Comparative evaluation of industrial hemp varieties: Field experiments and phytoremediation in Hawaii

Abstract

Industrial hemp (Cannabis sativa L.) is a fast-growing and high biomass producing plant species with wide usage of its materials such as fiber, food, and fuel. There are many varieties containing low concentration of tetrahydrocannabinol (THC). In the present study, it assessed the agricultural feasibility of three industrial hemp varieties with different water management and nitrogen fertilizer treatments, and determined the best ones to cultivate in Hawaii, then evaluated the effects of plant density on the yield and the potential phytoremediation for the herbicide atrazine. The field experiments indicated that it was difficult to grow the variety F75 in Hawaii with a final weight of 13 g and did not live for the full growth season. However, the subtropical fiber hemp variety CHG grew to height of about 190 cm and its weight varied from 150 g to 280 g between two planting densities (100 plants m−2 and 28 plants m−2, respectively). The subtropical seed hemp variety CHY was intermediate at a mean height and weight of about 130 cm and 130 g, respectively. Estimated crop yields were 19 tons acre-1 year-1 (dry weight) for CHG stalks that could be used for building construction and 16 tons acre-1 year-1 (dry weight) for leaves could be used as animal forage. Approximately, 1.7 tons of seeds could be harvested per acre per year from variety CHY. Little water consumption (10 mm week-1) was needed, which corresponds with drought resistance of CHG variety. Use of nitrogen fertilizer at a rate of 100 kg ha-1 did not improve growth of CHG variety more than the existing nitrogen levels in the soil. Phytoremediation potential of industrial hemp was also assessed by field pot studies, in which field soils were fortified with 0, 0.25 and 0.50 mg kg-1 of atrazine. The half-life (t1/2) of atrazine in hemp watered pots was 15 days, whereas t1/2 was approximately 50 and 28 days in the no plant non-watered pots and the no plant watered pots, respectively, suggesting the degradation of atrazine in soils showed a higher efficiency planted with hemp under water irrigation condition. The CHG plants accumulated atrazine from soils, and the enrichment factor in CHG was increased over the course of 28 days (from 0.22 %–0.31 % to 0.63 %–0.89 %), then decreased after 49 days (0.28 %–0.30 %). Overall, these findings revealed that industrial hemp plants were useful for phytoremediation of soils contaminated with atrazine.