Everglades Agricultural Area Research Articles

Spatial Distribution of Soil Nutrients in a Northern Everglades Marsh: Water Conservation Area 1

AbstractThe Florida Everglades developed as a nutrient‐poor, rain‐fed ecosystem. However, for the past 30 yr, the Everglades have received nutrient‐enriched surface water runoff from the adjacent Everglades Agricultural Area (EAA). This study examines the response of a pristine wetland, Water Conservation Area 1 (WCA 1), part of the northern Florida Everglades, to nutrient loading as documented by soil nutrient concentrations. During 1979 to 1988, WCA 1 received 138 t total P (TP) and 4919 t total N (TN), retaining 53% of the TP load and 58% of the TN load. Analyses of the spatial distribution of soil N and P showed steep gradients of TP along the western canal boundary, adjacent to inflow points importing EAA runoff. Surficial soils (0–10 cm depth) at interior marsh sites had a mean TP concentration of 368 mg kg−1, compared with 1028 mg kg−1 measured at sites adjacent to the western canal. Similar trends were observed for soil Ca and Mg, while C and N did not show the same boundary effects on spatial enrichment. Nutrient‐enriched sites also had higher porewater soluble reactive P (SRP; 0.15 mg L−1) and NH4‐N (1.65 mg L−1) than unenriched sites (SRP = 0.02 mg L−1, NH4‐N = 0.85 mg L−1). Of the 90 sites sampled, 66 sites consisted of sloughs and sawgrass (Cladium jamaicense Crantz); the remaining 24 sites were either cattail (Typha spp.) dominated or had a significant cattail presence. These 24 cattail sites were closest to the nutrient inflow areas and had the highest soil nutrient concentrations.

N and K Requirements of Carrot on Sandy Soils in Florida

Carrot production in Florida has been centered in two major organic-soil vegetable production areas. These areas are the Everglades Agricultural Area near Belle Glade, in southern Florida, and the Zellwood vegetable area in central Florida. The state of Florida is currently in the process of purchasing most of the organic soils used for vegetable production near Zellwood, leading to a movement of vegetable production to the surrounding sandy soil or to other vegetable production regions in the state. The move to sandy soils has lead to questions by growers about fertilization of vegetables such as carrot. We conducted a series of fertilization experiments with `Nantes' and `Imperator' carrot to evaluate yields and carrot quality responses to N and K. Carrot yield was maximized with 170 kg·ha–1 N, confirming current extension recommendations for carrot on sandy soils in Florida. The soil used for the K study tested medium (50 mg·kg–1) in K (Mehlich-1 extracted). Carrot yield responded positively to K up to 50 kg·ha–1 K, near the amount predicted for soils testing N medium in K.

In Situ Responses of Lake Okeechobee (Florida, USA) Phytoplankton to Nitrogen, Phosphorus, and Everglades Agricultural Area Canal Water

ABSTRACT Lake Okeechobee experiences blooms of cyanobacteria, perhaps due in part to the low nitrogen:phosphorus (N:P) ratios found in the water column, which may favor cyanobacteria over other phytoplankton taxa. The current strategy for managing the lake is to reduce external P loads. Some have recommended that pumping of N-rich water from the Everglades Agricultural Area (EAA), located adjacent to the south end of the lake, into Lake Okeechobee could increase N:P ratios and reduce cyanobacterial blooms until P loads are reduced. We conducted experiments to assess potential impacts of that strategy on phytoplankton in the lake's south pelagic region. Three in situ experiments were conducted during July 1994, with triplicated treatments (P, N, N+P, or EAA canal water additions) applied to 20-L clear plastic carboys, which were incubated in the lake for 3 days. In the first experiment, additions of P (50 μg · L−1) did not stimulate chlorophyll a or net primary productivity. Additions of N (500 μg · L−1) led to significant increases in both parameters. The greatest biomass and productivity increases (5-fold) occurred when the N and P were added together. In the second experiment, additions of N at 1X, 2X, and 4X the concentrations utilized in experiment 1 caused 3-fold increases in chlorophyll a and primary productivity. Nearly the same results were obtained in the third experiment, where EAA canal water was added to lake water in a 1:10 or 1:5 ratio, increasing soluble reactive P (SRP) by 17 and 34 μ · L−1, and dissolved inorganic nitrogen (DIN) by 175 and 350 μg · L−1, respectively. Although agricultural canal water often has been shown to contain herbicides which can suppress algal growth, no such effect was observed here. The yields of chlorophyll a per unit SRP or DIN in experiment 3, where canal water was added, were nearly identical to those in experiments 1 and 2, where N or N+P were added. In none of the experiments was there a shift from cyanobacteria to other algal taxa, despite the presence of small rapidly-growing chlorophytes in the lake water inoculum. The phytoplankton was dominated by cyanobacteria (70 to 81% of total phytoplankton densities), especially Lyngbya, Oscillatoria, Chroococcus, and Aphanocapsa, in all treatments, which encompassed DIN:SRP ratios from below 1:1 to over 140:1. From a management standpoint, these results indicate a potential for increased biomass of cyanobacteria in this N-limited lake if water pumping from the EAA were to be substantially increased.

MODELING FLOW IN THE EVERGLADES AGRICULTURAL AREA IRRIGATION/DRAINAGE CANAL NETWORK1

ABSTRACT: The south Florida ecosystem and Lake Okeechobee are important water resource areas that have degraded due to changes in hydroperiod, water supply, and water quality. Approximately 56 percent of the total phosphorus in water discharged from the Everglades Agricultural Area (EAA) is in particulate form. Currently, farm‐level best management practices are being implemented in the effort to reduce total phosphorus and sediment in off‐farm discharges. The objective of this work was to develop and calibrate a model describing water movement in primary EAA canals as a first step to development of a water quality (i.e., nutrient, sediment) model. The Netherlands‐developed mechanistic flow and water quality model (DUFLOW) was adapted for the EAA. Flow, stage, geometry, canal network, and meteorological data, October 13, 1993, to February 13, 1994, were used to adapt and calibrate the DUFLOW model for EAA water level and flow in primary canals. Direct runoff discharge into the primary canals from farm‐pump stations was used as runoff input for the model. The model results are comparable to an independently‐calculated water balance for the EAA. The calibrated flow model will be the basis for the calibration of sediment and chemical transport in the future.

Bacterial Leaf Spot of Cilantro in Florida.

In the 1995 to 1996 winter vegetable season, a leaf spot disease of cilantro (fresh coriander) (Coriandrum sativum L.) was widespread throughout commercial plantings in the Everglades Agricultural Area south and east of Lake Okeechobee. Symptoms first appeared as water-soaked spots ≤1 mm in diameter. These spots became dark brown to black and enlarged up to 2 mm in diameter. No chlorotic haloes developed around the lesions. The disorder was observed in numerous plantings of the cultivar Longstanding at four separate locations. Symptoms were apparent throughout each planting, with disease severity ranging from a few individual spots to numerous lesions covering nearly entire leaflets. Severe outbreaks were correlated with heavy precipitation events. In several instances, disease levels were great enough to render entire plantings totally unmarketable. A non-fluorescent bacterium was consistently isolated on King's medium B when a cooled inoculation needle was pushed through lesions. Six representative strains were chosen for further characterization. All strains were aerobic, gram-negative rods, and were oxidase and arginine dihydrolase negative. Levan was produced, but potato slices were not rotted. Tests for utilization of l-tartrate, l-lactate, and erythritol were negative. Biolog analysis identified all strains of the bacterium as Pseudomonas syringae. Highest similarity indices (0.52 to 0.81) were with P. syringae pv. pisi for four of the six strains. Suspensions of each strain were swab inoculated onto leaves of 4-week-old Longstanding cilantro seedlings in the greenhouse. Control plants were swabbed with sterile water only. Plants were covered with clear polyethylene bags for 72 h. Watersoaked spots were evident on test plants when bags were removed. Typical brown, greasy-looking leaf spots were seen by 6 days after inoculation. Control plants were symp-tomless. In a host-range study, cilantro and the following plants were mist-inoculated with a 107 CFU/ml suspension of each of the six test strains: carrot (Daucus carota L. 'Fancy Pack'), celery (Apium graveolens L. var. dulce (Mill.) Pers., 'June Belle'), garden pea (Pisum sativum L. 'Melting Sugar'), snap bean (Phaseolus vulgaris L. 'Pod Squad'), and onion (Allium cepa L. 'Evergreen Bunching'). Six days after inoculation, characteristic symptoms were evident on the cilantro. Four of the six strains produced a few (less than 10 per plant) bacterial leaf spot symptoms in carrot from which P. syringae was readily recovered. Some necrosis was observed on young, emerging leaves of snap bean. No symptoms were recorded for the other host species or the controls. This disease is similar to one reported on cilantro in California (1) and Germany (2).

Nitrogen mineralization in histosols of the everglades agricultural area1

A long‐term soil incubation and column nutrient leaching study was conducted to determine nitrogen (N)‐mineralization rates of selected Florida Histosols with drained and intermittent‐flooded conditions. Five surface soils from the Everglades Agricultural Area (EAA) were packed in columns (5‐cm i.d. containing the 0‐ to 15‐cm depth of each soil) and leached with 0.01M CaC12 followed by distilled water every 25 d for 1 yr. Drained columns were treated with a minus‐nitrogen‐phosphorus (NP) solution followed by applying ‐0.97 MPa tension to remove excess solution. Flooded columns received the same minus‐NP solution, but were flooded to a depth of 3 cm. Both treatments were incubated for 25‐d periods, solution sampled, and treatments reapplied. Because flooding conditions could not be maintained during the sampling period, this treatment is referred to as intermittent flooded. The ammonium‐nitrogen (NH4 +‐N) released from drained soils accounted for less than 6% of the total soluble N released from all soils, compared to more than 30% released from flooded soils. There were no differences in the amounts of soluble organic N from drained and intermittent flooded soils. Total soluble N from the surface 15‐cm of drained soils ranged from 217 to 509 kg‐ha‐1yr‐1, with 50 to 67% released as nitrate‐nitrogen (NO3 ‐‐N). In contrast, total soluble N released from flooded soils ranged from 168 to 345 kg‐ha‐1yr‐1, with less than 3% released as NO3 ‐‐N.

DRAINAGE GENERATION AND WATER USE IN THE EVERGLADES AGRICULTURAL AREA BASIN1

ABSTRACT: The Everglades Agricultural Area (EAA) covers 2,850 km2 in area and is characterized by high water table and organic soil. The area is actively irrigated and drained as a function of weather conditions and crop status. Anthropogenic activities in the basin have resulted in nutrient‐enriched drainage water that is discharged to Lake Okeechobee and the Everglades ecosystem. Water quantity and quality issues of the basin have become of increasing interest at local, state, and federal levels, so legislative and regulatory measures have been taken to improve water quality in discharges from the basin. In this study, simulation of hydrologic conditions and soil moisture were conducted using 100 years of daily synthetic rainfall data. From the simulations, the statistical distribution of half‐month drainage discharge and supplemental water use in the basin was developed. The mean annual drainage/runoff was 49 cm, the mean supplemental water was 30 cm, and the mean annual a real rainfall was 122 cm. On the average, drainage exceeded supplemental water use in the months of June to September while from December to March drainage and supplemental water use were equivalent. Supplemental water use exceeded drainage in the months of October, November, April, and May. High drainage occurred in June and September; smallest drainage was in February. On the average, the highest supplemental water use occurred in May and November. The 10‐year return period of annual drainage during wet and dry cycles were 60 cm and 38 cm per year, respectively. The semi‐monthly drainage coefficient of variation (cv) is above 100 percent for the period from the second half of October to end of April. The cv is lower than 100 percent for the remaining season (wet season). The purpose of this paper is to present the magnitude, temporal, and frequency distribution of drainage runoff generation and supplemental water use in the EAA basin. Information on statistics of drainage will contribute to the optimization of the design and operation of drainage water treatment systems.

Reconstructing Historical Changes in Everglades Plant Community Composition Using Pollen Distributions in Peat

ABSTRACT During the past century, the historical hydrology and nutrient regimes of the Everglades, a 700,000 hectare freshwater wetland in southern Florida, have been altered by agricultural and urban development. Changes in plant community composition (e.g. encroachment of cattail (Typha domingensis Pers.) into sawgrass (Cladium jamaicense Crsntz) and slough communities) have been observed in areas receiving nutrient and water loadings from agricultural activities. The distribution of 210Pb and pollen in depth increments of peat was measured at a nutrient-enriched site and an unenriched site in Water Conservation Area 2A (WCA 2A) to describe how nutrient enrichment and water management might have altered the historical plant species composition of the Everglades. Species composition of the plant communities has changed during the past 20 to 50 years at both enriched and unenriched sites. At the unenriched location, there has been a general shift in community composition since 1950 as slough species (arrowhead (Sagittaria spp.), water lily (Nymphaea spp.)) have decreased and terrestrial plants (pigweed (Amaranthaceae), ragweed (Ambrosia spp.), and Eupatorium spp.) have increased. The nutrient-enriched site also has seen an increase in terrestrial plant species since about 1950. In addition, since 1970, the sawgrass and slough communities at the enriched site have been replaced by a cattail-dominated community. The increase in terrestrial vegetation at both sites since 1950 could be due to drainage activities (construction of canals and levees) along the eastern perimeter of the Everglades and in the Everglades Agricultural Area (EAA) during the 1950s. The increase in cattail and concurrent decline in slough species at the nutrient-enriched site since 1970 probably is the result of the massive inputs of water (459,000,000 m3yr−1) and nutrients (1814 MT Nyr−1, 60 MT Pyr−1) from the EAA since WCA 2A was impounded in 1961.

Best Management Practices Enable the Coexistence of Agriculture and the Everglades Environment.

Situated at the northern end of the historical Florida Everglades is the 280,000-ha tract of land called the Everglades Agricultural Area (EAA). This land was diked, canalized, and drained in the early 1900s to encourage the production of primarily sugarcane, vegetables, sod, and rice on its Histosols. The phosphorus in drainage water from the EAA is believed to be causing undesirable changes to the ecosystem in areas subject to legislated environmental protection. Phosphorus (P) load reduction “Best Management Practices” (BMPs) are being developed and implemented in the EAA to reduce agricultural production impacts on the wetland areas. The BMPs can be categorized as fertilizer, water management, or particulate control related, and can be applied effectively across the EAA. Ten farms, representative of the EAA soils, rainfall, crops, farm size, geographic location, and water management practices, were used in the study. The farms were monitored under pre-BMP conditions for 1 to 3 years. By Jan. 1995, seven of the 10 farms were operating under project-designed BMP packages that included only the fertilizer and water management options. Depending on the method used for adjusting for hydrologic variability between years, calculated P load reductions ranged from 25% to 60% between 1994 and 1995.

Ecosystem Management to Achieve Ecological Sustainability: The Case of South Florida

The ecosystems of South Florida are unique in the world. The defining features of the natural Everglades (large spatial scale, temporal patterns of water storage and sheetflow, and low nutrient levels) historically allowed a mosaic of habitats with characteristic animals. Massive hydrological alterations have halved the Everglades, and ecological sustainability requires fundamental changes in management.The US Man and the Biosphere Human-Dominated Systems Directorate is conducting a case study of South Florida using ecosystem management as a framework for exploring options for mutually dependent sustainability of society and the environment. A new methodology was developed to specify sustainability goals, characterize human factors affecting the ecosystem, and conduct scenario/consequence analyses to examine ecological and societal implications. South Florida has sufficient water for urban, agricultural, and ecological needs, but most water drains to the sea through the system of canals; thus, the issue is not competition for resources but storage and management of water. The goal is to reestablish the natural system for water quantity, timing, and distribution over a sufficient area to restore the essence of the Everglades.The societal sustainability in the Everglades Agricultural Area (EAA) is at risk because of soil degradation, vulnerability of sugar price supports, policies affecting Cuban sugar imports, and political/economic forces aligned against sugar production. One scenario suggested using the EAA for water storage while under private sugar production, thereby linking sustainability of the ecological system with societal sustainability. Further analyses are needed, but the US MAB project suggests achieving ecological sustainability consistent with societal sustainability may be feasible.

Estimating a percent reduction in load

This article extends the work of Cohn et al. [1989] on estimating constituent loads to the problem of estimating a percent reduction in load. Three estimators are considered: the maximum likelihood (MLE), a “bias‐corrected” maximum likelihood (BCMLE), and the minimum variance unbiased (MVUE). In terms of root‐mean‐square error, both the MVUE and BCMLE are superior to the MLE, and for the cases considered here there is no appreciable difference between the MVUE and the BCMLE. The BCMLE is constructed from quantities computed by most regression packages and is therefore simpler to compute than the MVUE (which involves approximating an infinite series). All three estimators are applied to a case study in which an agricultural tax in the Everglades agricultural area is tied to an observed percent reduction in phosphorus load. For typical hydrological data, very large sample sizes (of the order of 100 observations each in the baseline period and after) are required to estimate a percent reduction in load with reasonable precision.

Agro-Economic Research Results and Environmental Regulations:

This paper confirms the negative impact of environmental constraints on farm profitability, and also demonslrates that results from agroeconomic research can lead to the discovery of practices that could be both environment-protecting and productivity-enhancing. Phosphorus applications on sweet corn and lettuce in the Everglades Agricultural Area are used as a case study.

Phosphorus Soil Test Correlation to Sugarcane Grown on Histosols in the Everglades

AbstractSugarcane (Saccharum spp.) in Florida is principally grown on Histosols in the Everglades Agricultural Area. Soil‐test‐based P fertilization recommendations have not been addressed since the 1970s. The objectives of this research were to evaluate the most acceptable soil test P extractant that best correlates to crop yield, and to define soil test P groupings associated with crop response to applied P. Results will be used in the future to recalibrate soil test data to yield and rate of P application. Phosphorus trials were conducted at four sites on organic soils between 1968 and 1972 and additionally at eight sites on organic soils between 1982 and 1990. Phosphorus applications ranging from 0 to 98 kg P ha−1 were broadcast or row‐applied in combination with different cultivars, and/or K, Si, or S rates at 12 sites (multiple experiments used per site per crop). The effectiveness of water, acetic acid, and Mehlich‐1 extractable soil P as yield response predictors was determined. Acetic acid extractable P was more highly correlated to sugar and cane yields (r = 0.72* and 0.63**, respectively) than water‐extractable P (r = 0.27** and 0.39**, respectively). Mehlich‐1 extractable P was poorly correlated to sugar (r = 0.25*) and cane (r = 0.05ns) yields. Acetic acid extractable P was selected as the best‐suited extractant related to crop yield response to P fertilization. Soil test calibration curves (i.e., relative yield as a function of acetic acid extractable P) were determined from the choice of seven types of regression models, in which the reciprocal function was chosen with the highest coefficient of determination (R2) and minimized residuals. Soil acetic acid extractable P criteria were developed to define soil test level groups associated with yield response conditions: low soil test levels ranged from 0 to 9 mg L−1, medium from 9 to 39 mg L−1, and high exceeded 39 mg P L−1.

HYDRODYNAMIC SIMULATIONS OF A CONSTRUCTED WETLAND IN SOUTH FLORIDA1

ABSTRACT: This paper describes the application of the SHEET2D model to the Florida's Everglades Nutrient Removal (ENR) Project. The ENR Project is a 3815 acre (1545 ha) pilot project, located in Palm Beach County. The operation of the treatment system will be used to demonstrate the performance of larger scale constructed wetland systems for removal of phosphorus from Everglades Agricultural Area (EAA) stormwater runoff. It is currently the largest stormwater wetland treatment system in the world.The SHEET2D model was used to analyze the performance of the ENR Project. SHEET2D is a two‐dimensional, depth‐averaged hydrodynamic model that is applicable to shallow water flow conditions. Subsequently, results from SHEET2D simulations were used to develop the ENEMOD model. ENRMOD is a lumped parameter box water quality model that can be used to analyze the long term performance of the ENR project with respect to hydrology and phosphorus uptake. Localized short‐circuiting in the agricultural ditches within the project area was analyzed by using the RBFVM‐2D model, which is a finite volume hydrodynamic model that is also applicable to shallow water flow conditions.The SHEET2D model was employed to simulate the hydraulics of the structures between cells and the hydrodynamics of the sheet‐flow moving across the buffer cell and treatment cells. Collection, distribution, and larger discharge canals within the project were simulated by means of the MultiBasin Routing (MBR) model features that are built into the SHEET2D model. Constant inflows (75 to 600 cfs [2.1 to 17 m3/s]) were used in all runs to simulate the discharge of the ENR Project based on the proposed operating schedule for the outflow pump station. The model simulated 30 days to reach steady state conditions. Under steady state conditions, the hydraulic retention times were computed for the project and the split of flow between the two treatment trains of the entire project from the common buffer cell. Additionally, design components such as height of the levees, capacity of the structures, and hydrographs at specified grids were obtained.

Agroenvironmental conflict and world food system theory: Sugarcane in the Everglades Agricultural Area

This paper presents a critique of the conceptualization of conflict over land-extensive rural production systems as presented by world food systems theorists. Two problems are identified. The first is historical; specifically, that the periodization of food regimes occludes Caribbean development and plantation agriculture, thereby missing the historical development of the social relations of certain commodity sectors. The second is geographical: that agroenvironmental conflict and sustainability are conceptualized either in terms of local/global (Friedmann, 1990, 1991) or in terms of North/South (Goodman and Redclift, 1991). The paper begins with a summary of the relevant arguments of world food theorists and then turns to the historical example of sugar production to examine its role in industrialization. The following section discusses arguments concerning agroenvironmental conflict that have emerged from food system theory, which emphasize contrasting ‘geographical’ components, either local/global or North/South. The limitations of this analysis are discussed with respect to the case of agroenvironmental conflict in Florida. Finally, a case study of the development of the Florida sugarcane industry is presented to illustrate a ‘First World’ environmental conflict over an agroindustrial production complex that cannot be categorized simply as a ‘consumption’ struggle.

Evaluation of sugarcane evapotranspiration from water table data in the everglades agricultural area

The limited fresh water supply in south Florida has emerged as a major point of contention between the urban, environmental, and agricultural sectors. The mandated water quality improvement measures suggest the retention of water on farms (up to 20% of historical drainage pumping) could further impact the regional water supply. Accurate measures of evapotranspiration (ET) are vital in order to prudently plan for the equitable distribution of water. The daily changes in field water table depths were used to evaluate the actual evapotranspiration for sugarcane grown in the Histosols of the Everglades Agricultural Area (EAA) in south Florida. Water table recorders were installed in eight independently irrigated and drained plots, each 0.55 ha. Water table monitoring was conducted for a period of two years, 1990 and 1991, and the results were the average of these two years. The crop was plant and first ratoon. Each month, periods of time when no rainfall, irrigation, or drainage occurred were selected for use in ET determination. The time periods ranged from 5 to 19 days. Assuming that there were no seepage or deep percolation the daily declines in water tables, which exhibited clear diurnal patterns, were then used to determine the change in soil water losses during the selected time periods, the change in soil water storage was representative of actual sugarcane ET. Pan evaporation and crop growth were also monitored. The amount of water released from the soil during drainage was determined in laboratory columns. Five transparent PVC pipes, 12.1 cm in diameter were used to remove undisturbed 110 cm deep cores from the field. The columns of soil were saturated and drained to determine the drainable porosity of the soil. The water table data exhibited diurnal trends, with declines close to zero at midnight and maximum declines occurring between 2:00 and 3:00 pm. The data showed that minimum ET rates occurred during December through February (0.7–1.5 mm day t−1 ). Maximum ET rates (4.5–4.6 mm day t−1 ) occurred during June through September. Total ET was 106.2 cm per year. Using the actual field measured ET, crop coefficients (K c) were calculated for sugarcane for the Penman, Thornthwaite, and Blaney-Criddle methods of determining potential evapotranspiration (ET p).

Agricultural Drainage Effects on Water Quality in Southeastern U.S.

A review of literature and summary of research results are presented on the effects of drainage on water quality in North Carolina, South Carolina, Georgia, and Florida. Principal findings from the predominate coarse-textured soils of the Atlantic Coastal Plain include increased nitrate-nitrogen losses associated with improved subsurface drainage. Benefits of drainage include potential reductions in organic nitrogen (N) and phosphorus (P) losses from these mineral soils. Results of drainage investigations on organic soils in the Everglades Agricultural Area of Florida indicate that phosphorus is the primary limiting factor for eutrophication problems in Lake Okeechobee. P losses can be potentially reduced by using slow versus fast drainage, retaining drainage water from vegetable and sugarcane fields (on sugarcane or fallow areas), and minimizing water-table fluctuations. Some of these potential practices and their resultant effects need additional verification for application to other areas and conditions.

USING TREE REGRESSION TO IDENTIFY NUTRITIONAL AND ENVIRONMENTAL FACTORS AFFECTING SUGARCANE PRODUCTION

A prediction function is developed for sugarcane yield using preplant soil nutrition levels, cultivar, and soil type. A tree regression approach is used because the resulting function encompasses the complexity of response between yield, multiple nutrients and other factors, while handling large amounts of data and providing information useful in the development of fertilizer and other production recommendations. Data collected from 148 control plots of experiments performed on commercial fields in the Everglades Agricultural Area of Florida are used to illustrate the method.

Strategies for protecting Florida's everglades: the best management practice approach

The Everglades Agricultural Area (EAA) is a small portion of the Everglades region, consisting of an artificially drained area of approximately 280 000 ha of organic soils providing a rich environment for the cultivation of primarily sugar cane, vegetables, rice, and sod. Hydroperiods and excessive nutrients in surface water inflows have been identified as potentially disruptive to the natural ecosystem, with phosphorus (P) deemed to be the limiting nutrient. Hence, agricultural drainage water from the EAA, containing higher than background P loads and concentrations, has been targeted as a source of the problem. To reduce P loads and concentrations in the drainage water leaving farms in the EAA, on-farm best management practices (BMPs) can be used. These BMPs have been identified and tested at the large plot scale and are presently being implemented and their efficacy verified at the farm level. It is currently estimated that P loading from the EAA can be reduced by 20% to 60% using BMPs. A 45% reduction should be attainable while keeping within acceptable cost/benefit ratios. The use of BMPs, however, will require higher levels of farm management and more sophisticated tools for decision-making.

Agricultural best management practices and surface water improvement and management

Restoration and enhancement of Lake Okeechobee and the Florida Everglades requires a comprehensive approach to manage agricultural runoff. The Florida Surface Water Improvement and Management (SWIM) Act of 1987 was promulgated to develop and implement plans for protecting Florida waters. The South Florida Water Management District was directed by Florida legislature to develop management plans for Lake Okeechobee (SWIM) and the Everglades ecosystem (Marjory Stoneman Douglas Everglades Protection Act of 1991). These plans require agriculture to implement best management practices (BMPs) to reduce runoff phosphorus (P) loads. The Lake Okeechobee SWIM plan established a P load reduction target for Lake Okeechobee and set P concentration limitations for runoff from non-point source agricultural sources. Agricultural water users in the Everglades Agricultural Area (EAA) are required to develop farm management plans to reduce P loads from the basin by 25%. The Everglades Forever Act of 1994 additionally emphasized linkage of these landscapes and consequent protection and restoration of the Everglades. Agricultural BMPs are being developed and implemented to comply with water management, environmental, and regulatory standards. Although BMPs are improving runoff water quality, additional research is necessary to obtain the best combination of BMPs for individual farms. This paper summarizes the development of comprehensive water management in south Florida and the agricultural BMPs carried out to meet regulatory requirements for Lake Okeechobee and the Everglades.