A majority of phosphorous from RU is broken down into AMPA, then to formylphosphonate, then to phosphate (the natural state of phosphorus we mine/use) as it continues to break down.

For most soils you're looking at 40-60 days for breakdown into it's final substances and the time it takes for those substances to be fully utilized by microbes depend on a few things. Applications less than 90-120 days apart, cold soil/air temperature, high water tables (breakdown is considerably slower by 2-4x in water saturated soil), and a few other things can make the breakdown phosphorus last even longer.

RU loves to hang around the soil and doesn't tend to leach too much. It heavily relies on microbes to break down everything direct surface exposure doesn't break down. Over time RU can create increased concentrations of phosphorus (for instance) in localized zones if plants/microbes aren't using it and other phosphorus inputs aren't managed.

While RU adds phosphate to soils, it's impact can be managed as part of a fertilizing regimen and many farmers do pay attention to it (well, most large commercial ones) if they're using a lot of it continuously. There's a lot of "phosphate salt" fertilizers/herbicides/etc out there and if you're dumping a lot of it on your land at some point you gotta pay attention.

Soil microbes tend to ebb/flow depending on what's going on in the soil. For the most part you see a bit of give/take fighting for resources on the microbe population end rather than a back/forth of extremes lasting a long period of time.

This post was edited by nc-crn on Fri, Jul 4, 14 at 0:11

Glyphosate products, synthetics, are not acceptable to organic growers.

So, NC, how then do farmers prevent what sounds like an inevitable phosphate build-up? P doesn't remove through cropping nearly as rapidly as N and K, correct?

Most farmers who use RU amounts that will build up in the soil tend to care a lot more about overall soil nutrient content rather than the microbial balance of the soil. That's just the nature of the type of farming they do...for better or worse. They would farm similarly/interchangeably no matter the herbicide/inputs they use, though.

While they do strive to manage the P, ultimately they don't care if it's a bit high because it rarely effects many crops negatively. Management is generally done by having a base line for existing P (soil test) and adjusting season-to-season or planting-to-planting with applications by adding less (to none) additional P in their fertilizer regiments.

The biggest downside to this is possible runoff contamination (in both ditches and waterways) rather than crop performance because a lot of the P residual from RU tends to hang out close to the surface rather than finding it's way deep into the soil profile. This isn't an issue for many farmers, but it is for some.

Tangential to this topic, then, the makers of RU and its equivalents must use large amounts of mined phosphorous.

The EPA and FDA are looking to raise the allowable residual of glyphosate products in our food, so if glyphosates do not get into the food chain why is that necessary?
Where glyphosates are used frogs and toads, and other lower life forms are being found with genetic changes that are quite scarey. Many of he target "weeds" are developing immunities to the glyphosates as well, first noted by Iowa State University researchers in the 1990's.