LONG-RANGE EFFECTS OF INTENSIVE CULTIVATION AND MONOCULTURE ON THE QUALITY OF SOUTHERN ONTARIO SOILS

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Abstract
Ontario holds a significant proportion of the land base for Canada’s food production. Many of the soils are vulnerable to the effects of erosion and intense cropping. Laboratory and field studies indicate that monoculture systems without grass-legume forages lower organic C and N equilibrium levels. Structure and tilth, in terms of total porosity and stable aggregation, are impaired. Marked increases in land areas in monoculture, particularly corn and beans, have occurred in the last 20 yr and could lead to lower yield potentials. However, contrary to this expected trend in soil productivity, Ontario’s census records indicate a yield increase of 1.88 t/ha for nine commonly-grown crops over the 20-yr period. Fertilizer recommendations at the end of the period have decreased to approximately 60% of the amount recommended at the beginning. Deterioration of soil by wind and water erosion is a matter of concern. While average losses are estimated between 0.07 and 1.9 t/ha for different watersheds, individual field situations exceed this and may create serious problems in yield reduction and impaired water quality.