WINETECH Technical Yearbook 2019

on specific analytical methods used by the local laboratories. Producers have no need to submit samples to overseas laboratories. Meticulous sampling is required, both with regard to the correct procedure and place. Any analysis and recommendation cannot be better than the sample received by the laboratory. Fertilisation programmes, lime applications, leaf nutrition, problem solving and nematode treatments are based on the analyses of the samples that were submitted. In order to obtain the best technical recommendation and economic value, the best possible sample should be analysed. Many technological aids are available to assist producers with better management decisions. Producers may use data sources, such as satellite images, NDVI, EMI scans, FruitLook, etcetera. One should nevertheless

remember that even though measurements fall within the ambit of these technologies, as does the indication of variations and problem areas, they are mostly unable to identify problems. Although the data are sometimes presented in an impressive format, interpretation is key as is processing of the information before it becomes useful to the producer. Identification of the problems or ground truthing still requires experts to visit the areas, make profile pits, take samples, make vineyard observations, interpret analyses, etcetera. The cu s toma r y p ra c t i ce i s to t ake one composite soil sample per block/ management un i t . Somet imes l a rge variations occur within blocks as a result of differences in nutrient status, salt accumulation, drainage, texture, and so

forth. In such instances composite samples may dilute the variation analysis and fail to indicate true problem spots. An approach to address this potential problem is to take more intensive samples in a grid pattern (grid sampling or point samples). A less intensive and usually more practical approach is to identify a zone (smart sampling) in a block and combine the samples in order to analyse one representative sample. This zone may be identified by studying soil borders or yield charts. It is important to take soil and leaf samples from areas with similar characteristics. If necessary, divide the block into smaller zones with similar vigour, yields, soil texture, slope and drainage. It is important, however, that these units should constitute manageable zones, especially in terms of irrigation and

fertilisation. Fine-tuning management of smaller existing production systems is extremely difficult. Within such zones/blocks sampling can be either in a random or zig-zag pattern, as long as care is taken that samples are uniform and distributed across the entire area. In instances where there are problematic areas, such as lower yield or inadequate grapevine growth, these should be sampled separately to determine the reasons for the poor plant performance in the respective areas. This will enable the producer to solve the problems by means of the necessary managerial inputs. The correct procedures for soil and leaf sampling are discussed in a subsequent article.

– For more information, contact Johan de Jager at dejagerj@vinpro.co.za.