Survey of winegrape irrigation practices in the Sacramento-San Joaquin Valley of California

Abstract

Context and purpose of the study – In California vineyards, irrigation is considered as one of the most important decisions growers will make. Recent research has revealed that decisions of when to begin irrigation and how much water to apply have considerable consequences for final grape quality and hence wine quality. However, it is unclear whether and to what extent the average winegrape grower uses objective data to begin irrigating or to determine the amount of water to apply. We proposed to survey winegrape growers in north-central California and determine to what extent they utilize objective data in their irrigation practices. We wished to learn whether they are aware of irrigation technology and use it, or whether they are aware but have declined for some reason to adopt it.

Materials and methods – We proposed to survey the irrigation practices of winegrape growers in the Lodi-Woodbridge Winegrape District (LLWD), spanning most of San Joaquin County and part of Sacramento County, north-central California. Survey questions were designed to address irrigation practices, estimate water use, and evaluate grower awareness of winegrape water requirements and local climatic and soil conditions. The survey document consisted of 32 questions in four categories:  grower demographics; current irrigation systems and practices; guidelines followed when making irrigation decisions; and perceived needs regarding irrigation guidance. One hundred fifty-five growers responded to the survey.

Results – Survey responses indicated significant interest among winegrape growers for more information about water management. Well over half of respondents (64.5%) indicated they would like more information on irrigation, and 74.5% lacked a plan for dealing with severe water restrictions. When asked about their current source(s) of information on irrigation, 66% cited their own experience; one third cited consultants; fewer than 25% consulted viticulturists; and only 6% talked with farm advisors. The vast majority indicated that decisions related to irrigation initiation were based at least in part on visual inspection, often citing past experience. Soil sensors, plant sensors and data from the California Irrigation Management Information System (CIMIS) were accessed by smaller numbers of growers, generally in combination with other approaches. Most respondents were aware of climate change, but only 51% followed research in water conservation. Drip irrigation accounted for 91% of the total area irrigated (over 43,000 acres), and groundwater was cited by 95% of respondents as the source of irrigation water. Most respondents affirmed knowing the application rate and uniformity of their irrigation systems, yet when asked whether they had actually evaluated these parameters, similar numbers replied “yes” and “no”.  Most growers denied having vineyard blocks with large vigor contrasts, but many stated that they adjust irrigation to deal with vigor variability. When asked to indicate preferred resources for information on grapevine irrigation, 74 (47.7%) selected written materials; 68 (43.8%) chose online materials; and 65 (41.9%) mentioned extension workshops. Going forward, additional surveys will be urgently needed to assess the state of water usage by California winegrape growers given the current situation of severe multi-year droughts.