The effect of soil structure differences in a silt loam soil under various farm management systems on soil physical properties and simulated land qualities

Five different farm management systems on the same soil were selected to study the effects of the enhancement of soil organisms on soil structure formation, on soil physical properties and simulated land qualities. The farm management systems were: a conventional high input system (CONV); an integrated system (INT) i.e. reduced N-fertilisation, reduced biocide use and shallower soil tillage; a minimum tillage system (MTnew) with only 7 cm ploughing which was just started; a minimum tillage system (MTold) with the same management over 18 years and a permanent pasture (P). The soil physical properties determined were: water retention and hydraulic conductivity curves. The land qualities which were simulated were the workability and the aeration status (air-filled porosity). Water retention and hydraulic conductivities curves of the topsoils (0–25 cm) of the different farm management systems involved, were different, as were those of the 25–50 cm layer of the arable systems on one hand and pasture land on the other. In the farm management systems, with the highest impact of soil organisms on the soil structure, i.e. pasture land and old minimum tillage, soil physical properties were most favourable for growing crops. The conventional and integrated systems had the least favourable properties. This was also true of the simulated land qualities. In spring the probabilities over a 30 year period, to work in the field (workability), for the old minimum tillage system were about 15% higher than for the integrated and conventional farm management system. Those of the permanent pasture were about 20% higher than the old minimum tillage system. The same trend was shown in autumn at harvest. The old minimum tillage system and permanent pasture had the lowest probabilities of an insufficient air fraction during the growing season. Those of the conventional and integrated systems were 20–40% higher over the growing season. Calculated yields for a potato crop showed the same trend except for MTold which had the lowest yields especially in years with a previous wet winter season. Of all crops potatoes react most sensitively to soil compaction and MTold had the most compacted soil. However, the increase in workability and aeration in this system compensated for the calculated yield reduction as the actual yields of CONV and MTold were similar. Consequently, farm management systems stimulating the presence and activities of structure-forming soil fauna will also stimulate t