Soil Phosphorus Availability and Other Nutrient Elements in a Two-Year Corn/Soybean Rotation.

Tillage management and cropping intensification influence soil nutrients supply and demand including P. Our objective was to investigate in a 2-year corn (Zea mays L.) and soybean (Glycine max L. (Merr.)) rotation, the long term effects on soil P status and other soil nutrients of an annual P application. The study was conducted in Quebec, Canada, on an experiment established since 1992 on a clay loam soil. Two tillage systems, no-till (NT) and mouldboard ploughing (MP), and three P fertilizer regimes (0, 17.5 and 35 kg P ha^–1 applied during the corn phase of the rotation) were implemented. Soil (0-15 cm) was sampled at the end of four successive cycles of the 2-year corn/soybean rotation (2000-2001, 2002-2003, 2004-2005, and 2006-2007). Higher yields were obtained in the MP. Exchangeable K was higher under NT compared with MP probably as a result of K released by crop residues not incorporated in the soil. The P budget across the four rotation cycles varied between 0 and -36 kg P ha^–1 for the treatments 35 P and 0 P, respectively. The P budgets showed that crop P exportation by the grain exceeded the P supplied by fertilizers. For the soil test Mehlich-3 P (PM3), the general trend was an increase from fall to spring in NT plots receiving the 35 P ha^–1 treatment. Soil test PM3 decreased across P treatments during the successive 4 rotation cycles. For the treatment 0 P, soil test PM3 decreased until reaching 30 and 25 mg P kg^–1 in the NT and MP, respectively. Decreasing soil test PM3 could be explained by the P budgets which were negative across P rates. In these 2-year corn/soybean rotation cycles where P was applied according to corn P requirements, a direct consequence was PM3 depletion in the soil.