Adjust spring rotation planner to the feed needs of your stock
Published 25/01/2011 | 05:00
Last week I explained what a spring rotation planner (SRP) was and how to create one so that you were ready to put it into action this spring.
An SRP can be applied to any farm size or shape and provides you with a target for the area to be grazed each week, and takes the guesswork out of grazing management. Again it's easy to create by drawing a line on a piece of graph paper, from the start of calving (Point A), with your longest rotation length until magic date plus 7-10 days (Point B), your shortest rotation length. This is shown by the solid line on the graph (right), with the relevant management data shown in the table (right) for a 60ha farm example.
As stated in the previous article, the SRP should not be used in isolation but used alongside your feed budget. Combining these two tools makes spring-grazing management most effective because, when the actual pasture cover is monitored against the target cover, the rotation length applied can be slowed down and/or supplements introduced.
Therefore, it's also important to plot the desired decline in average pasture cover (as shown with the dashed line), starting from an opening cover of 650kg DM/ha available and dropping to 400kg DM/ha in this example.
Basically, how this works is that, on March 12, the SRP indicates that you should reduce the rotation length to 1/60th (60days), which would provide 1ha/day grazing, or 7ha for that week (12-18 March). However, the dashed pasture cover line indicates that this should coincide with a pasture cover of 525kg DM/ha available. If when monitoring the pasture cover it is more than 50kg different from this target figure then action will be required. There will be more on this later.
Management points to consider for use and adjustment of the spring rotation plan:
- For every 100kg DM/ha that your grass cover is behind your grass budget at the start of calving, eg actual cover of 600kg DM/ha vs a projected grass cover of 700kg DM/ha on February 1, increase the starting rotation by 10 days (ie, 110 days vs 100days) of a normal spring.
- Most rotation plans work on the first rotation length being around 58-65 days (eg, February 1-April 5). If your first grazing rotation is shorter than this, then reduce your starting rotation length from 1/100 by 10 days for every seven days shorter in this period. For example, a rotation length from February 22-April 5 is 42 days, or around two weeks shorter, therefore the starting rotation length should be cut by 20 days to 1/80.
- On any one week of using the SRP, if your average pasture cover is more than 50kg DM/ha below target, then hold last week's rotation length for one more week.
For example, using the graph above on March 12, take the March 5 rotation length of 68 days and only graze 6.18ha rather than 7ha that week. When taking this action, supplement the cows with extra feed if required. Continue to hold this rotation length until pasture cover has recovered and is within 50kg DM/ha of its target for each relevant week.
Once back on track, resume your rotation length as indicated by the SRP for each appropriate week. In last year's extreme spring, when many farms had low pasture covers, this action was required early, with a long rotation length being appropriate until the end of March.