The effect of partial rootzone drying and foliar nutrition on water use efficiency and quality of table grape cultivars Crimson seedless and Dauphine
Thesis (MScAgric (Viticulture and Oenology))--University of Stellenbosch, 2007.
The South African and international table grape industries are growing rapidly, which necessitates the production of high quality export fruit at competitive production costs. For this reason, alternative irrigation methods are required to utilise water optimally while still attaining good quality table grapes. An increase in agricultural productivity may be dependent on either the availability of more water for irrigation or an increase in the efficiency of water use. The first aim of this study was to evaluate the effectiveness of the Partial Rootzone Drying (PRD) irrigation strategy in Crimson Seedless and Dauphine table grape production. This irrigation system is based on the drying of half of the vine roots, thereby allowing the plant to produce hormones like abscisic acid (ABA) in reaction to water stress. The hormone production in turn results in stomatal closure and the reduction of water loss via transpiration. The drying cycle is then repeated after 10 to 15 days on the other side of the vine, irrigating the previously dried roots. PRD will encourage a consistent production of the stress hormone abscisic acid (ABA), without actual water stress. This strategy reduces the amount of water used for irrigation, without an accompanying loss in fruit yield, as compared to conventional techniques. In this study, conventionally treated vines were irrigated according to historical block data and PRD-treated vines were irrigated at the same times. The second aim of this study was to monitor the efficacy of a foliar nutrient, Croplife. This foliar nutrient allegedly improves the uptake of foliar applied nutrients, assists with transport of all minerals through the leaves and enables the plant to attain higher pest and disease resistance thresholds. Conventionally treated vines that did not receive foliar nutrient treatment were compared to vines that received foliar nutrients as prescribed by the manufacturer. Vine cultivars Crimson Seedless and Dauphine, were grown under open hydroponic principles with drip and drip irrigation respectively in this experiment. For the hydroponic vines (Crimson Seedless), all vines were situated in the same row and 72 vines were divided into mini-plots of three vines. Treatments were then assigned to an equal number of plots at random. The same procedure was followed for the drip irrigated vines (Dauphine) but the vines were situated in two rows of equal length. Treatment effects were followed from budburst until harvest, where after post-harvest analyses were conducted. The first aim, namely to show that PRD is an effective irrigation strategy for table grape production in Crimson Seedless and Dauphine cultivars , has shown that vines did not exhibit signs of stress even though they received only half the conventional amount of water. This study was conducted over only one growth season and therefore no definite conclusions could be drawn about the long term effectiveness of PRD on table grapes. It did, however, confirm numerous results obtained from different studies on the use of PRD in wine grape production. The results obtained in the second part of the study were inconclusive and could not show that Croplife is effective in improving the uptake and transport of applied foliar nutrients. Because Crimson Seedless is cultivated under open hydroponic principles, nutrients can be absorbed by the roots via the soil and micronutrients are also available from chemical sprays during the season. There was no evidence to indicate that the use of Croplife increased nutrient absorption and transport, neither did it supplement or detract form the observed effect of PRD. Despite the limitations experienced during this study, it has shown that the use of PRD for table grape production may be a useful tool for improving water utilisation efficiency in future. The strategy will have to be developed systematically through experimentation to fully unlock the potential of the PRD management system for table grape production. This study provides a good starting point for future research required to elucidate numerous aspects of the PRD system and has clearly shown that established vineyards can be switched to a PRD system without a loss in table grape quality. It is envisaged that the advantages of this system could have a positive effect on the production of high quality fruit for the international market.