NUTRITION OF THE GRAPEVINE

New Zealand Journal of Agriculture, Volume 78, Issue 5, 16 May 1949, Page 465

NUTRITION OF THE GRAPEVINE

A N understanding of the processes involved in the growth of the grapevine and the means by which favourable conditions can be promoted is essential if consistently-good yields are to be obtained. This article by F. Berry Smith, Viticulturist, Department of Agriculture, Auckland, deals briefly with the scientific explanation of vine and fruit growth and explains how the facts are related to cultural practices which will ensure ■ that vines receive the nutrients necessary for vigorous growth.

THE grapevine like all green plants with a root system extracts the elements required for growth from the atmosphere and the soil. The gases used from the air are carbon dioxide and oxygen and are taken into the plant through minute pores in the leaves. The carbon dioxide by a remarkable process known as photosynthesis combines with water to form a sugar called dextrose, oxygen being liberated in the reaction. This synthesis is made possible by the activity of the green colouring matter, or chlorophyll granules, when stimulated by sunlight. The soluble sugar so formed serves as a food and, dissolved in the sap, is transported to all the growing parts. This sugar can be converted into cellulose, for building the woody structure and foliage, or into starch, in which form it is. stored as reserve food in the canes. When sugar is required for nourishment (such as when the vine becomes active after the dormant period) the stored starch is converted back to sugar by means of substances called enzymes. By using atmospheric oxygen the vine oxidises sugar to form tartaric and malic acid, the chief acids found in

the grape. The pigments of red and black . grapes are formed in the colourless state in the leaves and are conducted to the berries, where they assume colour by oxidation or combination with oxygen, which requires heat. The leaf of the vine is therefore the vital centre in which all the chemical substances which enter into the formation of the vine and its fruit are elaborated. Photosynthesis, also called carbon assimilation because in this manner the element carbon is obtained, can take place only in the presence of light and the process is accelerated by heat, reaching a maximum at about 98 degrees F. From this simplified scientific discussion of the factors involved in the nutrition of the vine in relation to its atmospheric surroundings it is possible to arrive at valuable practical conclusions. 1. To promote all the vital processes of the vine it should be trained, so that as much of the foliage as possible is displayed to the light. A sunny northerly aspect is very beneficial in the attainment of maximum light and heat. If the foliage is congested, much of it will be shaded from the light and heat. 2. As sugar is formed in the leaves preparatory to being conducted to the fruit, too drastic thinning of the vine would prevent adequate ripening of the fruit. 3. As the colouring of the fruit is an oxidation reaction which requires heat, the fruit should hang free of the foliage to derive all the heat possible from the sun. For proper ripening of the fruit heat and not light, as is popularly supposed, is required. To improve the colouring of grapes, particularly in the colder parts of the Dominion, it is advisable to expose the fruit by removal of some of the over-growing foliage.

4. Because of the higher tempera, tures near the soil, grapes will colour and ripen somewhat better when trained close to the ground, but the disadvantage of applying this practice to fullest extent to table grapes is that the fruit is disfigured by mud splashed up by rain. • 1 ; Elements Taken from Soil A " . , I.- i- k . Of the substances which the vine takes from the soil the elements removed in greatest quantity are nitrogen, potassium, and phosphorus. In expressed potassium as potash. Small quantities of calcium are required for nutrition and very minute amounts of ma. tigsLm mangTneie iion Sum Silphur chSrSr sflicok boron Sndzinc which are called trace elements, are essential for normal growth. In most soil s ? tPiprp is an amnio sunnlv of "the trace elements and manurial practice consists of replenishing the nitrogen, : phosphoric acid, and potash used by. the vine and removed annually from the vinevard bv crooning . tne vineyard Dy cropping. . . MAhiirinn manuring . . ■ It is not possible to recommend a general manurial programme which will exactly suit all conditions, but a useful guide in the case of a vineyard producing 3 to 4 tons of grapes per acre is to apply scwt. of superphosphate, ljcwt. of sulphate of potash, and, if necessary, up to IJcwt. of sulphate of ammonia ! per acre or the equivalent in other fertilisers. . In addition, it is usually necessary to make an annual application of lime at the rate of scwt. per acre. To maintain essential humus green manuring is vitally important. For vines trained on the overhead trellis or arched pergola, which are capable of carrying crops in the vicinity of 10 tons per acre, the quantities of manure should

at least be doubled, with the exception of lime. As vines are selective feeders and will not use more phosphoric acid and potash than they require, a dressing of these fertilisers somewhat above basic requirements is advantageous to ensure that vines are adequately supplied. The quantities already recommended are greater than the actual amounts removed by the vines in the formation of wood, foliage, an j f ru as allowance has to be made f or i osses by leaching and the conversion in the soil of part of the manure n to unavailable forms. » is necessary to be more circumspect about the rate of application of W nll use amounts of nitrogen out of all Proportion to their requirements. Exces? nitrogen results in rank growth, tlw? pvnenqp U «f e fhe Able to disease, at the expense of the Quantity and Quality of the fruit, However, the type of growth produced by excess nitrogen should not be mistaken for strong growth under favourable conditions. Vines growing strongly as a result of good, balanced nutrition and ample moisture will also exhibit an inability to produce good crops, if, by close planting on-a low trellis, growth is restricted. Vigorously growing —vines that have a large development of wood and foliage will require a lot of pruning if they are to be made to conform to the restricted area available on a low trellis, and hard pruning always means a reduction in fruit. If the same vines are given greater scope for their exuberance by training them on an overhead trellis or arched pergola, they will fruit abundantly. Growth is likely to become rank on rich soils with a high humus content and where this occurs nitrogenous fertilisers should not be applied nor should green manuring be practised for some time or until surplus nitrogen is explotted. In soils with a low humus

content such as heavy clay and light i sandy soils nitrogen deficiency will exist and suitable applications of nitrogen are necessary for proper develop, ment. The use of sulphate of ammonia has the undesirable effect of raising the acidity of the soil with the result that phosphoric acid may be rendered unavailable and the useful activity of earthworms decreased. Nitrate of soda, another form of nitrogen, has a bad effect on the mechanical condition of heavy soils by deflocculating the soil particles and rendering them very sticky and difficult to cultivate. Cover Cropping Cover cropping with blue lupins will impart an appreciable amount of nitrogen to the soil by the activity of bacterial colonies on the roots, which secure nitrogen from the air. To increase the nitrogen content of the soil it is preferable and safer to apply scwt. of dried blood and scwt. of bone manure with a cover crop of blue lupins, which are sown at the rate of about 901 b. to the acre. Dried blood is a nitrogenous manure containing 9 to 14 per cent, of nitrogen, compared with 20 per cent, in sulphate of ammonia. Where a crop of lupins is to be grown the vineyard should be cultivated during the first week in March to produce a good seed-bed and the cover crop and manures sown. A machine suitable for the purpose is shown on this page. The overall width is 6ft., leaving ample room to pass along 10ft. and Bft. rows. An important feature of the machine is an absence of revolving cogs in the distributing mechanism, which prevents the seeds from being mangled. A successful winter cover crop can be achieved only by sowing before soil temperatures are too low, and unless the crop is in before the end of March a poor stand of greatlyreduced value will result. If for some reason it is not possible to sow a cover crop, volunteer weed growth may be topdressed in the autumn as for lupins and this will contribute valuable organic matter to the soil. The cover crop should be turned in (a disc harrow or rotary hoe is ideal for this work) at the flowering stage or in early September and the operation followed by an application of scwt. of lime and Ijcwt. of sulphate of potash, which will complete the . manurial programme. A cover crop when turned under may temporarily depress the available nitrogen supply in the soil until , decomposition proceeds and for that reason it is advisable to have the crop down a few weeks prior to bud burst so that the vines will not suffer from temporary nitrogen deficiency in the early stages. Prunings may be' left on the vineyard and smashed up into small pieces by the discs or rotary hoe when the cover crop is being cultivated into the soil. The accompanying green matter will aid in the disintegration of the prunings in the soil. Where the vines are displaying sufficient vigour no nitrogen in addition to that imparted by the cover crop should be applied and the lupins should be sown with scwt. of superphosphate or bonedust only. •- Basic

slag is an excellent phosphatic fertiliser for the vineyard and may be used in place of superphosphate or bonedust. It is preferable to use the three fertilisers in rotation.

As a general practice the application of phosphatic fertiliser with the cover

crop and of potash and lime when the crop has been turned in in the early spring is recommended.

Functions of Plant Foods

Nitrogen is the nutrient which all plants need to grow leaf and wood. An ample supply of nitrogen promotes rapid growth of vine, characterised by an extensive area of dark green leaves and thick canes. Where a deficiency of nitrogen exists, growth is slow and weak and the leaves have a sickly, yellowish-green appearance. Excessive nitrogen has the bad effect of diverting most of the energy of the vine to producing wood and foliage and as a result the fruiting is impaired. Phosphoric acid stimulates root development and for this reason a liberal dressing of phosphatic manure is particularly desirable for young vines. It encourages fertility and the setting of fruit and promotes early ripening. Liberal dressings of phosphate appreciably enhance the quality and sweetness of grapes and this is reflected in the improved quality of the wine made from them. Potash promotes the ability of the plant to form carbohydrates (starches, sugars). It is the predominant stimulator of ripening of fruit and wood. It imparts strength and long life to vines and builds up resistance against pest and disease attack. Potash deficiency is revealed by flimsy, dull, anaemic leaves, badly-filled bunches of improperly-coloured fruit, or spongy wood lacking substance. The acidity of the grapes is reduced by neutralisation of the acids with potash absorbed from the soil as maturation proceeds. Considerable amounts of potash are also retained in the canes, so there is a steady and progressive depletion of the soil’s reserves, which must be replenished sooner or later to maintain healthy growth. On potash-starved soils growth response to additions of potassic fertiliser is slow and investigations have shown that it may take heavy doses for three seasons to achieve results.

Lime, apart from being an essential plant nutrient, improves the mechanical condition of the soil and renders other plant foods available by displacing them from combinations in the soil. It also neutralises organic acids formed in the soil by decomposition of plant growth. If the soil becomes too acid, phosphoric acid ceases to be available and toxic elements like aluminium become more easily available. However, the excessive use of lime will make the soil reaction alkaline and certain trace elements such as manganese, iron, zinc, and boron, which are all very essential to the vine, will become entirely unavailable. The pH (a measure for the intensity of the acid reaction of the soil) should be 6.0 to 6.5 and the exact lime requirement is the amount of lime needed to adjust the pH accordingly. This can be determined precisely only by a trained scientific worker with special equipment.

It should be appreciated that the correct use of fertilisers is an exacting business and careful scientific application is necessary to achieve and maintain maximum soil fertility. Green manuring supplies humus and where leguminous crops such as lupins, beans, and peas are grown they may contribute as much as 80 to 1001 b. of nitrogen, the equivalent of 4 to scwt. of sulphate of ammonia, to the soil. Though the humus resulting from green manuring makes a valuable contribution to the soil, it should be realised that the contribution is comparatively small and hardly more than sufficient to maintain the existing humus content of the soil. It is a mis. apprehension to suppose that an impoverished soil can be rendered fertile with humus derived from green manuring alone, as the small gain does little more than compensate for the continuous depletion occurring under cultivation. The only way. materially to improve the humus content of an impoverished soil is by heavy dressings (10 tons to the acre) of farmyard manure or compost. In addition to removing considerable quantities of. water from the soil in winter and helping to counteract waterlogging, good green crops absorb soil nutrients during growth and reduce losses caused by leaching. The salvaged plant foods are returned to the soil when the green crop is turned in and become available to the vines. A crop such as lupins, which have a vigorous, penetrating root system, tends to break up consolidated layers of soil and improve drainage. Trace Elements Instances of abnormal growth due to a deficiency of trace elements are rare. Boron: In the South Island a case of unhealthy vine growth concurrent with fruit that was not uniform in size and developed a rot was investigated by the Cawthron Institute and

proved to be due to boron deficiency. This was successfully remedied by the addition of borax at the rate of 2oz. per vine every 5 years. Overseas reports have referred to the condition as “hen and chickens” and describe one of the symptoms to be bunches in which part or whole consists of undersized, seedless berries. A spray consisting of 41b. of borax per 80 gallons of water, applied 2 to 3 weeks before blossoming, is an alternative treatment. ■ - Zinc: Stunted vines in parts of South Australia were found to be suffering from zinc deficiency. As a corrective measure the pruning cuts were painted with a zinc sulphate solution (ljlb. of zinc sulphate to 1 gallon of water). A condition in fruit trees termed “little leaf” and in citrus “mottle leaf” is caused by a lack or unavailability of zinc in the soil and is corrected by using a zinc sulphate spray (51b. of zinc sulphate and 2jlb. of hydrated lime per 100 gallons of . water). Iron: On soils with a high lime content iron is rendered insoluble by the alkaline reaction and vines growing there will suffer from a physiological disease, typified by a yellowish-green to yellow colour of the leaves, called chlorosis. On French vineyards this trouble was remedied by applying a strong solution of iron sulphate immediately after pruning. The action is explained by the fact that the sap pressure of the vine progressively falls in autumn and when it starts to recede the pressure becomes negative so that any liquid swabbed on to cut surfaces made by pruning will be absorbed into the body of the vine. Symptoms similar to those of chlorosis are produced by wet and badly-ventilated soils and also, as previously mentioned, by a lack of potash or nitrogen. A deficiency of other trace elements could cause abnormal growth, but there is little on record of sufficient importance to warrant comment.

MOST NECESSARY ELEMENTS

FUNCTIONS OF PLANT FOODS

> V -! i ll —~s SETS FOR TAKING OPOSSUMS