Thesis
The influence of tillage on vetch cover crop decomposition, N availability, and broccoli yield in organic reduced tillage agriculture
Washington State University
Master of Science (MS), Washington State University
2019
Handle:
https://hdl.handle.net/2376/102765
Abstract
In the maritime Pacific Northwest reduced tillage systems have been considered as a means to improve soil quality and control weeds, but effects on CC decomposition and N dynamics are largely unknown. A randomized complete block field experiment was conducted in 2015 and 2016 at the WSU Puyallup Research Extension Center (47.194225°N, -122.330693 °W) in western Washington. A fall planted common vetch (Vicia sativa L. spp nigra L.) cover crop was terminated with flail mowing and a broccoli (Brassica oleracea var italica) cash crop was planted into three different tillage treatments: no till, strip till, and full till. Vetch decomposition, nitrate and ammonium plant available nitrogen (PAN) at 0-15 cm and 0-0.9 m, gravimetric soil moisture, soil temperature, broccoli yield, and fertilization were compared to determine the influence of tillage treatment on vetch CC decomposition, N availability, and broccoli yield. Vetch litterbag decay constants (k) varied by year and tillage treatment; in 2015 the strip till and full till k value was -0.12 whereas in 2016 k was -0.04. In comparison, in the no till treatment k was -0.04 and -0.03 in 2015 and 2016 respectively. Percent residue remaining in the litterbags at day 84 ranged from 17.5, 13-16.7, and 38.6-45.3 in full till, strip till, and no till respectively in 2015 and 2016. In 2015, PAN at the 0-15 cm depth (day 14 and 28) was significantly greater in full till compared to no till and strip till at P<0.05. In 2015 postharvest PAN levels at the 0.3-0.6 m and 0.6-0.9 m depth were significantly greater in full till compared to no till at P<0.05. In 2015 gravimetric soil moisture was significantly greater in no till and strip till compared to full till at day 7 and 56 (P<0.05). In 2016 all tillage treatments produced significantly greater broccoli yields with fertilization and fertilized strip till had a greater yield compared to fertilized full till (P=0.098). The results of this study indicate that CC residue placement (surface vs. buried) influences the rate of CC decomposition and N availability which varies by year and tillage type.
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Details
- Title
- The influence of tillage on vetch cover crop decomposition, N availability, and broccoli yield in organic reduced tillage agriculture
- Creators
- Ryan Morris Tarbell
- Contributors
- Doug Collins (Degree Supervisor)
- Awarding Institution
- Washington State University
- Academic Unit
- Agricultural, Human, and Natural Resource Sciences, College of
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University; [Pullman, Washington] :
- Identifiers
- 99900525176501842
- Language
- English
- Resource Type
- Thesis