FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

CHAPTER 5

5 MAINTENANCE FERTILISATION

P I ETER RAATH, KOBUS CONRAD I E & DAWI D SAAYMAN

I NTRODUCTI ON The physiological and metabolic processes that enable grapevines to perform and produce optimally are affected by important macro- and micro –elements, with elements such as nitrogen, phosphorus, potassium, calcium, magnesium, boron, zinc, manganese, iron and copper playing important roles in grapevine functioning, growth, production and fruit quality. In contrast to most other horticultural crops, the nutritional requirement of grapevines is relatively low. In a well-prepared soil, where an extensive root system can develop, nutrients are absorbed from a large soil volume over a long period of approximately seven months. Due to these factors, visual deficiency symptoms do not develop as readily for grapevines as for many other crops (Saayman, 1981). Despite the absence of deficiency symptoms, a fair number of table grape producers will ascribe quality problems erroneously to insufficient fertilisation. For optimally fertilised vineyards, quality problems will be on account of other factors and additional fertilisation will have no effect. The diversity of South African soil types gives rise to unique challenges and different nutritional requirements in the different table grape areas. The aim of fertilisation programmes should be to address individual fertiliser requirements, in order to obtain a balanced growth and canopy-to-crop ratio, combined with rapid ripening of bunches and wood and good grape quality. In order to supply producers with guidelines for the creation of such optimal fertilisation programmes, the fundamentals of grapevine nutrition are discussed in this chapter.

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