Cow urine

Glen Herud @ Milking on the Moove talks about cow urine.


Urine Patch Contains Equivalent to 800kg Nitrogen per Ha
Here's what happens. Basically, here is a cow. This is a bit of a funny cow. She's a Friesian so what she does is she urinates into what you call a urine patch, which is about the size of a dinner plate. Within that dinner plate, there are 800 KGs of nitrogen per hectare. So there is an equivalent to 80 KGs of nitrogen per hectare. So the way I think of that, to make sense of it is if you take a hectare, which is a football field and let's say we had a way of getting all these cows lined up so they all urinated at once and all the urine patches covered one whole hectare. If they all urinated at once, that would be applying 800 KGs of nitrogen per hectare at once.


Average NZ Dairy Farmer Applies 150-200kg Nitrogen per Ha per Year
To give you an indication of how much that is, your average dairy farmer does around 150 to 200 KGs of nitrogen per hectare per year. They will do that over multiple small allocations of fertilizer. So, what I want to sort of get through to you is that there is a heck of a lot of nitrogen in a urine patch. What happens is that if you think about grass. I don't know, what we got? Five, six, seven grass plants within a urine patch? They've got their roots systems that go like that, probably around 30 centimeters deep. So what happens is the nitrogen comes in via the urine and while it's in the soil it turns into nitrate. It can be absorbed by the plants. If you look at this picture here, you can see these dark green patches in the paddock there. Those are fertility patches. They are either feces patches or urine patches. What's happened is that those grass plants there, have as much nitrogen as they can get and they've bolted away and they are nice and dark and green.


The Few Grass Plants in a Urine Patch can't Absorb all the 800kg of N
The problem is that there are 800 KGs of nitrogen being applied. Well, a heck of a lot of nitrogen will be applied and those few little plants, there is absolutely no way they are going to be able to absorb all that nitrogen. There is far too much.


What happens is the nitrate attaches to water molecules, H2O, because nitrate is soluble in water. Those water molecules filter down through the soil profile and drain away and they take the nitrate with them. Once they get below the roots’ depth of the plants, they can't get absorbed. It keeps on going, all the way down, until it gets into our groundwater. Then it ends up in our waterways. So that is very simply how nitrate leaching takes place. Essentially, excess nitrate that isn't absorbed by the plants ends up filtering through the soil profile and getting into our groundwater.


There are a couple of things that affect the rate of nitrate leaching. One of them is your soil profile. If you've got nice, well I shouldn't say nice, if you've got free draining soils that are kind of rocky, the water flows through those soils much more quickly. So, obviously the nitrate flows through quicker. If you've got heavier clay soils, then the water sort of sits there more and therefore the nitrates sits there more. The amount of water in the soil profile affects the rate of nitrate leaching. What happens generally is during the summer lots of nitrogen is sort of applied and it sort of sits there in the soil and then winter comes along and we get all this wet weather and it all sort of leaches out through the winter. What's the other thing that affects nitrate leaching? Oh, your plants, your root depths. If we can get plants that have twice the root depths, then there are obviously twice as much time for them to absorb nitrate. That's a very brief rundown. It will probably horrify a few scientists but that sort of serves the purpose of what we need to explain today.

So the next little while I'll start talking about how we can farm differently in ways to reduce our nitrogen leaching cap or nitrogen leaching rate. If you have been following the news you'll see that regional councils are starting to sort of propose nitrate caps, so saying that you can only leach around 25 KGs of nitrogen per hectare per year. Obviously, if you are a potato grower, they would horrify you and dairy farmers are equally worried about how they are going to be able to farm and meet that sort of a target. That's what I want to talk about in the next couple of weeks.