Current vegetable production systems use polyethylene (plastic) mulch and require multiple applications of agrochemicals. During rain events, runoff from vegetable production is enhanced because 50 to 75% of the field is covered with an impervious surface. This study was conducted to quantify off-site movement of soil and pesticides with runoff from tomato (Lycopersicon esculentum Mill.) plots containing polyethylene mulch and a vegetative mulch, hairy vetch (Vicia villosa Roth). Side-by-side field plots were instrumented with automated flow meters and samplers to measure and collect runoff, which was filtered, extracted, and analyzed to determine soil and pesticide loss. Seasonal losses of two to four times more water and at least three times as much sediment were observed from plots with polyethvlene mulch (55.4 to 146 L m(-2) and 247 to 535 g m(-2), respectively) versus plots with hairy vetch residue (13.7 to 75.7 L m(-2) and 32.8 to 118 g m(-2), respectively). Geometric means (+/-standard deviation) of total pesticide loads for chlorothalonil (tetrachloroisophthalonitrile) and alpha-and beta-endosulfan (6,7,8,9,10,10-hexachloro-1,5,5a,6,9,9a-hexahydro6,9-methano-2,4,3-benzodioxathiepin 3-oxide) for a runoff event were 19, 6, and 9 times greater from polyethylene (800+/-4.6, 17.6+/-3.9, and 39.1+/-4.9 microg m(-2), respectively) than from hairy vetch mulch plots (42+/-6.0, 2.8+/-5.0, and 4.3+/-4.6 microg m(-2), respectively) due to greater concentrations and larger runoff volumes. The increased runoff volume, soil loss, and off-site loading of pesticides measured in runoff from the polyethylene mulch suggests that this management practice is less sustainable and may have a harmful effect on the environment.

Runoff from tomato (Lycopersicon esculentum Mill.) production with polyethylene mulch has been implicated in the failure of commercial shellfish farms in the Mid-Atlantic Region of the United States. Copper, applied in the form of copper hydroxide, is the most widely used fungicide-bactericide for control of tomato diseases and recently has been detected in the Chesapeake Bay (USA) watershed. Elevated levels of copper have been shown to have adverse effects on shellfish, finfish, and other aquatic organisms. This research evaluates the off-site movement of copper with the dissolved phase and the particulate phase of runoff from controlled field plots containing tomato plants grown in either polyethylene mulch or a vegetative mulch, hairy vetch (Vicia villosa Roth.). Overall, runoff collected from polyethylene mulch plots contained significantly (p < or = 0.05) greater loads of dissolved- and particulate-phase copper than runoff from hairy vetch mulch plots. However, the loss of copper associated with the particulate phase was significantly greater (p < or = 0.05) than that associated with the dissolved phase of runoff from both mulch treatments, with the particulate phase accounting for more than 80% of the copper loads. The reported toxicity of copper to aquatic organisms and the greater runoff volume, soil loss, and off-site loading of copper measured in runoff from the polyethylene mulch suggests that this management practice is less sustainable and may have a more harmful impact on aquatic ecosystems.

The transport of runoff with high copper concentrations and sediment loads into adjacent surface waters can have adverse effects on nontarget organisms as a result of increased turbidity and degraded water quality. Runoff from vegetable production utilizing polyethylene mulch can contain up to 35% of applied copper, a widely used fungicide/bactericide that has adverse effects on aquatic organisms. Copper is primarily transported in runoff with suspended particulates; therefore, implementation of management practices that minimize soil erosion will reduce copper loads. Replacing bare-soil furrows with furrows planted in rye (Secale cereale) significantly improved the sustainability of vegetable production with polyethylene mulch and reduced the potential environmental impact of this management practice. Vegetative furrows decreased runoff volume by >40% and soil erosion by >80%. Copper loads with runoff were reduced by 72% in 2001, primarily as a result of reduced soil erosion since more than 88% of the total copper loads were transported in runoff with suspended soil particulates. Tomato yields in both years were similar between the polyethylene mulch plots containing either bare-soil or vegetative furrows. Replacing bare-soil furrows with vegetative furrows greatly reduces the effects of sediments and agrochemicals on sensitive ecosystems while maintaining crop yields.

Inositol phosphates are metabolically derived organic phosphates (P) that increasingly appear to be an important sink and source of P in the environment. Salts of myo-inositol hexakisdihydrogen phosphate (IHP) or more commonly phytate are the most common inositol phosphates in the environment. IHP resists acidic dephosphorylation and enzymatic dephosphorylation as ferric or ferrous IHP. Mobility of IHP iron complexes is potentially pH and redox responsive, making the time scale and environmental fate and transport of the P associated with the IHP of interest to the mass balance of phosphorus. Ferric and ferrous complexes of IHP were investigated by proton nuclear magnetic resonance spectroscopy ( (1)H NMR) and enzymatic dephosphorylation. Ferrous IHP was found to form quickly and persist for a longer period then ferric IHP. Dissociation constants derived from (1)H NMR experiments of chemically exchanging systems at equilibrium were 1.11 and 1.19 and formation constants were 0.90 and 0.84 for ferric and ferrous IHP, respectively. The recovery of P from enzymatic dephosphorylation of ferric and ferrous IHP was consistent with the magnitude of the kinetic and equilibrium rate constants.