9 April 1999

Researchers seek MIDaS touch for nutrient losses…

By Simon Wragg

TIGHTER controls on nutrient use can be expected unless losses from agriculture are cut substantially, warn researchers at ADAS Bridgets, near Winchester, Hants.

Speaking to members of the Maize Growers Association, researcher Julie Williamson said only 20% of nutrients used on-farm actually pass through the farm gate as produce. While some nutrients remain in the soil most are lost via leaching or erosion.

"Not only is there an environmental concern over nutrient losses, but loss of profit is also a concern. Nutrients not leaving the farm as produce have been paid for but have given no benefit," said Dr Williamson.

Where excessive nutrient losses continue, restrictions on nutrient use may be introduced, said ADAS researcher Andy Chalmers. At present controls over nutrient applications are largely voluntary.

"We could see more restrictions such as in Nitrate Vulnerable Zones where annual application of manure N must not exceed 250kg/ha to protect drinking water. There are already 68 NVZs and this could increase," said Mr Chalmers.

Adding to pressure for nutrient cuts, EU governments have agreed to cut ammonia pollution level in individual member states. "For the UK it could mean reducing losses from agriculture by 15-30% by 2010," he added.

To find ways of reducing nutrient inputs without affecting dairy income, researchers at Bridgets are looking at Minimal Impact Dairy Systems (MIDaS). The aim is to compare margins from dairy cows with average milk yields of 6500 litres – fed 1.4t concentrate – managed under various forage systems with different controls on fertiliser inputs (see table).

These systems include conventionally managed grass and maize forages, grass and cereal whole-crop, and low input grass and maize.

Initial results suggest little financial difference between commercial and restricted nutrient managed systems, explained herd manager Robert Bull. "Margin for the low nutrient system was not as bad as we expected. Restricting nutrients doesnt necessarily mean restricting margins."

However, margin for the grass/whole-crop system was affected by ensiling in too large a clamp to control spoilage, which reduced cow output, he said. To rectify this, researchers will ensile whole-crop in big bales this year.

While researchers anticipate margins will improve for the grass/whole-crop system with better management, the effect of lower nutrient inputs may also become clearer when soil indices decline as systems settle down.

Nutrient use and losses are being recorded for the three systems. "So far, only the conventionally managed grass and maize system is exceeding EU limits of 50mg nitrate/litre in total winter drainage," said Mr Chalmers.

MAFF may be keen to reduce nitrogen lost as ammonia from livestock housing and manure/slurry stores to comply with any future legislation, but there are several conflicting factors.

Straw-based systems are favoured on welfare grounds, and can reduce ammonia losses, compared with cubicle systems. "I wait to see whether MAFF can take this into account when drafting new legislation," said Mr Chalmers. Likewise, the suggestion by some researchers that slurry stores should be covered to reduce ammonia losses has major cost implications, which out-weigh any financial benefit in terms of nutrients saved.

After nitrogen leaching, phosphrous lost via soil erosion is a major concern for maize growers, warned ADASs Paul Withers. "It gets locked in soil and can be lost in surface run-off from maize ground which is often left bare over winter. To avoid erosion consider establishing cover crops."

Cover crops could include Italian ryegrass sown between maize seedlings in mid-June. Undersowing at Bridgets hadnt affected maize yields, said ADASagronomist Martin Froment.

"We should be aiming to reduce the need for phosphorus when drilling maize by placing fertiliser and slurry as close to the seed as possible. However, machinery designed for placement of slurry close to the seed still needs to be developed," said Mr Froment.

MIDaS (2) performance.

System A System B System C

Stocking rate (LU/ha) 1.89 1.71 1.71

Target fertiliser nitrogen rate, grazed grass (kg/ha) 260 200 200

Nitrogen rate, grass-clover mix n/a 50 n/a

Target fertiliser and slurry nitrogen rate, maize (kg/ha) 80 n/a 50

Milk yield (litres/cow) 6277 6021 6324

Yield from forage (litres/cow) 2719 2522 2680

Concentrate use (t/cow) 1.73 1.75 1.76

Total margin (£) 28595 22392 29304

MOPF (p/litre) 20.8 20.2 20.7

Type Good commercial practice with maize and grass. Low nutrient loss with whole-crop grass and clover. Reduce loss with maize and grass.

Land use 13ha permanent grass, 6ha maize. 15ha permanent grass, 3ha grass/clover ley, 3ha whole-crop wheat. 15ha permanent grass, 6ha maize.


System A* System B System C

Stocking rate (LU/ha) 1.89 1.71 1.71

Target fertiliser nitrogen rate,

grazed grass (kg/ha) 260 200 200

Nitrogen rate, grass-clover mix n/a 50 n/a

Target fertiliser and slurry nitrogen rate,

maize (kg/ha) 80 n/a 50

Milk yield (litres/cow) 6277 6021 6324

Yield from forage (litres/cow) 2719 2522 2680

Concentrate use (t/cow) 1.73 1.75 1.76

Total margin (£) 28,595 22,392 29,304

MOPF (p/litre) 20.8 20.2 20.7

*A: Good commercial practice with maize and grass. B:Low nutrient loss with whole-crop grass and clover. C:Reduce loss with maize and grass.