Every farm is unique, and that means every plan to minimise environmental impact is unique, too. Strategies that work for one system may not work for the farm next door, and vice versa. When it comes to pastures, however, science has shown us even small changes can make a big difference.
Grow in winter
With the wet winter-spring period the main risk time for N leaching, the more winter growth in the system, the more soil N is taken up. Modern plant breeding has helped greatly in this - today’s perennial ryegrasses grow 20-30% more winter DM than their 20-year-old predecessors. To really soak up even more N in winter, sow the highest yielding Italian ryegrass or cereal.
Nothing loses soil N in winter like bare ground. Post autumn fodder beet, for example, sow cool season oats or Italian/annual ryegrass to catch the remaining N before it may leach in winter. Don’t wait till the whole paddock is bare – sow half as soon as the crop is grazed. Earlier sowing gives much better yield and N uptake.
It means more careful weed and pest control, but establishing new pasture through minimum tillage releases less N than cultivation, and uses less diesel too. Long term it is better for soil structure too.
Mix it up
Deep rooted plantain is known to mitigate N leaching in several ways. Cool-season active plantain is even better – more growth when the risk of N loss is highest (and more feed it is needed most).
As ryegrass tillers grow to have 3 leaves, water soluble carbohydrate (WSC) goes up and protein (i.e. N) goes down. Many pastures in New Zealand are grazed at around 2-2.5 leaves/tiller; if grazing can be delayed until the 3 leaf stage, less N will comes out of livestock. With their high palatability, mixed diploid/tetraploid pastures are easiest to manage this way.
Use 24 hour grazing to give cows a new paddock in the afternoon. Cows eat about 70% of their intake in the first half of the grazing. Putting them into a new paddock when ryegrass carbohydrate levels are highest and protein levels are lowest in the late afternoon means there’s less N going into them. 24 hour grazing has no effect on cow production compared with 12 hour grazing (and is easier with half as many stock shifting decisions too!)
Raising per cow intake and MS production with tetraploid ryegrass and optimal grazing management can give the same total MS yield from fewer cows. The Lincoln University Dairy Farm is a great example of this, going from 680 cows to 560 cows and producing the same MS. This means more feed going into milk, less into cow maintenance, and a lighter environmental footprint. An added benefit is that fewer heifers are needed, further reducing the environmental footprint.
The same principles hold for breeding ewes, cows or finishing stock. Higher production per animal or faster growth rates means greater efficiency and a lower environmental footprint.
Fix for free
Legume-rich pastures need less artificial N fertiliser. Use high performance red, white and annual clovers, as they fix 25-30 kg atmospheric N/ha for every tonne of DM grown (and provide higher animal performance too).
Compacted, waterlogged soils release more greenhouse gases than soils with healthy structure. They are more prone to runoff and soil loss, with overland flow of sediment, phosphorus (P) and faecal material to waterways. They require more tractor work for seedbed preparation and sowing, and more fertiliser to ensure growth of subsequent crop or grass growth.
Mind the dirt
Soil bared out by over-grazing is at higher risk of wind-blow or gully erosion than soil protected by pasture plants, even on flat land. Maintaining vegetative ground cover through pasture maintains and improves soil organic matter and structure, and enhances biological activity.