Impact of soil compaction upon soil water balance and maize yield estimated by the SIMWASER model

The capability of the soil water balance model SIMWASER to predict the impact of soil compaction upon the yield of maize ( Zea mays L.) is tested, using the results of a field experiment on the influence of soil compaction by wheel pressure upon soil structure, water regime and plant growth. The experimental site was located on an Eutric Cambisol with loamy silt soil texture at an elevation of 260 m in the northern, semi-humid sub-alpine zone of Austria. Within the experimental field a 7 m wide strip was compacted by a tractor driven trailer just before planting maize in May 1988. Compression effects due to trailer traffic resulted in distinct differences of physical and mechanical soil parameters in comparison with the uncompressed experimental plots down to a depth of about 30 cm: bulk density and penetration resistance at field capacity were increased from 1.45 to 1.85 g/cm 3, and from 0.8 to 1.5 MPa, respectively, while air-filled pore space as well as infiltration rate were appreciable lowered from about 0.08–0.02 cm 3/cm 3 and from 50 to 0.5 cm per day, respectively. The overall effect was a clear depression of the dry matter grain yield from 7184 kg/ha of the non-compacted plot to 5272 kg/ha in the compacted field strip. The deterministic and functional model SIMWASER simulates the water balance and the crop yield for any number of crop rotations and years, provided that daily weather records (air temperature, humidity of air, global radiation, wind and precipitation) are available. Crop growth and soil water regime are coupled together by the physiological processes of transpiration and assimilation, which take place at the same time through the stomata of the plant leaves and are both reacting in the same direction to changes in the soil water availability within the rooting zone. The water availability during rainless seasons depends on the hydraulic properties of the soil profile within the rooting depth and on rooting density. Rooting depth and density are affected by both the type of the crop and the penetration resistance of the soil, which depends on the soil moisture status and may be strongly increased by soil compaction. The model SIMWASER was able to simulate these effects as shown by the calculated grain yields, which amounted in the non-compacted plot to 7512 and to 5558 kg dry matter/ha in the compacted plot.