I was shown something counter-intuitive on Blain Hjertaas's farm.
He outwinters his cattle, setting out large round hay bales in rows across the chosen fields during the preceding autumn. During the winter, electric polywire restricts the animals' access to the bales, being moved every two or three days to allow them to get to new bales. In effect the cattle are kept in a mob to consume the bales as well as the grass (which Blain has left ungrazed in that field for some months previously).
Now, I would expect that having large numbers of cattle on the land in winter would damage the sward. Also, the cattle never eat all the bale so I assumed the remaining large quantities of litter would prevent grass regrowing in these areas.
I was wrong on both counts. We inspected the field used by the cattle the previous winter and the effect was nothing short of amazing. Where the bales had lain, the grass was a rich green verdant colour, lush and sweet. Admittedly, in patches, matted hay still lay, rotting down. Blain said this would be gone by next year and in any case, he explained, it had been proven that the extra grass growth round these patches more than compensated for them.
Mob grazing in the spring and summer following also helps to remove the patches, as the hooves break up the residual hay, allowing grasses and other seeds to regrow.
The reason for the lush grass? A combination of additional fertility from the (bought in) bales, plus the extra carbon material laid down on the soil which was being converted into humus and thus aiding water retention and building organic matter.
Carbon in the soil. It should be every farmer's goal.