T. Németh, A. Huisz and T. Tóth. 2007. Effect of barley straw on the water-stability of soil aggregates in a long term fertilization experiment. Mineral versus organic fertilization. Conflict or synergism? 16th International Symposium of the International Scientific Centre of Fertilizers. 16-19. September 2007. Ghent, Belgium. Proceedings. Pp. 383-388. Abstract Degradation of soil structure and decline of structural stability are frequently caused by tillage, crop management and excessive wetting. As an indicator of structural stability, the water-stability of soil particles is often determined by wet sieving. Because of differences between field and laboratory circumstances and therefore lack of comparability, the former results are questionable. An optimised wet sieving method initiated by Six (2000) was adapted by us to investigate changes in soil structure and quality caused by different kinds of added organic matters. Samples originated from the long-term fertilization experiments of Keszthely, Western Hungary. The texture of the investigated soil is sandy loam, the type of soil is an Eutric Cambisol (WRB classification), or Alfisol (Soil Taxonomy). Barley straw was added as organic fertilizer in the experiment. According to data soil structure is improved by adding this readily decomposable organic matter since its decay produce gluing compounds. Mineral particles and microaggregates are bound together making new or bigger macroaggregates and the water-stability of existing macroaggregates increased.