Long term effect of liquid dairy manure application, crop rotation and tillage practices on soil nitrogen stocks

The use of liquid dairy manure as fertilizer is a common practice in dairy-based cropping systems which provides considerable quantities of nitrogen to the soil. The response of nitrogen stocks to repeated dairy manure applications has not yet been thoroughly studied despite its significance for plant nutrient supply and risks of environmental losses. The response of soil nitrogen stocks may vary depending on the nitrogen form (organic or mineral) and with the associated management practices such as tillage or crop rotations. The objective of this project situated in a nordic area of the province of Quebec (48°50’N, 73°33’E), was to estimate the nitrogen budget and to determine the response of nitrogen stocks along a soil profile (0-50 cm) to long-term (21 years) application of liquid dairy manure in combination with two crop sequences (continuous cereals vs. cereal-perennial forage rotation) and two fall primary tillage practices (moldboard plowing vs. chisel plowing). The nitrogen budget revealed the importance of the contribution of the atmospheric nitrogen fixation by the legumes to the soil nitrogen stocks. After 21 years, soil N stocks were 17% greater in the cereal-forage rotation than under continuous cereals. Moreover, the effect of manure was greater (+24%) when applied in the perennial-based rotation than under continuous cereals, suggesting a synergy in the effects of manure and the presence of perennial forages in the rotation.