Agronomic and economic performance of 26-year corn-soybean rotation affected by tillage and fertilization in eastern Canada

Adoption of conservation practices such as no-tillage (NT) may benefit soil properties and related yields. However, magnitude of changes is dependent upon time scale, soil characteristics, and climatic conditions, which has received little attention in eastern Canada. A 26-yr field experiment was conducted on a clay loam soil at L'Acadie, southwestern Quebec, to evaluate the effect of NT vs. moldboard plow (MP) and mineral N (0, 80, and 160 kg N ha(-1)) and P (0, 17.5, and 35 kg P ha(-1)) fertilization on grain yields, soil properties, and annual net returns of a corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation. Tillage was performed every year, while fertilizers were only applied to the corn phase. Throughout the years, the site responded well to N fertilization but not consistently to P. Tillage system did not affect corn grain yield in the first 10 yr, but yield gradually declined under NT and produced 2.3 Mg ha(-1) less than MP with recommended N rate in the last 8 yr. By contrast, NT reduced soybean yield in the first decade (0.32 Mg ha(-1)) but not thereafter. After 24 yr of implementation, NT largely increased organic matter and Mehlich-3 P and K in the 0-to-5-cm surface layer, but this did not translate into higher yields. Compared with NT, MP achieved CAN$200 ha(-1) more revenue during last years at recommended N rate despite higher operation costs. Results demonstrated that under northern latitudes, this clay soil was not appropriate for NT.