Scheduling drip irrigation for ginseng (Panax quinquefolius L.) grown under straw and bark mulch

Responses of ginseng to drip irrigation regimes and organic mulches were determined in two experiments beginning in 1998 and 1999. Treatments were four soil water content thresholds for irrigation: 0, 0.08, 0.12 and 0.16 m 3 m-3 (θ0, θ8, θ12, and θ16, respectively); combined with either straw or bark mulch. In its first growing season, ginseng did not require irrigation in 1999 or 2000. In subsequent years, irrigation was generally more frequent when applied at higher moisture threshold levels, but precipitation affected irrigation frequency under all treatments. Water use increased with crop age to 3 yr, to about 65% of the requirement of unshaded horticultural crops. Seed yield from 3-yr-old plants under straw mulch in 2001 was greater in response to θ12 and θ16 than to θ8 or θ0. Root yield response to irrigation threshold was linear for 2- and 3-yr-old plants under straw mulch in 2001, and quadratic for 3-yr-old plants under bark mulch in 2002. The optimal threshold to initiate drip irrigation was approximately 65% of field capacity.