2019 ASHS Annual Conference

Macrotunnel production systems contribute over $1 billion to California's economy and are one of the State's fastest growing agricultural sectors. Despite their increased use, guidance to help macrotunnel growers choose management practices that limit agricultural pollutant loads in stormwater-induced runoff is sparse. Using raspberry as a model crop, four management practices were evaluated for their efficacy in preventing nutrient runoff, managing weeds and costs. The four treatment practices included in three-year raspberry production cycle were: barley cover crop seeded at 500 lbs/A, weed barrier fabric, yardwaste mulch spread 2-3 inches thick, and polyacrylamide (PAM). Treatments were applied to the 300 ft by 6 ft wide post rows that collect runoff from adjacent 22 ft wide plastic-covered tunnels. Barley cover crop and mulch reduced combined nitrate and nitrite nitrogen in runoff 21 to 48% but only at some runoff events, yet reduced nitrate nitrogen in soil and leachate by 52-90% minimizing potential losses to groundwater. All treatments significantly reduced turbidity and phosphorus levels in runoff and had 75-97% less sediment accumulation compared to bare soil. Reduced soil losses after implementation of these conservation practices may decrease regulated legacy pesticide loads traveling to receiving waterways, thereby achieving water quality goals. Additionally, all treatments except PAM reduced weed densities of little mallow and annual sowthistle 48-87% compared to bare ground, which reduces the costs of weed management. Efficacy of treatments in improving runoff water quality and weed suppression deteriorated as bare ground areas within treatments became more exposed, suggesting importance of maintenance of their integrity throughout the raspberry cropping cycle. Barley cover crop had the lowest estimated costs (~$60.00 per tunnel period), while PAM and mulch were highest (~$193.00 per tunnel period).