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Grant agronomics
Grant agronomics
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Grant agronomics

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  • 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

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