grant agronomics
TRANSCRIPT
Agronomic Practices to Reduce Non-
Nutritive Elements in Food Crops
Cynthia Grant, Fangjie Zhao, Tomohito Arao
National Institute for Agri-
Environmental Sciences - Tsukuba
Cadmium
• Trace element naturally present in soils
– Naturally high levels and Cd:Zn ratios occur in some marine shales
• Added in fertilizers, soil amendments and industrial contamination– Extensive mine waste contamination in
rice land in many countries
• Food crops can accumulate Cd from the soil
• Health concerns over chronic toxicity from long-term consumption of Cd in food
• Restrictions have been placed on level of Cd in foods and fertilizers
Arsenic
• Trace element
• Geogenically elevated Asi in water is widespread in Asia– Limited area of industrial
contamination
• Food crops can accumulate Asi from the soil and affect human health
• Rice is a major source of Asi in the food chain– 50% or more of daily intake
– Anaerobic paddy conditions enhance availability
– Lesser problem with aerobic crops
– Rice takes up Asi through phosphate and Si pathway
• Effort in place in a number of countries to reduce As uptake by rice
Major Concern is with Staple Crops
• Crops such as wheat and rice that make up major portion of diet
• Rice is of special concern
– In particular for rice-based subsistence diets since nutritional value of overall diet affects absorption
• Rice can accumulate high Cd and As
– Major source of Cd and inorganic As in diet
• Cd and As in rice are highly bioavailable
– Inorganic As is more toxic than organic forms
– Rice is low in Zn and Fe• Zn and Fe will restrict absorption of Cd by gut
– Trace element deficiency increases risk
Factors affecting Cd and/or As Concentration of Crops
weather
Soil Characteristics
Soil Cd or As concentration
Crop RotationFertilizer management
Tillage and agronomic
management
Crop Genetics
Irrigation and water management
Reducing Risk of Cd and As Accumulation in Crops
• Reduce concentration in the soil
– Remediation practices such as soil
dressing or replacement, soil
washing or phytoremediation
• Reduce availability in the soil
• Reduce uptake by the plant
• Limit movement to edible parts
Site selection can have a large effect on Cd
concentration in crops
0
200
400
600
800
1000
1200
1400
Cd
Co
nce
ntr
ati
on
(p
pb
)
Minnedosa
Indian Head
Melfort
Morden
N Only
N and P
– Flax concentration in seed grown at four locations
As also varies substantially both from location to
location, and spatially within a field
Hossain et al. (2008)Norton et al. (2009)
Total As
Percentage Asi
Site and Soil Factors Affect Cd and As Phytoavailability
• Background level of Cd or As
• pH– Higher Cd availability at lower pH
• Soil organic matter content– Variable effects, but usually lower Cd availability with higher OM
• CEC– Higher CEC reduces phytoavailabilty
• Redox state
• Presence of other nutrients that complex or compete with the contaminant
Where possible, grow sensitive or accumulator crops on areas
with low availability -Not a feasible solution in most situations
Soil Dressing with Unpolluted Soil Can Remediate
• Very costly
• Requires thick dressing
• Shortage of unpolluted material for top-dressing
• Leads to loss of soil fertility and need for long-term addition of organic materials
• Raises paddy surface causing need for levees or changes to irrigation and drainage system
Soil washing can remove Cd from paddy soils
– About 60% of cost of soil dressing
– Can reduce Cd in rice substantially
– May need to correct soil fertilityArao et al. (2010)
Phytoremediation using high accumulating crops may
lower background levels of Cd or As
Arao et al. 2010
Agronomic Practices Are Less Costly and Suitable Across
a Wider Range of Contaminated and Uncontaminated Soils
• Cultivar Selection
• Water Management
• Fertilizer Management
• Crop Sequence
• Tillage
• Seeding Date, Rate
• Pesticide applications
Genetic Variability Exists in Cd and As Concentration and
Bioavailability in Crops
• Among species
– Much higher levels in durum wheat than bread wheat
• Among cultivars within a species
• Uptake into the plant
• Movement from root to shoot to seed
• Ratio of Cd to Zn and Fe– Zn and Fe reduce Cd absorption
• Possibly proportion of inorganic to organic As
• Breeding programs are in place for a number of staple crops
Select and grow cultivars with low As and
Cd content and/or bioavailability
Cd In Low- And High-Cd Durum Wheat Isolines
0.00
0.05
0.10
0.15
0.20
0.25
Gra
in C
d (
mg
kg
-1)
8982-SF 8982-TL W9260-
BC
W9261-
BG
W9262-
339A
Kyle
Low Cd lines
High Cd lines
Clarke et al. 2003
Stewart Valley-1995
– Low Cd lines retain Cd in the root
Seed Cd in Soybean at Three Manitoba Sites in 2005
Cultivar ranking
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28
Cd
(p
pb
)
0
200
400
600
800
1000
1200
1400
Morden
Homewood
Winnipeg
Cadmium Concentration of Rice Cultivars under High
Cd conditions (77 mg kg-1) soil Cd
Genetic Variability Also Exists for As in Rice
unpolished rice of 76 cultivars grown at two locations in Bangladesh
– Norton et al (2009)
Cultivar variation in As may relate to radical oxygen
loss and root porosity
Mei et al (2009)
Greater ROL increases Fe plaque formation and decreases As
availability
Water Management
• Flooded, reducing conditions increase As
availability
– Release As from iron oxides and hydroxides
– Reduce arsenate to more weakly adsorbed arsenite
– Affect formation of Fe-oxide plaques that adsorb As
• Flooding reduced rice Cd concentration
– Cd combines with S to form CdS (insoluble) if
flooded and CdSO4 (soluble) when not flooded
Arao et al. (2009)
Flooding decreased rice grain Cd but increased grain As
0.00
0.20
0.40
0.60
0.80
1.00
As o
r C
d (
mg
kg
-1)
Grain As Grain Cd
throughout
until 3 wks after heading
until heading
except 3 wks before and after heading
until 3 wks before heading
2 wks after transplanting and 3 wksbefore and after heading 2 wks after transplanting
Arao et al. (2009)
Aerobic conditions before and after
heading may provide a
compromise
Water regime affected both total arsenic concentration
and species in rice grain in pot studies
• Inorganic As is more harmful than methylated form such as DMA(dimethylarsinic acid)
• Aerobic or periodically aerobic conditions decreased total arsenic in rice grain but increased the proportion of inorganic As relative to DMA– Methylation may be response to
As stress
Li et al. (2009)
F-A or A-F changed from flooded to aerobic
or vica versa after flowering on day 96
Approximately 80% reduction in total As in grain, straw and husk by aerobic rather than flooded production
Growing rice in raised beds can reduce As
availability
• Higher redox potential in the raised beds causes adsorption of As onto oxidized Fe surfaces, reducing availability.
• Arsenic in the arsenate form in oxidized soils is suppressed by phosphate, unlike the arsenite that is in flooded soils
• Yield of rice on raised beds is less affected by soil As levels than in conventional paddies
Duxbury et al. (2007)
FAO-Cornell project
Arsenic in both rice grain and straw was lower in the
raised beds than conventional paddies
Duxbury et al. (2007)
FAO-Cornell project
Fertilizer Management
Fertilizer Management Can Influence Cd and As
Concentration
• Addition of Cd in fertilizer
• Effects on soil or rhizosphere chemistry
– pH, osmotic strength, exchange reactions
– Formation of iron plaque
• Competition for plant uptake
• Competition for translocation within the plant
• Effects on plant growth
– rooting, transpiration, dilution
Nitrogen fertilizer is the most commonly required
fertilizer for cereal production
• N fertilization can
increase both soil
solution Cd and durum
wheat grain Cd
concentration in pot
studies
R2 = 0.9558
R2 = 0.9108
0
50
100
150
200
250
300
0 200 400 600 800 1000
Urea added (ppm)
Gra
in C
d (
pp
b)
0.0
0.5
1.0
1.5
2.0
So
lutio
n C
d (
pp
b)
Grain Cd
Solution Cd
Mitchell 1999
Cadmium in durum wheat was increased by N fertilizer
under field conditions
• Both yield and Cd
concentration increased
• Effect was greater on lighter-
textured soil
• Increase occurred with all N
sources
• Similar results with barley
and flax
• Should avoid excess N
applications to minimize
effects
0
50
100
150
200
Gra
in C
d (m
g k
g-1
)
Clay Loam Fine Sandy
Loam
Control
Anhydrous ammonia
UAN
Urea
Ammonium nitrate
Gao et al. (2010)
Arsenic in rice may also be affected by N application
• Lower concentration of As when N was added in the nitrate form in pot studies
– Nitrate stimulated As co-precipitation of or adsorption to Fe (III) minerals in the soil
– Needs field testing
• Amount of nitrate added was unrealistically high in these studies
– Results may not transfer to “real-life”
– Required field testing with agronomic rates of application
0.0
0.5
1.0
1.5
2.0
2.5
3.0
As (
mg
kg
-1)
Shoot
Control
KNO3
NH4Cl
Chen et al. (2008)
Phosphate and Cadmium Concentration
of Sedimentary and Igneous Rocks
Source Average P2O5
Wt %
Average Cd
(ppm)
Range Cd
(ppm)
Morocco 33 26 10-45
Togo 37 58 48-67
Florida 32 9 3-20
Idaho 32 92 40-150
Senegal 36 87 60-115
Finland 40 <2 -
Russia 39 1.25 0.3-2.0
http://www.fertilizer.org/ifa/Home-Page/LIBRARY/Publication-database.html/Cadmium-Content-of-Phosphate-Rock-and-Fertilizers.html
Cadmium in Phosphate May Accumulate in
Soils From Long-term Applications
• Accumulation = Addition - losses
• Addition is affected by
– Cd concentration in fertilizer
– Rate of phosphate addition
– Frequency of application
• Losses are mainly by crop off-take
• Phytoavailability may also be affected by soil
characteristics and management
Sheppard, S.C., C.A. Grant. M.I. Sheppard, R. de Jong and J. Long. 2009. Risk indicator for
agricultural inputs of trace elements to Canadian soils. J. Environ. Qual. 38(3): 919-932.
Cd concentration of durum wheat increased with
application rate and Cd concentration
2008
0
20
40
60
80
100
120
140
160
0 20 40 60 80
P Fertilizer (kg/ha)
Gra
in C
d (
pp
b)
Low CdMedium CdHigh Cd
Averaged over sites
Seven years of application
Cd concentration of durum wheat after 7 years of fertilization
increased with Cd input but varied from soil to soil
R2 = 0.9789
R2 = 0.9886
R2 = 0.4772
0
50
100
150
200
250
0100
200300
400500
600
Cd added (g per ha)
Ellerslie
Carman
Sylvania
R2 = 0.7914
R2 = 0.3306
R2 = 0.7629
0
50
100
150
200
250
0100
200300
400500
600
Cd added (g per ha)
Gra
in C
d (
pp
b)
Spruce
Phillips
Ft. Sask.
pH<7.0pH>7.0
Even low-Cd P fertilizer can increase Cd concentration
in durum wheat in the year of application
0
25
50
75
100
125
150
0 10 20
P (kg/ha)
Gra
in C
d (
pp
b)
Russia (0.2 ppm Cd)
Florida (7.8 ppm Cd)
Idaho (186 ppm Cd)
Averaged over three years and three soils
(Grant et al. 2002)
Why Would Low-Cd P Fertilizer Increase Cd?
• Change in soil pH?
– MAP will acidify soil (Lambert et
al. 2008)
• Effects on mycorrhizae?
– P decreases colonization
• Impact on plant Zn?
– P fertilization can decrease Zn
concentration in plants
– Zn and Cd compete for uptake
– Zn can decrease plant shoot Cd
• Osmotic effects?
– High osmotic potential can
increase Cd availability
0
5
10
15
20
25
0 20 40 60 80
P Fertilizer (kg/ha)
Arb
us
cu
les
(%
)
Low Cd
Medium Cd
High Cd
10
20
30
40
50
60
0 20 40 60 80
P Fertilizer (kg/ha)
Gra
in Z
n (
pp
m) Low Cd
Medium Cd
High Cd
Reducing P Effects on Cd Accumulation in Crops
and Soils
• Reduce phosphate applications
– Increase efficiency of P applications• Seed-placed or side-banded applications
– Target rate of application to crop need
• Reduce Cd concentration of fertilizers
– Limited supply of low-Cd rock
– High cost of removal
• Effect of soil characteristics must be
accounted for when assessing risk
Phosphate Fertilizer and Arsenic
• Oxidized arsenic species arsenate acts as phosphate analogue
– Enters plant through phosphate co-transporters
– Phosphate will compete with arsenate for plant uptake
• BUT: phosphate also competes with arsenate and arsenite for adsorption on Fe-oxides
– Reduces As adsorption and increases availability
• Phosphate does not compete for arsenite form that is found under flooded conditions Phosphate
Effect of Phosphate Fertilizer on Arsenic is
Complicated
• Phosphate status of plant also affects – Phytosiderophore secretion by plant
– Fe-plaque formation higher under low P conditions
– Feedback regulation of arsenate uptake by P transporters
• Balance of competition in soils, for binding sites, and for plant uptake and transport
• Generally seems to increase As concentration rather than decrease it
In pot studies, P application increased grain As
concentration in rice under flooded conditions
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Gra
in A
s (m
g g
-1)
0 15 30
Arsenate (mg kg-1
)
0 mg P kg-1
50 mg P kg-1
Hossain et al. 2009
Sulphur application may also reduce As accumulation in rice, through
Fe-plaque formation, arsenate desorption and transport
Hu et al (2007)
– Solid bars had As added to the pot
Zn competes with Cd for uptake and translocation
0
200
400
600
20 25 30 35 40 45 50 55 60
Zn Content (ppm)
Ca
dm
ium
Co
nte
nt
(pp
b)
Beresford
Justice
Newdale
R2 = 0.94
Flax
Durum Wheat
0
20
40
60
80
100
Cd
Co
nce
ntra
tio
n
(p
pb
)
Control
Dual Band P
Dual Band P + Zn
Broadcast P
Broadcast P + Zn
– Zn fertilization can decrease crop Cd accumulation in the field
– Can have yield and nutritional benefit from increased Zn as well
5.5 6.0 6.5 7.0 7.50
2
4
6
8
10
12
14 Lockwood shaly loam
Romaine lettuce, 2nd Crop
Codex Limit
100 or 250 mg Zn kg-1
0 Zn
Lettu
ce C
d, m
g kg
-1 D
W
Soil pH at Harvest of Crop 2
– .
Effect of 100 or 250 mg kg-1 added Zn on Cd in
Romaine lettuce at varied soil pH
– Courtesy of Rufus Chaney
Without Regulations, Someone May Sell Cd Wastes
as Zn Fertilizer!
In 1999-2000, Zn by-product fertilizer from China was delivered to
northwestern US/Canada. Analysis showed that a Cd waste
comprised much of the load.
Sample Cd Zn Cd:Zn
------ mg/kg DW ------
Fume-Zn-1 46,400 345,000 0.135
Fume-Zn-2 72,800 313,000 0.233
Fume-Zn-4 215,000 216,000 0.995
Fume-Zn-5 199,000 230,000 0.865
Cenes ZnSO4 7.1 320,000 0.000022
Blue-Min 49. 420,000 0.000127
Iron applications may decrease accumulation of As in Rice
• Fe-oxide plaque at the root surface can be a source or sink for As
• Application of Fe2+ can increase plaque formation and increase As adsorption– Decrease available As for
plant uptake
– Effects shown under pot conditions
• Effects were shown with high rates of Fe application
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
Gra
in A
s (m
g g
-1)
0 15 30
Asenate (mg kg-1
)
0 mg Fe/kg
50 mg Fe/kg
Hossain et al. 2009
Application of Fe EDTA to the soil reduced rice Cd under
growth chamber conditions on contaminated soils
• Also increased grain Fe
concentration from 11.2 to
19.5 mg kg-1 Na2Fe
– Competition between Cd and
Fe for uptake and
translocation
• FeSO4 or foliar applications of
FeSO4 or Fe EDTA increased
grain Cd – unexpected
• Rate of Fe application was
very high
– May not have same effect at
rates of application that are
feasible for crop production
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
Cd
(m
g k
g-1
)
Brown Rice White Rice
Control
Soil FeSO4
Soil EDTA Na2Fe
Foliar FeSO4
Foliar EDTA Na2Fe
Shao et al. (2008)
Arsenic in paddy rice was inversely related to native silicic
acid in the soil solution (Bogdan and Schenk (2008)
– Indicates that soils with
high plant-available Si
can produce low plant
As concentration
– Si fertilization might
reduce As
concentration in rice
grain
Silicon Application can Reduce As Accumulation in
Rice
• Rice is a strong Si accumulator– Aids in stress resistance
– Si is often used as fertilizer to increase rice yield
– Well-water is often low in Si
• Arsenite is taken up and transported by Si pathway– Si and arsenite compete for uptake and
efflux transporters
Silicon application reduced As concentration and
proportion of inorganic As in rice grain in pot studies
• Si fertilization reduced As
uptake
– As accumulation lower in
shoots and to a lesser extent
in grain
– Win-win scenario
• Si decreased inorganic As
but increased DMA
– Greater effect in reducing
toxicity than in reducing total
concentration
• Si fertilization also increased
grain and straw yield Li et al. (2009)
Liming may reduce Cd availability on acid soils
• Cadmium phytovailability decreases with
increasing pH
– ALL OTHER FACTORS BEING CONSTANT
• Effects of liming are greatest in pot studies
• Effects in field have been mixed
– decreases, increases or no effect
• Liming of acid soils may improve yield and
reduce Cd
Effect of liming on Cd in wheat and carrot on two soils
0
20
40
60
80
5.0 6.0 7.0 8.0
Soil pH
Pla
nt C
ad
miu
m
Wheat-CL
Carrot-CL
Wheat-Moraine
Carrot-Moraine
Singh et al.
Effects of Crop Sequence
Cd accumulation in the seed in both soybean and durum wheat
was highest after canola and lowest after barley
0
50
100
150
200
250
300
350
400
450
Se
ed
Cd
(m
g)
Durum BRC Durum BRC-
North
Soybean
BRC
Soybean
BRC-North
Barley
Canola
Flax
P<0.0001P<0.0001
P<0.0001
P<0.0001
60%55%
60%
30%
Crop Rotation Effects
• Crop removal of Cd
– phytoremediation
• Effects of crops on soil biology
– Mycorrhizae assist plant in accessing Zn and P
– Reduced mycorrhizae could possibly reduce Zn and maybe increase Cd
• Effects on soil chemistry
– pH
– organic acids
• Release of Cd from residue
Flax Cd concentration increased with increasing Cd
concentration in applied wheat crop residue
Eastley et al.
Concentration of Cd in straw returned
to field differs from crop to crop
• Flax: 0.27-0.69 ppm
• Canola: 0.32-0.36 ppm
• Barley: 0.03-0.08 ppm
Higher concentration of Cd in durum
wheat or soybean after canola or flax may
be due to release of highly available Cd
from decomposing crop residue
Summary - Some Things Increase Cd and As
• Long-term addition of Cd in phosphate
– related to concentration and fertilization rate
• Phosphate, N and KCl can increase Cd in
year of application
– generally unrelated to Cd content
– related to impact on soil chemistry and plant growth
• Phosphate can increase As in rice
• Crop sequence may affect Cd concentration
Summary - Some Things Decrease Cd and As
• Remediation practices
• Cultivar selection
• Nitrate N may reduce As in rice
• Zn can decrease Cd in crops– Increase yield and nutritional quality, too
• S, Si and Fe may decrease As– Si is especially promising
• Liming may decrease Cd
– On low pH soils but variable results
• Aerobic or raised bed production can decrease As accumulation in rice, but may increase Cd
Concerns
• Limited agronomic work on As conducted under field conditions
• Much of the research work on both As and Cd is done in pot studies – Conditions often do not reflect real soil conditions
– Little field evaluation is available of many practices
– Responses may differ under field conditions
• Many practices are relatively expensive
• Trade-offs may occur with yield
Most Promising Management Practices?
• Aerobic production to reduce As
– Yield impact?
• Cultivar Selection
– Highly promising for both Cd and As
• Zn fertilization to reduce Cd
• Si fertilization to reduce As
• Liming to control pH
• Improved nutrient use efficiency to avoid excess
applications of N and P
Extra benefit of increased
yield on deficient soils
Thank you to Rufus Chaney for his input
and to you for your attention