Penn State’s High Tunnel Research and Education Facility shows that soluble salts can steadily accumulate in high tunnel soils, regardless of whether growers rely on inorganic fertilizers or organic nutrient sources.
Sampling in spring 2008 revealed salt levels ranging from 0.37 to 9.38 mmhos/cm, underscoring the risk of long-term buildup in protected growing systems.
High tunnels limit natural leaching because rainfall and snow are excluded. If drip irrigation is used it can further restrict the movement of salts out of the root zone. As salt concentrations rise, plant growth can suffer, particularly for salt-sensitive crops.
A two-year nutrient management trial compared inorganic fertilizer applications with compost amendments. Inorganic fertilizer delivered through drip irrigation provided 75 lb of nitrogen, 150 lb of phosphate, and 75 lb of potash per acre each year and resulted in little change in soil salt levels.
Compost, applied at depths of one or two inches, supplied much higher nutrient amounts. The heavier compost rate significantly increased soluble salt levels, with two inches raising readings by as much as 1.9 mmhos/cm over the study period. Elevated salts were associated with reduced pepper yields.
Managing salinity in high tunnels requires regular soil testing and careful nutrient use. Small Farmers are encouraged to avoid excessive compost applications and choose fertilizers with low salt indexes. Good site drainage and intentional leaching can help move salts below the root zone.
Applying about 15 cm of water can remove roughly half of accumulated salts, while deeper leaching is even more effective. Thoughtful irrigation and nutrient management are key to maintaining productive high tunnel soils.