FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

CHAPTER 3

BAS I C CATI ON SATURATI ON RATI O (BCSR) AND SUFFI C I ENCY LEVE L OF AVAI LABLE NUTR I ENTS (SLAN) – COMPAR I SON OF THE CONCEPTS As a guideline according to which soil analyses are interpreted, and fertilisers are applied, the basic cation saturation ratio (BCSR) concept (better known as the Albrecht system), is sometimes used. It assumes that plants will only grow optimally if there is a balanced ratio of cations (Ca 2+ , Mg 2+ and K + ) for every soil, according to its cation exchange capacity (CEC). Fertilisation is therefore done according to the soil’s needs, and not the need of the plant. In a review article, Kopittke & Menzies (2007) traced the BCSR concept back to the late 1800s and found that since the origin thereof, research data has been incapable of proving the existence of any “ideal” basic cation saturation ratio. Instead, they found that promotion of the BCSR concept resulted in inefficient use of resources and fertilisers. Research by various scientists has shown that the SLAN (sufficiency level of available nutrients) concept, where a minimum concentration of available nutrients in the soil is required for optimal plant nutrition, also applies to vines. Even though the “ideal” soil for grapevines can vary dramatically from region to region and between different soil types, its composition is based on a minimum level of nutrients that is required in the soil to supply the vine with the nutrients it requires. Nutrient element balancing is used in some cases to evaluate soil. This technique uses, for example, a Ca:Mg ratio of approximately 6 to indicate whether calcitic or dolomitic lime should be used. For vineyard soils the ideal saturation percentage of exchangeable cations is: Ca 80%, Mg 15% and K 4%, leading to a Ca:Mg:K ratio of about 20:3.75:1. In practice, however, it is not necessary to aspire to this “ideal” ratio for grapevines. Producers are therefore motivated rather to follow the SLAN concept, by making use of the minimum norms as provided in this manual. This will prevent over fertilisation and is an easier, scientifically more justifiable approach, applicable for all soil types.

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