D+C Development and Cooperation (No. 3, May/June 2002, p. 29)

Stop the problem of soil compaction in the World's cropping soils - forever! That was the challenging theme presented by Dr Des McGarry at the World Congress on Conservation Agriculture, which took place in Madrid (October 1-5, 2001).

"Of all the forms of land degradation in the world, soil compaction is certainly one of the most readily reversible and also totally unnecessary" said Dr McGarry. "From the subsistence farmer to large, mechanised corporate farms soil compaction is a "lose, lose, lose" situation. It is the direct opposite of "Conservation Agriculture" and demonstrates the use of non-sustainable agricultural practices that are degrading the land for future generations."

"Soil compaction is the loss of natural soil structure through excess tillage and traffic - especially damaging in moist to wet soils. Soil effects include human-made "pans" from 10 to 60 cm deep and very rough seedbeds. Crops suffer through restrictions to root growth, poor soil aeration, reductions in water infiltration and water availability, and poor germination in rough seedbeds. Greatly reduced fertiliser efficiencies also occur. Either plant roots cannot reach the fertiliser or the applied nutrients remain locked-up in the compacted soil because of reduced soil water dynamics".

Compaction is commonly cited as the most expensive form of land degradation. Costs occur at many different levels and the effects are additive. The most direct costs are from yield reductions; Dr McGarry citing examples of up to 100 per cent crop loss in dry years. Water-use, seed and fertiliser inefficiencies all cost. Rarely considered are costs of both forming and removing soil compaction. No one aims to form compaction but the tractors, tillage and livestock, individually and in combination are the causes. Cultivation is expensive in itself. However, if that cultivation causes compaction - then that is a "lose, lose" situation. Subsequent use of large (and expensive) equipment to remove that compaction is a further cost. And if conducted in moist-wet soil, will cause the compaction to worsen - a "lose, lose, lose" situation. "This is the downward spiral of land degradation" said Dr McGarry.

The outlook, however, is far from gloomy! Solutions already exist to rid any cropping/livestock system of compaction and to ensure that the problem does not re-occur. And the best part is that the highly practicable solutions are the self-same keys to achieving "Conservation Agriculture".

First is recognition of the problem. It is vital to know if compaction is your problem - to correctly target positive management practices. Investigation is best done through small, spade dug soil pits - and describing the soil structure displayed. Comparison of fields, parts of fields and with untouched land (like tree and fence lines) where possible readily provides information on extent and depth of any problem layers. Dr McGarry regularly runs courses in farmers' fields, worldwide, to empower the farmers in soil description for better management.

Second is commencing repair strategies - once compaction is recognised and located. In the past this involved large tractors and soil rippers. However, it is now known that employing Conservation Agriculture practices are easier, cheaper, more efficient and more environmentally friendly methods of breaking-up soil compaction than mechanical means. This "biological ripping" is achieved through the natural cycles of crop growth. For soils that crack (like Vertisols) the wetting and drying with crop growth activates the inbuilt swell/shrink mechanisms of these soils. Maximum effect is gained through building crop rotations and cover crops into the normal cropping sequences where the different root patterns ensure rapid, deep soil compaction repair. Non-cracking soils (like Oxisols) also respond well to biological means. Combining the Conservation Agriculture practices of zero till, stubble retention, and rotation and cover crops rapidly brings soil fauna back into soils and raises organic matter levels. Earthworms are especially important to improve aeration and to accelerate organic matter incorporation to give better soil stability.

Third are the prevention practices. Once soil compaction is under repair it is vital to reconsider on-farm practices to ensure the problem remains gone - forever! There are five main factors and again these practices are the foundations of achieving Conservation Agriculture: reduced (or zero) tillage, controlling traffic placement in the field, strategic tillage where only the plant zone is lightly cultivated, flotation tyres to spread the loads of heavy tractors and harvesters, and the use of crop rotations and cover crops. The aim is to get these factors working together and pick-out the parts that are best suited to your individual farm and farming practices. In this way not only will soil compaction become a thing of the past but also the soil structure will become better and better. The aim is soil structure optimisation - to actually make the soil health better through simpler, yet more productive farming practices.

"It is time to change the mindset of farmers and policy makers," says Dr McGarry. "Moving from animal drawn equipment to tractors may be attractive and necessary in today's economic climate. However, serious land degradation will ensue if Conservation Agriculture practices are not "imported" with the machinery! Vital is achieving a working-balance of the five prevention factors listed above. Only then will farm mechanisation achieve the combined goal of improved productivity and long-term land sustainability."