2018 ASHS Annual Conference

Organic vegetable farmers rely on intensive tillage to control weeds, incorporate amendments and residues, and prepare seedbeds. Intensive tillage, however, can lead to a decrease in long-term soil health. The use of black, impermeable, polyethylene tarps on the soil surface prior to planting reduces weed pressure, increases crop yield, and preserves prepared soil for several weeks. Cultivar ‘Boro’ beets were planted on two dates: 16 May 2017 and 15 June 2017. Tarps were applied and left in place for three time periods prior to projected planting dates: 1) either overwinter (early planting) or 10 weeks (late planting), 2) six weeks, and 3) three weeks. After tarp removal, plots were roto-tilled (4 in.), shallow-tilled (1 in.), or left as is (no-till), then direct-seeded with beets. No-till plots received no weed control, tilled plots were cultivated at 10 and 20 days post-planting. Weed pressure, crop yield, and soil conditions were measured at tarp removal, midseason, and at harvest. Use of tarps for any length created a seedbed free of weeds prior to planting and kept weed biomass lower than the control the first three weeks after planting. Total soil nitrogen increased linearly (R2 = 0.7) with increased tarp duration. While there was often a significant difference in weed biomass and crop yield between shallow- and roto-till treatments without tarps, there was never a significant difference between shallow- and roto-till treatments when tarps were used. A tarp duration of three weeks was sufficient to achieve reduced weeds and increased yield.