8 December 1995

MIDaS data shows big cost of reducing nitrates in water

By Sue Rider

IF dairy producers were to be forced to cut nitrates in water to below the EU drinking water limit of 50mg/litre they could find themselves at least £500/ha (£1235/ acre) worse off.

That reflects the increased milk production costs due to the greater land area, and investment in equipment and slurry storage, required to cut nutrient losses to that stringent level. The finding comes one year into the Minimal Impact Dairy Systems (MIDaS) project at ADAS Bridgets, Hants.

The three-year study, 50:50 MAFF and industry funded, is examining the impact of N control on dairying profits. It aims to find out what it would cost a typical dairy farm to cut the average concentration of nitrate in water draining from it to below the EU drinking water limit of 50mg/litre. That is tighter than the NVZ proposals, admits ADASs Steve Peel, who heads the MIDaS project. But it shows the costs involved if that target had to be met on farms.

The NVZ restrictions will apply to 650,000ha (1.6m acres) of England and Wales where recorded nitrate levels have exceeded EU limits of 50mg/litre of water. Within these nitrate vulnerable zones there are proposals announ-ced recently (see News) to limit organic manure applications to 250kg/ha (200 units/acre) of nitrogen on grassland. On sandy and shallow soils application of slurry, poultry manure or liquid sludge will be banned from September to November for grass fields. Inor-ganic N use is banned from Sept-ember to February unless there is a crop need.

"The future viability of milk production in NVZs would depend on achieving an acceptable balance between milk output and nutrient losses," says Mr Peel. He anticipates that all-grass dairy farms may have most difficulty striking this balance.

"Dairy farms can be major pollution sources. Not only point source incidents involving slurry or silage effluent but more insidious diffuse pollution of water by nutrient leaching and of the atmosphere by ammonia and nitrous oxide. As an industry we must be seen to be taking practical steps towards reducing this pollution," he says.

MIDaS comprises three systems. One – Current commercial practice (control), two – Reduced loss, high output, and three – Minimal loss and reduced fertiliser use and stocking rate to meet the EU 50mg/litre limit.

"System three works within severe environmental constraints, and even system two goes beyond what is proposed for NVZs," acknowledges Mr Peel.

Financial performance figures after year one show a margin over purchased feeds of £2508/ha (£1003/acre) for system one, £2345 (£938) for two and £2045 (£818) for three. Gross margins a hectare, less forage and capital costs, came to £1990, £1727, £1441 for each, respectively.

Mr Peel reports that under permanent grass leaching loss on the improved system was less, at 27kg/ha (21.6 units/acre) of nitrogen leached, compared with the control system at 60kg/ha (48 units/acre).

"In a typical winter at Bridgets we could afford to lose only 30kg/ ha of nitrogen if we had to meet the EU drinking water standard." &#42

ADASs Steve Peel is using porous pots to monitor nitrate leaching.