An eleven year study of nitrate leaching in vegetable production with winter cover crops Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/h702q925m

Descriptions

Attribute NameValues
Creator
Abstract or Summary
  • The Willamette Valley of Oregon has high rates of winter precipitation that cause leaching losses of residual fertilizer nitrogen (N) as nitrate (NO₃). Cover crops may have potential to mitigate N loss. Shallow groundwater was sampled for 11 years from plots planted in summer vegetables with and without winter cover crop management. A randomized complete-block split plot design was used with cover crop system as main plot and three N fertilizer application rates as subplots (N0 for no fertilizer, N1 for intermediate and N2 for the full recommended N inputs). The summer crops were corn (Zea mays L. cv. Jubilee), broccoli (Brassica oleracea L. Botrytis Group cv. Gem), or snap beans (Phaseolus vulgaris L. cv. Oregon 91G) and the cover crop treatments were conventional fallow (called C plots) or fall-seeded cereal rye (Secale cereale L var. Wheeler), triticale (Tritcosecale X L. var. Celia), or common vetch ( Vicia Sativa) / triticale mix cover crops during winter (called H plots). Cereal cover crops were used during the first eight years of the study while a legume / cereal mixture was used during the last three winters. Twenty-six 0.26 m² passive capillary samplers (PCAPS) continuously sampled water flux at a depth of 1.2 meters. Water was sampled from the PCAPS 249 times over the 11 year period. A calculated water balance gave an average collection efficiency of 76%. Elevenyear flow-weighted average N in the form of nitrate (NO₃-N) concentrations (mg L⁻¹) for fallow vs cover cropped plots were 16.7 and 11.9; 9.9 and 6.4; and 7.0 and 4.1 for N2, N1 and N0 plots, respectively. Calculated annual average NO₃-N mass losses (kg ha⁻¹) for C vs. H plots during the same period were 76.3 and 45.9, 40.0 and 30.2, and 29.0 and 17.3 for N2, N1 and N0 plots, respectively. Analysis of variance indicated that cover crops, N fertilization rate, and year had significant effects on NO3-N concentration and mass losses (P-value < 0.0001). The common vetch / triticale mix cover crop treatment had a significant effect on NO₃-N concentration and mass losses (P-value < 0.0001) during the low rainfall winter of 2000 and the average rainfall winter of 2002, but NO₃-N concentrations and mass losses during winter 2001 were among the highest observed throughout the entire study. These results may have been due to complicated environmental processes such as atmospheric N fixation, rainfall differences, and / or mineralization of organic matter. Further investigation is needed to test whether cereal cover crops are more effective NO₃ scavengers than legume / cereal biculture cover crops. Three conservative tracers were applied on three separate occasions over an eleven year period (Bromide (Br) 1992; Chloride (CF) 1995; Br 2000) and breakthrough was observed using PCAPS. Breakthrough curves were fit to solutions to the Advection Dispersion Equation (ADE) to generate transport parameters. Following the 2000 Br application, soil was sampled in May, September, and December, 2001. Soils in 10 or 20 cm depth increments were taken from the surface to 1.2 meters total depth and were extracted to determine Br and NO₃-N concentration profiles under the various treatments. Collection efficiencies of Br from PCAPS below H and C plots were significantly effected by cover crop treatment (P-value = 0.02) and were 35 and 47% of the applied mass, respectively. Soil concentration profiles of Br- and NO₃-N were markedly different between H and C plots, and showed evidence of cover crop uptake, immobilization and mineralization of both chemicals. On average, dispersivity values were 3.74, 20.6, and 16.1 cm for the 1992, 1995, and 2000 applications, respectively. Fitted dispersivity values ranged from 2 x10⁻² to 78.8 cm for individual samplers. Peak tracer concentrations reached sampler depth after 0.91, 0.60, 0.79 pore volumes corresponding to 404, 95, and 367 days for the 1992, 1995, and 2000 applications, respectively. Frequent, large rain events such as those experienced during the 1995 C breakthrough resulted in higher pore water velocities, smaller retardation factors (R), and higher dispersivity values, while below average cumulative rainfalls with few large rain events had the opposite effect (1992 Br breakthrough). There were no significant correlations between the log-normally distributed dispersivity values and calculated pore water velocities at the sampler level. Dispersivities at individual samplers showed no correlation in time. Observed Br soil profiles showed a ten-fold lower dispersion than predicted using PCAPS-based parameters. The results of this study suggested that even if fitting data sets well, the Advection Dispersion Equation is inappropriate for the description of solute spreading in structured soils under variable rainfall conditions.
License
Resource Type
Date Available
Date Issued
Degree Level
Degree Name
Degree Field
Degree Grantor
Commencement Year
Advisor
Committee Member
Academic Affiliation
Non-Academic Affiliation
Subject
Rights Statement
Language
Digitization Specifications
  • File scanned at 300 ppi (Monochrome, 256 Grayscale) using Capture Perfect 3.0.82 on a Canon DR-9080C in PDF format. CVista PdfCompressor 4.0 was used for pdf compression and textual OCR.
Replaces
Additional Information
  • description.provenance : Submitted by Erin Clark (ecscannerosu@gmail.com) on 2011-04-04T19:13:40ZNo. of bitstreams: 2Feaga Appendix C.zip: 7569387 bytes, checksum: b0884df19fcaafaaeee5fba76679b62d (MD5)FeagaJeff2004.pdf: 11021748 bytes, checksum: d38f13aaea6f167f6071e7c64b72e7d7 (MD5)
  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2011-04-05T16:03:07Z (GMT) No. of bitstreams: 2Feaga Appendix C.zip: 7569387 bytes, checksum: b0884df19fcaafaaeee5fba76679b62d (MD5)FeagaJeff2004.pdf: 11021748 bytes, checksum: d38f13aaea6f167f6071e7c64b72e7d7 (MD5)
  • description.provenance : Approved for entry into archive by Patricia Black(patricia.black@oregonstate.edu) on 2011-04-05T15:50:27Z (GMT) No. of bitstreams: 2Feaga Appendix C.zip: 7569387 bytes, checksum: b0884df19fcaafaaeee5fba76679b62d (MD5)FeagaJeff2004.pdf: 11021748 bytes, checksum: d38f13aaea6f167f6071e7c64b72e7d7 (MD5)
  • description.provenance : Made available in DSpace on 2011-04-05T16:03:07Z (GMT). No. of bitstreams: 2Feaga Appendix C.zip: 7569387 bytes, checksum: b0884df19fcaafaaeee5fba76679b62d (MD5)FeagaJeff2004.pdf: 11021748 bytes, checksum: d38f13aaea6f167f6071e7c64b72e7d7 (MD5) Previous issue date: 2003-02-07

Relationships

Parents:

This work has no parents.

Last modified
No preview available

Download the file

Items