Water footprint analysis of table grape production in the Berg River region of South Africa

Abstract

South Africa is a water-scarce country. There are limited research results available regarding the effects of overhead netting on vegetative and reproductive performance, as well as water use efficiency (WUE) and the water footprint (WF) of table grape vineyards. The main objective of this study was to accurately quantify the water use of table grape vineyards produced without netting vs. those produced under overhead netting. The study, conducted over one season (2018/19), included a field trial in three commercial Crimson Seedless production blocks on the farm Môrester near Piketberg, as well as survey, conducted on the twelve commercial Crimson Seedless blocks in the Berg River region. Growing degree days (GDD) in the open blocks during the season was slightly warmer, with higher GDD compared to the netted blocks. Open blocks had a faster accumulation of GDD, because of higher average temperatures at the beginning of the season compared to the netted blocks. This resulted in the open blocks being approximately a week earlier in terms of phenology budburst, compared to the netted blocks. Overhead netting has a strong impact on shoot development by significantly increasing shoot growth compared to open blocks. The highest yield was recorded in the open blocks D8, D29 and L87. WUE based on the irrigation and ET water use ranged between (1.96 and 2.61 t/m³), and (1.41 and 1.73 t/m³). The blue WF (Irrigation) determined from total and export production, ranged from (430 to 603 m³/ton), and (618 to 877 m³/ton). There was a strong positive correlation between weekly shoot growth and FruitLook CPB for the three field trial blocks, as evident from the R² values of 0.824 (M5); 0.967 (M10); and 0.860 (M12). FruitLook ET (estimated water use) is considered a reliable indicator of water use for open (uncovered) blocks, but not for blocks covered with overhead netting, because overhead netting influences spectral reflection of crops, thus affecting the remote sensing data values. Further research is needed to obtain accurate remote sensing values for estimating water use of blocks covered with overhead netting. More research is needed to quantify vineyard water use of netted blocks, compared to open blocks, including sap flow measurements to determine grapevine transpiration and establish vineyard transpiration values and using the universal soil water balance method to establish vineyard ET values.