Thursday, October 18, 2012

Mobile Cowshed & Nitrate Leaching Of Dairy Cows

The second reason why I think the mobile cowshed can be helpful is with nitrate leaching.

2.Nitrate Leaching
It's not obvious at first, but after researching nitrate leaching I saw how the mobile cow shed can be used to create a farming system which leaches less nitrogen.

It's important to note that the major cause of nitrate leaching from dairy farms is the cows urine. The cows urine patch is a very concentrated deposit of nitrogen and the grass within the urine patch is not able to absorb all the nitrogen. The result is the nitrogen converts to nitrate in the soil and then moves down the soil profile into the ground water.

This table taken from a report for Environment Bay Of Plenty, it shows the nitrate leaching rates of various farming systems.

Most New Zealanders would not know that market gardeners have almost twice the amount of nitrate leaching of a dairy farm. Neither would they know that cropping farmers leach just as much as an intensive dairy farm.
These figures seem to go against what I had always been told about urine and nitrate leaching, because there is no urine on a market garden. The reason cropping & market gardeners leach nitrates is because of the high fertilizer use and the high amount of plant residue left in the soil, especially over winter.

Market gardeners and cropping farmers make up such a small amount of land area compared to dairy and sheep. The huge growth in the dairy industry has seen it take up much more of the NZ land area and the high profile of Fonterra has led to the public attention around the leaching of the industry.

Sheep farms leach much less nitrate than a dairy farm, this is due mainly to the fact that sheep produce a smaller amount of urine in each patch and the grass can absorb it better. Also many sheep farms will be on dry land with very low annual rainfall. This means that these farms will have low stocking rates and dry soils leach less nitrate.

If we look at a standard dairy farm. The cowshed is usually placed in the middle of the farm. The cows have to be within walking distance of the cowshed, so they can be milked twice a day. This means the cows are restricted to that one piece of land.

It's common for a dairy farm to have a stocking rate of 2.7-3.0 cows per hectare. These cows start grazing in paddock number 1 and they will rotate around the farm and be back in paddock number 1 in 20-30 days (depending on grass growth rates etc). This means that the cows are urinating on the same ground month after month, year after year. 
The result is the continual application of urine onto the ground is causing excess nitrogen to be applied to the soil.

With the mobile system, the cowshed is mobile. This means the herd of cows can be mobile too. Which means that the cows don't have to be on the same land year after year. Which can result in a reduction in the amount of urine that is being applied to the land.

This allows farmers to be flexible about how they farm their cows.

If we use the example from my previous post of a 200 ha sheep farmer diversifying into dairy by milking 100 cows, we can see how this principle can be put into practice.

These 100 cows will need 33 ha at a stocking rate of 3 cows/ha. 

So in year 1 the cows can be milked on a 33 ha block at the front of the farm, the cows just rotate around the 33 ha block as they would on any farm. In year 2 the cows can be moved to a new 33 ha block situated in the middle of the farm. In year 3 the cows move again to another 33 ha block. This can go on and on until the cows return to the first 33 ha block some years later.

Once the cows have moved off each 33 ha block, it can run sheep again.

The result is less nitrogen is being applied to the soil.

An alternative grazing option would be to just start the herd at the front of the farm and simply rotate around the entire 200 ha property. It could take the whole year for the cows to move around the entire property. Which has the same result of having less nitrogen applied to the soil by the cows urine.

Cows put nitrogen into the soil via urine. Crops on the other hand take nitrogen out of the soil. So it makes sense to combine the two farming systems.

If the farmer planted a crop on the 33 ha block once the cows had moved to the new block, in theory this crop could adsorb the excess nitrogen deposited by the cows. Wheat is a very nitrogen hungry crop and it has a root system that can go down 1.5 metres, so this could be an ideal rotation. The cows naturally apply nitrogen to the soil and the crops naturally absorb the excess nitrogen out of the soil. This type of system could reduce the crops need for nitrogen fertilizer. High fertilizer use is one of the main causes of nitrate leaching on arable farms.

It could be possible to plant a winter active type crop, which will absorb the nitrogen out of the soil over the winter period, which is when a majority of nitrate is leached. 

This is the basic concept, obviously the cows don't apply nitrogen evenly (if they did we wouldn't have leaching problem), so crop yields may be lower in this type of system. There needs to be a lot more work done to look into this type of system.

By making the herd of cows mobile, it allows farmers to move the cows around. They can use the cows ability to naturally add nutrients to the soil as an advantage. It allows farmers to move the herd away again before the cows nutrients become a disadvantage.

A traditional dairy farm could run this system at the moment, but it will require a reduction in stocking rates to account for the addition of the crops. This becomes uneconomic as a traditional dairy farm model is based on the entire farm generating a high financial return. A reduction in cows which return $3,000/ha and the addition of crops which return $700/ha will seriously reduce the income of a dairy farm, which will make it uneconomic.
That's the real problem with nitrate leaching reduction measures. Farmers know how to do it, they just don't know how to do it economically.

By introducing dairy cows onto sheep/beef & arable farms these farmers are making an increase in income, so the mixed dairy/cropping/sheep example above is profitable for these farmers.

I seriously believe, that the future sustainable growth of the dairy industry lies in the hands of the sheep/beef and cropping sectors. New Zealanders will not tolerate the continued expansion of intensive dairy farms, as we have seen in the last 20 years. The proposed nitrate leaching restrictions that we are seeing, is the beginning. I think the dairy industry can continue to expand, it just has to do it differently. 

The integration of dairy cows onto sheep/beef and cropping farms is one way the industry can expand, which adds wealth to New Zealand but it can do it with out the adverse environmental effects.

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