31 May 1996

Growth assessment is key

Improved grazing management depends on careful assessment of grass growth. Jonathan Riley reports from Grassland 96

WITH concentrate prices rising, livestock producers must improve grazing management to make more effective use of grass.

This was the view expressed by New Zealand adviser Mark Blackwell to a keen audience at the British Grassland Societys stand at Grassland 96 (full report p48).

He said the secret of effective grazing management was to have a system that would encompass changes in grass growth as the season changed. It was vital for producers to assess grass either as sward heights or in kg/ha dry matter to be able to adjust grazing plans as the season progressed.

"As all other feeds are measured in kg, so assessing grass yield as kg DM/ha gives a more tangible picture of grass as a feedstock in a field. To measure grass yield in this way the density of the sward can be measured with a rising plate meter or sward heights can be converted," said Mr Blackwell.

Dairy Research and Consult-ancy also used the Grassland event to stress importance of assessing grass growth. When using sward heights DRCs David Roberts advised against taking too few measurements across the field and acknowledged that the varying density of herbage was not picked up measuring sward heights alone.

"Despite this shortfall, sward heights are easy to measure and these can be converted to kg DM/ha (see diag), until a producer is confident enough to assess grass mass by eye," said Dr Roberts. "By walking through grass and measuring changes in the stocks as often as once a day an invaluable picture of the swards feed value and the speed at which cows are consuming it can be gauged.

"The aim is to introduce cows into paddocks with a sward height of 10cm to 12cm and to move them on to the next paddock when the sward is reduced to 5cm to 6.5cm. Below this intakes fall," he said.

The DRC advises making a daily assessment where the average of 20 measurements across the field is taken. This allows close monitoring of the herbage available and action can be taken before production falls.

A weekly assessment and comparison of all paddocks should also be made so that the optimal paddock is grazed next. The weekly assessment is useful for modifying rotation length and assessing fertiliser and conservation requirements.

"From these assessments, producers can fine-tune a system. If too many paddocks are above 10cm more paddocks can be shut up for silage, more stock can be brought in or fertiliser applications on grazed swards reduced."

"If too many paddocks are below 10cm buffer feed, graze the herd in performance groups, with higher yielders on the best swards, and review fertiliser applications," said Dr Roberts.

New Zealand adviser Mark Blackwell encouraged producers to measure grass yield in kg DM/ha or as sward height, which could be converted.