Alfalfa reduces winter nitrate leaching relative to organic and conventional annual vegetable systems: Resin bag field measurements and modeling with HYDRUS-1D

Emily Woodward, Iael Raij-Hoffman, Kate Scow, Nicole Tautges

Research output: Contribution to journalArticlepeer-review

Abstract

Leaching of nitrate (NO3-) to groundwater is a major concern in California, where groundwater NO3- levels often exceed public safe drinking water thresholds. The state has enacted legislation to implement monitoring programs and management plans that will minimize future NO3- loadings to groundwater based on modeled NO3- leaching; however, a need remains for empirical NO3- leaching data and assessment of model suitability to specific systems. Moreover, debate remains around the ability of different management practices like cover cropping, replacement of chemicals with organic inputs, and cultivating perennials to reduce NO3- leaching in California's annual vegetable systems. We measured winter NO3- leaching over the wintery rainy season (October to March) within systems of the Century Experiment, a long-term cropping systems experiment in northern California evaluating effects of cover cropping, certified organic management, and alfalfa (Medicago sativa L.) incorporation in tomato (Lycopersicon esculentum Mill.)-maize (Zea mays L.) rotations. Anion exchange resin bags were installed at the bottom of the crop rooting zone (~65 cm) following tomato and prior to the onset of fall rains to adsorb leaching NO3- over the winter. Empirical resin bag NO3- leaching values were compared to modeled leaching results using HYDRUS-1D, which estimates water movement and reactive solute transport in soils. The rotation with alfalfa was the only system that reduced winter NO3- leaching (21.8 kg ha-1), compared to conventional management (bare winter fallow after tomato) (47.1 kg ha-1). Compared to conventional, certified organic management (44.7 kg ha-1) and inclusion of a winter cover crop (58.2 kg ha-1) had no significant impact on NO3- leaching. HYDRUS-1D model estimates for NO3- leaching were in good agreement with empirical field measurements in conventional and cover cropped systems, but less for certified organic and greater for the alfalfa systems. Results from this study show that perennial crops have potential to mitigate NO3- leaching losses across an agricultural landscape, and models like HYDRUS can provide useful estimates of NO3- leaching in some agricultural systems.

Original languageEnglish
Pages (from-to)450-465
Number of pages16
JournalJournal of Soils and Water Conservation
Volume77
Issue number5
DOIs
StatePublished - 1 Sep 2022
Externally publishedYes

Keywords

  • HYDRUS-1D
  • alfalfa
  • cover crops
  • nitrate leaching
  • resin bags

ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Water Science and Technology
  • Soil Science
  • Nature and Landscape Conservation

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