21 April 1995

Sample first for best feed value in grass silage

By Rebecca Austin

GRASS sampling prior to silage-making helps ensure optimum harvesting date and hence feeding value of ensiled material, say UK nutrition scientists.

Rapid analysis of cut grass will show whether fertiliser has been used fully by the plant.

It also checks grass maturity, water soluble carbohydrate (WSC)content, dry matter, digestibility and buffering capacity.

"When proteins are too high, the risk of butyric fermentation increases which turns silage unpalatable," says Dr Bruce Cottrill, ADAS nutritionist.

"There must also be enough sugar available for bugs to produce lactic acid. If there isnt, we can recommend the use of an acid additive. On the other hand when levels are higher than expected an innoculant will be required."

Farmlabs Dr Sue Russell is concerned grass will suffer luxury nitrogen uptake closer to silaging if it rains.

"Fertiliser went on late as it was wet," she explains. "But the recent dry spell means a lot has yet to be taken up by the plant."

This view is echoed by Dr Cottrill who reports some farmers were nearly two weeks behind with fertiliser applications due to wet weather.

Tony Evans from Genus agrees grass is low in protein and that sugar quality is poor at present. "But if the good weather continues we possibly wont have a problem because the increased rate of grass growth will use the nutrients."

Genus handled 1000 grass samples last season and 10 times more silage samples. "Producers using our grass sampling service will have a good chance of picking the right conditions and targets of digestibility and dry matter for silaging," he says.

As nitrate levels change dramatically from day to day, Mr Evans recommends cutting the crop within 48hrs of testing a sample. Dr Russell advocates a seven-day gap, but all are adamant samples must be representative of the crop to be ensiled. Grass should be cut at mowing height and samples taken across the field.