Possible flood irrigation technologies to reduce water use of Sultanina grapevines in a hot, arid climate

Abstract

Growth, production and water use efficiency of Sultanina grapevines irrigated by means of methods where only a fraction of the soil was wetted, were compared to full surface flood irrigation in the hot, arid Lower Orange River region of South Africa. Treatments included irrigation by means of 9.6 m wide beds (T1 and T2), 1.5 m wide beds (T3 and T4) and where every second work row was irrigated and the alternate rows during the following irrigation (T5 and T6). T1, T3 and T5 were irrigated at 14-day intervals, and T2, T4 and T6 were irrigated at 21-day intervals. Compared to wide bed irrigation (T1 and T2), 39% and 36% less irrigation water was applied than by narrow bed (T3 and T4) and alternate row irrigation (T5 and T6), respectively. For T3 to T6, plant available water in the wetted soil volume, as measured before irrigations, was depleted to a larger extent compared to wide beds. As a result, narrow bed and alternate row irrigation reduced vegetative growth significantly compared to full surface irrigation. Seasonal yield variation was explained by relating yield to August minimum relative humidity as well as pre-budbreak soil water content by means of multiple linear regression. The negative effect of dry atmospheric conditions on yield was aggravated by the higher degree of plant available water depletion in narrow bed and alternate row irrigation. Results indicated that irrigation cycles should not exceed 14 days during the growing season if the latter irrigation methods are applied. Water use efficiency for both narrow bed (T3) and alternate row irrigation (T5) was 3.3 kg m−3, compared to 1.9 kg m−3 for wide bed irrigation (T1). Neither irrigation method, nor irrigation cycle had a significant effect on fruit sugar accumulation. Due to drier soil conditions induced by partial soil wetting, total titratable acidity in juice of grapes irrigated by narrow beds (T3 and T4) and alternate rows (T5 and T6) was ca 0.6 g L−1 lower compared to grapes irrigated by wide beds (T1 and T2).