Soil water retention as affected by tillage and residue management in semiarid Spain

Conservation tillage preserves soil water and this has been the main reason for its rapid dissemination in rainfed agriculture in semiarid climates. We determined the effects of conservation versus conventional tillage on available soil water capacity (AWC) and related properties at the end of 5 years of management on a clay loam calcic soil (Calcic Haploxerept) in semiarid northern Spain. No-tillage with (NTSB) and without stubble burning (NT), reduced chisel-plough tillage (RT) and conventional tillage with mouldboard plough (MT) were compared in rainfed barley monoculture. Bulk density (¿b), organic matter content (OM), soil water retention (SWR) at matric potentials of 0 to -1500 kPa, and soil water content (SWC) were determined in the driest year of the 5-year study period. Soil OM in the upper 0.15 m was significantly higher (13%) under NTSB, NT and RT than under MT. Soil ¿b in the upper 0.15 m under NT and NTSB was greater than under RT and MT, but at a depth of 0.15–0.30 m was greater under RT than under the other treatments. Reorganisation of pore sizes due to tillage treatments affected AWC. Under RT and MT the largest percentage of the total soil porosity was occupied by pores >9 µm (equivalent pore diameter), in accordance with lower ¿b. Available water capacity was greater with NT than with RT and MT. Higher SWC under conservation tillage systems (NT, NTSB and RT) than under MT was attributed mainly to greater AWC and to the mulching effect of crop residues. Crop yield in the driest year of the 5-year period was lowest under MT whereas no differences among treatments were found over the 5-year period. Stubble burning did not affect AWC nor barley yield. Tillage had a greater impact on soil properties and on crop yield than crop residue management