Irrigation Research at Brock

This project is focused upon an important topic not only in Canada but also throughout eastern North America. Irrigation of woody perennial crops has heretofore not been a major concern. However, numerous dry growing seasons have caused the wine and tree fruit industries to reconsider irrigation. Several years of drought have resulted in problems including low yields, poor shoot growth and enological issues (low sugar; low pH & K; atypical aging). Irrigation may be a way of overcoming these problems, but there is a need to understand how physiological responses to water status affect vine performance and chemical composition of fruit. There is evidence that mild water stress imposed through irrigation deficits may reduce vine vigor and reduce competition for carbohydrates by the growing tips, and is likely to increase the quality of the fruit produced. Specifically, there is some evidence that reducing irrigation may lead to increased concentration of flavor compounds in the fruit.

This research is focused specifically on novel irrigation techniques that could be utilized with success in Niagara region to improve grape and wine quality. Partial Root Drying (PRD) and Regulated Deficit Irrigation (RDI) are two irrigation methods that are based on controlling long-distance chemical signaling in plants. Consequently, we expect that use of PRD will be successful in simulating drought conditions, with the outcome of increased abscisic acid (ABA) and its subsequent outcome: stomatal closure and reduced shoot growth. RDI, whereby irrigation water is applied in volumes less than evapotranspiration (ET), might also have a similar effect of PRD in modifying vine growth, yield, fruit composition, and possibly winter hardiness. Deficit irrigation is usually defined as withholding of irrigation water followed by re-watering to maintain soil water level above physiological wilting point but considerably below field capacity.

Objectives

The overall goal of this project was to provide irrigation to a premium winegrapes with the ultimate goal of improving yield, fruit composition, and wine quality. We tested various timings of irrigation imposed at fruit set, lag phase of berry growth, and veraison on four winegrape varieties: two reds (Baco noir and Cabernet Sauvignon) and two white varieties (Chardonnay and Sauvignon blanc). Also, we used two different methods of irrigation: RDI (50% ET and 25 % ET) and PRD. To quantify the impact of this water stress, data were collected on yield components, fruit composition and vine vigor, as well as measurements of soil and plant water status (soil moisture, leaf water potential, transpiration). The toys we used to measure soil and vine water status included a portable time-domain reflectometer (TDR) for relatively shallow (20 cm) soil depths, a profile probe for up to 1 m soil depths, a pressure bomb for vine leaf water potential and a porometer for leaf transpiration. We also made wines from the various irrigation treatments and analyzed these chemically and sensorially.

Irrigation setup

Four ongoing irrigation trials are being conducted at Lambert Farms, Niagara-on-the-Lake, ON. In 2005, two experiments testing timing of irrigation and ET level were initiated in Chardonnay and Baco noir blocks. The Chardonnay block (27 rows) was divided into three blocks, each containing seven single-row treatment replicates. Treatments were: Control -no irrigation; 100%ET with an early (irrigation begins at fruit set), or late start (veraison); 50%ET with a fruit set or veraison start and; 25%ET with a fruit set or veraison start. The Baco noir block (37 rows) was divided into three blocks containing 10 single- row treatment replicates. Treatments were: control -no irrigation; 100%ET with an early (irrigation begins at fruit set), midseason (lag phase), and late start (veraison); 50%ET with a fruit set, lag phase, or veraison start and; 25%ET with a fruit set, lag phase, or veraison start.

In 2006, two other experiments were initiated in Cabernet Sauvignon and Sauvignon blanc to test the effects of the partial rootzone drying irrigation method on white and red winegrapes. The PRD treatment consists of two pipes placed in the same row, with drippers (1.8 L/hour) placed alternatively on each pipe. Water is run through each pipe bi-weekly, so that half of the root system is continuously dry for each vine. The Cabernet Sauvignon (25 rows) was divided into four blocks containing five single-row treatment replicates. Treatments were: control (no irrigation); PRD (100%ET); full irrigation (100%ET); RDI (50%ET); RDI (25%ET). The Sauvignon blanc block (23 rows) was divided into four blocks containing four single-row treatment replicates. Treatments were: control (no irrigation); PRD (100%ET); full irrigation (100%ET) and; RDI (25%ET).

Results

Soil moisture and vine water status. There were significant differences among the Baco noir and Chardonnay treatments in terms of soil moisture; the trends for all treatments followed the rainfall trends each year with high values in July and the lowest in August. The 25%ET treatments and the late treatments were very close to the control treatment most of the season. Except for early irrigation treatments, all the treatments showed values lower than the wilting point throughout the season (13% for this soil series, Chinguacousy). In 2006, the results generally showed the same trend as 2005. We are still working up the 2007 data. Soil moisture values in Sauvignon blanc (and Cabernet Sauvignon) had different trends than Baco and Chardonnay, whereby a distinct separation among the treatments was observed at beginning of August. Full irrigation and 100%ET PRD had the highest soil water content in Sauvignon blanc. Generally, transpiration and water potential data followed those of soil moisture.

Yield components and fruit composition

There were large differences between 2005 and 2006 yields in Baco noir. We assume that this is because very low temperatures occurred in the winter of 2005, which damaged a high percentage of primary buds. No differences were found among control and irrigated treatments in terms of yield, clusters/vine and vine size. The 100%ET/lag phase had highest cluster weight and berries per cluster and lowest berry weight. In 2006, yield was almost four times higher than in 2005. Almost all irrigation treatments exceeded the control. In terms of berry composition, the most relevant observation was that highest anthocyanins were found in treatments under slight water stress (50 and 25%ET treatments). No yield or berry data were collected in Chardonnay in 2005 due to severe winter injury. In 2006, there were no differences in vine size, but the 100ET fruit set and 25%ET veraison treatments had highest yield. Early and late 100%ET treatments generated highest cluster weight and berries per cluster. Some irrigation treatments increased Brix but also titratable acidity (TA). In 2007, which was a drier year then 2006, treatment differences in yield components had a greater magnitude of difference. Almost all Chardonnay irrigation treatments increased one or more yield components. In terms of chemical composition, some irrigation treatments increased Brix and reduced TA slightly in 2007. Sauvignon blanc in 2006 had only a few variables affected by irrigation treatments. The most substantial increases were found in berry weight (all irrigated treatments) and titratable acidity (two treatments). The 25ET treatment seemed to stand out as the best.

We have been doing irrigation research in Niagara for 10 years. We have completed and published studies on Concord, Niagara, Sovereign Coronation, and Chardonnay. We have also worked out grower-friendly methods for calculating irrigation requirements for grapevines on a weekly basis. It will, of course, take some time to sort out all the effects of the different ET values and timings of the present RDI trials on Baco noir and Chardonnay, and the efficacy, if any, of the PRD treatments in the Sauvignon blanc and Cabernet Sauvignon. It is abundantly clear that we can see increases in yield, Brix, and color in red wine varieties with some irrigation treatments, particularly in dry years such as 2007. For those contemplating irrigation, it may mean the difference between survival and vine death in hot years such as 2007, but it can have positive effects even in years such as 2006 during which ample rainfall occurred.

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