In British Columbia, shifting precipitation patterns are becoming increasingly unpredictable and volatile. Wetter spring and fall shoulder seasons are impeding farmers’ ability to prepare and harvest their fields while warmer drier summers challenge their ability to provide their crops with sufficient water during the production season. This project was designed to identify practices that would improve organic vegetable farmers’ capacity to adapt to these changing conditions of too much or too little water.
Over a three-year period, we evaluated the field performance of a suite of novel soil management practices relative to, and in combination with, existing practices, on soil-water dynamics in a coordinated set of studies that includes controlled replicated experiments, and on-farm regional trials. Project objectives were:
- Quantify the effects of overwinter cover on soil physicochemical properties.
- Evaluate the interaction between overwinter cover and three nutrient amendment strategies on plant available nitrogen, volumetric water content and crop yield.
- Investigate the interactions between amendment application timing and tile drainage spacing on their effects on soil moisture and salinity and crop yield.
A combination of experimental and regional trials allowed for the comparison of management strategies under realistic conditions which is critical in evaluating their performance. Field trials were conducted on 15 organic practicing farms in BC to evaluate overwinter cover options, amendment application rates and timing and tile drainage across a variety of climates and soil types.
Key outcomes included:
- The use of plastic silage over the winter conserved soil nitrate and provided a significantly greater source of plant available nitrogen in the spring relative to cover crops or bare fields.
- We observed no increase in soil salinity after two winters of silage tarp use.
- Silage tarps showed meaningful impacts on field soil water, keeping fields drier during the winter rains than uncovered fields and then wetter as the production season started in the spring.
- We observed no interaction effect on plant available nitrogen between silage tarp use and various amendment treatments. Amendment treatments had minimal impacts on crop yields.
- Tile drains at 15 ft spacing significantly reduced spring soil moisture and electrical conductivity compared to 30 ft spacing but had no interaction effect with compost either fall or spring applied.
- There were no significant differences in crop yields due to fall or spring applied compost.