Influence of cover crops on nutrient availability in a sweet potato cropping system in South Florida Jeanna Ragsdale (Graduate committee: Yuncong Li, Thomas Obreza, Ashok Alva, Zhenli He) University of Florida IFAS Tropical Research and Education Center Jeanna Ragsdale (Graduate committee: Yuncong Li, Thomas Obreza, Ashok Alva, Zhenli He) University of Florida IFAS Tropical Research and Education Center

Introduction: Limitations to vegetable production in South Florida: Limitations to vegetable production in South Florida: Poor soil Calcareous soils Low organic matter Low water and nutrient holding capacities Poor soil Calcareous soils Low organic matter Low water and nutrient holding capacities

Calcareous Soils pH Low organic matter Reduced availability of Fe, Mn, Zn, Cu, Co, B, and P pH Low organic matter Reduced availability of Fe, Mn, Zn, Cu, Co, B, and P THE NATURE AND PROPERTIES OF SOILS 13 th Edition Nyle C. Brady and Ray R. Weil

Cover Crop Benefits Organic matter Soil structure Water holding capacity Soil microbial activity Soil porosity Organic matter Soil structure Water holding capacity Soil microbial activity Soil porosity Take up excess soil nutrients Soil erosion Weed and nematode suppression Carbon sequestration Take up excess soil nutrients Soil erosion Weed and nematode suppression Carbon sequestration

Objective: Improve nutrient availability and uptake for sweet potato Improve nutrient availability and uptake for sweet potato Approach: cover crops foliar applications of micronutrient fertilizer

Experiment and Treatments: Split Plot Design 4 main plots: Sunnhemp, Velvet bean, Sorghum-sudan, Control (Fallow) 3 subplots: foliar micronutrient fertilizer applications of Fe and Zn, and control 4 replications Split Plot Design 4 main plots: Sunnhemp, Velvet bean, Sorghum-sudan, Control (Fallow) 3 subplots: foliar micronutrient fertilizer applications of Fe and Zn, and control 4 replications

Cover Crop Management Planted in August No fertilizer used Planted in August No fertilizer used

Cover crops at 4 weeks Sunnhemp Sorghum-sudan Velvet Bean

Cover crops at 9 weeks Sunnhemp Sorghum-sudanVelvet Bean

Mowed and tilled in November

Sweet Potato (Boniato) Crop Management Planted in December Managed by grower Planted in December Managed by grower

Sweet potato crop at 4 months

Foliar application of Fe & Zn Chelated Fe (EDTA) and ZN At 1 lb / acre Chelated Fe (EDTA) and ZN At 1 lb / acre

Prior to harvest

Sweet potato harvest

Sweet Potato Harvest

Measurements: Cover crop biomass samples Mean average based on dry weight Soil and plant tissue samples: N, C, P, K, Mg, Fe, Zn, B, Mn, and Cu Cover crop biomass samples Mean average based on dry weight Soil and plant tissue samples: N, C, P, K, Mg, Fe, Zn, B, Mn, and Cu

Measurements: 1 : Cover Crop (prior to cutting) –Biomass –Total biomass nutrient contents 2. Soil nutrient concentrations –Prior to planting cover crops –Prior to cutting cover crops –After cover crop incorporation 1 : Cover Crop (prior to cutting) –Biomass –Total biomass nutrient contents 2. Soil nutrient concentrations –Prior to planting cover crops –Prior to cutting cover crops –After cover crop incorporation

Measurements: 3. Sweet Potato –Plant tissue nutrient concentrations before and after foliar applications of micronutrients 4. Sweet potato yield 3. Sweet Potato –Plant tissue nutrient concentrations before and after foliar applications of micronutrients 4. Sweet potato yield

Results

Cover Crop Biomass (Mg/ha)

Cover crop biomass total N (kg/ha)

Plant tissue N concentration (g/kg)

Cover crop biomass total Fe (g/ha)

Cover crop biomass total Zn (g/ha)

Plant tissue Zn concentration (mg/kg)

Cover crop biomass total B (g/ha)

Soil Nutrients

Soil total N (g/kg)

Soil total C (g/kg)

Sweet potato leaf tissue nutrient concentrations

Sweet potato leaf N (g/kg)

Sweet potato leaf C (g/kg)

Sweet potato leaf K (g/kg)

Sweet potato leaf Mg (g/kg)

Sweet potato leaf Fe (mg/kg)

Leaf Fe in iron subplots (mg/kg) after fertilizer application

Sweet potato leaf Zn (mg/kg)

Leaf Zn in zinc subplots (mg/kg) after fertilizer application

Sweet potato yield

Sweet Potato Yield

Summary: Cover Crop Biomass Sorghum and sunnhemp produced significantly more biomass than fallow and velvet bean Cover crop biomass nutrient content Corresponded with total biomass produced by each treatment except for N and Zn in sunnhemp plots and Zn in velvet bean plots Cover Crop Biomass Sorghum and sunnhemp produced significantly more biomass than fallow and velvet bean Cover crop biomass nutrient content Corresponded with total biomass produced by each treatment except for N and Zn in sunnhemp plots and Zn in velvet bean plots

Summary: Soil nutrients prior to cutting cover crops Soil samples showed no significant differences between treatment plots for N, P, Mg, Zn, Mn and Cu, but did show some significant differences for K, Fe, and B Soil nutrients after cover crop incorporation Soil N was significantly higher after cover crop incorporation in all treatment plots except sorghum-sudan. Soil Carbon was not significantly higher after incorporation or between treatment plots Soil nutrients prior to cutting cover crops Soil samples showed no significant differences between treatment plots for N, P, Mg, Zn, Mn and Cu, but did show some significant differences for K, Fe, and B Soil nutrients after cover crop incorporation Soil N was significantly higher after cover crop incorporation in all treatment plots except sorghum-sudan. Soil Carbon was not significantly higher after incorporation or between treatment plots

Summary: Sweet potato leaf nutrient concentrations Sunhemp plots contained significantly more N and Fe, and significantly less Mg Sorghum plots contained significantly more C Sweet Potato Yield No significant differences between cover crop plots or micronutrient treatment plots Sweet potato leaf nutrient concentrations Sunhemp plots contained significantly more N and Fe, and significantly less Mg Sorghum plots contained significantly more C Sweet Potato Yield No significant differences between cover crop plots or micronutrient treatment plots

Acknowledgments Graduate committee: Yuncong Li, Thomas Obreza, Ashok Alva, Zhenli He UF TREC: Newton Campbell, Tina Dispenza, Waldy Klassen, Guodong Liu, Teresa Olczyk, Laura Rosado, Yun Qian, Xing Wang, Qingren Wang, Guiqin Yu M & M Farms: Manelo Hevia David Long Graduate committee: Yuncong Li, Thomas Obreza, Ashok Alva, Zhenli He UF TREC: Newton Campbell, Tina Dispenza, Waldy Klassen, Guodong Liu, Teresa Olczyk, Laura Rosado, Yun Qian, Xing Wang, Qingren Wang, Guiqin Yu M & M Farms: Manelo Hevia David Long