Articles
IRRIGATION BUDGET AND PLANT GROWTH OF ASPARAGUS
Asparagus (Syn 4–56) crowns were planted in May 1992 and maintained at soil moisture levels near field capacity for the first year.
In 1993, irrigation treatments based on percentages of evapotranspiration (0%, 40%, 80%) were applied to asparagus during the summer (fern growing period). Prior to initiating the irrigation treatments, asparagus plants averaged 6 shoots, 83 roots, and 38 buds with a shoot and root fresh weight of 573 and 270 grams, respectively.
Soil moisture was monitored with a neutron probe and irrigations scheduled when the water budget (soil storage + rainfall – daily evapotranspiration) indicated that 50% of the available soil water was depleted.
As irrigation rate decreased from 80% ET to 0% ET, there was a linear decrease in fern, root, and bud number and fern and root fresh weight.
Increasing water use efficiency in vegetable production systems is becoming a major issue in the western United States.
Although asparagus has been classified as a drought tolerant plant, researchers have observed wilting, fern and stem dieback, and yield reductions under conditions of low soil moisture (Van Bakel and Kerstens, 1971). In greenhouse and field studies, asparagus seedlings grew best when soils were maintained close to field capacity (Sterrett et al., 1990; Wilcox-Lee, 1987). Irrigation supposedly benefits newly established plantings by allowing better crown and root development.
Soil moisture stress can have a long term negative effect on asparagus productivity.
Soil moisture stress reduces fern growth (Cannell and Takatori, 1970) and limits yield by reducing spear number (Takatori et al., 1970), spear diameter (Hartmann, 1981), and spear size distribution (Roth and Gardner, 1990). Decreasing the rate of water application decreased asparagus yields in the following year mainly by decreasing the weight of large diameter spears (Roth and Gardner, 1990). When precipitation levels increased during July and August, asparagus yields increased in the following year (Hartmann, 1981; Hartmann et al., 1990). Yields decreased when precipitation levels were high during September by promoting bud break and fern growth later in the year than desirable (Hartmann et al., 1990).
In the desert regions of the American South-west, asparagus production is dependent on irrigation though water use varies greatly in the area.
Hanna and Doneen (1958) reported that in coastal southern California, 92 cm of precipitation and irrigation were needed for asparagus production.
Cannell and Takatori (1970) reported water applications ranging from 51 to 77 cm were needed in northern California.
In the Imperial Valley, annual water requirements were in excess of 330 cm (Robinson et al., 1984) while Roth and Gardner (1989) reported water requirements of 270 to 310 cm