Effect of Drip Irrigation and Winter Precipitation on Distribution of Soil Salts in Three Season High Tunnels

High tunnels exclude rainfall and can lead to saline soil conditions that inhibit plant growth. In snow-prone regions, multi-bay tunnels are left uncovered during the winter to prevent snow damage to the structure. Exposing soils to precipitation during the winter period may allow excess salt to leach from the soil profile. Red raspberries (Rubus idaeus) were planted in April, 2010 under multi-bay high tunnels in East Lansing, Mich., USA (42.75 degrees N; 84.47 degrees W). Dairy-based composts were incorporated in the row before planting (2010) or spread over the row (2011). Plants were irrigated with a single drip line. Tunnels were covered with plastic from May to October. Soil was sampled at the end of the first season and the beginning and end of the second season, at three depths (2.5, 10, 25 cm), beneath and 40 cm to the side of the drip line. Soils were analyzed for total salt (electrical conductivity) and specific ions. Total salt was higher away from the irrigation line after the first season, but beneath the line following the second season. Total salt after the first growing season was highest at 2.5 cm depths (electrical conductivity 3.53 mS cm(-1)) intermediate at 10 cm (1.13 mS cm(-1)) and lowest at 25 cm (0.67 mS cm(-1)). Salt levels the following spring after soils had been exposed to winter precipitation had decreased to acceptable levels (0.14 to 0.20 mS cm(-1)) and were uniform with depth and distance from the trickle irrigation line (mean across depths and location 0.18 mS cm(-1)). After the second growing season, a similar stratification pattern was present. The primary ions contributing to soil salt were Ca, K, and Mg. Results indicate that excluding precipitation with high tunnels results in salt accumulation near the soils surface, but removing plastic and exposing soil to off-season precipitation is an effective method of alleviating salinity.