It is very important to follow the correct fertilisation programme. Both your grapevines and your wallet will benefit.

Provided nutritional deficiencies were adjusted according to prescribed recommendations at the time of soil preparation, grapevines should mainly have to receive nothing but a nitrogen supplement in the course of their lifetime. Grapevines have a good root system which enables them to take up most of the nutrients they require from the soil. The best times for application are when the roots of the grapevine grow actively, which of course depends on soil temperatures. For grapevines the times of root growth are four weeks after bud burst, after set and immediately after the harvest.

Fertilisation of young grapevines

Young grapevines differ from production grapevines in that their roots grow actively throughout summer. Consequently they are given fertiliser throughout the entire season. Small amounts of fertiliser applications are given on a monthly basis. The fertiliser is either applied via the irrigation system or placed by hand alongside the grapevines. If fertiliser or manure is applied manually, it should not be heaped against the trunk. If this happens, the fertiliser will burn the trunk and the grapevine will die. The fertiliser and manure should therefore be placed a small distance from the young grapevines’ trunks and preferably also under the drippers of a drip irrigation system.

It is important not to apply the fertiliser required by the grapevines all at once, rather divide it into applications that can be spread out across the growing season.

Fertiliser may be applied in three different ways, namely:

  • By hand;
  • Using tractors and fertiliser sprayers; or
  • As fertigation.

Where fertiliser is applied by hand, it is mostly strewn on the berm/vine row. Even application of fertiliser is an art, especially with highly concentrated products such as urea, where only a small amount is applied per hectare. If excessive amounts of urea are strewn in one spot, the roots may burn. To ensure accuracy, the amount of fertiliser to be given per grapevine must be calculated carefully. It should be weighed so that the people involved in the application have a good notion of the amount to be given to each grapevine. A small tin or cap is mostly used to measure the right amount for each grapevine.

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Use a cooldrink bottle cap to measure fertiliser that is applied by hand.

A cooldrink bottle cap of LAN weighs between 3 and 5 g.
Fertiliser may also be applied by tractors and fertiliser spreaders. Water soluble fertiliser applied via the irrigation system.

Example

Young grapevines’ requirement for the first season amounts to a total of 90 kg nitrogen (N) which is given in three applications, namely after bud burst, after set and after the harvest. The most commonly used source of nitrogen fertiliser is limestone ammonium nitrate (LAN) with a nitrogen content of 28%. Therefore 100 kg LAN (two bags of 50 kg each) contains 28 kg N and almost complies with the requirement of 30 kg N per application. Suppose there are 3 000 grapevines per hectare (100 x 100 m), then 100 kg LAN per 3 000 grapevines will amount to ±3,3 g LAN per grapevine. Three applications will deliver 10 g LAN per grapevine.

The fertiliser for each block must be meticulously calculated and weighed. This is to ensure that each block receives the recommended dosage.

If tractors are used to apply fertiliser and/or manure, the spreader must first be calibrated. This means the spreader must be set to apply the correct amount of fertiliser at a time. Also ensure that the spreader bin is clean and that there is no clogging. It is important to note that different blocks require different fertilisation. This means that the calibration of the strewer must be adjusted depending on the product and the amount to be applied.

Manure or lime spreader may be used to apply manure and/or enriched organic mixes. Such spreaders must also be calibrated. It is always possible that the manure may contain stones which will damage or break the spreader. To prevent this a sieve may be applied to the top of the spreader.

Liquid fertiliser is usually delivered in bulk by tankers directly into the fertiliser tank on the farm. From here it is distributed via the irrigation water to the blocks that require fertilisation. For an accurate application the irrigation system should be in good condition and no sprayer or drippers should be clogged.

Water soluble fertiliser is high quality concentrated products that are easily dissolved in water and applied by the irrigation system in the vineyards. When water soluble products are mixed, it is essential to adhere to the recommended dosages. If too much fertiliser is added to the tank, everything will not dissolve and the irrigation lines may become clogged. There should be water in the tank before adding the fertiliser. If not, the fertiliser at the bottom of the tank may form a hard clump which will dissolve with difficulty.

If too much fertiliser is applied, the portion not used by the grapevines may be leached out of the soil. Such leached nutrients end up in soil water and rivers and cause pollution. The sandier the soil, the easier it will be for nutrients to leach out.

Too much fertiliser, nitrogen especially, can also cause excessive nutrient uptake by grapevines, which will then grow profusely. Profuse growth means that a lot of topping is required and leaves will have to be broken out. The grapevine also bears less grapes because it becomes infertile and the quality of the grapes is moreover inferior. In addition profuse canopies are conducive to diseases and rot.

It is therefore important to apply the right nutritional elements in the right quantities. Not only does this ensure that the requirements of the grapevine are met, it also prevents money being wasted on too much or unnecessary fertiliser.

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