Compaction and good practices in eastern Turkey, Part I

摘要

An analysis of the relative contribution of loading and shearing by tractors, smearing by tillage equipment and irrigation water on soil compaction on the Narli Plain irrigation development, eastern Turkey. Soil compaction is a often a limitation at Narli. It is most severe on land used for over 4000 years and absent on land brought into cultivation 40 years ago. Previous research has shown a sequence of deterioration involving changes in pore size distribution, penetrometer resistance and moisture relationships. The soil structure in the field at 30 cm was distinct and comprised an unusual and distinctive platy morphology. The platy structures were very regularly spaced breaking into strongly angular fragments of about 5 to 10 mm in diameter. This work aimed to investigate this morphology beyond existing work and to produce it in a simulation experiment in the laboratory. In particular, the work aimed to explain the relative contribution of loading by agricultural vehicles, the shearing effects of wheels, the actions of tillage tools and the contribution of soil and water weight in producing the compaction. In addition, the aim was to understand the role of the number of damaging operations on soil compaction and therefore the number of years needed to produce deterioration. This would allow forecasts to be made on the 'fate' of well-structured soils and suggest which agricultural practices were in most need of improvement through technology transfer, extension and training. The methods involved a laboratory simulation of forces and processes, representing 2, 20 and 50 years of operations at the soil moisture content of the lower plastic limit. Soil samples were quantified using thin sections and scanning electron photomicrographs together with undisturbed field samples. Soil loading was the most important factor associated with compaction at Narli. This is followed by shearing effects of wheels, then smearing by tillage equipment and finally irrigation water which had little effect in this simulation. In the absence of natural processes or remedial tillage, compaction takes about 10 years to become significant and about 20 years to become severe in this simulation. The work suggests that there is a good 'window of opportunity' to modernise and actualise good practices through extension and training. Reducing the compacting effects of load is the priority but without excessive slip.