Influence of cover crops on nutrient availability in a sweet potato cropping

system in South Florida

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:Introduction:Limitations to vegetable productionin South Florida:Limitations to vegetable productionin 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 SoilsCalcareous Soils

• pH 7.5-8.5

• Low organic matter

• Reduced availability of Fe, Mn, Zn, Cu, Co, B, and P

• pH 7.5-8.5

• Low organic matter

• Reduced availability of Fe, Mn, Zn, Cu, Co, B, and P

THE NATURE AND PROPERTIES OF SOILS13th EditionNyle C. Brady and Ray R. Weil

Cover Crop BenefitsCover 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:Objective:Improve nutrient availability anduptake for sweet potatoImprove nutrient availability anduptake for sweet potato

Approach: Approach: •cover crops•foliar applications of micronutrient fertilizer

Experiment and Treatments: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 ManagementCover Crop Management

• Planted in August• No fertilizer used

• Planted in August• No fertilizer used

Cover crops at 4 weeksCover crops at 4 weeks

SunnhempSorghum-sudan Velvet Bean

Cover crops at 9 weeksCover crops at 9 weeks

SunnhempSorghum-sudan Velvet Bean

Mowed and tilled in NovemberMowed and tilled in November

Sweet Potato (Boniato) Crop ManagementSweet Potato (Boniato) Crop Management

• Planted in December• Managed by grower• Planted in December• Managed by grower

Sweet potato crop at 4 monthsSweet potato crop at 4 months

Foliar application of Fe & ZnFoliar application of Fe & Zn

• Chelated Fe (EDTA) and ZN

• At 1 lb / acre

• Chelated Fe (EDTA) and ZN

• At 1 lb / acre

Prior to harvestPrior to harvest

Sweet potato harvestSweet potato harvest

Sweet Potato HarvestSweet Potato Harvest

Measurements: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: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: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

ResultsResults

Cover Crop Biomass (Mg/ha)

c

a

b

c

0

2

4

6

8

10

12

14

Weeds Sorghum-sudan

Sunnhemp Velvet Bean

Mg

/ha

Cover crop biomass total N (kg/ha)

Cover crop biomass total N (kg/ha)

b

a

b

c

0

100

200

300

400

500

600

Weeds Sorghum-sudan

Sunnhemp Velvet Bean

kg

/ha

Plant tissue N concentration (g/kg)

Plant tissue N concentration (g/kg)

ba

a

b

ba

0

2

4

6

8

10

12

14

16

18

20

Weeds Sorghum-sudan

Sunnhemp Velvet Bean

g/k

g

Cover crop biomass total Fe (g/ha)

bc

ba

a

c

0

200

400

600

800

1000

1200

1400

Weeds Sorghum-sudan

Sunnhemp Velvet Bean

g/h

a

Cover crop biomass total Zn (g/ha)

ba

bc

a

c

0

500

1000

1500

2000

2500

Weeds Sorghum-sudan

Sunnhemp Velvet Bean

g/h

a

Plant tissue Zn concentration (mg/kg)

a

c

cb

b

0

10

20

30

40

50

60

70

80

90

100

Weeds Sorghum-sudan

Sunnhemp Velvet Bean

mg

/k

Cover crop biomass total B (g/ha)

c

b

a

c

0

500

1000

1500

2000

2500

3000

3500

4000

Weeds Sorghum-sudan

Sunnhemp Velvet Bean

g/h

a

Soil NutrientsSoil Nutrients

Soil total N (g/kg)Soil total N (g/kg)

0

0.5

1

1.5

2

2.5

3

Weeds Sorghum-sudan Sunnhemp Velvet Bean

g/k

g

pre-plant

pre-cut

after-incorporation

Soil total C (g/kg)

46

48

50

52

54

56

58

60

Weeds Sorghum-sudan

Sunnhemp Velvet Bean

g/k

g

pre-plant

pre-cut

after-incorporation

Sweet potato leaf tissuenutrient concentrationsSweet potato leaf tissuenutrient concentrations

Sweet potato leaf N (g/kg)Sweet potato leaf N (g/kg)

b

b b

a

26

27

28

29

30

31

32

33

34

35

Weeds Sorghum-sudan

Sunnhemp Velvet Bean

g/k

g

Sweet potato leaf C (g/kg)Sweet potato leaf C (g/kg)

b

baba

a

417

418

419

420

421

422

423

424

425

426

427

Weeds Sorghum-sudan

Sunnhemp Velvet Bean

g/k

g

Sweet potato leaf K (g/kg)Sweet potato leaf K (g/kg)

b

b

ba

a

25.5

26.0

26.5

27.0

27.5

28.0

28.5

29.0

29.5

30.0

30.5

Weeds Sorghum-sudan Sunnhemp Velvet Bean

g/k

g

Sweet potato leaf Mg (g/kg)Sweet potato leaf Mg (g/kg)

aaa

b

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

Weeds Sorghum-sudan Sunnhemp Velvet Bean

g/k

g

Sweet potato leaf Fe (mg/kg)Sweet potato leaf Fe (mg/kg)

b

b

b

a

25

26

27

28

29

30

31

32

Weeds Sorghum-sudan Sunnhemp Velvet Bean

mg/k

g

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

ba

a

ba

b

24

25

26

27

28

29

30

31

32

Weeds Sorghum-sudan Sunnhemp Velvet Bean

mg

/kg

Sweet potato leaf Zn (mg/kg)Sweet potato leaf Zn (mg/kg)

a

aa

a

0

5

10

15

20

25

30

35

Weeds Sorghum-sudan

Sunnhemp Velvet Bean

mg/k

g

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

aaa

a

0

5

10

15

20

25

30

35

40

45

Weeds Sorghum-sudan Sunnhemp Velvet Bean

mg

/kg

Sweet potato yieldSweet potato yield

Sweet Potato YieldSweet Potato Yield

a

aa

a

0

1

2

3

4

5

6

7

8

9

10

Weeds Sorghum-sudan Sunnhemp Velvet Bean

Kg

/plo

t

Sweet Potato YieldSweet Potato Yield

aa

a

0

1

2

3

4

5

6

Iron Zinc Control

Kg

/plo

t

Summary: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: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: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 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