3 May 1996

Test before you cut for top crop in the clamp

Testing grass pre-cutting could make good sense this season. Jessica Buss reports

TESTING grass intended for cutting helped one Staffordshire producer make competition winning silage that analysed and fed well.

It also enabled the 140 cows at the Mallaber brothers 145ha (358-acre) Park Farm, Drakelow, Burton-on-Trent, to exceed target yields of over 8000 litres a cow. This was achieved at a feed rate of 0.23kg/litre to give a margin over concentrates of £1800 a cow.

Two samples analysed on May 10 last year showed the grass was ready to cut because sugar levels and D-value were high (see table).

Most of the farms first-cut silage is taken from 24ha (60 acres) of Italian ryegrass. The rest is longer-term permanent pastures but these contain new varieties that have high sugars, claims Peter Mallaber. After a 24-hour wilt the crop was harvested by contractor. Most of the silage was made without additive, although a little was made with some acid.

The Mallabers ADAS Midlands nutrition consultant, Tim Davies, advises analysing grass before cutting on all permanent pasture, especially fields that have received slurry and fertiliser and when the weather is cold and dull. It is also worthwhile when there is residual fertiliser from last year as appears to be the case this season.

It is in these fields that excess nitrogen is a risk because it will depress grass sugars. Lack of sugar causes poor fermentation. "Italian and modern diploid and tetraploid grasses tend to have high sugar irrespective of the weather," he says.

"With these the trick is getting enough water out of the crop to increase silage dry matter."

The most important results on the grass analysis will be D-value, sugar and dry matter content, says Mr Davies. "When digestibility is high, cutting can be delayed to allow the crop to bulk up. But when it is below 70, get on with it."

Grasses in the midlands usually reach a D-value of 70 by the third week in May, even in late seasons, he says. Ideally the crop should be cut at 70-72 D-value.

"After digestibility, check the sugar content. If it is above 3% in the fresh grass, there is no need for an additive, even when direct cutting." In fact a high dry matter concentrates sugars in the crop.

"But when sugars are low wilting to 25-30% DM will usually give a good fermentation. When it is impractical to wilt use an effective additive that is acid-based for consistent results," he says.

Inoculants are used for peace of mind and safety, for nobody likes to handle acids. But although more user-friendly, inoculants are still not consistent enough to give good fermentation when sugars are low and or the weather wet, he warns.

Dry matter content would give a guide on how long a wilt the crop needs. Mr Davies advises aiming for 26-28% DM silage because it encourages intake and promotes health. At over 30% DM there was an increased risk of aerobic spoilage and yeast cultures causing waste.

"For best results cut, wilt using a tedder and a rowing-up machine, and then get the crop clamped quickly," he says. Wilting this way does cause some field losses but will cut clamp losses mainly due to effluent, so the two generally balance out.

"Consolidate in the clamp carefully, especially on the shoulders. Sheet down immediately, overlapping top and side sheets, which are best held down with plenty of tyres for a good seal. To reduce the chance of aerobic spoilage when the pit is opened expose as little as possible and use a block cutter to keep the face tidy," he says.

Nitrate levels should not alter silage making decisions, claims Mr Davies. The nitrate content of grass does not cause butyric fermentation. But when nitrate depresses grass sugars and increases the protein level of the crop it can reduce fermentation.

"High ammonia in silage comes from protein breakdown and by clostridial organisms. The protein breakdown occurs when too little acid is produced in the fermentation because of a lack of sugar." &#42


Take a sample, seal in a bag and post to lab. Results should be available by phone or fax within 24 hours. ADAS charges £22 a sample.


Grass and silage analysis at Park Farm

Pre-cutSilage

Dry matter (%)2124

Crude protein (%)18.519

Sugar (fresh wt) (%) 4.5Sugar (DM) (%)23

ME (MJ/kg)11.8

FME (MJ/kg) 8.5

Nitrate N/ ammonia (%) 0.1 7

D-value7474


&#8226 D-value: When high, cutting can be delayed to allow crop to bulk up. When below 70, cut.

&#8226 Sugars: When above 3% in fresh crop no need for additive.

&#8226 Dry matter: Is a guide to how long a wilt the crop needs.

Peter Mallaber took a grass test last year before taking a cut for silage. It enabled him to take a cut that gave a top quality feed.

ADASnutrition consultant Tim Davies advises checking the dry matter, digestibility and sugar level of grass before cutting for silage.