Effect of land management practices and environmental parameters on growing season denitrification rates under dairy crop rotations in Atlantic Canada
Fuller, K.D., Burton, D.L., Grimmett, M.G., Franklin, J., Drury, C.F., Zebarth, B.J., Vernon Rodd, A., St. George, E. (2016). Effect of land management practices and environmental parameters on growing season denitrification rates under dairy crop rotations in Atlantic Canada. Canadian Journal of Soil Science, [online] 96(1), 86-103. http://dx.doi.org/10.1139/cjss-2015-0035
Denitrification losses from agricultural land have been identified as a significant nitrogen (N) loss pathway that contributes to poor utilization of applied N. Higher losses have been reported when inorganic fertilizer N is substituted with an organic N source such as livestock manure. This research examines the relationships between denitrification rates, land management practices and soil processes when using spring applied liquid dairy manure (LDM) as principal N source. Mean daily denitrification rates (DDRs) in a perennial hayfield (PH) rotation and a corn-soybean-wheat (CSW) rotation with or without tillage (T and NT respectively) ranged between 0.9 and 27.0 g N ha−1 day−1. Mean, seasonal DDRs in the PH rotation were significantly lower in three out of six seasons when compared with the CSW-T and (or) CSW-NT rotation. When averaged across the six season study period, the mean DDR in PH of 4.4 g N ha−1 day−1 was also significantly lower than CSW-T and NT (7.6 and 8.1 g N ha−1 day−1, respectively). There were no significant effects of tillage in the CSW rotations in any of the six growing seasons. When treatment and growing season data were combined, a positive relationship between water-filled pore space (WFPS) and DDR indicated a threshold of approximately 40% WFPS for onset of significant denitrification. Similarly, the relationship between soil nitrate levels and denitrification rates in the population data set demonstrated that NO3− began to limit DDR below 2-5mg N kg−1. This 6-year study of denitrification losses suggests a primary effect of WFPS, a secondary effect of O2 consumption as reflected by soil respiration, and nitrate limiting only at relatively low concentrations. Environmental variables were more consistent drivers of denitrification in three manure-fed crop rotations typical of Atlantic Canada dairy operations than were land management decisions and practices.