GROWTH, YIELD AND WATER-USE EFFICIENCY OF WINTER BARLEY IN RESPONSE TO CONSERVATION TILLAGE IN A SEMIARID REGION OF SPAIN

In the semi-arid areas of Aragon (NE Spain), dryland crop production i s limited by low and variable precipitation. Conservation tillage has been proposed as a promising strategy to improve soil and water conser vation in these areas. A long-term field research project to determine the feasibility of conservation tillage was initiated in 1989 at four locations, three on loam to silt loam soils (Xerollic Calciorthid) an d one on a silty clay loam (Fluventic Ustochrept), receiving between 3 00 and 600 mm of average annual rainfall. This study compared, under b oth continuous cropping and cereal-fallow rotation, the effects of con ventional tillage (mouldboard plough) and two conservation tillage sys tems, reduced tillage (chisel plough) and no-tillage, on winter barley (Hordeum vulgare L.) growth and yield, and water use efficiency durin g the first two growing seasons. Whereas a similar crop response betwe en the conventional and reduced tillage treatments was generally found at all locations, poor performance with no-tillage was observed at th e most arid sites. At these sites, lower early growth of barley with n o-tillage resulted in a 53% reduction in grain yield, compared to conv entional tillage. This unfavourable crop response to no-tillage was du e to a lower crop water use, mainly starting with the stem elongation stage (20% lower than the tilled treatments), and a larger proportion of total water use lost as evaporation (69% compared to 50% of tilled treatments). Values of water use efficiency for grain production (0.7- 17.0 kg ha(-1) mm(-1)) and transpiration efficiency (7.4-23.8 kg ha(-1 ) mm(-1)) were within the ranges reported for cereal crops in Mediterr anean environments. Fallowing in the cereal-fallow rotation proved to be an inefficient practice for improving soil water storage and subseq uent crop yield, under both conventional and conservation management. Based on the study, we conclude that, up to now, only reduced tillage provides an alternative to conventional tillage to maintain crop produ ction in the dryland cereal-growing areas of Aragon. (C) 1997 Elsevier Science B.V.