Transcript Influence of cover crops on nutrient availability in a sweet potato cropping system in South Florida Jeanna Ragsdale (Graduate committee: Yuncong Li, Thomas Obreza,

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
Introduction:
Limitations to vegetable production
in South Florida:
Poor soil
• Calcareous soils
• Low organic matter
• Low water and
nutrient holding
capacities
Calcareous Soils
• pH 7.5-8.5
• Low organic matter
• Reduced availability
of Fe, Mn, Zn, Cu,
Co, B, and P
THE NATURE AND PROPERTIES OF SOILS
13th Edition
Nyle C. Brady and Ray R. Weil
Cover Crop Benefits
• 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
Objective:
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
Cover Crop Management
• Planted in August
• No fertilizer used
Cover crops at 4 weeks
Sorghum-sudan
Sunnhemp
Velvet Bean
Cover crops at 9 weeks
Sorghum-sudan
Sunnhemp
Velvet Bean
Mowed and tilled
in November
Sweet Potato (Boniato)
Crop Management
• 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
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
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
Measurements:
3. Sweet Potato
– Plant tissue nutrient concentrations
before and after foliar applications of
micronutrients
4. Sweet potato yield
Results
Cover Crop Biomass (Mg/ha)
a
14
12
Mg/ha
10
b
8
c
6
4
c
2
0
Weeds
S orghums udan
S unnhemp
V elv et B ean
Cover crop biomass total N
(kg/ha)
a
600
500
kg/ha
400
b
300
b
200
100
c
0
Weeds
S orghums udan
S unnhemp
V elv et B ean
Plant tissue N concentration
(g/kg)
20
a
18
16
g/kg
14
ba
ba
12
10
b
8
6
4
2
0
Weeds
S orghums udan
S unnhemp
V elv et B ean
Cover crop biomass total Fe
(g/ha)
1400
a
1200
ba
g/ha
1000
800
600
400
bc
c
200
0
Weeds
S orghums udan
S unnhemp
V elv et B ean
Cover crop biomass total Zn
(g/ha)
2500
a
g/ha
2000
ba
1500
1000
500
bc
c
0
Weeds
S orghums udan
S unnhemp
V elv et B ean
Plant tissue Zn concentration
(mg/kg)
100
a
90
80
mg/k
70
60
b
50
cb
40
c
30
20
10
0
Weeds
S orghums udan
S unnhemp
V elvet B ean
Cover crop biomass total B (g/ha)
4000
a
3500
3000
b
g/ha
2500
2000
c
1500
1000
c
500
0
Weeds
S orghums udan
S unnhemp
V elv et B ean
Soil Nutrients
Soil total N (g/kg)
3
2.5
g/kg
2
pre-plant
1.5
pre-cut
after-incorporation
1
0.5
0
Weeds
Sorghum-sudan
Sunnhemp
Velvet Bean
Soil total C (g/kg)
60
58
g/kg
56
54
pre-plant
pre-cut
after-incorporation
52
50
48
46
Weeds
S orghums udan
S unnhemp
V elvet B ean
Sweet potato leaf tissue
nutrient concentrations
Sweet potato leaf N
35
(g/kg)
a
34
33
g/kg
32
b
31
30
29
b
b
Weeds
S orghums udan
28
27
26
S unnhemp
V elve t B ean
Sweet potato leaf C
(g/kg)
427
a
426
425
424
g/kg
423
422
ba
ba
421
b
420
419
418
417
Weeds
S orghums udan
S unnhemp
V elvet B ean
Sweet potato leaf K
30.5
(g/kg)
a
30.0
29.5
g/kg
29.0
ba
28.5
b
28.0
27.5
b
27.0
26.5
26.0
25.5
Weeds
S orghum- s udan S unnhemp
V elvet B ean
Sweet potato leaf Mg
4.0
a
a
a
3.5
(g/kg)
b
3.0
g/kg
2.5
2.0
1.5
1.0
0.5
0.0
Weeds
S orghum- s udan
S unnhemp
V elvet B ean
Sweet potato leaf Fe
(mg/kg)
32
a
31
mg/kg
30
29
28
b
b
b
27
26
25
Weeds
S orghum- s udan S unnhemp
V elvet B ean
Leaf Fe in iron subplots (mg/kg)
after fertilizer application
32
a
31
30
mg/kg
29
ba
28
27
ba
b
26
25
24
Weeds
S orghum- s udan
S unnhemp
V elv et B ean
Sweet potato leaf Zn
(mg/kg)
35
30
a
a
a
a
mg/kg
25
20
15
10
5
0
Weeds
S orghums udan
S unnhemp
V elv et B ean
Leaf Zn in zinc subplots (mg/kg)
after fertilizer application
45
a
40
35
a
a
a
mg/kg
30
25
20
15
10
5
0
Weeds
S orghum- s udan
S unnhemp
V elvet B ean
Sweet potato yield
Sweet Potato Yield
10
9
8
Kg/plot
7
a
6
a
5
4
a
a
3
2
1
0
Weeds
S orghum- s udan S unnhemp
V elvet B ean
Sweet Potato Yield
6
a
5
a
a
Kg/plot
4
3
2
1
0
I ron
Z inc
C ontrol
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
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
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
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