Irrigation water use and yield of Thyme in the Virgin Islands

Thyme (Thymus vulgaris L) is one of the major culinary herbs with economic importance in the Virgin Islands. In spite of this, little research has been undertaken to improve its crop cultural management practices. The traditional practice of growing herbs in the Virgin Islands requires frequent watering by hand with sprinkler cans or garden hose. This practice is inefficient and uses high amounts of water and labor. This experiment was conducted to determine the minimum irrigation water requirement of thyme with and without mulch. Treatments consisted of 3 irrigation levels corresponding to soil water tensions of 20, 40, and 60 k.Pa. Half of the treatments were mulched using a black plastic weed barrier ground cover. A rainfed plot without mulch served as the control. Differences in yield among treatments were significant, although rainfall was high during the growing season. Total fresh and dry matter yields were highest from treatment with an irrigation level maintained at soil water tension of 20 kPa without mulch. Generally, all treatments with mulch and the control had yields lower than treatments without mulch. This indicated that mulching is not necessary for thyme when rainfall is high and soil moisture is not a limiting factor. Total irrigation water use was highest (5.85 I/plant) in treatment with higher irrigation level (20 kPa) in both mulch and unmulched plots. Treatments under 60 kPa had the least water use. Based on the results, it appears that the minimum water requirement for growing thyme in the Virgin Islands can be met by maintaining a soil water tension of 60 k.Pa.