Timothy A. Lang

Long-term water quality trends after implementing best management practices in South Florida.

A mandatory best management practices (BMP) program was implemented in the Everglades Agricultural Area (EAA) farms basin-wide in 1995 as required by the Everglades Forever Act to reduce P loads in drainage water reaching the Everglades ecosystem. All farms in the EAA basin implement similar BMPs, and basin wide P load reductions have exceeded the 25% reduction required by law; however, differences remain in water quality between subbasins. Our objective was to determine long-term trends in P loads in discharge water in the EAA after implementing BMPs for 7 to10 yr and to explore reasons for differences in the performance of the subbasins. Two monitoring datasets were used, one from 10 research farms and the second from the EAA basin inflow and outflow locations. Mann-Kendall trend analysis was used to determine the degree of change in water quality trends. A decreasing trend in P loads was observed in general on sugarcane (Saccharum officinarum L.) farms, while mixed crop farms showed either decreasing or insignificant trends. The insignificant trends are probably related to management practices of mixed crop systems. Decreasing trends in P loads were observed in the outflow of the EAA basin, S5A, and S8 subbasins from 1992 to 2002. Inflow water from Lake Okeechobee had increasing P concentration from 1992 to 2006 with the highest trend in the east side of the lake. This analysis indicated there may be other factors impacting the success of BMPs in individual farms including cropping rotations and flooding of organic soils. Elevated P concentrations in Lake Okeechobee water used for irrigation may pose a future risk to degrade water quality on farms in the EAA, especially in the S5A subbasin.

Tree-based modeling of complex interactions of phosphorus loadings and environmental factors

Phosphorus (P) enrichment has been observed in the historic oligotrophic Greater Everglades in Florida mainly due to P influx from upstream, agriculturally dominated, low relief drainage basins of the Everglades Agricultural Area (EAA). Our specific objectives were to: (1) investigate relationships between various environmental factors and P loads in 10 farm basins within the EAA, (2) identify those environmental factors that impart major effects on P loads using three different tree-based modeling approaches, and (3) evaluate predictive models to assess P loads. We assembled thirteen environmental variable sets for all 10 sub-basins characterizing water level management, cropping practices, soils, hydrology, and farm-specific properties. Drainage flow and P concentrations were measured at each sub-basin outlet from 1992-2002 and aggregated to derive monthly P loads. We used three different tree-based models including single regression trees (ST), committee trees in Bagging (CTb) and ARCing (CTa) modes and ten-fold cross-validation to test prediction performances. The monthly P loads (MPL) during the monitoring period showed a maximum of 2528 kg (mean: 103 kg) and maximum monthly unit area P loads (UAL) of 4.88 kg P ha(-1) (mean: 0.16 kg P ha(-1)). Our results suggest that hydrologic/water management properties are the major controlling variables to predict MPL and UAL in the EAA. Tree-based modeling was successful in identifying relationships between P loads and environmental predictor variables on 10 farms in the EAA indicated by high R(2) (>0.80) and low prediction errors. Committee trees in ARCing mode generated the best performing models to predict P loads and P loads per unit area. Tree-based models had the ability to analyze complex, non-linear relationships between P loads and multiple variables describing hydrologic/water management, cropping practices, soil and farm-specific properties within the EAA.

Best Management Practices and Long-Term Water Quality Trends in the Everglades Agricultural Area

The Everglades Agricultural Area (EAA) in South Florida, part of the historical Everglades, was initially drained in the early 20th century for agriculture and flood protection. The organic soils have been subject to subsidence caused by organic matter oxidation. Soils are deeper east of Lake Okeechobee compared to soils south of the lake. The area is mostly planted to sugarcane and other crops such as rice, vegetables, and sod. Concerns about quality of water leaving the EAA led to a regulatory program for mandatory best management practices (BMP) since 1995 to reduce phosphorus (P) loads out of the EAA by 25% compared to historical levels. The program is highly successful, with 100% grower participation and exceeding P load reduction required by law. Trend analysis conducted on selected EAA farms, subbasins, and whole basin show, in general, decreasing trends in P concentrations, drainage flow, and P loads. Differences are noted between farms and subbasins due to factors that include rainfall distribution, water management practices, irrigation water quality, soil type/depth, and cropping systems. Water management practices were the dominant factors affecting P loads out of the EAA. Water management research that targets farms with deeper soils is recommended to achieve additional P load reductions. Other practices to improve BMP performance include minimizing generation and transport of sediments from farm canals. The quality of irrigation water from Lake Okeechobee is of concern of its impact on BMP performance.

Effect of Flood Depth on Rice Water Weevil (Coleoptera: Curculionidae) Populations in Florida Rice Fields

Abstract  The rice water weevil, Lissorhoptrus oryzophilus Kuschel, is an important pest of rice (Oryza sativa L.) grown in Florida. Reports on the effect of flood depth on rice water weevil populations have been inconsistent. Our objective was to determine if flood depth has any significant effect on rice water weevil populations and other arthropods in rice grown in Florida. Sampling was conducted using adult foliar damage scars, core samples for larvae, and sweep nets for arthropods above the water. Results showed that shallow flooding reduced rice water weevil populations in Florida. Sweep net data showed that flood depth had little, if any, effect on populations of damselflies (Odonata), leafhoppers (Cicadellidae), spiders (Arachnida), or stink bugs (Oebalus spp.).

Sugarcane by-products used as soil amendments on a sandy soil: Effects on sugarcane crop nutrition and yield

ABSTRACT Agricultural by-products applied as soil amendments have the potential to improve crop production on low organic matter (OM) soils. This two-year study investigated the use of two readily available sugarcane (Saccharum spp.) milling by-products, mill mud, and mill ash, as soil amendments to improve first sugarcane crop (plant cane) and subsequent crop (first ratoon) grown on a sandy Spodosol. Sugarcane was grown in lysimeters receiving mill mud, mill ash, and a 50:50 (v:v) mill mud to mill ash mix. Amendments were applied at low, medium, and high application rates (5, 10, and 15 cm depths, respectively) and then incorporated 30 cm deep. Amendment effects on plant nutrition, soil characteristics, and crop yield were determined. High rate applied mill mud and mill ash had the highest soil OM content for both years and soil OM did not significantly change between crops for all treatments except for high rate mill mud, which increased the second year (ratoon crop). Leaf nutrient levels for nitrogen (N), iron (Fe), and copper (Cu) for all treatments both years were insufficient; nutrient levels for magnesium (Mg), manganese (Mn), and silicon (Si) were within marginal to sufficient range for all treatments both years. All amendments produced significantly higher biomass and sucrose yields for plant cane and first ratoon crops compared to the control. Mill ash treatments produced the greatest increase in sucrose and biomass yields from plant cane to ratoon crops, which corresponded with an increase in potassium (K) in leaf tissue. However, mid and high rates of mix produced the highest sugarcane biomass and sucrose yields for the both the plant cane and ratoon crops.

Capturing Flow-weighted Water and Suspended Particulates from Agricultural Canals During Drainage Events

The purpose of this study is to describe the methods used to capture flow-weighted water and suspended particulates from farm canals during drainage discharge events. Farm canals can be enriched by nutrients such as phosphorus (P) that are susceptible to transport. Phosphorus in the form of suspended particulates can significantly contribute to the overall P loads in drainage water. A settling tank experiment was conducted to capture suspended particulates during discrete drainage events. Farm canal discharge water was collected in a series of two 200 L settling tanks over the entire duration of the drainage event, so as to represent a composite subsample of the water being discharged. Imhoff settling cones are ultimately used to settle out the suspended particulates. This is achieved by siphoning water from the settling tanks via the cones. The particulates are then collected for physico-chemical analyses.