Nitrogen dynamics after low-emission applications of dairy slurry or fertilizer on perennial grass: a long term field study employing natural abundance of d15N

Authors: ZHANG, H - Agriculture And Agri-Food Canada; HUNT, D - Agriculture And Agri-Food Canada; ELLERT, B - Agriculture And Agri-Food Canada; MAILLARD, E - Agriculture And Agri-Food Canada; COMPTOB, J - Agriculture And Agri-Food Canada; Kleinman, Peter; Spiegal, Sheri; BITTMAN, S - Agriculture And Agri-Food Canada

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2021
Publication Date: 6/9/2021
Citation: Zhang, H., Hunt, D.E., Ellert, B., Maillard, E., Comptob, J., Kleinman, P.J., Spiegal, S.A., Bittman, S. 2021. Nitrogen dynamics after low-emission applications of dairy slurry or fertilizer on perennial grass: a long term field study employing natural abundance of d15N. Plant and Soil. 465:415–430. https://doi.org/10.1007/s11104-021-04998-7.
DOI: https://doi.org/10.1007/s11104-021-04998-7

Interpretive Summary: Efficient use of manure is key to the long-term sustainability of animal production systems. Researchers with Agriculture and Agri-Food Canada and USDA’s Agricultural Research Service, used naturally occurring differences in nitrogen isotopes to compare long-term efficiencies of commercial fertilizer and dairy manure in tall fescue  grass pastures in the Pacific Northwest. They found that the grass was able to take up nitrogen from the manure and the commercial fertilizer with similar efficiency. Results support efforts by the two organizations to pursue long-term strategies for sustainable intensification of agriculture in North America.

Technical Abstract: Natural abundance d15N is a useful metric for examining the fate of N amendments over time in agricultural systems. The long-term effects of surface banding of liquid dairy manure (LDM) compared to mineral fertilizer (MIN) on herbage and soil are not well known. This study investigated the effects of long-term (15-yr) applications of LDM and MIN on tall fescue (Festuca arundinacea Schreb.) N uptake, soil N stock (40 cm depth), and d15N natural abundance in grass and soil. Annual application rates (nominal) were 200 and 400 kg mineral N ha-1 in MIN (requiring400 and 800 kg total N ha-1 for LDM, half of which is mineral N) applied in 4 equal doses over the growing season. Grass N uptake was higher for LDM than MIN at equivalent mineral-N rates. At similar total applied N (the 400 kg mineral N ha-1 for MIN and the 200 kg mineral N ha-1 for LDM) grass N uptake  was similar. Total N stocks were increased to 40 cm by the LDM, whereas the additive effect of applied MIN was apparent only at the 0-5 cm depth.. The d15N natural abundance in whole soil and fine heavy fraction of soil (i.e., silt and clay) was significantly greater for LDM than MIN treatments at 0-5 cm soil, pointing to greater increases in soil N from LDM-N and preferential storage of that N in the fine heavy fraction, but it is not clear how stable or available this N is over time. The d15N natural abundance of grass increased (from 5.99 to 7.40%) in LDM treatments but decreased (3.62 to 0.77‰) in MIN treatments over time, suggesting that grass N uptake varied by its applied N source reflecting both current and legacy N. Our results show that d15N natural abundance can be used as a tool for studying long term N sources in crop and soil.