CRITICAL LEVELS OF CACO3 IN WHITE LUPIN (LUPINUS-ALBUS L) CULTIVATION

Fourty-four fine-textured soils, with total CaCO3 content from 0 to 46%, were sampled from several areas in Burgundy. They were used to study white lupin behaviour in a greenhouse experiment with the cultivar Lublanc. This behaviour was also studied in an additional trial using soils obtained by mixing one of the 44 soils with increasing amounts (0-15%) of a limestone sieved at 2 different sizes. Soil characteristic, which most explained the lupin results (chlorotic leaf symptoms, chlorophyll leaf content, total dry matter yield), was the content of CaCO3 with a size smaller than 50-mu-m. Total CaCO3 content was nearly as explicative for the natural soils. Lupin results on the contrary were poorly related to DTPA or (COONH4)2- extractable Fe soil content and to water or CaCl2 soil pH. IPC (capacity index for chlorosis) was not so good an indicator of white lupin behaviour as it was of CaCO3 content. From the results of these experiments, 10 parts per thousand CaCO3 with a size smaller than 50-mu-m is a critical level for cultivar Lublanc; 25 parts per thousand total CaCO3 can also be considered as critical in fine-textured soils.