The 2011 ASHS Annual Conference

Strawberries (Fragaria x ananassa Duch.) grown on the central coast of California have an annual value of more than $1 billion. Ground water, the dominant water source in this region, is impaired from leached NO₃ –N and salts from seawater that has intruded into the aquifer because of excessive agricultural pumping. We conducted a study surveying water use in 34 commercial fields during the 2010 production season to assess if current irrigation practices posed a risk to ground water supplies. Plantings of cv. Albion and a proprietary cultivar were evaluated.  Flow meters were installed in fields to measure applied water volumes. In a subset of 17 fields, crop water requirement was estimated from canopy cover and reference evapotranspiration (ET) data, and confirmed by soil moisture monitoring using granular matrix sensors and tensiometers. Average water applied to the 34 fields was 53 cm between January and October 2010 and ranged from 26.7 cm to 93.2 cm.  Rainfall averaged 37 cm during the same period with 90% of the precipitation occurring from January through April when crop ET was lowest. Crop canopy cover of Albion and the proprietary variety were statistically similar throughout the season. Variation in total seasonal crop ET among sites was a function of maximum canopy cover and reference ET values. Total crop ET ranged from 36.1 cm to 67.3 cm for the 17 intensively monitored sites and applied water ranged from 49% to 150% of the crop ET requirement. Applied water was less than crop ET at half the 17 sites and more than 120% of crop ET at 2 of 17 sites.  Total fruit yield of the proprietary variety was not correlated with the volume of applied water. The highest potential for leaching of NO₃-N was during the high rainfall period.  The combination of soil moisture and crop ET data indicated that drainage was minimal between May and October and the potential to leach NO₃-N was low during this period. On average, strawberry growers applied water volumes approximately equal to the crop water use requirement.