Handbook for Irrigation of Wine Grapes in South Africa

Chapter 8

the beam of infrared thermometers increases with distance to the object, the distance to the canopy must always be the same. Following these precautions will allow reproducible measurements that can be compared over time as the soil dries out. 8.4.2.4 REMOTE SENSING Vineyard water requirements can also be determined by means of remote sensing based on satellite imagery. In this regard, FruitLook was developed in the Netherlands for irrigation scheduling of various crops. Currently it is widely used by grape growers in the Western Cape. FruitLook uses satellite imagery and weather information to estimate vineyard water use on a field by field basis. In addition to crop water requirements, estimations of growth and leaf nitrogen content are also provided (Table 8.3). FruitLook is an open access, online platform initiated by the Western Cape Department of Agriculture. Access can be obtained on www.fruitlook.co.za. To allow growers to access FruitLook, Hortgro and the Integrated Application Promotion Program of the European Space Agency also provided initial financial support. In the Western Cape, FruitLook enables grape growers to obtain estimates of vineyard water use during the growth season, i.e. from September to April. The information is updated, and made available, on a weekly basis. However, growers have access to historical data via the website. At present, FruitLook can provide information on 96 000 ha of wine grapes. It should be noted that satellite imagery cannot be used where vineyards are covered, e.g. with plastic sheets or netting. TABLE 8.3. Summary of additional vineyard information provided by FruitLook. Variable Parameter Growth Biomass production (kg/ha)

Leaf area index Vegetation index

Crop water use

Actual evapotranspiration (mm/week) Evapotranspiration deficit (mm/week) Crop factor Biomass water use efficiency (kg/m 3 water) Nitrogen content in top leaf layer (kg/ha) Nitrogen content in all leaves (kg/ha)

Leaf nitrogen

Estimations of ET obtained by FruitLook were compared to ET determined by means of the universal soil water balance as described in Section 8.3. The comparison was carried out in a micro-sprinkler irrigated Cabernet Sauvignon vineyard in a sandy soil near Rawsonville. This particular vineyard experienced almost no water constraints, i.e. midday Ψ s was generally -0.6 MPa or higher (Myburgh & Howell,

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