The Rata Blog

Discover innovations, news and tips from NZ's own farm machinery attachments manufacturer.

The Mole Plough: An Effective Subsoil Drainage Machine

Posted by Casey-lee Cranston on Oct 27, 2023 10:37:54 AM

There are many benefits to be had from improving drainage in fields. Regardless of the crop or pasture being grown, too much soil moisture can hinder or reduce the performance of the yield.

Mole ploughing is widely used in New Zealand on heavy soils to improve the productivity of pasture and crops by creating water pathways through the field to permanently open or subsurface drains. This method of soil drainage is one of the most cost effective ways to overcome water logging issues with minimal disturbance to the surface and standing crops or pasture.


‘The Mole Plough: An Effective Subsoil Drainage Machine'

The Rata mole plough is a simple and effective way to lay field drains in the sub-soil clay. There is no need for pipes. Just simply pull the mole plough through the sub-soil starting at the lowest end of the field, or where you want the water to drain to, and pull towards the higher end of the field. In most situations the mole plough can be pulled at spacings up to 1.8m apart to be completely effective. The Rata Mole Plough is designed with a long beam that follows the contour of the ground, allowing the mole plough plug to effectively follow the contour of the ground without being affected by the tractor.


The long beams on the Rata Mole Plough produce a consistent gradient parallel to the surface, while the torpedo on the end of the blade directs the blade at a consistent depth. This provides the opening for the mole plug to expand the subsoil leaving a tunnel for the excess water to flow down, towards the main exit drain. The subsoil above the mole plug should be dry enough to avoid damage but give good traction and encourage upward fracturing to the surrounding soil.


'Benefits of Using Mole Plough for Subsoil Drainage'

The benefits of using a Rata mole plough are particularly noticeable once the field has been drained of excess water that would normally pond on the surface or otherwise waterlogging the soil, causing it to be sour or lacking in oxygen. This provides better utilisation of fertiliser and nutrients. There are many benefits of subsoil aeration, but to sum it up as a general increase in pasture growth or crop yields of 20% when done correctly (more in some circumstances). A cost savings tip would be to invest in a Rata Mole Plough. This will be an initial cost to start with, but will benefit you in the long run. The method of soil drainage is one of the most cost-effective ways to overcome water logging issues with minimal disturbance to the surface and standing crops or pasture. Would you like to grow more grass and higher crop yields without having to spread more fertiliser or work up your paddocks? As fertiliser prices are increasing, the less you can use the better. The Rata Mole Plough is used on heavy soils to improve the productivity of pasture and crops by creating water pathways through the field to permanentley open or subsurface drains. The actual depth of the subsoil will differ from farm to farm, but it is obvious that it is significantly deeper than the working depth of the majority of traditional tillage techniques. Most conventional tillage techniques, which concentrate on the upper soil layers, are unable to penetrate this layer of soil, which gradually compacts over time and restricts the root growth of pastures and crops, resulting in reduced yields. The more vigorous root growth allows roots to grow to deeper levels, making the pasture and crop more resilient to summer dry’s and winter wet periods.


'Steps to Effectively Use Subsoil Aerators for Optimum Crop Health'

Did you that know mole drains can last up to 15 years or more?

It all starts with the direction of travel with the mole in the ground. Pulling a mole drain downhill can be counterproductive as the water has nowhere to flow to and will just pool at the end of the mole drain where the drain leaves the ground and not drain effectively.

Another good tip is to try to start from open drains if they are available, or from natural waterways like a creek. If neither of these terrain features are available, starting in a lower corner of the paddock may be acceptable if the water can then drain off the property and into waterways. The key thing is to ensure the water will flow away from the area of ponding or sogginess and this involves using gravity to take it downhill. This will ensure the water that is drained away by the mole drain has somewhere to go and you’ll likely see more success with quicker drainage times from your efforts.

If you have open drains with single wire fences, we have a model specifically made for operating in those conditions, the Access Mole Plough.

Subsoil types best suited to mole ploughing are clays and heavy soils that mould well and will hold the shape of the mole plough’s revolving plug. If you are in NZ, you can find your area’s soil type in the link below: (look at the type around 30-50cm deep as this is the ideal depth to mole drain, deep enough so that it won’t get ploughed up and shallow enough so the water doesn’t have to travel through too much soil to get to the mole channel)

Most soil types in NZ can have effective mole drains installed. In the right conditions, a well thought out and properly installed mole drain can last 15 years or more, however most mole drainage networks work best if they are reinstalled every 2-3 years. In particularly with fine sandy soils, a yearly refresh of the drainage network may be necessary, but usually this type of soil has excellent drainage and if there is water ponding it is not likely to be for the reason that the water cannot drain through the soil properly, and you’re not likely to see a large benefit from mole drainage.

On the other end of the scale, heavy subsoils such as clays are ideal for mole drainage schemes as they both hold a mole channel very well and also naturally drain very poorly, so benefit greatly from mole ploughing efforts. Peaty subsoils also benefit from mole drainage, although not as much as clays, it is definitely still a worthwhile investment if water ponding and/or soggy paddocks are occurring.

The Rata Action Mole Plough is particularity well suited to heavy and tightly packed soils, with a ram that forces the blade forward, making the process of pulling the mole plough from the ground when the run is finished much easier - no more taking metres and metres to pull the mole plough out of the ground, just tilt the blade forwards and it comes out within a couple of metres, ensuring you can mole plough as far as possible.

Too often mole ploughing is seen as a quick fix to get rid of excess surface water in times of heavy rain, however once surface ponding happens, the best time for mole ploughing is over, and the mole drains created will only last a matter of months versus years when done right, not to mention the soil compaction incurred from driving over waterlogged ground. Mole ploughing when it is too dry results in the soil around the drain cracking, and when it is too wet it will not hold the channel the torpedo is trying to create. Get the timing right when the subsoil is slightly on the moist side of damp, and the drain will set into shape and last for a lot longer.

Topics: Insider, Tips, Hacks & How To's, Working Smarter, Soil Aeration & Drainage