Abstract:
Several irrigation treatments were evaluated on Sovereign Coronation table grapes at two
sites over a 3-year period in the cool humid Niagara Peninsula of Ontario. Trials were conducted
in the Hippie (Beamsville, ON) and the Lambert Vineyards (Niagara-on-the-Lake, ON) in 2003
to 2005 with the objective of assessing the usefulness of the modified Penman-Monteith equation
to accurately schedule vine irrigation needs. Data (relative humidity, windspeed, solar radiation,
and temperature) required to precisely calculate evapotranspiration (ETq) were downloaded from
the Ontario Weather Network. One of two ETq values (either 100 or 150%) were used in
combination with one of two crop coefficients (Kc; either fixed at 0.75 or 0.2 to 0.8 based upon
increasing canopy volume) to calculate the amount of irrigation water required. Five irrigation
treatments were: un irrigated control; (lOOET) X Kc =0.75; 150ET X Kc =0.75; lOOET X Kc
=0.2-0.8; 150ET X Kc =0.2-0.8. Transpiration, water potential (v|/), and soil moisture data were
collected each growing seasons. Yield component data was collected and berries from each
treatment were analyzed for soluble solids (Brix), pH, titratable acidity (TA), anthocyanins,
methyl anthranilate (MA), and total volatile esters (TVE). Irrigation showed a substantial
positive effect on transpiration rate and soil moisture; the control treatment showed consistently
lower transpiration and soil moisture over the 3 seasons. Transpiration appeared accurately
reflect Sovereign Coronation grapevines water status. Soil moisture also accurately reflected
level of irrigation. Moreover, irrigation showed impact of leaf \|/, which was more negative
throughout the 3 seasons for vines that were not irrigated. Irrigation had a substantial positive
effect on yield (kg/vine) and its various components (clusters/vine, cluster weight, and
berries/cluster) in 2003 and 2005. Berry weights were higher under the irrigated treatments at
both sites. Berry weight consistently appeared to be the main factor leading to these increased
yields, as inconsistent responses were noted for some yield variables. Soluble solids was highest under the ET150 and ET100 treatments both with Kc at 0.75. Both pH and TA were highest
under control treatments in 2003 and 2004, but highest under irrigated treatments in 2005.
Anthocyanins and phenols were highest under the control treatments in 2003 and 2004, but
highest under irrigated treatments in 2005. MA and TVE were highest under the ET150
treatments. Vine and soil water status measurements (soil moisture, leaf \|/, and transpiration)
confirmed that irrigation was required for the summers of 2003 and 2005 due to dry weather in
those years. They also partially supported the hypothesis that the Penman-Monteith equation is
useful for calculating vineyard water needs. Both ET treatments gave clear evidence that
irrigation could be effective in reducing water stress and for improving vine performance, yield
and fruit composition. Use of properly scheduled irrigation was beneficial for Sovereign
Coronation table grapes in the Niagara region. Findings herein should give growers some strong
guidehnes on when, how and how much to irrigate their vineyards.
