Technical Yearbook 2024

grapevines irrigated with 135 L of municipal wastewater per week 4 produced more and heavier bunches, which increased yield compared to grapevines irrigated either with 45 L of municipal wastewater per week or 135 L of fresh water per week. As was reported for cane mass, 10,11 yield results confirmed that irrigation with TMW did not pose a salinity hazard under the given conditions. Low rainfall during the initial stages of berry development in the 2017/18 season (data not shown) probably explains the lower yields produced by the RF grapevines compared to the mean yields produced in the 2013/14 to 2016/17 seasons (Figure 2). Juice characteristics Despite the high amounts of K + applied via TMW irrigation during this study, no detrimental effects regarding juice quality were observed (Table 3). In fact, irrigation tended to improve the juice quality compared to the RF control treatments. The different irrigation treatments did not affect the juice TSS of the Sauvignon blanc grapes at the shoulder site. In contrast, the RF treatment plots of the Cabernet Sauvignon grapevines at the backslope and footslope sites had slightly higher TSS compared to the irrigated treatments (Table 3). This was probably due to actively growing shoots and excessive vegetative growth of the irrigated grapevines during the ripening period which was a stronger sink for photosynthates than the ripening grapes. 15 The higher yields of the irrigated treatments may also have obstructed sugar accumulation due to sink competition. 19 Since all the Cabernet Sauvignon grapes had to be harvested on the same day due to logistical reasons, the RF

10 12 14 16 18 20

A

2017/18 4-Year mean

0 2 4 6 8

Yield (t/ha)

RF

SLD

DLD

10 12 14 16 18 20

B

2017/18 4-Year mean

0 2 4 6 8

Yield (t/ha)

RF

SLD

DLD

10 12 14 16 18 20

C

2017/18 4-Year mean

0 2 4 6 8

Yield (t/ha)

RF

SLD

DLD

FIGURE 2. Effect of rainfed conditions (RF) and irrigation with treated municipal wastewater via single (SLD) and double dripper line (DLD) on the yield in (A) Sauvignon blanc on a shoulder, as well as Cabernet Sauvignon on (B) a backslope and (C) a footslope during the 2017/18 season compared to the mean for the 2013/14 to the 2016/17 seasons.

plots probably accumulated more sugars over the ripening period. It was previously reported that grapevine water constraints enhance berry sugar content in low-yielding grapevines, whereas it reduces the

berry sugar content of high-yielding grapevines. 20 In the 2017/18 season, TSS followed similar trends compared to the mean of 2013/14 to 2016/17 seasons (Figure 3).

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TECHNICAL YEARBOOK 2024