LIMING.

Otago Witness, Issue 2499, 5 February 1902, Page 6

LIMING.

Curtailment in the use of lime would certainly be justifiable if a lavish and extravagant use of it in the past had been practised, but in the colony the material has only been available in districts wide apart, and at prices prohibitive of its general, but needful, application. Now, however, the cas«^ is altogether different ; it is almcst everywhere ijrocurable at a. moderate price, and farmers are beginning to learn that in the interests of the cheapest and most economical method of crop production, its use must be resorted to much more than has been the case hitherto. Since lime is not only an essential plant food, bub acts as a stimulant to the soil, and sets free its fertilising resources, thus promoting and hastening abundant crops, it may rightfully be regarded as an indispensable factor in the fertility of soils which are poor in lime,^ and for that reason yield poor and costfv crops. At the present time the great obiect is to produce crops at the smallest possible expense, and the value of lime in this respect has been very truly and strikingly demonstrated in the annals ot- British and Continental agriculture. If a soil contains no carbonate of lime, or merely tiaces, it may safely bi; concluded that f-uch a soil is in need of lime, since if is only carbonate of lime, and that combined with humic acid — the latter htin^ converted mto carbonate of lime by oxid-ition, and exerting its action ia the toil as sueh — that is al^lc to fcSecfc

the necessary changes in the soil, thus, by effecting neutralisation of the harmful frea acids, giving rise to the slightly alkaline reaction which is favourable for the oxidation of organic matter, as well as the important processes of nitrification. When we apply artificial mamires — by artificial manures, we mean nitrogen, phosphate, and potash — we do so for the purpose of supplying the plant with food ; but with lime it is entirely different ; not only is it a plant food in itself, but it has several other important functions to perform in the soil. Let us now consider some of the most important of these. (1) In the first place it supplies the plant with food — i.e., it has just the same function to perform as nitrogen, phosphate, and potash in this respect, and here it may be observed that "it is the substance which is in least quantity that rales the crop," and that one substance cannot supply the place of another, so that if there is not enough of lime ir- the soil for the crop, it matters not how much the other ingredierv may be in excess, they cannot take the place of lime. (2) Lime sweetens sour land and renders harmless certain compounds of iron, etc. When we speak' of sour land, we mean it contains some acid body. When lime comes in contact with an acid body it neutralises or renders it harmless. (3) Lime causes the more rapid decdmposition •of organic matter in the soil. The organic portion of a soil is the part which disappears, wnen we burn it — itis simply the remains of former vegetation and animal matter — while the portion which will not burn is called the inorganic or mineral matter. (4) Lime sets potash free from the mineral portion of the soil. Some soils contain a large quantity of potash, but it is not in a form in which it can be of service to tlie plant. One of the effects of lime is to set part of this potash free from the combinations in which it exists, and convert it into a valuable manure. (5) Lime makes stiff soils to be more easily wrought. (6) Lime prevents, or at least minimises, disease, such finger-and-toe. (7) Lime helps in the process of nitrification, or, as it may be put. assists in the production of nitrate in the soil ; and this is what may be considered the most important work lime has to •peforra in the soil. What is nitrification? and how is it that lime assists it? Nitrification is the process by which all forms of nitrogen in the soil (except nitrates) are worked up" and converted into a nitrate, so that the plant can feed op it. There are three different forms ot nitrogen — (1) nitrates. (2) ammonia, (3) organic nitrogen. The first and second do not differ very much in appearance : they are both whitish salts, which dissolve very . readily in water ; but there is this great difference between them : the nitrate is ready for the plant, while the ammonia is not — it lias first to be converted into a nitrate, and this is called the process of nitrification. The organic nitrogen, like the ammonia, has also to be made into a nitrate, and in some cases this will take a considerable time before it is accomplished. By what means does this process of nitrification, or this production of nitrate, take place in the soil? The means by which nitrification takes place in the toil is owing to the agency of minute microscopic plants called bacteria or germs, which are continually at work wherever the conditions are favourable, making nitrate for the use of the plant. What are the conditions necessprv in the soil for the production of those nitrates? First of all we must have fresh air. You must remember it is not a chemical change, but a vital process, and wheiever life is concerned, whether plant or animal, we must have fresh air to enable that organism to breathe. Secondly, we must have heat ; and thirdly, moisture. Those ars two conditions which we may say are beyond the control of the farmer. The best temperature is about summer heat, and this is the time when the most nitrate is produced in the soil. At a lower temperature .the bacteria become sluggish or inactive, and at a still lower they stop work altogether. Fourthly, we have compound of nivrogen. That is the raw material out of. which the finished article is produced. Fifthly, we have lime. This is a condition which we can control at pleasure. When we apply lime to some soils we are starting a manufactory for the production of nitrate. Such soils are those containing organic matter, or. in oth-er words, soils containing roots and dung, and these are the soils above all others where we may expect a return for money laid out in lime. In the organic matter, there is a large quantity of t^iis valuable and expensive ingredient — nitrbgen — for which we pay enormous hums every year in the form of nitrate of soda, sulphate of ammonia, compound manures, etc., but as long as it remains in the organic state, it is of m usd to the plant. When we apply lime, the organic matter is decomposed by the agency of bacteria, and we get nitrate produced at a cheap rate ; not only is it cheap, but it is manufactured gradually as the plant requires it, and the plant gets a regular supply of nitrate. Without lime nitrification is at a standstill.

A number of ingredients are mentioned commonly as essential to the well-being of plants. These are nitrogen, phosphorus, and potash But if these were all, whence came the skeleton ot the man, of the cow, or of the sheep? There were lime, magnesia, and others, which were relatively equally important as plant foods as nitrogen, phosphorous, and potash.