Keywords: Soil compaction, controlled traffic farming, soil structure, crop productivity.
Where agriculture has become highly mechanised, the soil is regularly compacted by machinery wheels. To alleviate this traffic-induced soil compaction, the soil is usually loosened before growing the next crop. This cycle of compaction and tillage is a major inefficiency in terms of the use of energy and labour, particularly when the soil is tilled to greater depth. Insufficient alleviation of compaction during seedbed preparation may cause a compacted rootbed despite yearly tillage. The common understanding is that a certain soil has an optimum, relatively low density state at which most of the processes such as transport of water, diffusion of gases, transition of organic matter by soil biota, chemical reactions and root penetration proceed most favourably for crop productivity.
A way to prevent the compaction cycle and a compacted rootbed is controlled traffic farming (CTF), preferably in combination with reduced or zero tillage. In this system over-compaction is restricted to precise traffic lanes, where it improves wheel performance, while allowing natural, uncompromised soil processes and productivity elsewhere in the field. Compared with random traffic farming, improvement of soil structure in the plant beds is reported for CTF in almost all experiments. Very low bulk densities, leading to yield reduction, have been reported occasionally in CTF systems with yearly tillage but can be avoided easily by seedbed firming when required. A soil with such low density was never reported in experiments with reduced till and zero till CTF systems. Generally, crop productivity in CTF systems is equal or better than in random traffic systems, based on the crop yield per hectare including the traffic lanes. In dry areas, this may be partly caused by improved water conservation. Some data are available on the efficiency of fertiliser use in CTF systems, indicating that 15 — 30% less nitrogen fertiliser could be used in CTF compared with random traffic farming, without compromising crop yield. Benefits of controlled traffic farming for the environment include better infiltration and drainage of the soil, less water run-off and soil erosion, less denitrification and emissions of the greenhouse gas nitrous oxide (N2O) and the potential reduction in use of fertiliser and fossil energy.
G D Vermeulen, Wageningen UR, Plant Research International, Agrosystems, P O Box 616, NL-6700 AP Wageningen, Netherlands, and
W C T Chamen, CTF Europe Ltd., Maulden, Bedford, MK45 2AU, UK.
28 pages, 10 figures, 2 tables, 73 references.