A LYSIMETER STUDY OF SOIL COMPACTION EFFECTS ON EVAPOTRANSPIRATION INA BARLEY CROP

The effects of soil compaction on yield, evaporation and plant water u ptake were studied on soil cores (height 300-350 mm diameter 295 mm), collected from field plots with three different compaction levels. The soil cores were extracted with a drill, fitted into PVC cylinders (di am. 295 mm, height 500 mm) and sealed at the bottom to form lysimeters . The soil was a silty clay with 48% clay. Evaporation and transpirati on were studied in separate lysimeters, without and with plants, respe ctively. Water loss was determined by weighing and, in the lysimeters with plants, also by using TDR (time domain reflectrometry) at differe nt depths. Evaporation was little affected by compaction, especially w hen the soil was covered with a seedbed. From bare soil, the evaporati on during 30 days was 2 mm lower in loose soil than in compacted soil. Plant water uptake, dry matter yield and water use efficiency (biomas s (g)/transpired water (kg)) decreased with increasing level of compac tion. TDR had a low accuracy in determining the absolute values of the soil water content, especially in dry soil, probably due to measureme nt problems in connection with soil cracking. However, TDR readings of changes in water content with time corresponded very well to data obt ained by weighing the lysimeters.