Alfalfa Effects on Soil Fertility

摘要

The importance of leguminous crops in enhancing soil fertility in a rotation with cereals is well known. What is still uncertain is the mechanism of this improvement and how long it lasts. Basically, it can depend on the soil enrichment in organic matter, on the amount of N fixed by rhizobia or on both (Levin et al., 1987). In many parts of the World a pluriennial stand of leguminous forage crop is considered fundamental for the sustainability of agricultural systems (Russelle et al., 2007). The scarce literature on the topic, however, reports contrasting results, and in some instances the benefits of meadows revealed not so long (Toderi et al., 1985). A long-term experiment, started in 1966 and still conducted in the eastern Po Valley (Cadriano, BO) compares 2-year rotation (corn-wheat CW) with 9-year rotation (alfalfa, alfalfa, alfalfa, C-W, C-W, C-W), combined with two rates of cattle manure supply (none and 20 t ha~(-1) year~(-1) of fresh manure) and 3 mineral fertilization rates (N0P0, N1P1, N2P2) in a split-plot replicated twice (56 m~2 sub-plots) on a medium textured soil, with low organic matter content. The effects of alfalfa on the subsequent successions of corn and wheat are shown and compared to the corn and wheat crops inserted in 2-year rotation (without alfalfa). Discussed data are the averages of four cycles of the 9-rotation.