Root growth during postharvest irrigation of warm-climate grapevines

In warm climate regions of Australia grapevines may retain leaves for up to four months after harvest. However, a dry postharvest period may reduce root growth, nutrient uptake and the replenishment of carbohydrate reserves. This can impact on canopy function in the current season as well as canopy development and berry ripening in the following season. This research examined the role of the root environment, particularly soil temperature and moisture, on fine root growth after harvest in 2013. Three postharvest irrigation strategies were compared using mature field-grown Shiraz. These included no postharvest irrigation (NPHI), early postharvest irrigation (EPHI) and late postharvest irrigation (LPHI). The EPHI treatment maintained soil moisture in the readily available range for a period of 15 days after harvest. The LPHI treatment was applied at 30 days after harvest, and similarly maintained soil moisture for a period of 15 days. Minirhizotron tubes were used to monitor root growth across all three treatments. Fine root growth in EPHI increased nearly sixteen-fold 20 days after irrigation. Maximum root growth rates were observed at seven days after harvest in the EPHI treatment and these growth rates were maintained for seven days prior to declining. The root growth response to the LPHI treatment was much less pronounced. Soil temperature during EPHI was warmer by 6°C when compared with LPHI. These results indicate that moisture but not necessarily soil temperature (in the conditions of this experiment) are critical factors influencing fine root growth in the postharvest period.