Nutritional status of geologically different vineyards in Helderberg

[摘要] ENGLISH ABSTRACT: Little scientific information regarding the effect of different geological parent materials ongrapevine performance is currently available in South Africa. This aspect is of specialsignificance for the Helderberg area, where parent material may change from granite to shaleover a short distance. This results in shale- as well as granite-derived soils often occurringwithin the same vineyard. The objectives of this study were to (i) quantify the nutritional statusand other soil properties of different parent materials (shale and granite) and overlying soils (ii)investigate the impact of geological differences in the soil on the vine nutritional status andcertain vine parameters. This study was done over two seasons (2006/2007 and 2007/2008).Two Sauvignon blanc and two Cabernet Sauvignon vineyard blocks were selected at twodifferent localities for each cultivar in the Helderberg area, South Africa. Shale- and granitederivedsoils were identified within each block.Kaolinite was the dominant mineral, whereas quartz and feldspar were sub-dominant. Traces ofmica were also present in some shale- and granite-derived soils. Granite- contained significantlyhigher contents of coarse sand than shale-derived soils, whilst the opposite occurred in terms offine sand. These differences affected the water holding capacity, in general making it higher inshale- than granite-derived soils. Shale-derived soils had higher concentrations of total K butgranite-derived soils had a higher ability to release K as they contained higher concentrations ofsoluble K. The Q/I parameters, potential buffering capacity of K (PBCK) and equilibrium activityratio of K (ARK) showed no consistent responses to geological differences.Potassium concentrations were higher in the leaf blades (obtained before harvest in 2007) fromSauvignon blanc grapevines on granite- than on shale-derived soils. Potassium concentrationsin the Cabernet Sauvignon juice (obtained in 2007) tended higher in juice from granite- thanfrom shale-derived soils. In 2008, K concentrations tended higher in juice from shale- than fromgranite-derived soils for both cultivars. The pH of the Sauvignon blanc juice (obtained in 2008)tended higher in juice from shale-than from granite-derived soils, thus corresponding with the Kconcentrations in the juice in this season. Nitrogen concentrations were higher in CabernetSauvignon juice (obtained in 2007) and Sauvignon blanc juice (obtained in 2008) from shalethanfrom granite-derived soils. In terms of vine water status, vines on granite-derived soilsappeared more stressed than those on shale-derived soils in both seasons at one of thevineyards.In these Sauvignon blanc and Cabernet Sauvignon vineyards, the K nutritional status was notaffected by geology in a consistent manner but there were some noticeable tendencies for aspecific cultivar during certain seasons. On account of vines being planted on shale- andgranite-derived soils within the same block, soil preparation was done similarly for both soils,and they were exposed to similar irrigation schedules, canopy management strategies andclimatic conditions. Therefore, there is a high probability that all these practices may havenegated the effect of geology on the K status of soils and especially on juice K concentration atthe time of harvest. It was clear that seasonal differences and fertilisation affected the nutritionalstatus of the vines more than geology.

[发布机构] Stellenbosch University