J-ROOTING: A GROWTH INHIBITOR

Clay soils, with their complex physical structure, are far harder to manage than sandy soils that have little or no structure. They are usually 'layered' with definite horizons, but this is not necessarily apparent from the condition of the topsoil above. An inspection hole would be required to really understand the complexity of the soil underneath, but a few general guides can be applied.

What happens over time is that the clay particles from the topsoil are leached into the subsoil. This is not a problem in areas of natural vegetation that has never been cleared, as the tree roots that are growing in the subsoil will keep it opened up so that drainage and root penetration is not impeded. Studies have shown that soil compaction under these conditions is not significant. However, when these soils are used for cropping or grazing over a long period of time, the clay in the top of the subsoil may become compacted and this will impede drainage and root penetration. If this compaction is severe, breaking it up with rippers is necessary.

If ripping is required, a depth of 50 60cm is usually sufficient, as the area of greatest compaction will be in the top of the subsoil. A square or rectangular tyne is better than a round one, as the aim of the operation is for the tyne to lift the soil as it is pulled along under the ground. This lifting effect will fracture the clay and break up the compaction; the only problem is to decide when to carry out this operation. Too dry and you bring up huge clods that take too much time to break down for planting: too wet and the ripper slices through the soil like a knife through soft butter, still leaving the compaction, but with glazed channels and rip lines. If trees are planted between the rip lines, they are still planted in compacted ground and will not attain optimum growth. If they are planted on the rip-lines, the roots will follow the line of least resistance and grow along the rips. The roots will not spread out in all directions as they would in a more porous soil and that is why they are so easily blown over. This problem is called 'J-rooting'.

If ripping is done successfully, at the optimum time, the porous soil conditions created will persist for quite a long time, possibly years, unless the ground is subject to intensive agricultural use. This means that ripping can be done well in advance of estimated planting and emphasises the advantage of long term planning in land use.