Too Much Water or Too Little? Climate Resilient Vegetable Farming

Project Leads: Dr. Kira Borden and Raelani Kesler

Project Personnel: Carson Li, Morgan Hamilton, Hannah Friesen, Amanda Dickson-Otty, Inbar Avrahami Saraf, and Yiming Zhang

Supervisor: Dr. Sean Smukler

Project Partners:

Project Funding:

Overview:

Vegetable farmers in BC experience many challenges in managing water on their farms that are related to soil health that are likely to increase with the expected changes in precipitation due to climate change. Increased shoulder season (spring and fall) precipitation shortens the soil workability time window in which the soil moisture is appropriate for tillage. This shortens the growing season and increases the challenge of successfully managing cover crops and amendment applications.  A shortened season can result in a delay of cover crop termination, incorporation and break down, a well as a delay in amendment applications and subsequently planting of the cash crop in the spring and potentially impacting nutrient availability to the vegetable crop.  A delay in the start of the production season can then delay cover crop establishment in the fall. In BC, common overwintering cover crops are best established by mid-September, while some vegetable crops continue to be harvested into the winter. Farmers must balance the loss of income from the shortened growing season or risk soil erosion and nutrient leaching from a bare fallow field. While the benefits of cover crop are well known, many farmers in BC are not able to either get them successfully established or cannot maintain them throughout the winter resulting in reduced benefits. 

In an attempt to protect the soil from exposure over the winter, small scale producers have begun to cover sections of fields that are ill-suited for cover crop with silage tarps. The use of tarps to cover soil changes soil hydrology and temperature, both of which are important environmental factors for soil health.  Without the inputs from cover crop biomass soil organic matter and health may be negatively impacted and eventually lead to reduce soil water-holding capacity and water infiltration.  Alternatively, farmers have installed drainage tile help moderate shoulder season soil moisture but this too can lead to losses of soil organic matter.  With projected drier production seasons soil water-holding capacity is likely to become more important and alternative ways to manage soil water must take into account their impacts on soil organic matter and overall soil health. 

Our research aims to quantify the impacts of three alternative approaches to soil management: fall applications of organic amendments, tile drains and overwinter tarping.  

Research questions:

How do these three alternative soil management approaches affect:

  1. Soil moisture and nutrient availability in the following spring?
  2. Crop yield in the following growing season?
  3. Key indicators of soil health?

Overwintering research sites:

In the fall of 2019, trials were established on 2 mother farms and 12 daughter farms in three regions, the Lower Mainland, Vancouver Island and Kootenay Mountains. The project was repeated for a second year beginning fall of 2020.

At the experimental Farms UBC and Green Fire we have installed the following treatments in a 2-factor randomized complete block design (n=4):

  • Over winter treatments (x2)
    • Tarp
    • Cover crop
  • Nutrient treatments (x4)
    • Control (no addition)
    • High compost
    • Low compost
    • Compost + Fertilizer

On regional farms, we have installed two treatments:  One tarped and untarped plot established on each farm 

Measurements and data collection include:

  • Yield and crop nutrient (N&P) content
  • Soil volumetric water content
  • Soil temperature
  • Soil nutrient and chemical analysis
  • Electrical conductivity

Tile drain and fall amendment research site:

On one operational farm in Delta we have installed a 2-factor randomized complete block design (n=3):

  • Tile drainage (x2)
    • 15-foot tile spacing
    • 30-foot tile spacing
  • Nutrient management (x3)
    • Fall application of compost
    • Spring application of compost
    • Control

Project Results

Organic BC podcast episode UBC field trials: Using tarps as overwinter soil cover, March 7, 2022.

Project results presented at the Soil Management Workshop in March 2022.

A video presentation of findings presented at the Canadian Society of Soil Science Conference in June 2021 can be viewed here.