Those who have read the articles will have correctly formed the conclusion I am a great believer in the use of topping as an important tool in pasture management.
Before going any further, I had better define, for the possible benefit of overseas readers, what is meant by the term, topping.
It was originally coined to describe the practice of cutting off the top of a pasture that had formed a large proportion of seed head – with the idea that removing it would encourage the grass plant to revert back to producing more leaf and thus enhance pasture quality.
However, in its common usage the practice would probably be better described as bottoming because, rather than just taking the top of the pasture, the mower is set low so stalky growth is also removed as are, more importantly, weeds and undesirable grasses. This latter function is actually likely to be a more important reason for topping in summer and autumn.
So, having now defined what we are talking about, let’s look at the dos and don’ts for a successful topping operation.
The first thing to decide is the type of machine to use. For many farmers the choice will be automatic because the only machine available will be a hay mower. In a lot of circumstances this should be the preferred option in any case, where the topped pasture is targeted on being eaten by grazing animals, typically after being wilted for a while to make it more palatable.
Quite a few farmers will take this a step further and top the paddock before the cows go in, claiming this will increase both utilisation and intake. To my knowledge there is no scientific evidence to either prove or disprove this.
A modification of this, which can be quite useful, is to top half the paddock before the cows go in, thus giving them the choice between cut and wilted or fresh pasture, with the idea that having options will increase intake.
Then, in the next round, the process is reversed so the half topped in the last round offers fresh leafy feed with the other half now being tidied up.
Another option is a light grazing only then a cutting and drying with the to-be-expected heavy toppings baled as a light crop of hay, This win-win combination of forage conservation and pasture control has a further advantage of quick drying of the crop because of its lightness and, if rain does intervene, the potential to write the crop off with no great loss.
The other machine option is of course the rotary slasher type – one that is designed mainly to do this type of work.
In the situation where the paddock has been grazed and all that is left is rank, unpalatable and useless drymatter this is the machine of choice. It will lacerate the vegetation into mulch-like status which will aid its quick breakdown and incorporation into the soil organic matter.
In doing so it will largely avoid creating those dense lumps of cut grass that will smother regrowth from underneath them. Most importantly, it will do a superb job in spreading all the dung pats on the pasture – with obvious benefits – even though there could be a bit of extra work involved in hosing down the tractor after the job is done.
The rip, tear, bust characteristics of these machines in doing this job when conditions require it make them a much better option than hay mowers, which, as they are designed to do, will lay the cut grass gently into swaths to await further processing rather than pulverising and scattering it and contaminating it with dung and dirt, which, of course, immediately brings up another point – that of cutting height.
To do the job properly it is important to have the blades set low – no matter what type implement is being used. In an unevenly surfaced paddock this will create some difficulties.
A hay mower will tend to ride over the humps so that the grass in the hollows will not be cut off at a desirably low enough level.
The rotary slasher type will be far less discerning and basically, if a hump gets in its way, it will be decapitated. This scalping effect does not augur well for effective regrowth because it quite often leaves considerable areas of bare ground that can be slow to recover and are also susceptible to weed invasion. Fixing the problem by raising the cutting height is no solution because it will severely reduce the effectiveness of the whole operation.
Probably the best approach, apart from having perfectly flat paddocks, is to forget the negatives and concentrate on the positives – that the topper is doing a job in levelling the paddock so that there won’t be so much of a problem next time round and ultimately, with a bit of luck, the aforementioned objective of a completely flat paddock will be achieved.
This also brings up another important point. It is absolutely essential to have sharp blades so a clean cut is obtained.
As a corollary, high blade revs are important for the same reason – even if it means slower speeds. A clean surgical cut will give much faster regrowth than one where the grass has actually been bludgeoned rather than cut.
Dull blades are also more likely to tug the plant out of the ground and weaken the root system. This effect can actually be quite marked in autumn when pasture pulling can often be a problem.
Finally, a word on the application of topping in weed control is worth a mention. In my view the overall most serious weed on NZ dairy farms is Californian thistle.
While other weeds like docks and buttercup can be prolific and unsightly, they don’t detract too much from the successful utilisation of pasture drymatter because cows will graze right up to and around them.
Not so with Californian thistle. Because of its extensive rhizome rooting system, Californian thistle can rapidly intensify and colonise on areas where it has become established, giving rise to big patches of densely canopied thistle, through which the stock will not enter – let alone graze.
Topping this dense cover and, in particular, mulching the thistles gives the grasses tending to be smothered a chance to get away and, more importantly, be available for the next grazing as, by and large, cows will not be much deterred by any small, leafy, regrowth thistles.
There is also plenty of anecdotal evidence that cutting mature Calis just before rain means water will seep down the exposed hollow stems and rot out the root system. It does seem to be true but, having said that, I certainly would not rely on this as a sole method of control.
