Monday, February 9, 2015

A Question of P

I recently participated in a panel at the Chatham-Kent Farm Show.  My contribution to the panel was a focus on the principles of good agronomy.  One principle I chose to discuss regarded the apparent decline in soil test P & K levels.  A farmer in the audience asked me to reconcile the recent problems with algae blooms in  Lake Erie against my argument that we are not applying enough phosphorous.
It was an excellent question.  I partially addressed it by relating back to the 80's when a similar problem occurred with too much P being washed into Lake St Clair and Lake Erie. This was caused by an explosion in corn acres accompanied by too much tillage.  Soil erosion was the main factor causing soil P to be washed along with valuable topsoil down the rivers.  The Land Stewardship program was initiated by OMAF which paid farmers to adopt no-till and conservation tillage practices to address the erosion issue.  The program had the desired effect and farmers quickly adopted conservation tillage practices.  One additional side effect of this program was unleashing Peter Johnson on the farm scene through his first job at OMAF as a Land Stewardship coordinator.  I voiced the opinion that we are heading backward in our tillage practices and have not done enough to stop the flush of sediment down the river that occurs every time we are blessed with a 2" rainfall.  I have listened to my friends from the Ausable-Bayfield Conservation Authority describe the nutrient flushes that occur with heavy run-off periods. These heavy flushes are more common now than 30 years ago thanks to the greater frequency of heavy rain events.
Recently agriculture has been front and centre regarding the environment and our effect on bees and other pollinators.  Some of the criticism is valid, however much is not.  The urban policy makers are far removed from the farm gate and will remain so. I can hear the comments echoing in my ears from some farmers that our urban neighbours are also part of the phosphorous problem, thanks to overloaded sewage systems and no one addresses that issue.  Why are we always on the hot seat?  While this argument is partially true, the fact remains that agriculture practices are a significant source of P loading in our lake water. In my opinion, we in agriculture cannot stake the moral high ground of being good stewards of the environment without taking this issue seriously.
We also have been learning over the last two years that the P problem is more complicated than we initially believed, thanks to something know as dissolved P.  Dissolved P is the tiny fraction of total P that is susceptible to loss in water.  Water leaves our field in the surface water run-off that may or may not contain soil particles and in our tile drains. This surplus water often contains phosphorous. Fertilizer and manure contribute to soluble P levels.  The fact that they provide readily available sources of phosphorous is why they are efficient sources of nutrients for crop production.  At the same time they are most susceptible to losses of dissolved P immediately following application.

Could it be that our increasing love with the value of tile drainage be a contributor to algae blooms?
Could it be that surface applications of P fertilizer in the fall be a contributor to algae blooms?
Could it be that surface application of manure be a contributor to algae blooms?
The answer to these questions is definitely yes.

Two different studies in two watersheds conducted over multiple years in northern Indiana and central Ohio discovered that half of the dissolved P and half of the total P in the watersheds originated from tile drainage.  More disconcerting was the amount of P coming out of those tiles was in concentrations high enough to encourage algae growth.

Measuring Phosphorous Losses from Midwest Fields

Closer to home, Ontario research by Dr Merrin MacRae has confirmed that phosphorous discharge from tile drains can be the main contributor to P losses.
In a weird twist surface applications of fertilizer and manure, without immediate incorporation leave the soluble fraction of the phosphorous more susceptible to movement into surface water. Mixing nutrients with a little bit of soil reduces the amount of soluble P that is susceptible to loss. In no-till fields surface applications of phosphorous allow the soluble P to access tile water via earthworm holes.  A little tillage can be a good thing when it comes to P.

So if we have identified a problem, what can we do to reduce the amount of dissolved P entering our watersheds?  Quite a lot, to be honest.

1.  Apply phosphorous in bands and reduce broadcast applications.  Banding P reduces the total amount of P that comes in contact with the soil water which will reduce the amount of dissolved P that is susceptible to loss.
2.  Time phosphorous applications close to when crops are actively growing.  A significant amount of dissolved P is lost through the winter months.  Fall applications of P are therefore more susceptible to loss.  A growing crop will take up dissolved P as it becomes available.
3.  Winter wheat or other types of fall and winter cover crops help to take up soluble P.  A bit of common sense, but how much difference this makes during the winter months is unknown.
4.  Use technology to identify the different yield zones in our fields and soil test according to yield zone.  Apply P according to crop removal within those zones.  Put less P on the low yielding areas and more P on the high yielding areas.

Coming back to the question posed by the farmer in Chatham, part of my thinking remains the same. Low phosphorous soil test levels still need to be addressed.  Changing our mindset to look at phosphorous buildup applications in the same way we look at nitrogen application I think is in order.
In other words apply phosphorous in the spring and summer only, apply phosphorous every year according to crop needs and if possible, use a small amount of tillage to incorporate surface applied phosphorous.

I think we can manage that.

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