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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 Crop Genetics Soil Characteristics Tillage and agronomic management Soil Cd or As concentration Fertilizer management Crop Rotation 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 – Flax concentration in seed grown at four locations 1400 1200 Cd Concentration (ppb) 1000 800 600 N Only 400 N and P 200 0 M In M M in el or di ne fo de an rt do n H sa ea d
  • 8. As also varies substantially both from location to location, and spatially within a field Percentage Asi Total As Norton et al. (2009) Hossain et al. (2008)
  • 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 Stewart Valley-1995 Low Cd lines 0.25 High Cd lines Grain Cd (mg kg ) 0.20 -1 0.15 0.10 0.05 0.00 8982-SF 8982-TL W9260- W9261- W9262- Kyle BC BG 339A – Low Cd lines retain Cd in the root Clarke et al. 2003
  • 16. Seed Cd in Soybean at Three Manitoba Sites in 2005 1400 1200 1000 Morden Homewood 800 Winnipeg Cd (ppb) 600 400 200 0 0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 Cultivar ranking
  • 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 Greater ROL increases Fe plaque formation and decreases As availability Mei et al (2009)
  • 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 throughout 1.00 until 3 wks after heading until heading 0.80 except 3 wks before and after heading As or Cd (mg kg ) -1 until 3 wks before heading 0.60 Aerobic conditions before and after 3 wks 2 wks after transplanting and before and after heading heading may provide a 2 wks after transplanting compromise 0.40 0.20 0.00 Grain As Grain Cd Arao et al. (2009)
  • 22. Water regime affected both total arsenic concentration and species in rice grain in pot studies • Inorganic As is more Approximately 80% reduction in total As in harmful than methylatedgrain, straw and husk by aerobic rather form such as than flooded production DMA(dimethylarsinic acid) • Aerobic or periodically aerobic conditions decreased total arsenic in rice grain but increased the proportion of inorganic As relative to DMA Li et al. (2009) – Methylation may be response to F-A or A-F changed from flooded to aerobic As stress or vica versa after flowering on day 96
  • 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 2.0 increase both soil 300 R2 = 0.9108 Solution Cd (ppb) 250 solution Cd and durum 1.5 Grain Cd (ppb) 200 wheat grain Cd R2 = 0.9558 150 1.0 concentration in pot 100 studies 50 Grain Cd 0.5 Solution Cd 0 0.0 0 200 400 600 800 1000 Urea added (ppm) Mitchell 1999
  • 28. Cadmium in durum wheat was increased by N fertilizer under field conditions • Both yield and Cd concentration increased 200 Control • Effect was greater on lighter- Anhydrous ammonia UAN Grain Cd (m g kg-1) textured soil 150 Urea Ammonium nitrate • Increase occurred with all N 100 sources • Similar results with barley 50 and flax • Should avoid excess N 0 applications to minimize Clay Loam Fine Sandy effects Loam 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- Control precipitation of or adsorption to KNO3 3.0 Fe (III) minerals in the soil NH4Cl – Needs field testing 2.5 As (mg kg ) • Amount of nitrate added was -1 2.0 unrealistically high in these 1.5 studies 1.0 – Results may not transfer to “real-life” 0.5 – Required field testing with 0.0 agronomic rates of application Shoot Chen et al. (2008)
  • 30. Phosphate and Cadmium Concentration of Sedimentary and Igneous Rocks Source Average P2O5 Average Cd Range Cd Wt % (ppm) (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 Averaged over sites 2008 Seven years of application 160 140 Grain Cd (ppb) 120 100 80 60 Low Cd 40 Medium Cd 20 High Cd 0 0 20 40 60 80 P Fertilizer (kg/ha)
  • 33. Cd concentration of durum wheat after 7 years of fertilization increased with Cd input but varied from soil to soil pH>7.0 pH<7.0 250 250 Ellerslie Spruce Carman Phillips R2 = 0.4772 200 200 Sylvania Ft. Sask. Grain Cd (ppb) 150 R2 = 0.7629 150 R2 = 0.9886 100 R2 = 0.3306 100 R2 = 0.9789 50 2 R = 0.7914 50 0 0 0 0 0 0 0 0 0 10 20 30 40 50 60 0 0 0 0 0 0 0 10 20 30 40 50 60 Cd added (g per ha) Cd added (g per ha)
  • 34. Even low-Cd P fertilizer can increase Cd concentration in durum wheat in the year of application Averaged over three years and three soils 150 125 Grain Cd (ppb) 100 75 50 Russia (0.2 ppm Cd) Florida (7.8 ppm Cd) 25 Idaho (186 ppm Cd) 0 0 10 20 (Grant et al. 2002) P (kg/ha)
  • 35. Why Would Low-Cd P Fertilizer Increase Cd? • Change in soil pH? 25 20 – MAP will acidify soil (Lambert et Arbuscules (%) al. 2008) 15 10 • Effects on mycorrhizae? Low Cd 5 Medium Cd – P decreases colonization High Cd 0 • Impact on plant Zn? 0 20 40 60 P Fertilizer (kg/ha) 80 – P fertilization can decrease Zn concentration in plants 60 50 – Zn and Cd compete for uptake Grain Zn (ppm) Low Cd Medium Cd 40 – Zn can decrease plant shoot Cd High Cd 30 • Osmotic effects? 20 – High osmotic potential can 10 increase Cd availability 0 20 40 60 P Fertilizer (kg/ha) 80
  • 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 0.8 0.7 0.6 Grain As (m g g ) -1 0.5 0.4 0 mg P kg-1 0.3 50 mg P kg-1 0.2 0.1 0 0 15 30 -1 Hossain et al. 2009 Arsenate (mg kg )
  • 40. Sulphur application may also reduce As accumulation in rice, through Fe-plaque formation, arsenate desorption and transport – Solid bars had As added to the pot Hu et al (2007)
  • 41. Zn competes with Cd for uptake and translocation Durum Wheat Control Flax Dual Band P 600 100 Dual Band P + Zn Cd Concentration Cadmium Content (ppb) R2 = 0.94 Broadcast P 80 400 Broadcast P + Zn 60 (ppb) 200 Beresford 40 Justice Newdale 20 0 20 25 30 35 40 45 50 55 60 0 Zn Content (ppm) – Zn fertilization can decrease crop Cd accumulation in the field – Can have yield and nutritional benefit from increased Zn as well
  • 42. Effect of 100 or 250 mg kg-1 added Zn on Cd in Romaine lettuce at varied soil pH – . 14 Lockwood shaly loam Romaine lettuce, 2nd Crop Lettuce Cd, mg kg DW 12 -1 10 0 Zn 8 6 4 Codex Limit 2 -1 100 or 250 mg Zn kg 0 5.5 6.0 6.5 7.0 7.5 Soil pH at Harvest of Crop 2 – 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 0.7 sink for As 0 mg Fe/kg 0.6 50 mg Fe/kg • Application of Fe2+ can Grain As (m g g-1) 0.5 increase plaque formation 0.4 and increase As adsorption 0.3 – Decrease available As for 0.2 plant uptake 0.1 – Effects shown under pot conditions 0 0 15 30 • Effects were shown with -1 Asenate (mg kg ) high rates of Fe application 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 Control Soil FeSO4 – Competition between Cd and 1.6 Soil EDTA Na2Fe Fe for uptake and 1.4 Foliar FeSO4 Foliar EDTA Na2Fe translocation 1.2 Cd (mg kg-1) • FeSO4 or foliar applications of 1.0 FeSO4 or Fe EDTA increased 0.8 grain Cd – unexpected 0.6 • Rate of Fe application was 0.4 very high 0.2 – May not have same effect at 0.0 Brown Rice White Rice rates of application that are feasible for crop production 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 80 Plant Cadmium 60 Wheat-CL 40 Carrot-CL Wheat-Moraine 20 Carrot-Moraine 0 5.0 6.0 7.0 8.0 Singh et al. Soil pH
  • 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 450 P<0.0001 P<0.0001 400 Barley 350 55% Canola 60% Flax 300 Seed Cd (mg) 250 200 P<0.0001 150 P<0.0001 30% 100 60% 50 0 Durum BRC Durum BRC- Soybean Soybean North BRC BRC-North
  • 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 Extra benefit of increased • Zn fertilization to reduce Cd yield on deficient soils • Si fertilization to reduce As • Liming to control pH • Improved nutrient use efficiency to avoid excess applications of N and P
  • 60. Thank you to Rufus Chaney for his input and to you for your attention