EFFECT OF RETENTION OF RUN-OFF WATER AND GRAZING ON SOIL AND ON VEGETATION OF A TEMPERATE HUMID GRASSLAND

A 4-year field trial was carried out on a Typic Natraqualf to modify the surface run-off, to change the soil water regime and improve forage productivity. Water was retained by earth banks which were built along contour lines. The area was grazed by cattle at a density of six animal units per hectare during five or six occupation periods per year. To study the effect of cattle trampling, 1 ha within the water retention area was excluded from grazing. It was found that surface accumulation of water led to higher soil water contents and prevented salt ascension by capillarity from the water table (Electrical Conductivity of A, horizon, 1.4 dS.m-1 against 3.4 dS.m-1 in the control area). Soil salinization in the control area was associated with soil water evaporative losses and the water table depth, when it was less than 1.5 m deep. Soil alkalinity (pH and SAR) showed variations closely related to salinity. The already impaired soil physical properties were not significantly affected by livestock trampling in the water retention area. A dramatic change in plant community composition was observed. Most halophitic species disappeared and the area was covered by hydrophilous grasses. This determined a 4-fold increase in higher quality forage. Run-off water retention proved to be a promising way to change temporarily the status of the soil and to cause a large change in grassland characteristics and productivity.