Handbook for Irrigation of Wine Grapes in South Africa

TABLE 7.14. Effect of partial root zone drying (PRD) on irrigation volume, midday Ψ S , cane mass, berry mass, yield and overall sensorial wine quality of Merlot near Ashton in the Breede River valley (Lategan & Howell, 2010a & b). Data are means for three seasons. Irrigation strategy Irrigation volume (m 3 ) Ψ S (MPa) Cane mass (t/ha) Berry mass (g) Yield (t/ha) Quality (%) 4.1 a 1.5 a 20.5 a 44.0 b PRD – switched every 7 days 1 972 -1.1 a 3.9 a 1.4 a 21.5 a 50.0 a PRD – switched every 14 days 2 037 -1.1 a 4.1 a 1.5 a 22.0 a 49.7 a PRD – switched every 21 days 2 247 -1.1 a 3.9 a 1.4 a 20.9 a 54.3 a * Values followed by the same letter within a column do not differ significantly (p ≤ 0.05). TABLE 7.15. Effect of low frequency drip irrigation and the PRD strategy on irrigation volume, midday Ψ S at harvest, cane mass, berry mass, yield and overall sensorial wine quality of Merlot near Wellington in the Coastal region (Myburgh, 2011a & b). Data are means for 2003/04, 2004/05 and 2005/06 seasons. Irrigation strategy Irrigation volume (m 3 ) Ψ S (MPa) Cane mass (t/ha) Berry mass (g) Yield (t/ha) Quality (%) 1.5 a 1.2 a 11.7 a 51 a PRD – switched every 14 days 1 746 -1.1 a 1.5 a 1.3 a 12.4 a 51 a * Values followed by the same letter within a column do not differ significantly (p ≤ 0.05). TABLE 7.16. Effect of high frequency drip irrigation and the PRD strategy on irrigation volume, cane mass, berry mass, yield and sensorial wine quality of Merlot near Wellington in the Coastal region during the 2006/07 season (Myburgh, 2011b). Irrigation strategy Irrigation volume (m 3 ) Cane mass (t/ha) Berry mass (g) Yield (t/ha) Quality (%) Conventional, single line drip 1 614 -1.0 a* Five irrigations during season 1 272 -1.2 b*

High frequency, single line drip 3 667

1.9 a*

1.5 a 17.1 a

46 a

PRD – switched every 14 days 2 392 51 a * Values followed by the same letter within a column do not differ significantly (p ≤ 0.05). 1.9 a 1.4 b 17.1 a

In many of the overseas research studies, the PRD strategy was also compared to control strategies where unnecessarily large volumes of irrigation water were applied by means of double line drip irrigation systems. Apparently the latter was used to match the double lines of the PRD strategy. Irrigating the double line control and the PRD strategy at the same frequency created the perception that the PRD strategy requires 50% less irrigation water. In reality, the same volume of water that would have been applied by means of single line drip irrigation had been applied by the PRD strategy. Furthermore, when the irrigation is switched to the “dry” side in the case of the PRD strategy, the soil water needs to be restored to field capacity.

208 CHAPTER 7 – IRRIGATION STRATEGIES