[Grapevine Nutrition]

viti-notes [grapevine nutrition]

Nitrogen fertilisation

Viti-note Summary: Urea • The role of nitrogen in Urea is mobile in the soil and can be grapevine function actively taken up by vines. However, it is usually broken down into to the relatively • Mobility and behaviour immobile form ammonia which dissolves of nitrogen fertilisers in the soil water to become ammonium. • Sources and losses of Ammonium nitrogen Ammonium can be taken up by vines, • Nitrogen management however, it is toxic in high concentrations. in the vineyard Bacteria convert ammonium into nitrite (which is also toxic to plants). • During vineyard Nitrate establishment Nitrite is quickly converted into nitrate. • In mature vineyards Nitrate is the form of nitrogen most Figure 1. Nitrogen defi ciency sypmptoms on • Timing the application readily used by vines. Nitrate is readily grapevines. Initial symptoms include leaf chlorosis leached through the soil profi le and may of nitrogen for effi cient on older leaves, worsening to necrosis. (Photo uptake move out of the root zone rapidly in courtesy of Mardi L. Longbottom) free-draining soils or after heavy rainfall • Prior to budburst or irrigation. The role of nitrogen in grapevine • Between fruit set function The accessibility of nitrogen by vines and veraison Nitrogen plays a major role in all relies on the presence of suffi cient soil • Post harvest grapevine processes and a signifi cant water. Water movement into vine roots amount of nitrogen is essential for transports nitrate. If soil moisture is • Environmental and normal vine growth. More than any other insuffi cient, uptake of nitrogen will be sustainability issues nutrient, a defi ciency of nitrogen may limited. A range of factors (e.g. soil type, • Eutrophication affect key metabolic functions and retard irrigation and rainfall) affect how the shoot development and bunch formation. various forms of nitrogen move through the soil profi le. With a few exceptions, nitrogen is only found in moderate to low quantities in Nitrogen is mobile within the grapevine, the soils of Australian vineyards. However and can move from mature organs to nitrogen fertiliser should be applied to areas of new growth. As such, defi ciency vines carefully as excessive availability of symptoms appear fi rst on older leaves. nitrogen increases shoot growth at the Symptomatic leaves may fall prematurely cost of fruit development. Over supply of (see section 4.2.10 for more detail). nitrogen can also delay fruit maturity and Nitrogen immobilisation and the carbon Other topics in this may result in poor bud fruitfulness in the to nitrogen ratio (C:N) Viti-Notes series include: following season. Immobilisation (also known as ‘draw • Nitrogen fertilisation down’) is a state of temporary nitrogen • Phosphorus fertilisation Mobility and behaviour of defi ciency in soil. Immobilisation occurs • Potassium fertilisation nitrogen fertilisers when organic mulches that are high in Fertilisers contain nitrogen as urea, carbon and low in nitrogen (high C:N • Petiole analysis ammonium or nitrate. It is important ratio), such as vine litter, dry slashed • Soil acidifi cation to understand the nitrogen cycle when grass or straw from cereal cover crops, • Liming applying nitrogenous fertilisers so that are incorporated into the soil. Micro- • Trace Elements the fate of the nitrogen can be predicted. organisms and bacteria scavenge

nitrogen from the soil to fuel their own metabolism • Removal of soil containing organic material and as they break down these materials. This can create a nitrogen by water runoff or erosion; temporary nitrogen deﬁ ciency for vines. Immobilisation • Production of nitrogen gas by bacteria in poorly can be corrected by applying a base rate of nitrogen at drained soils; the same time as the mulch. If materials with a high C:N ratio are left on the surface of the soil rather than being • Conversion of nitrogen to ammonia gas by high soil incorporated, they decompose slowly and have little surface temperatures; impact on the soil nitrogen balance. • Temporary immobilisation by turning in of high In contrast, when materials which are low in carbon carbon content mulches such as dry grass/straw. but high in nitrogen (low C:N ratio) such as leguminous cover crops are incorporated in the soil, they decompose rapidly and release a large ﬂ ush of available nitrogen Nitrogen management in the vineyard for vines. If these low C:N ratio materials are left on Nitrogen is available in a number of forms in both the surface, breakdown will be slower but still quicker naturally occurring and commercial fertiliser products. than the decomposition rates of most high C:N ratio These products have a variety of characteristics and materials. Examples of C:N for typical vineyard inputs are can behave differently in different soil/water conditions given in Table 1. (Table 2).

Table 1 C:N ratio for a range of viticultural inputs On sandy soils such as those in parts of the Riverland (adapted from Miller 1993) and Sunraysia, it may be necessary to apply greater quantities of actual nitrogen per hectare to compensate Component C:N Ratio for potentially higher losses of nitrogen via leaching in these soils. Drip irrigated vines commonly experience Grass (dry weight) 40:1 to 80:1 High C:N leaching from the soil under drip emitters and thus Mustard residues 20:1 to 30:1 require supplementary nitrogen application. Legume residues 15:1 to 20:1 Nitrogen supplements may be necessary to compensate for poor vine vigour resulting from pest or disease Soil organic matter 10:1 to 12:1 attack, e.g. nematodes, or other debilitating factors. In

Microbes 4:1 to 9:1 Low C:N some vineyards a leguminous cover crop grown over winter may provide suffi cient nitrogen. Maintenance of adequate nitrogen levels in the vineyard may mean annual or more frequent fertiliser application Sources and losses of nitrogen in some situations. There are a number of methods of fertiliser application, each with various factors to In addition to the processes discussed in the previous consider: sections, nitrogen can also be sourced from: • Nitrogen fertiliser applied to the soil surface by • Fixation from the atmosphere by free-living bacteria broadcast or banding should be incorporated into the and algae; soil by irrigation, rain or tillage. Failure to incorporate • Fixation to a ‘plant ready’ form in soil by bacteria the fertiliser may mean loss of nitrogen via conversion living inside the root nodules of legumes; to ammonia gas (volatilisation); • Decomposition of organic plant/animal matter in soil; • Foliar applications of nitrogen should only be used as a supplement to an appropriate seasonal soil fertiliser • Nitrogen in irrigation water; program; • Applied nitrogenous fertilisers. • Fertigation offers better control of application, however high rates of urea or ammonium-based fertilisers applied through fertigation can result in Nitrogen may be lost from the vineyard system via: ammonium toxicity and soil acidifi cation; • Removal of bunches and prunings from vines; • ONLY LOW BIURET UREA SHOULD BE APPLIED IN FOLIAR • Removal of leguminous cover crops as opposed to SPRAYS TO AVOID DAMAGE TO FOLIAGE. mulching or turning them in; • Leaching from the soil profi le beyond the root zone;

During vineyard establishment Nitrate compounds Young vines usually require about 2-5 g of actual Soluble; N per vine per week (observe vine vigour and leaf Moves freely in the soil; colour to determine if this rate needs to be altered). Use calcium nitrate on acidic soils to avoid acidiﬁ cation. Taken up by plants in the transpiration stream; Urea and ammonium nitrate can be used on neutral to Easily leached through the soil proﬁ le; alkaline soils. Non-acidifying, but expensive.

In mature vineyards Complex organic molecules In warm regions apply 50-60 kg of actual N per hectare in spring or split applications between spring and post Organic materials sourced from vines and weeds, animal harvest is a good starting point. Observe vine vigour and plant ‘manures’ and organic mulches; to determine an appropriate application rate. In cooler Need to be extensively broken down and converted to regions the application rate is likely to be approximately ammonium or nitrate by soil organisms; 20 kg of actual N per ha applied in spring or post harvest. In these areas inputs from rainfall, cover crop Also acts to improve soil structure; turnover, contaminated bore water etc. are sufﬁ cient to Can harbour pathogens. supply the needs of the vines without additional fertiliser.

Timing the application of nitrogen for effi cient Table 2 Characteristics of nitrogen-containing fertiliser products. uptake The application of a mobile nutrient like nitrogen should Urea follow periods of active root growth. These occur at two main times of the season: Very soluble in water; • Around 4-6 weeks after budburst (dependent on soil Easily leached through the soil profi le; temperature and moisture levels); Requires microbial activity to transformation it to • Post harvest i.e. in the second fl ush of root growth (if ammonium or nitrate before it is taken up by roots; there are no limiting factors, e.g. drought). Lost as ammonia gas in moist alkaline soils; Timing of nitrogen application is much more effi cient Often the cheapest form of nitrogen; using fertigation because smaller amounts can be applied at regular intervals (bearing in mind the peak uptake Acidifying effect on soil. periods). The amount applied can then be adjusted according to vine vigour and leaf colour. If fertigation is not an option then split applications of Ammonium compounds nitrogen fertiliser are most effective: Usually soluble; • At least 4-6 weeks after budburst; Absorbed onto clay particles in the soil making it less • Approximately 2 weeks after fl owering. available to vines, but also less likely to be lost via leaching; Generally transformed to nitrate before it is taken up by Prior to budburst the roots, however ammonium can be actively taken up The application of synthetic nitrogen fertilisers prior to by vines; budburst is futile as there is little or no root growth at Toxic to vines in high concentrations; this time to facilitate uptake. This early in the season vines are still using nitrogen stored from the previous Lost as ammonia gas in moist alkaline soils; season to support its growth. The probability of leaching Acidifying effect on soil. Sulphate of ammonia is very is also high in many areas due to spring rainfall. acidifying.

Between fruit set and veraison Acknowledgement Applications of nitrogen between fruit set and veraison The Australian Wine Research Institute would like to can enhance amino acid concentration in berries. acknowledge: However, nitrogen application around veraison and • Cooperative Research Centre for Viticulture (CRCV) during ripening requires caution to avoid prolonging or and all involved in the VitiNotes series (1996 – 2006) promoting excess shoot growth. particularly L. Chvyl and C. Williams. • Mardi L. Longbottom for the update of this document. Post harvest Further information When the supply of available nitrogen is suffi cient Training between harvest and leaf fall, grapevines store nitrogen over winter in the woody tissues for use the following For regional specifi c training in grapevine nutrition spring. Nitrogen should be applied in the post harvest management, the AWRI is running Research to period if leaves are healthy. If the leaves have started to Practice: Managing grapevine nutrition in a changing senesce or are in poor condition, uptake of nitrogen will environment. be low and most will be lost to leaching through the Contact soil profi le. Marcel Essling: [email protected] for more information.

Environmental and sustainability issues Useful references: There are a number of issues relating to both the Nicholas, P. 2004. Soil, irrigation and nutrition. sustainability of the nitrogen resource in a given vineyard Adelaide: Winetitles. and the use of nitrogenous fertilisers in the greater environment. These include: Articles about grapevine nutrition and viticulture in general are available to the Australian wine industry • Leaching losses from the vineyard; through the Australian Wine Research Institute library. • Soil acidiﬁ cation; Visit http://www.awri.com.au/information_services/jfml/ for details. Product or service information is provided to inform the Eutrophication viticulture sector about available resources and should As discussed in previous sections, these issues are best not be interpreted as an endorsement. managed by appropriate fertiliser selection and timing of application.

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