Attention to grass growth ensures a consistent supply of highly digestible grazing

grass growth ensures a consistent supply of highly digestible grazing

By Michael Calvert

Most farms are now achieving maximum grass growth. It is the time of year where the rate of accumulation may start to tail off depending on soil moisture and temperature.  

Management through this spell will have an impact on the rest of the grazing year.  Standard grass growth curves like the one below are a useful guide to what rate of growth can be expected but year to year and farm to farm there will be a lot of variation around these averages.  This means that although this information is very useful, it is not a substitute for monitoring grass growth on your farm. 

Grass growth
Average monthly grass growth between 2009 and 2019.

Source: AHDB

It is critical to deal with these growth rates correctly. If we shut up too much for silage, we can easily run into a shortage. If we can’t keep up with the grass, we waste it and leave too much behind. This makes the next grazing poorer and creates a vicious circle of low intakes and even more waste for the rest of the season. In my previous blog, I discussed the importance of rotation length. Dealing with the potentially surplus grass at any stage is the key to maintaining the correct rotation length.

Grass wedge management

The grass wedges shown below have been created using AgriNet grass management software. The blue line represents the grass demand, the number at the top of each bar represents the days since the last grazing. The thickness of the bar represents the size of each paddock.

This example from last year shows a typical grass wedge in mid-May, the next grazing in paddock 14 is over 3800kgDM/ha.  Even if cows could eat through this, they will be slower into the next paddock which will be rapidly catching up. In this example, the surplus which is represented by the amount of grass above the blue line is considerably above the target for the paddocks next to be grazed. 

A grass wedge in mid-May, demonstrating the kg DM/ha in each paddock.
A grass wedge in mid-May, demonstrating the kg DM/ha in each paddock.

The wedge below shows the same grazing block projected forward one week with no action. The problem just gets worse with even more grass accumulated above the blue target line. The paddock just grazed will have had lots of grass left over, cows will have trampled it and the quality the next grazing will be severely compromised. They could be left longer to tidy it up, but this will suppress intake and create an even bigger headache of surplus grass in the next to graze paddocks.

A grass wedge demonstrating the kg DM/ha in each paddock.
A grass wedge demonstrating the kg DM/ha in each paddock moved one week forward with no action.

By setting aside paddocks for silage we can adjust the amount of feed available and predicted to grow to match the grazing animals’ feed intake requirement. Below is the wedge after paddocks 14, 15 and 17 were allocated for baling.  These three fields were cut at the point they would have been grazed and we can see they are still showing in the wedge.

wedge after paddocks 14, 15 and 17 were allocated for baling.
A grass wedge after paddocks 14, 15 and 17 were allocated for baling.

We also decided field 36 wasn’t needed in the grazing rotation for a few weeks and it was added to the area allocated for first cut silage. This disappears off the wedge and we don’t worry about it until it is ready to come back into the grazing platform again. The key is to not create a “flat spot” in the wedge. This could leave you lacking grass very quickly and spin rotation length out of control. If the weather was hot and dry, fields might be slow to recover so it’s important to try and get the balance right. In this example, more fields were cut and baled a fortnight later. Doing this matched the timings of when they might have been grazed and the balance was maintained.

Keeping our grass wedge balanced helps us to provide the cows with a similar level of cover every time they enter a paddock to graze. This keeps feed quality consistent and reliable. Achieving this requires little more than a supply of reliable data provided by regular, at least weekly, grass measuring. It can then be analysed and processed to make the right decision on areas to set aside or introduce into the rotation.