Saturday, 13 August 2011

The Impact of Mob Grazing

Mob grazing is about repairing the soil. Large amounts of litter (ie plant material, not plastic bags and old newspapers) is laid down on the surface of the soil by the grazing animals as they pass through, replicating what the large grazing herds of Europe and North America did over tens of thousands of years (until man wiped them out). In fact, grassland has evolved under such conditions, namely a short period of intense grazing and trampling as the herds passed by, followed by a long rest period for regrowth.

So, large amounts of litter are laid down on the soil. Blain Hjertaas called this the 'armour' - it protects the soil from damage by rainfall, from extremes of heat and cold, from sunlight, from hoof damage. Greg Judy called it a mattress. I'd call it a mulch. I forgot to ask Neil what he called it, but you get the picture!

This is a mob-grazed field approximately ten days to two weeks after grazing. Neil's in the middle of a drought, so the alfalfa is the first to regrow. Note how deep the litter or 'armour' (or mattress' or ...)is.

 When the litter's peeled back, the new grass regrowth can be seen. Within a few weeks. the litter will be buried under a sea of green grass, and it will be starting to be broken down by the worms, the bacteria, the fungi, the nematodes and all the other creepy crawlies that live in a healthy soil. It won't be long before it forms a layer of compost.

This was a clod cut at random from a field. The top inch and a half of the 'soil' was nearly all organic matter, in the process of being converted into nutrient rich, water-retentive, aerated topsoil.

One of the secrets to good mob grazing is to give the plants enough recovery time. There is no magic formula for this. Location, altitude, latitude, rainfall, temperature, cloud cover, management, etc all impact on this. Neil used to be on 90 days recovery, though as his land has improved, he's seen that come back to 60 days. Blain favours 100 days to allow all his plants to recover.

Neither of them are too concerned about seed heads either. In fact, they like to see them, for two reasons: One is that it shows the plants are fully recovered from the previous round of grazing / trampling and will have replenished their root carbohydrate stores fully. This will allow speedy regrowth post-grazing. The second reason is that seed heads are a valuable source of carbohydrate. They balance the protein lower down in the leaf and lead to excellent growth rates. A sign that the protein: energy balance was right in both Neil's and Blain's animals was that their dung was tight and well formed, not sloppy and loose (a sign of too much protein, and typical of the dung of conventionally grazed cattle).

Neil's kubota in a mature stand of grass. Note the depth of grass cover on there. 60 days ago it looked like the picture above, a layer of litter with very little green showing. Litter doesn't stop a healthy grass plant from regrowing. In fact, it maintains a suitable microclimate around the roots and encourages regrowth. Blain believes his soil remains active in the middle of a Saskatchewan winter, and as soon as the snow melts the already-warm roots help the grass plant to explode into life

The cows enjoying the mature, well grown grass

1,000 head of cattle. This is animal impact. They will move to the next strip in two and a half to three hours. There's approximately 1.2m pounds in weight of cattle grazing this strip. They're gaining weight at c.0.75kg/day though Neil believes they will get closer to 1kg/day shortly

1 comment:

  1. tom

    Did you know on the african savannah that the termites are thought to process more grass than all of the big graziers combined (zebra, gazelle, wildebeest)?

    Makes your think about the role of the insects in grass processing.