8 March 1996

Grass silage is at risk from leaching

GRASS silage quality could be at risk if producers fail to reduce bag fertiliser applications for first-cut. ADAS dairy consultant manager Mark Roach issues the warning after recording higher than average nitrogen in soil this spring.

Last years dry summer followed by a dry winter in many areas saw ground failing to reach soil water capacity so leaching has been reduced. Autumn and early winter applications of organic manure and slurry will, therefore, supply more nitrogen in the spring than in a normal year because less has been leached. "When this nitrogen is still present producers should reduce nitrogen applications for first-cut," he says. "A crop 20% higher in nitrogen at cutting will dilute the sugars and result in poorer fermentation."

Mr Roach recommends taking account of local and autumn fertiliserto judge by how much to reduce spring nitrogen applications. Soil nitrogen analysis needs careful interpretation.

It may be necessary to reduce applications by 13 to 38kg/ha (10 to 30 units/acre). But when too little nitrogen goes on yield can be reduced, he adds.