1 / 28

Summary of soil P levels and stratification

Summary of soil P levels and stratification. GLPF Grant- Team meeting #5 July 23-24, 2013. Lake Erie eutrophication and dissolved P loads. Maumee and Sandusky Rivers are the two largest tributaries to Lake Erie 74-78% Agriculture. Data from: Heidelberg Tributary Loading Program .

keziah
Download Presentation

Summary of soil P levels and stratification

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Summary of soil P levels and stratification GLPF Grant- Team meeting #5 July 23-24, 2013

  2. Lake Erie eutrophication and dissolved P loads • Maumee and Sandusky Rivers are the two largest tributaries to Lake Erie • 74-78% Agriculture Data from: Heidelberg Tributary Loading Program

  3. Conservation practices in the Lake Erie Watershed • Large-scale conservation practices have been adopted throughout the Lake Erie basin to reduce soil erosion • No-till or reduced till • Conservation reserve program • Has successfully reduced sediment loading (Richards et al. 2008, 2009)

  4. Why is dissolved P increasing? From Sharpley 2003 From Vadas et al. 2005 • Typical agronomic soil tests use 0-8” cores • P stratification occurs under no-till practices from the lack of soil mixing and application of surface fertilizers • Runoff in Maumee and Sandusky Rivers tend to be surficial and interacts with the top 1-2” of soil

  5. Why is dissolved P increasing? • Dissolved P in runoff can increase under no-till management From Kleinman et al. 2011

  6. Research Questions • How high is soil P and what is the extent of P stratification in the Sandusky River Watershed? • Paired with certified crop advisors (CCAs) to collect soil samples from >1500 fields • Most soils were split into 0-2” vs 2-8” samples (n=1405) • A subset of soils were split into 0-1, 1-2, 2-5, 5-8” samples (n=234) • Mehlich3 extractable P measured at a soil test lab

  7. Soil Profile

  8. Research Questions • Does DRP readily exchange with the typical agricultural soil? • Dilute Aqueous Soil Solution (DASS) • Extracted DRP from 1 g of soil in 1 L of distilled water

  9. Research Questions • Does DRP readily exchange with the typical agricultural soil? • DiluteAqueousSoil Solution (DASS) • Extracted DRP from 1 g of soil in 1 L of distilled water • How variable is P stratification within a given field spatially and temporally? • Select fields received gridded sampling every ~10 meters to examine spatial variation (n=78) • A subset of fields were sampled in 2009 and again in 2012 to examine temporal variation (n=74)

  10. Soil P levels • Ranges from 2.8 – 291 ppm • Mean = 41.3 ppm • Median = 35.8 ppm • 90th percentile = 72ppm • 90% of the data are <72ppm 90th 75th 50th 25th 10th

  11. The extent of P stratification • Top: Mean/median = 59/55 ppm, ranged from 4.0 – 319 ppm • Bottom: Mean/median = 35/28 ppm, ranged from 2.0 – 291 ppm • Top 2” are significantly higher than the bottom (paired t-test, P<0.001, n=1526)

  12. The magnitude of stratification: ratio • The ratio of top:total ranged from 0.3 – 3.4 • Mean = 1.54 Median = 1.48 • The ratio was highest at lower soil test P • Dividing by a smaller # ? Top > Total Top = Total Top < Total *Using a correction factor not possible

  13. The magnitude of stratification: ratio • Ratios need to be on a log-scale • Ratio 2:1=2 ; ratio 1:2=0.5 • The ratio is significantly higher than 1 (one-sample t-test, P<0.001)

  14. The magnitude of stratification: difference • The difference (top–total) ranged from -78 – 176 ppm • Mean = 18 ppm Median = 15.8 ppm • The difference is significantly greater than zero (one-sample t-test, P<0.001) • The difference was highest at higher soil test P Top > Total Top = Total Top < Total

  15. 4-part stratification Median • Stratification evident even in the top 1” of soil (ANOVA, P<0.001, n=232) • Although the degree of stratification varied some… 60 54.5 49 34 26

  16. 4-part stratification Median • Stratification evident even in the top 1” of soil (ANOVA, P<0.001, n=232) • Although the degree of stratification varied some… • 85% of the samples had some degree of stratification 60 54.5 49 34 26

  17. 4-part stratification Median • Stratification evident even in the top 1” of soil (ANOVA, P<0.001, n=232) • Although the degree of stratification varied some… • 85% of the samples had some degree of stratification 60 54.5 49 34 26

  18. Dilute aqueous soil suspension (DASS) • DRP from 1 g of soil extracted with 1 L of distilled water over 16h • DRP readily exchanges with water • Mean DRP = 0.037 mg P/L • Ranged from 0.003 – 0.115 mg P/L • DASS was positively related to soil test P (log-transformed, r2=0.73, p<0.001) • Mean DRP = 0.026 mg P/L • Ranged from 0.009 – 0.047 mg P/L

  19. Temporal variation in P stratification Ratio Difference Total M3P • Sampled 74 fields in 2009 and again in 2012 • No distinct trends in how fields changed from 2009-2012

  20. Temporal variation in P stratification • Significant, but slight increase in total M3P from 2009-2012 (means: 2009 = 43ppm, 2012 = 47ppm; paired t-test P=0.007) • No significant change in the ratio (means: 2009 = 1.83, 2012 = 1.81) or the difference (means: 2009 = 30ppm, 2012 = 32ppm)

  21. Temporal variation in P stratification 2012 > 2009 2012 = 2009 • D M3P is the difference between 2012 and 2009 • Means: • Top= 5.9 ppm ± 3.0 SE *(significantly >0, one-tailed t-test, P=0.05) • Bottom = 4.1 ppm ± 2.1 SE • Total = 4.5 ppm ± 1.6 SE *(significantly >0, one-tailed t-test, P=0.05) • Top is more variable than bottom 2012 < 2009

  22. Spatial variation in P stratification • Gridded sampling in 3 fields

  23. Spatial variation in P stratification: Total M3P (ppm) Grid 2 Mean M3P: • Grid 1 = 50.5 ppm • Grid 2 = 54.1 ppm • Grid 3 = 58.4 ppm Grid 1 Grid 3

  24. Spatial variation in P stratification: Ratio top:total Grid 2 Mean Ratio: • Grid 1 = 1.4 • Grid 2 = 1.3 • Grid 3 = 1.2 Grid 1 Grid 3

  25. Spatial variation in P stratification: Difference top-bottom (ppm) Grid 2 Mean difference: • Grid 1 = 18.1 ppm • Grid 2 = 10.9 ppm • Grid 3 = 7.3 ppm Grid 1 Grid 3

  26. Spatial variation in P stratification: Coefficient of Variation • CV= standard deviation mean • As much variation by field as across 1400 fields for total M3P and the difference • Variation in the ratio lower by field

  27. Summary • Most (90%) total soil test P levels are <72ppm • Soil P stratification is prevalent in the Sandusky River Watershed • P in soil readily exchanges with water and this exchange is predicted by M3P • Fields tend to accumulate P over time and this accumulation appears to be higher in the top 2” of soil • Variation in P levels and stratification can be as high within a field as across 1400 fields

  28. Questions?

More Related