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Fwaa jan 12 2017 n content


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importance of Nitrogen for plant growth; methods for measuring and estimating plant N content

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Fwaa jan 12 2017 n content

  1. 1. Measuring and Estimating N Levels in the Crop Canopy Olga Walsh, PhD Cropping Systems Agronomist & Extension Specialist University of Idaho, Parma Research & Extension Center FWAA Winter Conference, Boise, ID January 12, 2017
  2. 2. BS Soil Sci: St Petersburg Russia – 1997; MS Soil Sci – 2007 and PhD Soil Sci- 2009, OSU, Stillwater, OK; Soil Nutrient Management - Montana State Univ - 2010 – 2014 Cropping Systems Agronomist, Univ Idaho – from 2014
  3. 3. Presentation Outline: 1. Nitrogen (N) role in plants 2. Plant N content 4. Measurement vs estimation 5. Measuring N: plant tissue testing 6. Estimating N: chlorophyll meters & charts 7. Estimating N: crop sensors 8. Using UAVs (Drones)
  4. 4. Nitrogen role in plants
  5. 5. N function and deficiency symptomsN is important for high photosynthetic activity, vegetative growth and protein building
  6. 6. N and photosynthetic activity  Process by which plants use the energy from sunlight to produce sugar from CO2and H2O.  Sugar is converted into energy in plant cells, used for growth and development  N – major component of Chlorophyll (green)  Plants sufficient in N are healthy and vigorous and have high photosynthetic activity
  7. 7.  Chlorosis = yellowing of the leaves  Pale green to yellow lower (older) leaves  Why lower leaves? N is MOBILE in plant  New leaves develop, take nutrients from the old leaves and use them to grow. The old leaves are left without enough nutrients  display the symptoms. N and chlorosis Adequate N Limited N, 2005
  8. 8. N and vegetative growth  Low N  smaller leaves, poor stand establishment, stunted plants, slow growth CYMMIT, 2006 Low N Adequate N
  9. 9. N and vegetative growth  N - essential element of all amino acids in plant structures (building blocks of plant proteins)  Important in the growth and development of vital plant tissues and cells  Enables plants to grow and reproduce (component of DNA)
  10. 10. N and root growth  Plants adapt to nutrient availability by changing their root system architecture to efficiently explore soil zones containing the limited nutrient.  Root growth affects overall plant growth  Root growth is affected by N Giehl & von Wirén, 2014
  11. 11. Plant N content
  12. 12. Plant N content  Healthy plants often contain 3 to 4 % of N in above-ground tissues.  This is a much higher concentration compared to other nutrients.  N content is an important characteristic often used for evaluation of crop health and nutrient status.
  13. 13. N demand by crops High demand (> 120 lb N/a removed in 1 season Moderate (50- 120 lb N/a removed in 1 season Low demand (<50lb N/a removed in 1 season
  14. 14. Sufficiency  Deficient – nutrient is at low concentration, severely limits yield, produces distinct deficiency symptoms; Extreme deficiency plant death  Insufficient - nutrient is below amount required for optimum yields; Symptoms seldom evident  Sufficient - nutrient present in adequate amounts for optimum crop growth  Excessive - nutrient is sufficiently high to result in a corresponding shortage of another nutrient  Toxic – element concentration is sufficiently high to significantly reduce plant growth; Severe toxicity  plant death
  15. 15. Measuring vs estimation
  16. 16. Measurement vs Estimation  Several methods are available for direct measurement and indirect estimation of N content in plant biomass.  Direct = measuring exactly the thing that you're looking to measure  Indirect = measuring something by measuring something else
  17. 17. N measurement & estimation
  18. 18. Measuring N: Plant tissue analysis (potato petioles)
  19. 19. Plant tissue analysis  Directly measures nutrient levels in the plant  The supply of available nutrients is reflected in plant nutrient content  Use of plant tissue analysis allows producers to evaluate the effectiveness of fertilizer management  N taken up by potatoes can be detected in petiole nitrate analysis within 3-4 days after fertilizer application  Indicates the N status of the plant in the past 2-3 days, very good tool for in- season N decisions
  20. 20. Response to NResponsetoNitrogen Deficiency Sufficiency Toxicity Relative foliar N content
  21. 21. N content & fertilizer rates  N content can be used to guide N fertilizer applications Increasing N fertilizer rate Increasingcropyield Physiological optimum Top yield Bare economic optimum Can cause 10-15% yield loss BUT symptoms are rare
  22. 22. N uptake in potatoesTotalNuptake, kg/ha 200 100 50 0 N uptake Effective N management matches N
  23. 23. Petiole sampling Agvise Lab, 2017
  24. 24. Effect of petiole position on nutrient concentration Agvise Lab, 2017
  25. 25. Petiole N – lab test • Petiole samples tested each week help determine the current nitrogen status of the potato crop • N in the form of nitrate (NO3-N) is extracted from potato leaf petioles with 2% acetic acid (at room temperature) and analyzed by flow injection
  26. 26. Potato petiole levels
  27. 27. Potato petiole sampling  Early in the season - petiole nitrate levels are expected to be high (20,000 - 30,000 ppm)  During rapid vegetative growth & beginning of tuber bulking - petiole levels are expected to drop  If temp warms up quickly after cool period – explosive rapid vine growth  drop in petiole N levels to 5000 ppm or lower = dilution of the nitrate in the potato petiole, BUT the canopy can look lush and green  Apply more N? - If the total soil N >60 lb/a  No need to additional N fertilizer
  28. 28. Estimating N: Chlorophyll meters & Leaf color charts
  29. 29. Chlorophyll & Plant N • Chlorophyll is positively and linearly correlated with plant leaf N – can use chlorophyll to estimate NChlorophyll concentration Leaf N concentration
  30. 30. How Chlorophyll meters work  The meter measures the ratio of radiation transmittance from two wavelengths:  red……..strongly absorbed by chlorophyll, and  near infrared……..not absorbed by chlorophyll  Meters expose a portion of a leaf to abundant light and measure how much was NOT captured by chlorophyll in the photosynthetic process
  31. 31. Chlorophyll Meters FieldScout, $2,850 Spectrum Technologies; Apogee Instruments, atLeaf 2017 SPAD, $2,700
  32. 32. SPAD meter accuracy Xiong et al, 2017 • SPAD values are highly correlated with chlorophyll content (left) AND with plant N content (right)
  33. 33. Chlorophyll Meters  SPAD, FieldScout - values proportional to amount of chlorophyll in the leaf  MC-100 – values of actual chlorophyll concentration Primack, 2015 atLeaf readings SPADreadings $2,700 vs $250
  34. 34. From Chlorophyll to N rate • 6 years of field trials • Relationship between Chlorophyll and Economic N rate (Figure 1) • Developed N recommendations (Table 1)
  35. 35. Leaf color charts Board + App = $150 IRRI; Spectrum Technologies, 2017 As low as $1.00/unit
  36. 36. Estimating N: Crop Sensors
  37. 37. Optical Crop Sensors;;;
  38. 38. Sensor-Based N Rate 1. We need a lot 2. We don’t need much 3. We need a little1. High Yield Potential, plants some- what deficient in N 2. Very high Yield Potential, almost adequate N nutrition 3. Low Yield Potential, plants are very deficient
  39. 39. Sensor Basics • Emits light and measures reflectance from plants • Red light is used for photosynthesis (absorbed) • NearInfrared light – not enough energy, not used (reflected) • Sensor reading - Similar to a plant physical examination, 2014
  40. 40. Sensor Basics • Sensor can detect:  Plant Biomass  Plant Chlorophyll  Crop Yield  Water Stress  Plant diseases, and  Insect damage  Sensors are used by agronomists, breeders, plant pathologists, weed scientists, crop consultants, growers, 2014
  41. 41. red redNIR NIR 30%50% 60% 8% NDVI = (NIR-red)/(NIR+red) Sensor detects the amount of light reflected from the crop and calculates NDVI Tubana, 2007 NDVI = 0.76 NDVI = 0.25
  42. 42. What the GreenSeeker sensor “Sees” The vigor of the leaves and the ratio of plant to soil affect NDVI values N-Tech Ind., 2009
  43. 43. N-Tech Ind., 2009 What the GreenSeeker sensor “Sees”
  44. 44. From sensor to N Rate  Established Reference Strip (at seeding)  Compared to the rest of the field (sensed at tillering)  Now we know: yield potential and crop responsiveness to N  How do we determine the needed N rate?  Need a formula (algorithm) to translate sensor readings into N recommendation
  45. 45. NDVI vs crop yield NDVI sensors can estimate crop yield with 90-95% accuracy Walsh et al, 2013
  46. 46. NDVI vs yield NDVI explained 68% of variation in wheat yield. Combining NDVI and plant height increased accuracy of yield prediction to 73%. Walsh et al, 2015
  47. 47. Using UAVs (Drones)
  48. 48. DRONE STUDY - Objectives To establish a UAV-based methodology for in-season prediction of:  wheat N content  grain yield potential, and  and prescribing N fertilizer rates
  49. 49. Drone Study
  50. 50. N rates and crop sensor data UAV-based NDVI map showing N rates applied Map showing UAV- based NDVI values Walsh et al, 2016 Spring wheat, Parma, ID, 2016
  51. 51. 3-D view of wheat plots, Rupert, ID
  52. 52. NDVI data collected with UAV
  53. 53. Measured vs estimated plant N Walsh et al, 2017 Drone images provide accurate estimation of plant N content
  54. 54. Thank you! Questions? Olga Walsh University of Idaho, Parma R&E Center Tel: (208)722-6701 Web: IDCrops ( Twitter: @IDCrops