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United States Department of Agriculture

Agricultural Research Service

Title: Demonstration and Evaluation of South Dade Basin Vegetable Crop Best Management Practices: Summer Cover Crops to Control Herbicide and Fertilizer Leaching

Authors
item Potter, Thomas
item Bosch, David
item Joo, Hyun - UNIV OF N CAROLINA
item Schaffer, Bruce - UNIV OF FLORIDA
item Munoz-Carpena, Rafael - UNIV OF FLORIDA

Submitted to: USDA Miscellaneous Publication 1343
Publication Type: Government Publication
Publication Acceptance Date: April 20, 2004
Publication Date: April 20, 2004
Citation: Potter,T.L., Bosch,D.D., Joo,H., Schaffer,B., Munoz-Carpena,R. Demonstration and evaluation of South Dade basin vegetable crop best management practices: summer cover crops to control herbicide and fertilizer leaching. 2004. USDA Miscellaneous Publication 1343. Contract Number: C-12331. South Florida Water Management District, West Palm Beach, Florida.

Interpretive Summary: Vegetable, tropical fruit and ornamental crops are produced on about 30,000 ha in Florida's Miami-Dade County. Farming contributes substantially to the region's economy with combined annual revenues >$1 billion. Successful crop production often requires intensive pesticide and fertilizer use. This combined with the fact that local soils are susceptible to leaching indicates that ground and surface water quality may be at risk from agrichemical contamination. To better understand the environmental costs and benefits of agriculture in the region, the contribution that agrichemical use water quality impairments must be clearly defined. There is also a continuing need to demonstrate the efficacy of best management practices (BMPs) in reducing negative water quality impacts. These were the objectives of a 3.5-year study conducted at University of Florida Tropical Research and Education Center in Homestead, FL. Sweet corn was grown using grower recommend practices on plots where groundwater monitoring wells installed. After harvest, ½ were planted with a vigorous summer cover crop, Sunn Hemp (Crotalaria juncea), with the remainder left fallow. In total 4 corn crops were planted and harvested and >1700 water samples collected and analyzed during the study. Corn yield and quality were consistently high while levels of fertilizer and pesticide residues in groundwater were generally low. Drinking water standards were exceeded for one or more parameters in <1% of samples. The was explained by that fact the sweet corn like most vegetable crops in the region was produced during the winter dry season. Because rainfall is low during the growing season leaching rates are low. In the case of pesticides the very high soil dissipation rates were a contributing factor. After application most of the pesticides degraded or other dissipated before residues could be leached. We also found that the cover crop reduced the herbicide residues that did leach by nearly 40%. Results have demonstrated that ground water contamination due to agrichemical leaching during vegetable crop production in the region is likely low and that a significant reduction in herbicide leaching can be achieved by cover crop use. This observation in addition to other cover crop conservation benefits indicates that growers should be encouraged to maintain vegetative cover on their fields whenever they are not in crop production.

Technical Abstract: Pesticides and fertilizers are used intensively to produce vegetable, tropical fruit and ornamental crops on about 30,000 ha in Florida's Miami-Dade County. Use of these agrichemicals appears to threaten surface and ground water quality in the region; however, a link between agrichemical use by local growers and impaired water quality has not been demonstrated. Studies which assess whether or not there is a linkage are needed. There is also a continuing need to demonstrate the efficacy of best management practices (BMPs) which minimize water quality impacts during crop production. These were the objectives of a 3.5-year study conducted at University of Florida Tropical Research and Education Center in Homestead, FL. Sweet corn (Zea Mays L.), was grown using grower recommend practices on replicated 0.15-ha plots where groundwater quality monitoring wells were installed. After each corn harvest, ½ the plots were planted with a vigorous cover crop, Sunn Hemp (Crotalaria juncea), and ½ were left fallow. The Sunn Hemp was tilled into the soil prior to planting the next corn crop. In total 4 corn crops were planted and harvested and >1700 water samples collected and analyzed. Corn yield and quality compared favorably with the best local growers while water quality impacts, as indicated by ground water sample analysis results were low. Fertilizer and/or pesticide residues were greater than drinking water maximum contaminant levels (MCL) in <1% of all samples. These results are explained by the fact that the sweet corn, like most vegetables crops in the region, was produced during the winter dry season. Low rainfall translated to low agrichemical leaching. Another factor which likely contributed to low pesticide residue levels in ground water was their rapid soil dissipation. DT50 values of the herbicide atrazine were <8 days. Water quality data also showed that atrazine leaching was reduced by '34% on plots managed with the cover crop. Results have demonstrated that ground water contamination due to agrichemical leaching during vegetable crop production in the region is likely low and that a significant reduction in herbicide leaching can be achieved by cover crop use. This observation in addition to other cover crop conservation benefits leads to the conclusion that growers should be encouraged to maintain vegetative cover on their fields whenever they are not in crop production.

Last Modified: 11/22/2014
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