The Looming Soil Phosphorus Shortage



I sometimes feel a little bad for phosphorus. Nitrogen gets all the attention when it comes to fertility planning. Sure, most farmers are committed to throwing down a little phosphorus-rich starter fert, and, yes, nitrogen is needed in the largest quantities, but little ol’ immobile phosphorus is just not getting the respect it deserves. Even sulphur seems to get more hype these days, given the rapid increase in canola acres over the last five to 10 years.

Western Canadian farmers are blessed with relatively young phosphorus- and potassium-rich soils. Add in good organic matter levels (though not great, and eroding in some areas), and the nutrient-supplying capacity of our soils has kept farmers blissfully unaware of the phosphorus mining going on down below. The rub here is that as average yields climb and “highly available” products become more common, the underlying phosphorus-releasing capacity of the soil is becoming eroded.

Don’t just take my word for it, go take a look at your soil tests. (If you happen to be missing a few year’s worth of soil tests, take a look at reasons why you should soil test here and a unique way of using the results here.) Phosphorus management it a long-term project — maintaining soil levels requires annual management with the next two to five years in mind. As one soil scientist said, specialty P products most certainly work, however they are for “land renters and retiring farmers.” In short, managing phosphorus needs on an annual basis at best caps yield, at worst, however, could cause a major wreck.

The Canola Council of Canada recently highlighted work that Jeff Schoenau is doing near Saskatoon. He calls phosphorus deficiency the “hidden hunger” because deficiency symptoms are a poor indicator of phosphorus soil levels. In fact, you could be losing yield without ever noticing a change in your crop.

So what’s to be done about it? As mentioned, if you’re not soil sampling, there’s no time like the present. Secondly, even without a soil test, take a look at the last five years of crop removal rates of phosphorus and balance that against what you’ve added back, keeping in mind that canola can remove 1.5 pounds of P205 PER BUSHEL each year. Click here for some help on determining rates. Seeing a big gap? Time to bump your phosphorus application rates (safely, of course).

And just let me just throw this out there: when is the last time you thought about manure? Yes, really. I fully and completely recognize that grain farmers love their independence from the demands of having livestock, but there’s no reason why grain farmers can’t benefit from this nutrient-rich byproduct of animal production. Manure is cheap, full of organic matter and a whole host of micronutrients, and, if properly composted, rather compact. Call your meat-growing (or milk-making) neighbour and offer to take some poop off their hands. Your soil will thank you for it.

And, lastly, think long term with phosphorus. Extra pounds put down now will always be there and available at a time when you didn’t know you needed them. Renting land? Work long-term phosphorus management into the rental agreement. Prove your worth as a soil steward and make sure your landlord acknowledges the value of your investment. Everybody wins.


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