WINETECH Technical Yearbook 2019

THE ROLE OF SOIL AND LEAF ANALYSES IN VINEYARD MANAGEMENT (PART 3)

JOHAN DE JAGER & BENNIE DIEDERICKS: Vinpro, Paarl KEYWORDS: Leaf analyses, soil analyses, vineyard management. JULY 2019

Is it worth the effort for producers to take regular soil and leaf samples, or does this only generate more data without adding real value? In this article, the third and last, the focus is on leaf analyses which provide a scientific basis to: • Serve as an aid in the evaluation of the soil’s ability to provide nutrient elements. • Evaluate the effect of the fertilisation programme on the nutritional status of the grapevine. • Diagnose nutritional deficiencies. Leaf analysis is a direct measurement of the grapevine’s nutritional status at the time of sampling, in other words what is presently happening within the leaf. As a diagnostic aid, leaf samples have inherent shortcomings. Apart from seasonal variations for which it is sometimes difficult to compensate, factors such as scion and rootstock cultivars, climate, diseases, cultivation practices and soil type also impact on the nutritional status of the leaves. Leaf analysis in itself cannot be used to draw up a fertilisation programme, it should serve as a complement to soil analyses.

It is probably not necessary to sample all the blocks annually; identify a number of monitoring blocks that are representative of the farm and sample these alternately. This will help to compile a history of norm for the farm. New analyses should then be interpreted in the light of farm norms. This will assist producers to observe and reach a better understanding of seasonal variations in analyses. The sampling method depends on the objective: • Monitoring of nutritional status: This approach is used to judge a vineyard’s general nutritional status and to evaluate fertilisation requirements or practices. • V i s ua l de f i c i en c y s ymp t oms o r dev i a t i on s : V i s ua l symp t oms o f deficiencies or toxicities (Photo 1) are more prevalent during the active growing season until the harvest. In such situations the affected leaves, as well as healthy leaves, should be sampled. The healthy leaves serve as control/ reference. If sound clues are lacking, take both the leaf blade and petiole (Figure 1), but analyse them separately.