Seasonal nitrate levels in the soil solution of an organic pasture managed for nature conservation

Abstract

Extensive management of pastures is considered as an option to enhance nature conservation in agricultural landscapes. Partial reduction of the grazing frequency from four to two rotations and discontinuing the tending of sod and sward have been tested for extensive management of a mixed pasture at the Nova Scotia College of Agriculture in Truro since 2004. It is not well known how extensification affects the N cycle of organic pastures without mineral fertilizer or manure applications. Moisture and temperature of the topsoil and nitrate content of the leachate extracted with ceramic suction cups at 0.5 m depth were monitored prior to grazing and during sward regrowth in the first and second rotation in spring of 2005 and 2006. In each year, more than 75 % of all samples contained less than 2.5 mg NO3-N L-1. A significant seasonal nitrate dynamic suggests that plant N uptake reduces nitrate leaching in the first rotation, while soil biological activity increases N supply due to soil warming in excess of plant uptake, thus raising the nitrate level in the second rotation. Extensification significantly reduced soil temperature with a concomitant albeit small decrease of nitrate levels in the soil leachate. The pasture cycled nitrogen very tightly with little room for leakages as a result of imposed treatments during the spring season. Key words: Pasture, organic, temperature, nitrogen, leaching