FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

CHAPTER 5

TABLE 16: Maximum K norms for soils of different textures and mineralogy’s, in order to ensure sufficient potassium nutrition for table grape vineyards.

Breede River and Hex River valley

Berg River Region

Olifants River region

Texture

Mpumalanga Oranje River Region

Sandy soils (< 10% clay and > 85% sand) Loamy soils (10 – 20% clay) Clayey soils (> 20% clay)

80 mg kg –1

100 mg kg –1

80 mg kg –1

100 mg kg –1

120 mg kg –1

120 mg kg –1

140 mg kg –1

Between the pea size and veraison stage, the K requirement of the bunch is virtually fully (97%) supplied by “new” K, absorbed from the soil (Table 17). Between veraison and harvest, however, only 52% of the bunch’s requirement is supplied from the soil, while the rest (48%) is supplied by the vine’s reserves, mostly from leaves and shoots (Conradie, 1981). This confirms that K is highly mobile within the plant, and that vines that had been adequately fertilised up to veraison, will not need additional fertilisation in the form of foliar nutrition at veraison. As for all macro-elements, the value of K foliar applications is questionable, because the amounts that may end up within the vine will be completely inadequate. If foliar nutrition induces a positive reaction it will only point towards inadequate irrigation or fertilisation practices.

TABLE 17: Provision of K to bunches from bud break to harvest, based on a production of 30 ton per hectare.

Growth stage Bud break to pea size Pea size to veraison Veraison to harvest

Requirement/ provision to bunches

Bunch requirement (% of annual requirement) Fraction (%) supplied by the soil Absolute amount accumulated in bunches (kg ha –1 )

31.0

41.1

27.9

100

97

52

19.2

25.4

17.2

The leaf analysis norms for K are indicated in Table 18. Once again, the same precautions regarding the use thereof, as discussed for N are applicable, namely large variations with regard to cultivars, cultivation areas, sampling time, sampling position, seasonal climatic differences and soil types. The norms make provision for all situations and are consequently have a very wide range.

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