FERTILISATION GUIDELINES FOR THE TABLE GRAPE INDUSTRY

approximately 10 kg P ha –1 can be followed, which for the sake of convenience, can be broadcast as a single instalment at the end of the season (February to March), so that it can also be utilised by the cover crop and transported to the deeper soil layers. Potassium fertilisation is required if the K content of the soil is < 80 mg kg –1 or constitutes less than 4% of the CEC of the soil. As with P, the deficiency can be corrected with a single application or deep placement in soils containing more than 10% clay. In relation to phosphorous, K is assimilated in the same amounts by rootstocks as by scions, and as an alternative guideline a K application of approximately 45 kg ha –1 yr –1 can be done, especially on sandy soils. This amount of K can be applied together with N in 3 – 5 instalments during the season. Proportionally, uptake of Ca by rootstocks is significantly higher than for table grapes, but no Ca fertilisation is recommended if the soil pH KCl is 5.5 or higher. Where this is not the case, a single application of approximately 1 ton ha –1 gypsum should be enough to meet the Ca needs of rootstocks, while it will also serve as a source of sulphur (S). Periodic soil analyses for S content is also advisable. In relation to table grapes, magnesium is also assimilated to a greater extent by rootstocks. However, no specific norms for the Mg content of soils or Mg fertilisation is recommended, because a Mg deficiency is readily manifested by very characteristic leaf symptoms, before vine performance is negatively affected. Intervention by means of Mg sulphate applications can therefore be done timely, if such symptoms are indeed observed. NURSER I ES Few experimental results (local and international) relating to grapevine nursery fertilisation are available, and in the past, there was mainly reliance on practical knowledge for guidelines. However, there is not a good correlation between nursery success and fertilisation according to this approach. In Wellington, indications have been found that the increase of dry material for grafted vines in a nursery is comparable with cane productions in rootstock mother blocks. Using this as point of departure, fertilisation in nursery can be done similarly to rootstock fertilisation, but at higher levels due to the intense irrigation and accompanying leaching that occur in nurseries. Seasonal guideline quantities for N, P and K are presented in Table 32. In the case of solid fertilisers, LAN is the preferred N carrier as it contains lime which serves as source of Ca, as well as single superphosphate P carrier because it contains gypsum which serves as source of both Ca and S. KCI is preferred as K carrier because CI is also an essential nutrient and not harmful at the amounts at which it is applied. The ratios of the elements can be used in the composition of liquid fertiliser, where amounts can be decreased with about 15% due a greater expected efficacy.

106 | FERTILISATION OF ROOTSTOCK MOTHER BLOCKS AND NURSERIES