Effectiveness of Three "Best Management Practices" for Reducing Non-Point Source Pollution from Piedmont Tobacco Fields

We evaluated effectiveness of three BMPs for tobacco production: no-till (NT) versus conventional tillage (CT), grassed field-side filter zones (GFZs), and forested filter zones (FFZs) for two years. Level spreaders were installed within both FFZs and GFZs zones to convert channelized runoff into sheet flow. The primary objective was to test three BMPs in series to determine the total reduction in suspended solids and nutrients as runoff exited the lower flumes of the FFZs. A secondary objective was to compare yield and quality of tobacco from NT versus CT. Another secondary objective was to compare the effectiveness of the same FFZ first with a mature stand of pines and hardwoods, and later with vegetation following clear cutting. The study was conducted on the Oxford Tobacco Research Station in Granville County, North Carolina. Total suspended solids (TSS) leaving tobacco fields were reduced by 70% to 90% by use of NT compared to CT. Nutrient discharge from NT and CT fields was so low that no clear trends were seen. There was a tendency toward slightly more nutrient release from NT than from CT fields which is consistent with previous reports by other authors. GFZs fbnctioned very well in retaining solids and nutrients in early summer, but seemed to overload during late summer, probably due to limited infiltration capacity. Forested filter zones with their higher infiltration capacity, were able to back up the GFZs when they overloaded and exported sediment and nutrients to the FFZs. In combination, GFZs and FFZs retained 80 to 95 percent of all sediment and nutrients entering the zones, proving to be an extremely effective combination. Dense ground vegetation in the cut-over FFZ more than doubled its capacity to effectively detain sediments and nutrients, compared to the effectiveness of the same FFZ when it was covered by a stand of mature mixed pine-hardwood. Detention rates jumped from 32% with a mature forest to 72% with dense ground vegetation which followed the clear cut. As found in our previous studies, a small number of major events each year accounted for at least 80% of all sediments and nutrients exported from the fields. In this study, one event in December, 2000 delivered more sediment to the filter zones than all other events monitored over the two year period. In both crop years, yield was lower and grade was slightly lower for tobacco from NT compared to that from CT. In the first year, yields from NT and CT were below the regional average. In the second year, yields from NT and CT were higher than the regional average. Based on this research, we recommend the use of some form of conservation tillage for tobacco and other tilled crops, and the use of grassed and forested filter zones with level spreaders. TABLE OF CONTENTS . ACKNOWLEDGMENTS . i l l ABSTRACT . v LIST OF FIGURES . ix . LIST OF TABLES . xi11 . SUMMARY AND CONCLUSIONS xv RECOMMENDATJONS . xvii TNTRODUCTION . 1 OBJECTIVES . 3 REVIEW OF LITERATURE . 3 . NON-POINT SOURCE POLLUTION IN THE SOUTHEAST 3 CONSERVATION TILLAGE . 3 . Conservation Tillage and Runoff 3 . Conservation Tillage and Sediment 4 . Conservation Tillage and Nutrients 4 . Conservation Tillage and Tobacco 4 FORESTED FILTER ZONES . 6 . FORESTED VERSUS GRASS FILTER ZONES 6 . BENEFIT OF DISPERSING RUNOFF 7 METHODS . 9 . EXPERIMENTAL WATERSHEDS 9 . Tobacco Tillage Comparison 9 Grassed Filter Zones . 1 1 Forested Filter Zones . 12 rNSTRUMENTATION . 12 . Flumes, Samplers and Data Recorders 12 . REVISED RATING TABLES FOR FIELD FLUMES 12 . Calibration of GFZ and FFZ Flumes 13 . FIELD AND LABORATORY DATA 14 BMP Evaluation . 14 . Sample Collection and Analysis 14 . CULTIVATION ACTIVITIES AND OBERVATIONS 16 . PERFORMANCE OF WATER SAMPLING SYSTEM 16 RESULTS AND DISCUSSION . 18 . EFFECTIVENESS OF NO-TILL, GRASSED AND FORESTED 18 FILTER ZONES Infiltration . 18 Peak Flow Rates . 18 Total Suspended Solids . -22 Nutrients . -29 . VEGETATION MANAGEMENT IN AS FFZ 35 . TOBACCO YIELD AND QUALITY 35 DESIGNING SYSTEMS FOR LARGE EVENTS . 36 . LIST OF REFERENCES -43 . APPENDIX 1 APPENDIX TABLES 1.9 47