Sloping land should be grazed from the top down to allow the crop to act as a buffer for any run-off that may occur, she said. There should always be a three-metre buffer zone around all waterways.
In bad weather shifting breaks more frequently and offering more supplement can help reduce soil damage as can splitting the mob in two and temporarily reducing the stock density. Back fencing can also prevent further damage to wet paddocks.
Lifting fodder beet before the cows run on to the crop can stop them digging the bulbs out of wet soils.
Sacrifice paddocks are useful in very bad weather but as one farmer pointed out, no one pays for the sacrifice paddocks.
Mathers said depending on the soil type some paddocks should not be consecutively grazed by cattle over winter because this doesn’t allow time for the soil to recover.
She recommended using minimum tillage when establishing crops for grazing, but this does depend on the previous crops.
Mathers said the best scenario is direct-drilling straight into a sprayed-out grass paddock. This produces a lot of organic matter in the soil and leaves the soil aggregates intact.
Once the crop has been grazed growers should be trying to get another crop into the ground as soon as possible in spring to use up nitrogen left behind after grazing.
Crops such as Italian ryegrass, oats and other cereals are ideal options because their deep roots mean they can access nitrogen that after winter is typically sitting below 30cm. To ensure there is no surplus nitrogen in the crop going into winter, growers need to ensure fertiliser inputs match crop demand. This is particularly important in autumn when plant growth starts to slow down.
In terms of nutrient management lower yielding crops, such as forage oats, grown over a larger area are a better option than very high-yielding crops grown in a small area because the larger area dilutes the nitrogen loading.
Winter-active crops are a good forage option because they can uptake nutrients over the colder months. Multi-purpose crops such as oats and triticale can also be a useful nutrient management tool because they will regrow after being grazed in winter and use up surplus nitrogen.
Getting a crop back into the ground as quickly as possible after grazing can help mop up excess nitrogen.
Research projects
FAR is involved with two projects investigating the impacts and management of dairy grazing on arable soils.
The first of these is a Sustainable Farming Fund project looking at sustainable winter dairy grazing. FAR are interviewing farmers in six regions to determine how they manage their dairy grazing systems. The aim of the project is to create grazing management plans.
The second is a Ministry of Business, Innovation and Employment project, Pasture 21, which is looking at reducing nitrogen losses under forage crops. It is a six-year project carried out in conjunction DairyNZ, Plant & Food New Zealand and other industry bodies. The aim of the project is to reduce nitrogen losses by 2% by 2020.
