Using less N but more often, reduces pollution

22 December 2000

Using less N but more often, reduces pollution

Grazing-based spring calving

systems were the topic of a

Mole Valley Farmers

conference held in Devon last

week. John Burns reports

DETAILED research is urgently needed into air and water pollution from grazing-based spring calving milk production systems, relative to other systems.

That was the majority view at a two-day conference organised by Mole Valley Farmers and held at the Institute of Grassland and Environmental Research, North Wyke.

Extended grazing enthusiast Tim Wall, who farms on wet land in Devon, described how he timed his modest applications of nitrogen – always as urea – to modify the natural growth pattern of grass to suit his spring calving dairy herd. He used less in late spring and early summer and more in late autumn and winter.

That prompted worries from scientists that there would be excessive losses from out-of-season applications. But Dr Wall countered that with a claim that overall his current system was less polluting than his previous more conventional one.

In 1995, before he began changing to low-cost production, his output of milk and livestock was much the same as it is now, except sheep were taken in during the winter. He used to feed a lot of concentrates, maize silage and brewers grains.

By switching to spring calving and relying heavily on grazed grass, he had greatly reduced his use of power as well as fertiliser, concentrates and other bought-in feeds. Therefore, he concluded that overall his current system must be more environmentally friendly and more efficient in energy use than the previous one.

Dr Walls fertiliser applications are timed to ensure good grass production early and late in the year, minimise the early summer peak, and reduce the August trough in grass growth. He applies no fertiliser between mid-April and late June.

"You must avoid having to make too much silage in May. For one thing fields often take six weeks to recover after a heavy silage cut." He applies up to 62kgN/ha (50 units N/acre) in early August and another 25-37kg/ha (20-30 units N/acre) in September to maximise autumn grass growth.

"We have more grass/ha then than at any other time of year. Growth rate then slows down, but it doesnt go to head and quality does not deteriorate."

In early October he starts closing up fields for early spring grazing. Every field is rested for about 120 days after its last autumn grazing. Then 25-37kgN/ha (20-30 units N/acre) is applied when fields are shut up, though none is used in December. Sometimes he may apply 25-37kg/ha in January and will regularly use a similar amount in February, while 62kg/ha (50 units/acre) each in March and early April complete the annual cycle.

Lorna Brown, North Wyke soil scientist working on systems to minimise nitrogen losses, said there was evidence that soil nitrogen built up during summer and so there was often no need for any fertiliser in autumn.

Very late and very early applications would result in high % losses to atmosphere or water courses, she suspected. But it appeared that research had never been done to measure losses from a system such as that practised by Dr Wall.

Malcolm Gibb, North Wyke, suggested the station could provide facilities for a detailed comparison of the two systems, but a proposal to measure the losses from an extended grazing systems had still not found funding.

References to inevitable restrictions on farming methods to reduce pollution of air and water prompted farmer Ben Shepherd to call for urgent action. "We must be proactive and pre-emptive. This work needs doing now." &#42


&#8226 Research required now.

&#8226 Consider pollution risks.

&#8226 Source of funding?

Tim Wall believes his little, but often approach to nitrogen application is less polluting than conventional fertiliser programmes.

Low-cost systems for wintering dry cows

&#8226 Stubble turnips or forage rape, or a mix of the two, broadcast with compound fertiliser into standing cereal crops 10 days before combining. Straw round-baled, net-wrapped, and left in the field for feeding with the crop. Nitrogen fertiliser applied as soon after that as possible. Typical daily intake 8-10kg straw and 4kg dry matter from the forage crop which will maintain cow condition.

&#8226 Italian ryegrass sown into spring barley at the two leaf stage. Compound fertiliser after harvest, light grazing by youngstock, more nitrogen fertiliser, then left to grow to 4-5,000kg DM/ha in January and block-grazed before being drilling spring barley.

&#8226 Italian ryegrass sown late March, well fertilised with nitrogen, and big baled in late May. Second cut big baled eight weeks later. All bales stored in the field. Grass left to grow to 4500kg DM/ha before controlled grazing, using silage to eke it out.

&#8226 Take winter grasskeep as is done for sheep

&#8226 Rent land from arable farms and grow catch crops.

&#8226 Use set-aside. Limited amounts of fertiliser can be used between September and mid-January.

&#8226 Winter on maize stubbles on light land with a run-back to grassland. Feed silage on the stubble.

&#8226 Take advantage of the growing number of farms with empty cubicles and spare silage. Examples were quoted of cows being cubicle-housed and fed for £5/week including labour.

&#8226 Kale drilled in June after Italian ryegrass and strip grazed throughout the winter. Kale easily flattened by quad bike to allow electric fence to be erected. Kale followed by spring barley.

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