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

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)

Why is dissolved P increasing? 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 From Sharpley 2003 From Vadas et al. 2005

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

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)  Mehlich 3 extractable P measured at a soil test lab

Soil Profile

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

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 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)

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

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)

The magnitude of stratification: ratio The ratio of top:total ranged from 0.3 – 3.4  Mean = 1.54Median = 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

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)

The difference (top–total) ranged from -78 – 176 ppm  Mean = 18 ppmMedian = 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 The magnitude of stratification: difference

4-part stratification Stratification evident even in the top 1” of soil (ANOVA, P<0.001, n=232) Although the degree of stratification varied some… Median

4-part stratification 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 Median

4-part stratification 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 Median

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 = mg P/L  Ranged from – mg P/L DASS was positively related to soil test P (log-transformed, r 2 =0.73, p<0.001) Mean DRP = mg P/L Ranged from – mg P/L

Temporal variation in P stratification Sampled 74 fields in 2009 and again in 2012 No distinct trends in how fields changed from Total M3P RatioDifference

Temporal variation in P stratification Significant, but slight increase in total M3P from (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)

Temporal variation in P stratification  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

Spatial variation in P stratification Gridded sampling in 3 fields GridAcresn Sample distance TillageDrainage m Rot. no till (till for corn) Somewhat poor, tiled mWell-drained, tiled mWell-drained, tiled

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

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

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

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 Spatial variation in P stratification: Coefficient of Variation

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

Questions?