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Changes in soil profile carbon and nitrogen dynamics <BR>by agricultural management practices (Communication session)

EUROSOIL2020CONT-2496

SURFACE-APPLIED ORGANIC AMENDMENTS MODIFY NITROGEN DYNAMICS DOWN THE SOIL PROFILE IN AN IRRIGATED VINEYARD

Mehdi Sharifi^{* 1}, Lori Phillips², Seanna Zintel¹

¹Agriculture and Agri-Food Canada, Summerland Research and Development Centre, Summerland, ²Agriculture and Agri-Food Canada, Harrow Research and Development Centre, Harrow, Canada

Content: Organic amendments contain soluble nitrogen (N) that can be easily transported down the soil profile. This soluble organic N can modify the soil microbiome and consequently affect N dynamics in soil profile. The effects of wood+bark chips mulch and a combined application of compost plus mulch on soil mineral N, soluble organic N and mineralization of organic N was assessed in soil samples collected from a Merlot (Vitis vinifera L.) vineyard in the semi-arid Okanagan Valley, British Columbia, Canada. Amendments were first applied in spring of 2011 and reapplied every 2 years, with the latest application being in August 2018; mulch and compost application rates in 2018 were 387 and 18.4 Mg ha^-1 row^-1 dry basis, respectively. Soil samples were collected from 15cm intervals to 60cm depth in November 2018 from replicated plots of each treatment and untreated control plots. A 100 d aerobic incubation experiment at 25^oC and 55% water-filled pore space with periodical leaching was conducted for each treatment-depth combination to determine potentially mineralizable N (N₀) and cumulative soluble organic N (DON). Thirty gram soil samples mixed with washed sand (1:1 ratio) and packed in a plastic Buchner funnels. Leaching with 0.01 N CaCl₂ and minus-N nutrient solution were conducted at 0, 3, 6, 10, 17, 24, 31, 45, 72, and 100 d after incubation. Cumulative soluble organic N ranged from 6 to 51 mg N kg^-1 soil and significantly reduced with soil depth. The differences in DON among treatments in each soil depth was significant in order of mulch+compost>mulch>control. Mulch+compost resulted in 165%, 108%, 126%, 147% greater DON in 0-15, 15-30, 30-45, 45-60 cm soil depth intervals, respectively compared with control treatment. Cumulative nitrate leached during the incubation ranged from 12 to 53 mg N kg^-1 soil and followed the same pattern as DON. Potentially mineralizable N ranged from 29 to 267 mg N kg^-1 soil. Treatments affected the N₀ only in 0-30 cm soil depth in order of mulch+compost>mulch>control. Mineralization rate constant values increased by depth, but were not affected by treatments. Surface-applied organic amendments significantly changed the distribution of labile forms of N  (nitrate and DON) in soil profile to 60 cm depth compared with non-amended control. More stable forms of N (soil organic N and N₀) affected by treatments only in 0-30 cm soil depth. Changes in soil profile labile N were associated with altered microbial functional potential. Vertical distribution of soluble N in the soil profile can impact soil and plant health management and consequently affect the resilience of vineyards to climate change.

Disclosure of Interest: None Declared

Keywords: compost, microbial functional potential, mineral nitrogen, potentially mineralizable nitrogen , soluble organic nitrogen, wood-based mulch