Yes - and what's going on behind the scenes here is that we assume that fertilizer contributes to the DP fraction only in the season of application, but with manure we account for DP contributions in the first season of application AND the second and third seasons after application (this is all based on work that Peter Vadas did). In the second season following application, 20% of the manure total P remaining on the soil surface is expected to become water soluble. In the third season following application, 5% of the total P remaining on the soil surface is expected to become water soluble.

Vadas, P.A., L.B. Owens, and A.N. Sharpley. 2008. An empirical model for dissolved phosphorus in runoff from surface-applied fertilizers. Agric. Ecosys. Environ. 127-59-65. Vadas, P.A., L.W. Good, P. A. Moore Jr., and N. Widman. 2009. Estimating phosphorus loss in runoff from manure and fertilizer for a phosphorus loss quantification tool. J. Environ. Qual. 38:1645-1653. Vadas, P. A. and P. J. A. Kleinman. 2006. Effect of methodology in estimating and interpreting water-extractable phosphorus in animal manures. J. Environ. Qual. 35: 1151-1159. Vadas, P.A., W.J. Gburek, A.N. Sharpley, P. J. Kleinamn, P. A. Morre, Jr., M. L. Cabrera, and R. D. Harmel. 2007. A model for phosphorus transformations and runoff loss for surface-applied manures. J. Environ. Qual. 36:324-332

Vadas, P.A., Gburek, W.J., Sharpley, A.N., Kleinman, P.J.A., Moore, P.A., and Cabrera, M.L. et al. 2007a. A model for phosphorus transformation and runoff loss for surface-applied manures. J. Environ. Qual. 36: 324–332. doi: https://doi.org/10.2134/jeq2006.0213

Depending on how much detail we decide to include about this earlier (see comment in section 3.1.1.3), could add sentence here:

"As in section 3.1.1.3, there are some examples of the P index increasing with the October drill treatment. This can be attributed to the increased fraction of P remaining on the surface from fall surface applications when the cover crop no-till drilled compared to fall incorporated applications when no cover crop was present."

Strike

Strike

Replace "All" with "Most" since we do see a few cases where the Oct CC actually increases P Index

This is no longer true for the St. Charles soil (or for this ASD), but it is still true for some soils/regions.If we want to keep things simple, could strike this sentence and the following one.

I looked around to see if the sentence citing Bundy could fit elsewhere but didn't find any obvious place since the effect of nutrient source was consistently so small relative to other things.

Recommend striking this sentence now that the difference rounds to zero. If we wanted to provide a specific example that supports the previous sentence about legacy P, could include some info about the relative contributions of "soil" vs. "applied P" to the surface soil total P we calculate in the P Index, which is an important part of the particulate P calculations.

Picked one "baseline" example. This is where we fall apply fertilizer at a rate equal to crop removal on St. Charles SiL with 50ppm STP:

Surface soil **total ** P concentration is 420 mg/kg, which breaks down to ...

• 12 mg/kg from the fertilizer application
• 408 mg/kg from the soil (calculated with the nonlinear equation we looked at together last week using STP and SOM)

This particular example is on the low end of what we would see for the contribution from applied nutrients because our baseline "fall chisel disk" tillage system has incorporation passes in the fall and spring that leave very little amendment P on the surface.

replace "fertilizer" with "nutrient" (covers both fertilizer and manure)

With the bug fixes, this difference is now small enough that it rounds to zero.

crop removal = 3.72<br /> 20% reduction = 3.68

With the updated results, now have a small average increase with the October CC. This can be attributed to fall surface (unincorporated) fertilizer applications

In Fig 3.4, all four of the points with >5 PI shown for CC Oct Drill have STP = 100 and P applied = crop removal and fall surface fertilizer application

In this specific case, the values of these four points did not increase with the bug fixes, but a different correction I made to a subset of October CC and September CC fields related to incorporation method brought many of the other values down (so now these stick out)

Pick up here

Link to relevant existing resource explaining P fractions etc. https://ipcm.wisc.edu/wp-content/uploads/sites/54/2022/11/UnderstandingSoilP04.pdf

Yes - and for context (not sure it's worth including), we calculate the amount of residue added to the soil surface as a result of the manure applications and use this as an input to RUSLE2 when we run soil loss. For the range of manure application rates in the Cg-Sg rotation, that amounts to 834 - 1390 lb/acre dry matter residue being added to the soil surface

"perennial cool season grass"

"at the downslope edge" - suggesting this wording because I have been surprised at the number of Snap users (and agency personnel!) who forget this point

missing the "CC" in front of Sep here to match graph label

typo: shows