SOIL MANAGEMENT

Hawke's Bay Tribune, Volume XXVI, Issue 111, 23 April 1936, Page 12

SOIL MANAGEMENT

Fertility and the Successful Orchard MANURING PROGRAMME In ths conduct of a successful orchard, sound soil management is a first essential. The consistent clean cultivation that is carried on in most well-kept orchards tends to upset the balance of nature. The cumulative depletion of soil fertility has to be checked to keep the growing trees healthy, The growing of cover crops is essential to maintain the trees in a vigorous condition and to allow a percentage of exhausted plant iood to be returned to the soil. 'lhe supply of organic matter is of importance and the best results are obtained in getting fertilisers down to the root zone. The harvesting of deciduous fruits will shortly be completed and consideration can be given to the orchard manuring programme.

Tear alter year crops are harvested from many orchards, and little or no effort is made to replace the plant foods taken from the soil. The consequent cumulative depletion of soil fertility is therefore very marked. This depletion of plant food must be replaced if the trees are to remain in a vigorous condition and continue to produce remunerative yields of high quality fruit. This replacement of plant food has been stressed in these columns for many years now. and while fruit-growers a s a whole recognise the value of applications of artificial fertilisers, and the practice is almost general( there are still many who fail to realise that the growing of cover crops is now considered to be an essential practice if the health of the trees is to be maintained and a percentage of exhausted plant food returned to the soil. As a rule far too much reliance is placed on these annual applications of artificial fertilisers, and. as pointed out by Mr Frank M. Read, M.Agric. Sc., in the March issue of the “Journal of Agriculture,” approximately £lOO,OOO is expended annually by the horticultural industry on manures, and whereas ten years ago the emphasis was largelyton phosphatic manures, it now rests more strongly on nitrogen. Such a marked change in practice might suggest that a great deal of money has been wasted in artificial fertilisers, for there is no corresponding change in orchard conditions to account for the difference. MUCH YET TO LEARN. As Mr Read states, It probably indicates that at the moment a great deal of money is still being wasted, for there is still much to learn about this important phase of orchard work, and the radical differences between the practices of even neighbouring orchardists and most fertilising programmes are characterised by a lack of definiteness. Mr Read also points out that the widespread use of artificial fertilisers is not matched by consistent experimental results supporting their use. No definite response to fertilisers has been obtained from fruit trees in the heavier types of soil, even where manures have produced marked responses in annual crops or grass, and it would appear that in such soils a deficiency of any element shows itself in most other crops long before it is evident on fruit trees. Nitrogen has caused a definite response in many places on soils of the sandy or gravelly type, which are usually low in this constituent, but it has not shown a consistent response in trees under conditions which produce very marked responses in legumes and other crops. Phosphoric acid even in soils known to be comparatively low in that element does not seem to have had anywhere a signicaut effect on the growth and yield of most fruit trees, certainly not apples. Potash until recently had “hown no remarkable effects on fruit trees, certainly not apples. Potash until recently had shown no remarkable effects on fruit trees, but since the war experiments at Long Ashton. England, have established that it is essential on many areas in England, and it may yet find a place here. There is one factor on which all up-to-date orchardists are all agreed, and that is that for an orchard to maintain fertility the supply of organic matter must be maintained. The consistent clean cultivation with frequent stirrings of the soil during the summer months undoubtedly tends to upset the balance of Nature by the great reduction in the growth of surface plants, and the life and decay of these surface plants play an important part in the provision of that organic matter which is required by the soil organisms. It can therefore be taken as a maxim that the yearly ploughing under of a liberal amount of green stuff is a first essential in orchard management, and it is almost as true that where the natural growth of green stuff is abundant and is ploughed under suitably, the position on that orchard is generally quite satisfactory. PROVISION OF GREEN MANURE. There would appear to be three main methods of providing soil humus, states Mr Read. They are as follow: — 1 We can sow a crop of peas, beans, oats, barley, rape, or, in fact, any crop which will grow well and give a goo-I bulk within a few months. In general, the leguminous crops are preferable when they will grow strongly; but if they will not thrive the crop most suitable to the district should be sown early so that it secures a good start before the cold weather comes. March is the best month from this point of view. 1 know many orchardists will say that they rarely have time to put in a green crop, and that, any way, harvesting operations extend into March, and later still, so that if a crop were sown it would be trampled on and spoiled. It is undeniable that some orchardists ao, nevertheless, manage to sow the crop satisfactorily, generally by doing alter-

nate rows in alternate years,' so that there is still room to reach every tree without walking or driving over the sown area

2. We can establish such a plant as subterranean clover, which will reseed itself naturally. This has been done with apparently satisfactory results. There does not appear to be mu:h difficulty in reseeding subterranean clover when it is ploughed under, as is the general rule at present, in September or later, for the plants go on maturing after ploughing, and until the surface is broken down by the cultivators and harrows. But the tendency in many districts now is toward earlier ploughing to avoid ascospore infection in the control of black spot of apples, to improve conditions for fruit setting, and to minimise competition for soil moisture between trees and greenstuff, and so on. If thui desirable tendency be followed, therefore, it would be wise to leave the unploughed strips of clover between the trees until the seed has formed.

3. The third alternative which may bo uselul as a stop-gap, but wmeh would not appear to bo as permanently satisfactory as the two above, is to allow the miscellaneous herbage to grow by ceasing cultivation in late February or early March. This can probably be encouraged by top-dressing with artificial fertilisers in autumn. Superphosphate or sulphate of ammonia has in general given most noticeable results to date. The final choice between these two fertilisers should be made after trial. On the whole, superphosphate tends to be more generally effective for this purpose in the northern orchards, while a nitrogenous manure, such as sulphate of ammonia, is more usually effective in the south. These results, however, depend largely on the type of herbage. Clovers seem to prefer superphosphate, while Capeweed responds more usually to nitrogent. The results from grasses are variable. READILY SOLUBLE FERTILISER. Where soil humus is maintained in the manner described previously, the most satisfactory type of fertiliser to use is the readily soluble quickly-acting form applied either in autumn for the benefit of the greenstuff, or in spring, two or three weeks before bud burst, for the more immediate benefit of the tree.

Nitrogen in the form of sulphate of ammonia; phosphoric acid, in the form of superphosphate; and potash, in either the sulphate or muriate (except in the saline areas where the muriate should not be used) should, singly or in combination, supply the needs of most orchards. All of these, of course, will not be needed in every case. The quantities of fertiliser to be applied will vary with tree size, and the following suggestions refer to mediumsized trees: —

For autumn broadcasting or drilling in with the green crop, superphosphate or sulphate of ammonia should be used at the rate of 1 to 2cwt per acre, in accordance with the conditions previously discussed. For spring application to deciduous trees, 31bs of 2-2-1 mixed manure, which contains two parts of superphosphate, two parts of sulphate of ammonia, and one part of sulphate of potash is to be recommended, except when growth is very restricted and leaves are yellowish. In such cases 31bs of sulphate of ammonia is to be preferred for a year or so, until growth improves.

Citrus trees, on general results so far obtained, would benefit from 31bs of sulphate of ammonia just before the spring growth period, and again just before the main autumn growth. METHODS OF APPLICATION. Having decided on sound lines that one or more artificial fertilisers are required, the grower is still faced with problems of great magnitude, for.it does not necessarily follow that by applying them to the soil they are actually caused to be absorbed by the tree’s roots. In fact it is certain that very little of the fertiliser applied is absorbed, even under the most favourable conditions. There are several reasons for this. Firstly, the root system ot the average orchard tree is situated in a zone some distance from the surface, and the fertiliser must penetrate to this zone through a blanket of surface soil. During its progress nitrogen tends to be rapidly absorbed by the roots of the surface-growing plants, but is otherwise able to move downward without much obstruction.

Phosphoric acid and potash, however, move downward only with great difficulty. Chemical reactions rapidly convert the soluble phosphoric acid into an insoluble form, and the potash, particularly in those soils in which potash is necessary, is absorbed by the clay particles very rapidly indeed, and held there in a form no more valuable to the tree than much of the potash previously in the soil. It is important, therefore, that, in applying fertilisers, they should be placed as deeply as possible, either by being broadcast and then ploughed under immediately, or by being placed in deep furrows. In short, every means at the orchardist’s disposal should be used to place the fertiliser in the actual effective root zone. From this point of view irrigation water, or liberal falls of rain, are of the greatest importance, and should be fully exploited to wash down soluble fertilisers.