1. Agronomic Practices to Reduce Non-
Nutritive Elements in Food Crops
Cynthia Grant, Fangjie Zhao, Tomohito Arao
Cynthia.grant@agr.gc.ca
National Institute for Agri-
Environmental Sciences - Tsukuba

2. 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

3. 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

4. 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

5. Factors affecting Cd and/or As Concentration of Crops
weather
Soil Characteristics
Soil Cd or As concentration
Crop Rotation
Fertilizer management
Tillage and agronomic
management
Crop Genetics
Irrigation and water management

6. 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

7. Site selection can have a large effect on Cd
concentration in crops
0
200
400
600
800
1000
1200
1400
CdConcentration(ppb)
M
innedosa
Indian
H
ead
M
elfort
M
orden
N Only
N and P
– Flax concentration in seed grown at four locations

8. 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

9. 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

10. 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

11. 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 fertility
Arao et al. (2010)

12. Phytoremediation using high accumulating crops may
lower background levels of Cd or As
Arao et al. 2010

13. 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

14. 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

15. Cd In Low- And High-Cd Durum Wheat Isolines
0.00
0.05
0.10
0.15
0.20
0.25
GrainCd(mgkg-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

16. 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(ppb)
0
200
400
600
800
1000
1200
1400
Morden
Homewood
Winnipeg

17. Cadmium Concentration of Rice Cultivars under High
Cd conditions (77 mg kg-1) soil Cd

18. Genetic Variability Also Exists for As in Rice
unpolished rice of 76 cultivars grown at two locations in Bangladesh
– Norton et al (2009)

19. 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

20. 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)

21. Flooding decreased rice grain Cd but increased grain As
0.00
0.20
0.40
0.60
0.80
1.00
AsorCd(mgkg
-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 wks
before and after heading
2 wks after transplanting
Arao et al. (2009)
Aerobic conditions before and after
heading may provide a
compromise

22. 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

23. 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

24. Arsenic in both rice grain and straw was lower in the
raised beds than conventional paddies
Duxbury et al. (2007)
FAO-Cornell project

25. Fertilizer Management

26. 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

27. 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)
GrainCd(ppb)
0.0
0.5
1.0
1.5
2.0
SolutionCd(ppb)
Grain Cd
Solution Cd
Mitchell 1999

28. 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
GrainCd(mgkg-1
)
Clay Loam Fine Sandy
Loam
Control
Anhydrous ammonia
UAN
Urea
Ammonium nitrate
Gao et al. (2010)

29. 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(mgkg
-1
)
Shoot
Control
KNO3
NH4Cl
Chen et al. (2008)

30. 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

31. 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.

32. 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)
GrainCd(ppb)
Low Cd
Medium Cd
High Cd
Averaged over sites
Seven years of application

33. 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
0
100
200
300
400
500
600
Cd added (g per ha)
Ellerslie
Carman
Sylvania
R
2
= 0.7914
R2
= 0.3306
R2
= 0.7629
0
50
100
150
200
250
0
100
200
300
400
500
600
Cd added (g per ha)
GrainCd(ppb)
Spruce
Phillips
Ft. Sask.
pH<7.0pH>7.0

34. 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)
GrainCd(ppb)
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)

35. 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)
Arbuscules(%)
Low Cd
Medium Cd
High Cd
10
20
30
40
50
60
0 20 40 60 80
P Fertilizer (kg/ha)
GrainZn(ppm)
Low Cd
Medium Cd
High Cd

36. 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

37. 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

38. 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

39. 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
GrainAs(mgg
-1
)
0 15 30
Arsenate (mg kg
-1
)
0 mg P kg-1
50 mg P kg-1
Hossain et al. 2009

40. 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

41. Zn competes with Cd for uptake and translocation
0
200
400
600
20 25 30 35 40 45 50 55 60
Zn Content (ppm)
CadmiumContent(ppb)
Beresford
Justice
Newdale
R2 = 0.94
Flax
Durum Wheat
0
20
40
60
80
100
CdConcentration
(ppb)
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

42. 5.5 6.0 6.5 7.0 7.5
0
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
LettuceCd,mgkg
-1
DW
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

43. 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

44. 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
GrainAs(mgg-1
)
0 15 30
Asenate (mg kg
-1
)
0 mg Fe/kg
50 mg Fe/kg
Hossain et al. 2009

45. 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(mgkg-1
)
Brown Rice White Rice
Control
Soil FeSO4
Soil EDTA Na2Fe
Foliar FeSO4
Foliar EDTA Na2Fe
Shao et al. (2008)

46. 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

47. 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

48. 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)

49. 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

50. 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
PlantCadmium
Wheat-CL
Carrot-CL
Wheat-Moraine
Carrot-Moraine
Singh et al.

51. Effects of Crop Sequence

52. 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
SeedCd(mg)
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%

53. 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

54. Flax Cd concentration increased with increasing Cd
concentration in applied wheat crop residue
Eastley et al.

55. 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

56. 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

57. 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

58. 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

59. 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

60. Thank you to Rufus Chaney for his input
and to you for your attention