Nitrogen (N) occupies a central position in the metabolism of the vine. Nitrogen in viticulture has a great influence on growth, fruit setting and yield. The largest amount is tightly bound in the organic matter. Of the bound nitrogen, only about 1% is released annually by the action of soil microorganisms. This can result in a subsequent delivery of approx. 50-150kg N/ha/year. The intensity of the mineralisation of nitrogen is not optimally adapted to the seasonal needs of the vine. A shallow soil loosening early to mid-May can promote nitrogen release and result in its availability in time for increased needs of the vine.
Nitrogen fertilization in juvenile plants
In the year of planting and also in the following years, water supply is of crucial importance for the growth of the vine. At good soil conditions, none or only a small amount of nitrogen fertilization is required in the first years of development. The cover crops must be supplied with nitrogen, especially under unfavourable soil conditions, in order to prevent competition with the vines. The quantities vary depending on the soil conditions in the range of 0-30 kg N/ha/year. A possible nutrient supplementation in the planting year is foliar fertilization in the juvenile plant, which has a favourable effect, especially in periods of drought.
Nitrogen fertilization in yield plants
Nitrogen is an important nutrient for grapevine development. However, location and weather also have a significant influence on the photosynthesis performance and thus on quality and yield.
In yielding plants, the nitrogen requirement depends on the organic matter in the soil, the yield performance, the variety and the tillage and water supply. A means of measuring nitrogen demand is the speed of growth.
Phosphorus and potassium
In contrast to nitrogen fertilization, that of phosphorus and potassium is not time-bound. A basic fertilization in autumn before tillage is useful. In juvenile plants with sufficient nutrient supply, no fertilization measures are necessary, since the uptaken quantities are small. If there is a pronounced lack of phosphorus, targeted fertilization of the subsoil can be carried out based on the plant extraction.
If, despite potassium fertilization, symptoms of deficiency appear, a potassium fixation should be assumed. This can also be determined using a soil sample.
Since vines only partially tolerate chloride, chloride-free fertilizers should be used or at least fertilizers containing chlorides should be used only in autumn. Juvenile plants and rootstocks must be fertilized without chloride.
A liming is recommended if the need has been proven by a soil examination.
Boron deficiency occurs especially in dry years on sandy and clayey soils. Grape vines need boron, a foliar fertilization is preferable to soil fertilization.
Iron (Fe) and manganese (Mn)
Iron is actively taken up as Fe++, Fe+++ and as Fe chelate via the root. It is important for chlorophyll formation and the growth process. The mobility of iron in the plant is low. Its availability in the soil is often inhibited by bicarbonate enrichment. Symptoms of iron deficiency are foliar yellowing (chlorosis) and a lack of shoot development. The deficiency is more pronounced on dense clay-rich soils or on calcareous sites; however, an oversupply of phosphate or copper can also increase the symptoms.
Manganese is actively taken up via the root as Mn2+ ion or as Mn chelate and is important for the activation of a range of enzymes. The mobility of manganese in the plant is moderate. There is also an antagonistic interaction between manganese and iron. Excess manganese predominates on acidic soils and waterlogged soils under anaerobic conditions.