Handbook for Irrigation of Wine Grapes in South Africa

Contents

8.2

Qualitative assessment of root systems ..................................236 Indirect estimation of evapotranspiration ........................238 Crop coefficients .............................240 Evapotranspiration models ..............241 Direct soil and plant based measurements ...............................250 Soil based measurements ...............250 Wetting front detectors ....................250 Gravimetric samples .......................251 Neutron probes ...............................253 EnviroScan ® sensors .......................256 Diviner 2000 ® probes ......................257 DFM ® probes ...................................258 Tensiometers ...................................260 Watermark ® sensors ........................265 Plant based measurements .............267 Grapevine water potential ...............267 Diurnal trunk shrinkage and expansion ........................................271 Infrared thermometry .......................273 Remote sensing ...............................277 Setting refill lines for irrigation strategies based on grapevine water status ......................................279 Conclusive remarks ......................282 Introduction ....................................284 Types of cold damage ...................285 Prediction of cold damage ............287 Measures to reduce the risk of cold damage ..............................293 Viticultural aspects ..........................293 Soils and tillage ...............................294 Overhead sprinkler irrigation ...........296 Other methods .................................297 Managing vineyards following cold damage ...................................298 Conclusive remarks ......................299

6.3

Factors affecting grapevine water status ....................................155 Cultivars ...........................................155 Atmospheric conditions ...................158 Soil water status ..............................160 Soil salinity .......................................161 Trellis system ...................................162 Canopy management ......................163 Crop load .........................................164 Leaf damage by pests ....................166 Grapevine water status classification ..................................168 Grapevine responses in relation to midday stem water potential ..........172 Class I – No water constraints .........173 Class II – Low water constraints ......173 Class III – Moderate water constraints .......................................173 Class IV – High water constraints ......175 Class V – Severe water constraints ...175 Conclusive remarks ......................175 Introduction ....................................178 Irrigation strategies .......................180 Irrigation of newly planted grapevines .......................................181 Low frequency irrigation ..................184 Medium frequency irrigation ...........189 High frequency irrigation .................193 Pulse irrigation .................................195 Deficit irrigation ...............................197 Different pre- and post-harvest irrigation frequencies .......................198 Partial root zone drying ...................206 Irrigation during the post-harvest and dormancy periods ....................209 Irrigation strategies during critical drought periods ...............................213 Practices to reduce unnecessary water losses .....................................214

8.3

6.3.1 6.3.2 6.3.3 6.3.4 6.3.5 6.3.6 6.3.7 6.3.8

8.3.1 8.3.2

8.4

8.4.1

8.4.1.1 8.4.1.2 8.4.1.3 8.4.1.4 8.4.1.5 8.4.1.6 8.4.1.7 8.4.1.8

6.4

6.5

6.5.1 6.5.2 6.5.3

6.5.4 6.5.5

8.4.2

8.4.2.1 8.4.2.2

6.6

7 Irrigation strategies 7.1

8.4.2.3 8.4.2.4

7.2

8.5

7.2.1

7.2.2 7.2.3 7.2.4 7.2.5 7.2.6 7.2.7

8.6

9 Preventing cold damage in vineyards 9.1

7.2.8 7.2.9

9.2 9.3 9.4

7.2.10

9.4.1 9.4.2 9.4.3 9.4.4

7.2.11

7.2.11.1 Reducing evaporation losses ..........215 7.2.11.2 Reducing excessive transpiration ......221 7.2.11.3 Preventing irrigation system losses ....226 7.3 Possible ways to use irrigation water more efficiently ....................229 7.4 The water footprint of wine ..............233 7.5 Conclusive remarks ......................234 8 Practical irrigation scheduling 8.1 Introduction ....................................236

9.5

9.6

References ..................................... 300 Abbreviations, acronyms and symbols ........................................307

IRRIGATION OF WINE GRAPES 13