WATER USE AND YIELD OF BASIL AS INFLUENCED BY DRIP IRRIGATION LEVELS AND MULCHING

Basil (Ocimum basilicum L.) is one of the popular herbs with culinary importance in the Virgin Islands. Local herb growers traditionally water their crops with sprinkler cans and garden hoses. This method results in inefficient use of water, a scarce resource in the Virgin Islands. A field experiment was conducted in 1994 to determine the minimum requirement and efficient use of irrigation water for basil. Basil was grown in plots with and without mulch and drip-irrigated at various levels to maintain soil moisture tensions of 2 0 , 4 0 and 60kPa. A black fabric weed barrier ground cover was used in mulched plots. A rainfed plot without mulch was included as a control. Total fresh basil yield was highest (42.3 t/ha) in plots with no mulch and irrigated to maintain soil moisture at 40 kPa. Yield from this treatment was significantly different from other treatments except treatments irrigated at a soil moisture of 20 kPa with and without mulch. Similar results were obtained with leaf fresh yield. Yields from all drip-irrigated plots were significantly higher than the control. Total plant dry matter yield (5.79 t/ha) was highest in the treatment irrigated at 40 kPa without mulch, but was not significantly different from other treatments except the control. Water use was highest in the treatment irrigated at a soil moisture of 20 kPa with no mulch and lowest in the mulched plots irrigated at a soil moisture of 60 kPa. Mulching reduced water use of basil by 50%. Water use efficiency was highest when basil was irrigated to a soil moisture of 60 kPa combined with mulching. For this treatment water cost to produce a kilogram of fresh basil was US$1.97 compared with $5.76 when basil was irrigated at soil moisture of 20 kPa without mulch. This study shows that basil can be grown with minimum irrigation water equivalent to soil moisture of 60 kPa with mulch. At this level, water use is reduced and efficiency is improved