The effect of crop load on quality in drip irrigated grapevines

PROJECT TITLE:    The effect of crop load on quality in drip irrigated grapevines

Project leader:       Carolyn Howell (ARC Infruitec-Nietvoorbij)

Contact:                     howellc@arc.agric.za

Duration:                   1 April 2023 – 31 March 2027

Problem identification and project objectives:

The optimal crop load of table grapes varies from one cultivar to another. However, it is probably one of the most important management tools in the production of table grapes to ensure economic sustainability by maximising the production of export quality grapes. Growers are under increasing pressure to consider the financial implications of their management practices because of high export standards required and pressure to keep input costs as low as possible. In addition, water resources are generally limited in most table grape growing regions in South Africa and inconsistent rainfall can cause periodic droughts such as the one experienced in the Western Cape during the 2017/18 growing season. This scenario could worsen if climate change reduces rainfall and increases temperatures. The table grape industry needs to reduce its water footprint to convince consumers who are becoming increasingly conscious of the environmental impacts of agricultural production that scarce water resources are being used responsibly. One way to define the water use efficiency (WUE) of table grape production is unit of grapes produced per unit of volume of irrigation water applied (kg/m3). In reality, the WUE can only be improved (i) if more grapes are produced by using the same volume of water or (ii) if the same mass of grapes is produced by using less water. Most of the irrigation research in South Africa has focused on reducing the volume of water applied rather than manipulating the crop load of the grapevine. The volume of water applied can be reduced substantially by using drip irrigation. Therefore, a further way to increase WUE could be to manipulate the crop load of the grapevines. In addition, if higher crop loads are to be applied to improve economic sustainability it would be important to determine whether the accepted norms for nutrients used in the industry are still sufficient to sustain higher than recommended crop loads for grapevines.