This project set out to collect field data using neutron probes. Its objective was to establish benchmark information on how the grapevine extracts water from granitic sandy loam soils. Wine grape producers would then be able to use that information to improve the application of irrigation water, enhancing Fair Play’s wine grape economy and its water resources.
The wine industry in the Fair Play area, begun in the 1980s, has grown to 10 vineyards, and more growth is expected. Project coordinator Brian Fitzpatrick operates Fair Play Winery & Lodge, a small, vertically integrated and organically certified winery growing wine grapes of several varieties. Cooperator Bill Bertram runs Perry Creek Vineyard, Fair Play’s largest winery with 72 acres. Bertram uses integrated pest management and traditional vineyard management.
Fair Play has limited water supplies and no formal water management agency. Indeed, some growers opt for dry farming, relying on their deep soils and seasonably wet springs to grow grapes without irrigation.
This study is monitoring soil moisture with neutron problems to gather field data that will help those who do irrigate improve the efficiency of their applications. Participants are measuring moisture extraction to learn how, when and from where the grapevines, native grasses and cover crops use the water.
The study found that irrigation water moved through the soil profile more slowly than previously thought, prompting changes in irrigation management.
Previous notions that applied irrigation water moved rapidly downward had led vineyard owners to use short drip irrigation sets of 12 hours or less. However, through field monitoring with neutron problems in 2000, the project team found that the water moved less rapidly than had been thought. When irrigation water was applied through drip emitters at 1 gallon per hour, it took more than 20 hours to fill the first foot of soil to field capacity, at 0.94 inches, while the second foot increased by only 0.26 inches.
The data suggest irrigation sets of greater duration on mature vines with extensive root systems, which can extend as deep as 9 feet. On newly planted and one- to two-year-old vines, where water will be extracted mainly from the first foot, irrigation sets of less than 20 hours should be sufficient.
The project also found water extraction the entire depth of the soil, mainly from native grasses and winter annuals in the first foot, then from the vine roots down to as deep as 9 feet. To reduce nutrient deficiency induced by water stress, common in the Fair Play area, the research suggests rewetting the extensive vine root system. Such a practice will also help maintain a larger, actively growing root system, making the plant less vulnerable to feeding by pocket gophers.
Learning that the drip-applied irrigation water moved more slowly than had been thought, members of the project lengthened their irrigation sets to as much as 70 hours in mature vines.
In 2001, the project team collected data from four more monitoring sites to address questions about the effects of irrigation frequency. Members assessed three neutron probe sites, one with 1 gallon per hour emitters, another with 2 gallon per hour emitters and a third dry farmed. Clearly, the drip-irrigated sites produced more grapes than the dry-farmed sites – in one case nearly three times as much. However, the measure of quantity is less important to wine grape growers than is quality, and, says the project report, “Making separate batches of wine and evaluating their respective quality is beyond the scope and duration of this experiment.”
Brian Fitzpatrick, project co-coordinator, says the data collected clearly demonstrated inadequacies in the area’s drip irrigation practices and have pointed growers in a new more efficient direction.
“Building on the foundation of benchmark information collected,” he says, “we can pursue the answers to yet other questions in our quest to irrigate wisely with this precious resource.”
The value of this project has been to challenge the current methods of drip irrigation, something that has not occurred for more than 20 years. In addition, use of the neutron probes will help growers better understand vineyard water use.
The project suggests that the common practice of short-duration sets, which mainly fill the first foot of the soil profile, may benefit new or one-year vines with their small, shallow-developing root systems. However, a cautionary note is that frequent rewetting of the soil encourages growth of weeds that compete for nutrients and attracts root-feeding pocket gophers.
In addition, irrigators can save water, and the attendant pumping costs, by delaying irrigation until later in the season. In a normal year, winter moisture provides enough water for early plant growth. What’s more, early-season irrigation may stimulate more growth than is necessary to produce a modest crop of fine wine grapes. In an area like Fair Play, where there is no delivered water and pumping costs are high, savings can be significant.
FARMER ADOPTION AND DIRECT IMPACT
While a number of growers chose to participate in the local water agency neutron program, many did so with little understanding of the potential benefits. Now they will be able to see the benefits, or the lack of them, on their own vineyards, and they all will benefit from the data being collected.
It should be noted that some growers practicing dry farming on mature vines balked at monitoring soil moisture after the charts of the previous season showed no available water for most of the summer. With no ability or interest in irrigating, they saw no need to continue. However, project co-coordinator Brian Fitzpatrick says he believes that once these growers see yield results from applied water, and now that they realize the winter rainy season doesn’t always recharge the soil water, they will either validate their dry-farming practices or see the benefits of effective irrigations.
FUTURE RECOMMENDATIONS OR NEW HYPOTHESES
This project’s results, say the coordinators, are merely a beginning to gathering more information needed to become more efficient users of irrigation water. More fieldwork is needed. They hope to have demonstrated the need to gather data that will help area grape growers understand their water sources and the recharge of the groundwater system.
DISSEMINATION OF FINDINGS
Project co-coordinator Fitzpatrick presented information on the project to the El Dorado County Grape Growers Association in 2000. In addition, the project received attention that year when the El Dorado County Water Agency agreed to help underwrite the cost of two neutron probes per site per farm, and more than 50 sites received probes.
The next step in outreach will be to make the SARE project report is available online and to schedule presentations to grape growers about the results and the need for more information.