Tremblay, G. J., Boisvert, J., Fréchette, G. É., Saulnier, M., Alexandre, R. and Vanasse, A. 2011. Mid term evaluation of mineral fertilizer requirements (N, P, K) of a field crop rotation on a clay soil. Can. J. Soil Sci. 91: 637-646. In Quebec, the recommended fertilizer requirements have been lowered since 1994. A study was undertaken from 1998 to 2005 in a 4-yr rotation of wheat (Triticum aestivum L.), soybean [Glycine max (L.) Merr.] and grain corn (Zea mays L.) to verify the mid-term mineral fertilizer requirements (N, P, K) for these field crops. Four levels of nitrogen (N) and three levels of phosphorus (P) and potassium (K) were compared on a clay soil of the Saint-Lawrence Lowlands. Nitrogen requirements based on this study corresponded to the recommended levels of each field crop tested. Recommended phosphorus rates did not maintain initial P_M-III soil level (1998). However, crop yields were not affected by this decrease in soil P_M-III level. To improve fertilizer recommendation tables, it should be relevant to determine with more accuracy the critical phosphorus and potassium values for field crops on other typical Quebec soils.