Response of Shiraz/101‐14 mgt to in‐row vine spacing

Abstract

Context and purpose of the study ‐ Knowledge of vine reaction to plant spacing under high potential soil conditions is restricted. This study was done to determine effects of vine spacing (with fixed row spacing) of Shiraz/101‐14 Mgt on a high potential soil on vine physiological reaction, growth, yield and grape composition. The study is targeting economic viability by considering establishment, yield, grape and wine quality, and expected longevity.

Material and methods – The project is carried out in the Breede River Valley, Robertson, South Africa. Shiraz(clone SH 9C)/101‐14 Mgt vines were planted during 2008 to a VSP trellis with a fixed row spacing of 2.2 m and a row orientation of approx. NNE‐SSW (30°). In‐row vine spacing varies from 0.3–4.5 m with increments of 30 cm (from 15151–1010 vines/ha), totalling 15 treatments. Treatments were irrigated similarly per week (based on ET0 values and standard seasonal crop factors). Grapes are harvested at two ripeness levels.

Results ‐ After establishing the experiment vineyard in 2008, results have been generated over six seasons with complete pruning system (2‐bud spurs, equally spaced) and cordon development. Canopies developed uniformly with cordon extension. General vegetative growth over treatments varied according to seasonal conditions. Except for individual leaf size, vegetative growth parameters (trunk circumference, shoot and cane mass) were mostly reduced for narrower spaced vines. Yield:cane mass ratios showed an increasing trend from narrow to wide vine spacing. Fertility, together with bunch mass, seemed to increase from narrow to wide spacings. Bunches of narrow spacing treatments seemed more compact. Physiological parameters revealed a complex interplay between vine structure expansion, microclimate, water relations, photosynthetic output, and carbon distribution. Grape composition followed trends of decreasing sugar levels (°B) and pH, and increasing titratable acidity (TA), from narrow to wide spacing. In line with physiological symptoms of stress and available leaf area per yield, sugar accumulation of wider spacings seemed delayed. A balance between oenological advancement, wine style and production returns per investment is critical. Total costs (as measured in this study), labour and yields showed very clear trends with an apparent optimal from 1.8–2.4 m vine spacing. Final sustainability would depend on the total cost of production, farm conditions, and labour skills.