Wood chips to help solve nitrogen problem
Preventing nitrogen getting into waterways is high on the priority list for many farmers and growers.
Traditionally drains are installed by backhoes or trenching machines, both relatively slow and expensive, so a system new to New Zealand, but used in the US for around 20 years, might be worth a closer look.
Soilmax Gold Digger drain ploughs, imported by the Law family in Taihape, look like oversized sub-soilers, using a curved-profile leg to install plastic drainage pipe at the target depth.
Made from military grade T1 steel, the plough is lighter and slimmer than machines made from more traditional steels and is said to be easier to pull.
At the base of the leg a replaceable shoe creates a curved profile to support the drainage pipe, while the leg serves to break up the topsoil to provide a porous layer for rapid water reticulation. On the top of the machine, a locally sourced pipe reel holds the 100m drainage coils typically found in NZ.
Gradient control is achieved using a simple water level and depth chain on slopes, and an optional laser or GPS can be fitted for work on the flat or for operators requiring greater accuracy.
It’s said to be extremely fast, with reports of 100m being ‘pulled in’ in 5-6 minutes depending on soil conditions; the standard machine is capable of working to depths of 1.7m.
Power requirement depends on terrain, soil type and topography; the distributor notes that weight and traction is more relevant and recommends a tractor weighing a minimum of 10 tonnes and a rear lift capacity of around 2t.
Key to installation success is a tractor equipped with a creep box or a CVT style transmission that can achieve slow, constant speeds, which then gives the machine time to lift the ground and create some shatter as the pipe is installed.
Pipe breakages are said to be minimal, because traction is normally lost before anything breaks.
Asked whether backfill is placed over the pipe, Soilmax NZ points to US research suggesting this practice is unnecessary; over two-three years the airgaps between the stones fill with silt, removing any benefit; using the topsoil already there tends to promote a permanent drainage channel over the pipe.
After installation the paddock will show some signs of ‘heave’ along the drain line, but reports suggest this be left to settle naturally over the following months rather than re-compressing the column of topsoil.
