Managing soil sustainably on small-scale vegetable farms: Lessons learned from high tunnel and open field vegetable production

ABSTRACT Small-scale vegetable farms are increasingly important to local food systems, but the soils on these farms are not well understood, particularly in high tunnel production environments. Therefore, this study aimed to 1. Compare soil nutrients and soil health metrics in high tunnels and nearby open fields. 2. Document soil nutrient accumulation on diversified vegetable farms and assess loss potential. 3. Explore the impacts of specific management practices (input use, cover crops, tillage, and soil testing) and farm demographics on a variety of soil health and soil nutrient metrics. Just under half of the high tunnels in this study had soluble salt accumulation, which was associated with higher soil nitrate concentrations. The pH of many high tunnel soils was above the optimal range for crop production, which was correlated with irrigation water alkalinity. Some high tunnel soils had rapid water infiltration rates, with implications for irrigation water management. Both high tunnel and open field soil were rich in nutrients compared with other Minnesota farms. Preliminary assessments suggested risks to surface and groundwater from nutrient runoff and leaching. While farmer experience and more years in vegetable production were negatively associated with soil health metrics, management practices including reduced tillage, organic management, and application of plant-based compost were positively associated with soil health. Cation exchange capacity and permanganate oxidizable carbon did not provide significantly more insight than simply measuring organic matter. Arbuscular mycorrhizal fungal spore counts were inconclusive, but aggregate stability and bulk density were responsive to farmer reported soil management activities. Core ideas High tunnel soil tends to be rich in nutrients and organic matter. They also accumulate soluble salts, likely from excess inputs Irrigation water routinely tested high in pH and alkalinity. These factors may explain high soil pH in high tunnels. Small-scale vegetable farms often have high concentrations of soil nutrients in both high tunnels and open fields, with potential to cause environmental contamination through leaching and runoff Vegetable production may be inherently hard on soil health, but conservation practices including reduced tillage, organic management, and use of plant-based composts can improve soil health in these production systems