Effects of ecological soil management on workability and trafficability of a loamy soil in the Netherlands

Effects of ecological and conventional farming in an identical loamy soil were expressed in terms of the land qualities workability and trafficability using conditions in an old meadow as a reference, Threshold values for workability, determined by the lower plastic limit occurred al matric potentials of -120, -45 and -35 cm for the ecological, conventional and old meadow system, respectively. The corresponding trafficability threshold values, obtained by penetrometer measurements, were -160, -15 and -120 cm matric potential. An additional field-traffic experiment showed that deleterious effects of driving over a wet field were relatively small for the conventional system, and more pronounced for the old meadow and the ecological system. A dynamic simulation model for water flow was applied, using measured soil hydraulic parameters, to calculate soil water content and workable and trafficable periods during the year by use of the threshold values. Thirty years' climatic data were used in order to obtain probability graphs. The probability of a field to be workable and trafficable was largest for the conventional system, and least for the ecological system, while the old meadow had a high probability of being workable and a low probability of being trafficable. The occurrence of five consecutive days with an appropriate topsoil moisture content for workability and trafficability was considered to represent the potential start and end of any growing season. The probability of being able to sow or plant at what is considered the optimum dare by agronomists was high for the conventional field (77% for cereals; 93% for potatoes and sugar beet) and low for the old meadow (10% and 33% respectively) and very low for the ecological field (0% and 17% respectively). The moisture supply capacity of the soil, defined as the ratio between actual and potential transpiration, was most favourable for the old meadow, least favourable for the conventional field and with the ecological field in between. Potential productivity of the ecological system was thus higher than the conventional system, but the risk of compaction was higher as well. putting relatively high demands on the management abilities of ecological farmers.