Soils: put back what you take out

There is an old saying along the lines that all good husbandry men leave their farms in better shape for their sons than when they took over the farms.

We all espouse and try to practise the ideals of good soil husbandry and sustainable agriculture. We also aim continually to increase crop and pasture vields but, unfortunately, we have not always been very successful. One only has to look at average wheat yields to see how badly we have lived up to that aim.

Low rainfall is often blamed for low crop yields. In this driest of continents, it is incumbent on us all to use efficiently the limited amounts of rainfall.

Research has shown that crop yield potential in many situations is far greater, even in research plots, than the actual yield achieved. On the farm, the situation is even worse, with crop yields often reaching little more than half their potential, based on the effective rainfall. Low soil fertility has been shown to be a major reason for this low level of water use-efficiency.

What can we do to maintain our soil resource and still produce profitable crops that meet the needs of the specialised markets that we in Australia must compete in?

There is no one single action that will instantly overcome all our problems. However, it should come as no surprise to anyone that we have been running down our soil fertility. How often do we hear, for example, that we are not producing the same crop yields, let alone protein levels, that our predecessors used to produce when they first started to crop the land.

The reason is that in many cases we have been mining the soil, taking out good crops for many years, living off the soil's native fertility and not replenishing anything. This is a recipe for declining yields, declining grain protein levels, declining soil fertility and declining bank balances.

Probably the quickest way of lowering the amount of organic matter, as well as destroying soil structure, reducing water penetration and retention in the soil and causing other undesirable effects, is over-cultivation.

For many years cultivation practices left a lot to be desired. Let's be thankful that many of those old ways have been replaced by such practices as reduced tillage, stubble retention, and other ways of reducing the amount of organic matter lost from our farms.

The best way of actually controlling the fertility of the soil is through the use of properly conducted soil analysis programs, supplying the needs of the crop and supplementing the soil's fertility through a sound fertiliser program.

In this way, crop production can be 'optimised'; that is, the crop can be, up to a point, tailor-made for a specific market, the soil resource can be maintained or improved, the overuse of fertiliser can be minimised, and damage to the environment can be avoided.