Performance and legacy effect of crop rotations on eastern Canadian dairy farms

Abstract

Crop rotations on dairy farms in eastern Canada nowadays include fewer perennial crops and more nitrogen-demanding annual crops. This study compared, over a 7-year rotation cycle, the agronomic performance and the legacy effect of six crop rotations that varied in crop types (perennial or annual) and nutrient sources (mineral or organic). Crop yield and nutritive value were determined on a yearly basis and cumulated over the rotation cycle. The legacy effect was assessed by growing forage corn (Zea mays L.) in year 6 and soybean [Glycine max (L.) Merr.] in year 7 in all rotations. The legacy effect of perennial forage crops manifested with a 78% lower weed biomass at harvest of forage corn in year 6 and a 14% greater soybean yield in year 7. A greater soil-derived corn nitrogen uptake in year 6 after repeated slurry applications indicated a modest legacy effect of organic fertilization on soil N supply capacity. The presence of perennial forage crops or the use of organic fertilization did not affect cumulative dry matter or crude protein production over the 7-year rotation cycle. The addition of alfalfa (Medicago sativa L.) in mixture with perennial grasses improved forage yield (+26%) and nutritive value (greater digestible energy and crude protein concentration) in post-seeding years. In perennial-based rotations, adding alfalfa to grasses resulted in greater dry matter (+22%) and crude protein (+46%) productions over the 7-year cycle despite a fourfold reduction in N fertilizer input, attesting to the high N use efficiency of perennial legume-based cropping systems.