COMPARATIVE STUDIES OF THE EFFICIENCY OF LIME REFUSE FROM SUGAR BEET FACTORIES AS AN AGRICULTURAL LIMING MATERIAL P. González-Fernández 1 , R. Espejo-Serrano 2 , R. Ordóñez-Fernández 1 , F. Peregrina-Alonso 2 1 C.I.F.A. “Alameda del Obispo”. Apartado 3092, 14080 Córdoba. pedro.gonzalez.fernández@juntadeandalucia.es 2 E.T.S.I.Agrónomos. Univ. Politécnica. Ciudad Universitaria. 28040 Madrid. ABSTRACT Lime refuse from several sugar beet extraction factories was used in a field assay to study its behaviour as an amendment material for an acid soil (plinthic Palexerult). A finely pulverized dolomitic lime was used as a reference. A total of 6.3 t/ha of dolomitic lime and 7.4 t/ha of sugar factory lime scum were employed. Two years after its incorporation into the soil the effects of the lime scum on the change cations were similar to those caused by the dolomitic lime. Throughout six years and six crops it was observed how, in the plots amended with lime refuse, a slightly higher pH was maintained than that measured in the plots without lime, and with fewer fluctuations. Once the maximum pH value was reached in the treated plots, the rate of the pH decline was similar to the acidification process undergone by the soil in the con- trol plots and fitted the regression: pHw = - 0.000435* daa + 6.93 where daa are the days after the application of the amendment. The recycling of sugar beet factory lime refuse as a liming material for acid soils was seen to be a valuable and efficient alternative to traditional limes and dolomites. INTRODUCTION The correction of the excessive acidity of soils by using lime is a very old agricultural prac- tice. Limestone (CaCO 3 ) is the liming material most used although there are many other sources of neutralizing and correcting materials for the yield limiting effects of soil acidity. Those promi- nent among them are: dolomites (Ca CO 3 *MgCO 3 ), burnt lime (CaO), hydrated lime (Ca(OH) 2 ), burnt magnesite (MgO), pulverized magnesite (MgCO 3 ) and their different mixtures. The above materials are sometimes not available to farmers or their price is prohibitive for their use in agriculture. It is therefore important to seek other local sources of acidity correcting materials such as: mollusc shells, paper industry residues, ash, basic steel industry refuse, etc. In our case we have studied the efficacy as a liming material of sugar factory refuse lime (SFRL). This sugar foam waste results from the purification-flocculation of colloid matter from the liquor extracted from sugar beet. In this process, slaked lime and carbon dioxide are used to purify the liquors. The composition varies in accordance with that of the limestone used in the manufacture of slaked lime. SFRL is the residue of these materials together with notable amounts of organic matter and micronutrients. MATERIALS AND METHODS The study was carried out in a trial field established on mid-final Pliocene raña (Espejo, 1978) located on the boundaries of Cañamero (Cáceres) and Valdecaballeros (Badajoz) in the west of Spain. 157 Nutrient and Carbon Cycling in Sustainable Plant-Soil Systems