Clayton L. Rugh, Scott A. Merkle, and Richard B. Meagher

The use of plants to stabilize, reduce, or detoxify aquatic and terrestrial pollution is known as phytoremediation. We have employed a molecular genetic approach for the development of potentially phytoremediative species using a bacterial gene for ionic mercury detoxification. One gene of the bacterial mercury resistance operon, merA, codes for mercuric ion reductase. This enzyme catalyzes the reduction of toxic, ionic mercury to volatile, elemental mercury having far lower toxicity. Early attempts to confer Hg++ resistance to plants using the wildtype merA gene were unsuccessful. We hypothesized the highly GC-skewed codon usage was ineffective for efficient plant gene expression, and sequence modification would be necessary to confer merA gene activity and ionic mercury resistance in plants. A directed mutagenesis strategy is being used to develop modified merA gene constructs for transformation and analysis in plants species. Transgenic Arabidopsis and yellow-poplar plants having modified merA codon usage display Hg++-resistance. Arabidopsis plants with modified merA were observed to evolve ≈4 times the quantity of Hg0 from aqueous Hg++ in controlled experiments. In contrast, plants with unaltered merA coding sequences display unstable and inactivated gene expression. Our progress towards further merA modification and transgenic plant development will be reported. Additionally, the theoretical phytoremediative benefits and potential advantages of merA-expressing plant species will be discussed as part of our long-term goals.

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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.