Optimum N could bring cash reward

31 January 1997

Optimum N could bring cash reward

INCREASING nitrogen fertiliser applications on grass to an optimum level could save £49 a cow compared with average use.

Richard Martin of ICI Fertilizers says optimum use of 300-370kg N/ha (240-296 units/acre) will produce higher grass yields than the 175kg/ha (140 units/acre) average annual N application to grassland.

Figures from a recent, ICI-sponsored, Kingshay Farming Trust study put the cost of producing milk from grass at 3.3p/litre or 4.3p/litre for silage.

But higher grass yields would reduce the cost of producing each litre from grass or grass silage by 0.7 and 0.8p/litre respectively, claims Mr Martin. That cuts production costs to 2.6p/litre from grass and 3.5p/litre from silage.

On this basis, Kingshays Martin Hutchinson says the lower production costs from using optimum N would allow a producer averaging 2600 litres a cow from forage – half grazed and half silage – to reduce production costs by £19.50 a cow a year.

The extra grass produced allows an extra 1000 litres a cow to be produced from forage at 3.05p/litre compared with 6p/litre off concentrate – saving 2.95p/litre. This makes an extra saving of £29.50 a cow possible, producing a £49/cow saving.

Mr Martin advises against increasing total N applications for first-cut silage and suggests highest yields come with 131kg/ha (105 units/acre) in a split application.

"The earlier you bring a small proportion of the nitrogen forward the better the seasons production will be," says Mr Martin. "Aim to apply nitrogen 12 weeks before first-cut silage, but not before mid-February or if the ground is waterlogged and leaching is likely."

He suggests an application of 40kg/ha (32 units/acre) could increase silage yield by 30%. For grazing ground spread a small amount of nitrogen seven weeks before turnout.

A soluble source of phosphate in spring can also encourage grass growth. Mr Martin claims that 40-50% of soils are deficient in phosphate and applying 43kg/ha (34 units/acre) of spring phosphate fertiliser gives scope for increasing grass yields by up to 50%. Even at a phosphate soil index of 2 the nutrient is unavailable to the surface roots in early season while the deep roots remain dormant.

In addition sodium applications of 25kg/ha (20 units/acre) ensure the sward is palatable and can increase the availability of minerals reducing staggers and infertility.

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