Grass Budgeting

Grass budgeting like financial budgeting is an attempt to balance supply and demand. Cattle have to be fed 365 days a year, however grass does not grow evenly throughout the year.

Most grass is grown in early summer. Some of the farm is closed off for silage at this time to feed to the stock during the winter months. Grass budgeting is an attempt to store grass in the field than rather in the clamp.

Grazed Grass

Silage is 2-3 times as expensive as grazed grass so we try and make as much use of grazed grass as possible. This is why we turnout our cows as early as possible and try and keep them out as long as possible. A wedge of grass is built up in late summer / early autumn. Some of this wedge is used to keep the cows out until early December and some is used to turn the cows out early the next spring.

If grass supply gets too far ahead of the cows then the grass will get stemmy and less palatable. Cows will not eat the grass down properly. If action is not taken to remedy this the farmer will end up with his sward quality declining with each rotation.

If grass supply is inadequate then the farmer will have to fall back on more expensive conserved or purchased feed.

Grass budgeting is a balancing rod to help the farmer walk the tightrope between grass surplus and grass shortage.

Measurement

The cornerstone of grass budgeting is grass measurement. Grass covers are measured in kilograms of dry matter per hectare (kgDM/ha). There are three common methods of assessing pasture cover.

Eye Assessment

Also known as eyeballing. You need to be a fairly accomplished grazier to attempt this. You will need some form of calibration. Accuracy is not liable to be very high.

Cutting and weighing

This involves using a quadrat (usually 25cm square) and a pair of clippers to cut a known area of grass. This is then dried in a microwave and weighed using very accurate scales. While perhaps the most scientifically accurate method of determining pasture cover it is very time consuming and not really practical for a commercial farmer.

Rising Plate Meter

This is by far and away the most popular method of determining grass cover. This measures compressed sward height. By taking a series (30 - 40) of readings across a paddock and putting the results through an equation it is possible to make a reasonably accurate determination of grass cover. The advantage of this method is that a paddocks cover can be worked out in a few minutes.

Average Farm Cover

This is perhaps the most important measurement that can be derived from the use of a platemeter. This is the average cover across the whole farm. Through experience and discussion with other farmers it is possible to set targets for Average Farm Cover at various times of the year. These targets will vary from farm to farm depending on available grazing area, climate, calving pattern and stocking rate.

Residual Cover

This is the amount of grass cover left on the paddock after the cows have finished grazing. If the cows are pushed too hard then their milk production will suffer. If the grazing is too lax then the sward quality will deteriorate and eventually require topping. We try and fill the gap between optimum cow intake and leaving the paddocks well cleaned by operating a leader - follower system. In the spring paddocks should be grazed down to around 1500 kgDM/ha.

Available Cover

This is the difference between the opening cover and the closing cover. Teagasc the state farm advisory service in the Republic of Ireland will often use this expression to describe pasture cover while most others use the Total Farm Cover.

Growth

By comparing two different set of readings it is possible to determine daily growth rates. This is a very useful in deciding whether to bring in or remove areas from the grazing ground.

Grass Budget

If we know the area available for grazing, the number of milking cows and expected intake and we can estimate the growth rate then it is possible to predict what will happen to total farm cover.