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Fate of manure nitrogen applied for grass silage production

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The full proceedings paper is at: www.extension.org/72781

Previous research conducted in western Washington State has demonstrated that when manure N is applied at rates greater than needed for grass uptake, excess N in soil in the form of nitrate-N can leach to shallow groundwater during the months of high rainfall. In a prior study, it was evident that tillage and reseeding of the cropland was a contributor to loss of nitrate–N from soil to underlying groundwater. The objective of this study was to characterize the effect of re-seeding of cropland using minimum tillage and conventional tillage methods on crop uptake of nitrogen, soil nitrate-N concentration, nitrate concentration in shallow ground water underlying the field, and the relationships between these matrices.

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Fate of manure nitrogen applied for grass silage production

  1. 1. Fate of Manure Nitrogen Applied for Grass Silage Production Joe Harrison and Lynn VanWieringen, Washington State University Barb Carey, Washington Department of Ecology
  2. 2. Previous research conducted in western Washington has demonstrated that when manure N is applied at rates greater than needed for grass uptake, excess N in soil in the form of nitrate-N can leach to shallow groundwater during the months of high rainfall. In the prior study, it was evident that tillage and reseeding of the cropland was a contributor to loss of nitrate–N from soil to underlying groundwater. 0 5 10 15 20 25 30 35 40 45 Nitrate-N(mg/L) MCL 2004 2005 2006 2007 2008 Error Bars = +/- 1 SD 2009 Tillage
  3. 3. Objectives  Characterize nitrogen inputs, outputs and underlying GW nitrate concentration in a typical manured field over the aquifer.  Propose adjustments in management practices to minimize nitrogen leaching. Purpose A two- year study was initiated in 2009 to study the fate and transport of nitrogen from dairy manure when applied to cropland that was reseeded to grass for silage production.
  4. 4. nitrification Organic Nitrogen DenitrificationLeaching Volatilization Nitrate NO3 - Ammonium NH4 + N2 or N2O Plant Uptake NH3 Ammonia N Cycle
  5. 5. BertrandCreek Two wells side by side—one shallow and one deep well First three wells drilled Study site and well locations
  6. 6. Bedrock -700 -600 -500 -400 -300 -200 -100 0 100 200 300 400 500 0 2 4 6 8 10 12 14 Sea Level Sumas-BlaineSurficial Aquifer Everson-VashonSemi-confining Unit Feet West East Miles Vertical scale greatly exaggerated Bertrand Creek Study Site
  7. 7. One-half of a 22- acre grass field was prepared with conventional tillage, and one-half was prepared with minimum tillage in May of 2009.
  8. 8. Samples of manure were taken at each application for nutrient content Application rate was recorded
  9. 9. Grass samples were taken just prior to Each cutting for yield and nutrient content
  10. 10. Temperature, pH, dissolved oxygen, and conductivity are measured in a flow Cell assembly before the water is exposed to the atmosphere.
  11. 11. Tillage and Harvest  In 2009, after the grass was reseeded, the conventional till grass was harvested 2 times, and the minimum till grass was harvested 3 times.  Due to a poor stand establishment, the minimum till area received minimum till treatment again in 2010.  In 2010, the conventional till grass was harvested 4 times and the minimum till grass was harvested twice.
  12. 12. 0 10 20 30 40 50 60 70 80 90 1st Qtr 2nd Qtr 3rd Qtr 4th Qtr East West North
  13. 13. 0 10 20 30 40 50 60 70 80 90 1st Qtr 2nd Qtr 3rd Qtr 4th Qtr East West North Figure 1. Soil nitrate concentrations during the study period.
  14. 14. 0 5 10 15 20 25 Averagenitrate-Ningroundwater(mg/L)
  15. 15. Summary  There was no evidence of a difference in groundwater nitrate due to the tillage treatment.  Results from this case study indicated that the type of tillage had an impact on the timing of increases in soil nitrate.  However, variability in denitrification conditions in monitoring wells obscured comparison of groundwater nitrate effects between the two management practices.
  16. 16. Nitrogen Application and Harvest  Total nitrogen applied for minimum till and conventional till, respectively, were: 523 and 440 lbs/acre (2009), and 697 and 697 lbs/acre (2010).  Total nitrogen harvested for minimum till and conventional till respectively, were: 310 and 298 lbs/acre (2009), and 425 and 477 lbs/acre (2010).
  17. 17. Soil Nitrate  Soil nitrate-nitrogen for the minimum till plot remained below 30 ppm in 2009 except on one occasion. Soil nitrate for the minimum till plot was observed to increase to 40 and 60 ppm in 2010.  Soil nitrate-nitrogen for the conventional till plot increased to 60 ppm in 2009, and 35 ppm in 2010.
  18. 18. 0 10 20 30 40 50 60 70 80 90 1st Qtr 2nd Qtr 3rd Qtr 4th Qtr East West North
  19. 19. Nitrogen Mass Balance Inputs Outputs  Manure  Fertilizer  Irrigation water  Atmospheric input  Soil organic matter  Grass crop  Volatilization  Denitrificatio n Residual • Soil nitrate • Groundwater nitrate • Soil ammonium • Soil organic matter
  20. 20. Root Zone Water Table (Saturated) Unsaturated Zone Manure (Ammonia, Organic N) NO3-N- N2 gas denitrification NO3-N- Organic N Some mineralizes NO3-N- Summer NH4-N NO3-N-
  21. 21. Water Table Root ZoneNO3-N Fall-Winter Precipitation/Recharge (10-30 inches/year in US portion of the aquifer) Organic N N2 gas denitrification Winter NO3-N
  22. 22. 0 2 4 6 0 200 400 600 800 mbelowwatertable Farm A Farm B Farm C 1 year since recharge 2 years since recharge 3 years since recharge Groundwater recharged under Farm B 2 years ago Groundwater recharged under 4 to 6 farm fields upgradient 3 years ago Distance (meters) Vadose zone (Adapted from Ryan, 2008) Water Table Generalized groundwater flow beneath fields in the Abbotsford area 8 miles northeast of the study site showing that water near the top of the water table represents the most recent water recharged from above.
  23. 23. Water Table (Saturated) Nitrate (NO3-N-) Atmospheric N2 gas Soil Nitrate (NO3 --N) Organic N Ammonia (NH4 +-N) Nitrate (NO3-N-) Grass N Harvested Manure Ammonia (NH4 +-N) Organic N Plant & Microbial Residues Vadose Zone Groundwater Irrigation: Ammonia, Total N Ammonia Ammonia Soil Organic Matter Inorganic Fertilizer

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