14 February 1997


Improving nitrogen efficiency on dairy farms might not be too costly, says new research. Sue Rider reports

COMMERCIAL dairying is not synonymous with environmentally acceptable practice. Dairy farms are often specialist units with high inputs of nitrogen and phosphorus – both as fertilisers and purchased feeds. Stocking rates are high, there is often no arable land on which to use slurry and dirty water, and many units also grow maize which can cause high loses of N and P through leaching, run-off and erosion.

But commercial units can reduce nutrient losses while remaining profitable, according to Steve Peel of ADAS Bridgets Research Centre, Winchester, Hants. He heads the minimal impact dairying systems (MIDaS) project, set up in 1994 to find out how to make grass based dairying environmentally acceptable.

"Our results are good news for many dairy farmers," says Mr Peel. "They show that nitrate in water draining from dairy farms can be reduced towards the EU requirement of 50mg/litre with no great impact on profit."

Margins a cow are similar for commercial practice and when management has been adjusted to reduce nutrient losses to EU limits (see Table 1).

Nitrate leaching reduced

Based on this evidence, Mr Peel suggests nitrate leaching could be reduced on dairy farms with only small changes made to existing management practice – provided at least three months manure storage is available. By acting now farmers could avoid the strict legislation that is already in place in much of northern Europe, he says.

"In Britain the legislation is so far relatively limited and reliance is placed on the voluntary Codes of Good Agricultural Practice. But if this is not successful legislative pressure could mount."

The MIDaS project is attempting to find out how dairy farms could reduce losses while maintaining profits. It comprises three self-contained systems – each with its own area of land, silage clamps, and slurry collection and storage areas.

System 1 is the control – representing high output from commercial practice; system 2 is reduced loss, high output; and system 3 is minimised loss, reduced intensity. Each system runs 36 cows with a target milk yield of 6000 litres a cow. All three systems meet the COGAP but systems 2 and 3 include management changes designed to reduce nitrogen and phosphorus losses including:

&#8226 Large reductions in fertiliser

  N, particularly for grazing

&#8226 Use of maize, with cover crop

&#8226 Dietary manipulation,

  reducing N and P intake

&#8226 No application of manure

  until December (System 2)

&#8226 No application of manure

  until February (System 3)

&#8226 Injection of slurry (System 3)

&#8226 Reduction in stocking rate

  (System 3)

"System 3 was never meant to appeal to commercial dairy farmers; its there to ensure we can meet EU targets and to guage the effect of doing that on profitability," says Mr Peel. "System 2 is one which could be implemented in the short to medium term in an attempt to meet targets with minimal impact on profit."

Averaged over the first two years, nitrate leaching losses have been substantially reduced on the improved systems – from 60kg N/ha on system 1 to 29kg N/ha on system 2 and 27kg N/ha on system 3 (see Table 2).

"This is good news for dairy farmers given that, with our typical rainfall at Bridgets, the target leaching loss to meet EU limits is under 30kg N/ha," says Mr Peel. "But there is much more variation between fields than anticipated."

Results with maize have been less successful. Total N supply to the 1995 crop was cut, and nitrate leaching was also reduced, but still remained above target. Leaching from maize in 1995/96 was 41kg N/ha on System 2, and 36kg N/ha on System 3, despite an undersown cover crop which took up 30-40kg N/ha by January 1996.

Undersown cover crops

"Leaching after maize was higher than predicted, despite very light applications of manure, and use of an undersown cover crop."

More encouraging was that ammonia losses after broadcast slurry applications were less than predicted on all systems. Losses were lowest on the improved systems, largely due to rapid ploughing-in of slurry before maize. Ammonia loss after slurry injection was greater than anticipated.

As for financial performance, in the 1995/96 year, target milk yield was exceeded on all three systems, although this required more purchased feed than budgeted (see Table 1). System 3, the most environmentally improved, had a margin over purchased feed of £1472/cow. But due to its lower stocking rate, its margin over feed and fertiliser was £2315/ha (System 1, £2742/ha) and due to the cost of five months slurry storage its gross margin less forage and capital costs was only £1614/ha compared with £2076/ha on system 1 which only has one months storage. &#42

Dairy farming can be made greener, with no great impact on profit, says ADASs Steve Peel (left).


&#8226 On many dairy farms, and intensive beef units, current losses of nutrients are like to be too high to be environmentally acceptable.

&#8226 Storage of manure, careful application in spring or summer, and reductions in fertiliser use, can substantially reduce nitrate leaching.

lThere is scope to manipulate diets to reduce excretion of nitrogen and phosphorus.

lIt is too early to say whether reductions in stocking rate are required on many farms.

lAlthough better use of nutrients in manures saves fertiliser, the cost of slurry storage means that environmentally improved systems are likely to be less profitable. However, many farms already have three to four months slurry storage, and this may be all that is required.

Table 1: Financial performance, April 95 – March 96

System S England

123 3/95 2/96

Margin over purchased

feed (£/cow)1485140814721332

Margin over purchased

feed (p/litre)21.320.320.921.2

Margin over feed

and fertiliser (£/ha)2742258423152709

Gross margin less

forage and

capital costs (£/ha) 207618801614na

Source: ADAS Milk Cheque

Table 2: Annual nitrogen leached (kg/ha) average for 1994/95 and 1995/96

System 1

Permanent grass69

Italian ryegrass40

Whole system60

System 2

Permanent grass21


Whole system29

System 3

Permanent grass16


Whole system27

*Target (to meet EU Drinking Water Directive at ADAS Bridgets) is 30