2017 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 and economic viability in preventing nutrient runoff and managing weeds. The four treatment practices included: 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 350 ft by 4 ft wide post rows that collect runoff from adjacent 22 ft wide plastic-covered tunnels. Analysis of runoff collected from two rain events showed that barley cover crop residues reduced combined nitrate and nitrite nitrogen in runoff 21 to 48% and phosphorus 29% compared to bare ground, while the other treatments had no consistent effect. All treatments did, however, reduce runoff turbidity: 360 nephelometric units in bare ground was reduced to 10-92 in mulch, 84-162 in weed barrier, 47-215 in barley residue and 44 to 231 in PAM. Reduced soil (sediment) 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 by 48-98% compared to bare ground, which reduces the costs of weed management. It was observed that efficacy of treatments in improving runoff water quality and weed suppression deteriorated as bare ground areas within treatments became more exposed, suggesting that it is important to maintain their integrity throughout the raspberry cropping cycle.