ROCK FRAGMENTS .2. THEIR IMPACT ON SOIL PHYSICAL-PROPERTIES AND BIOMASS PRODUCTION UNDER MEDITERRANEAN CONDITIONS

The effects of rock fragments on soil temperature, soil moisture conservation, night time water vapour absorption and wheat biomass production were investigated. Under conditions of moderate water stress, water conservation was generally greater in the stony soils. Under conditions of pronounced drought; the opposite occurred, with stony soils conserving less water than soils free of stones, though soils with large cobbles on the surface conserved the most water. Stony soils were generally warmer during daytime and cooler at night than soils free of rock fragments. In the warmest month (July) the diurnal amplitude reached 14.3 degrees C in the control soil and 24.1 degrees C in the stony soils. Night time absorption of water vapour in the upper 15-20 cm was less for the stony soil (17.8% cobble cover), than for the stone-free soil. Cobbles on the soil surface increased biomass production by increasing moisture conservation. After removing all the stones from the surface of 16 plots, total dry matter yield of rainfed wheat was on average 20% less than from plots with stones on the surface.