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 conse rvation, night time water vapour absorption and wheat biomass producti on were investigated. Under conditions of moderate water stress, water conservation was generally greater in the stony soils. Under conditio ns of pronounced drought; the opposite occurred, with stony soils cons erving less water than soils free of stones, though soils with large c obbles on the surface conserved the most water. Stony soils were gener ally 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 soi ls. Night time absorption of water vapour in the upper 15-20 cm was le ss for the stony soil (17.8% cobble cover), than for the stone-free so il. Cobbles on the soil surface increased biomass production by increa sing moisture conservation. After removing all the stones from the sur face of 16 plots, total dry matter yield of rainfed wheat was on avera ge 20% less than from plots with stones on the surface.