THE JUDICIOUS AND ECONOMICAL APPLICATION OF LIKE TO SOILS.

Otago Witness, Issue 2467, 26 June 1901, Page 6

THE JUDICIOU S AND ECONOMICAL APPLICATION OF LIKE TO SOILS.

According to the Piotham&ted experiments, there is an annual loss of lime from the soil per imperial acre of about scwt, removed by crops and drainage. It mufct be obvious, therefore, that the former should not hesitate to see that this defect be made good as quickly as possible, so that one of the most important factoif- in the fer-

tilily of his soil may be supplied. At the present time the great object is to produce crops ab the smallest possible expense, and the value of lime in thh respect cannot be •too forcibly impressed upon the minds of farmers. No one who, like the writer, has had an opportunity of seeing the excellent results of the application of lime to soils poor in lime in thousands of cases, and various districts of England and Irehind, can entertain any doubt of its extreme value. Indeed, it may be a^berted that it is moie economical under present conditions than it was when agriculture was in a more favourable state. At the same time it is needful to state that in the country distiicts referred to above, too many instances were observable in which lime dressings were extravagan and necessarily injurious. In this colony curtailment in the use of lime would certainly be justifiable if a lavish use of it in the past had been practised. On the contrary — mainly because it was unobtainable at a reasonable fuuire — it tag aos been applied to the ex-

tent that in the interests of the cheapest and most economical method of crop production it ought to have been applied. The disabilities have been removed by the considerable reduction in the price of lime, and its free carriage on Government railways for a distance of 100 miles from the kilns or loading-station. There are four substances which are apt to be deficient in a soil," and which requne tn be added to it if we are to keep up the teitility and to continue producing craps. These substances arc — nitrogen, phosphate, potash . and lime. When aitificial manuies are applied, the three first-named ?re generally supposed to be meant, and for Ilia purpose of supplying the plant with feed, but with lime it is entirely different for, to quote a st-indaid authority, "Not oiily i-> it a plant food 4n itself, but it Las •^'«ei'>>l oilier iinpoitant functions to parfonn in Lhe .soil."" As stated in the former article referred to, in order to obtain a proper idea of the nature of lime, the changes it undergoes in the soil, and the different foiins in which it exists, it will be necessary to show its composition fiom a. chemical point of view. ■

LIMESTONE

Limestone before it is burnt, just as ifc is taken out of the quarry* is competed of a solid body called lime, and a gas, carbonic acid gas, or carbon dioxide, so thafc limestone Jias the composition, of these two united, and is called carbonate of lime. When .the limestone is put into a kiln with sufficient fuel to raise the temperature to a certain point, the limestone is broken up, the carbonic acid gas escapes into the atmosphere, and there is the lime or limeshells left, and it is generally called quick or caustic lime. When water is added to the limeshell it falls clown into a> fine powder, and is called slaked lime, and it still retains in an appreciable degree its quick or caustic properties. What will take place if it is left exposed to the atmosphere for some time? The atmosphere contains a quantity of this gas — th» carbonic acid gas — which was expelled from the limestone when it was burnt, and if we expose the slaked lime it will absorb the carbonic acid gas back from the air, and return into the original state it was in. before it was burnt — that is. carbonate of lime, and it is now spoken of as mild lime — that is, lime -which has been exposed for some time to the air. In outward appearance, as far as the eye can detect, there is no difference, but in the soil they produce different effects.

FUNCTIONS OF LIME

In the first place, lime supplies the plant with food— i.e., it has just the same function to perform as nitrogen, phosphate, and potash in this respect. The strength of a chain is its weakest link, so the strength of a soil is measured by the minimum quantity of any one of the essential ingredients of pknt food. One substance cannot supply the place of another, so that if there is not enough of lime in the soil for the crop, it matters not how much, the other ingredients may be in excess, they cannot take the place of the lime. There may be very few soils in which there is not. enough of lime to supply the plant with what it requires, but plenty — in fact, far too many, have not enough of lime ice promote the physical and bacteriological changes produced by its agency. (2) Limesweetens sour land, and renders harmless certain compounds of iron. When land is spoken of as being sour, it implies that 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 decompositiop of organic matter in the soil. The organic portion of a. soil is the part which disappears when we burn it — it is simply the remains of former vegetable and animal matter — while tha portion which will not burn is called the inorganic or mineral matter. Some substances contain a large quantity of organic matter, while others contain very little. If strawis burnt the most of it will disappear, leaving only a small quantity of ash ; the great bulk of straw is organic matter. So it is with soils, som: contain very little organic matter, such as light sands or stiff clays, while peat contains an excessive quantity. Again, there are soils which contain what may be called a proper proportion ; these are old pastures and land under rotation which have received large quantities of dung. (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 ia winch it can be of service to the 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 soilsmore easily wrought ; a point well known to every practical farmer. (6) Lime prevents or at least minimises diseases, such as finger-and-toe in turnips. (7) Lime assists in the process of nitrification, or as it may be put, assists in the production of nitrate in the soil; and tins is wkit may ba considered the most important work lime has to perform in the f>oil.

NITRIFICATION.

What is nitrification? and how is, it that liznc assists it? Nitrification is the pioces? by which all forms of nitrogen in the soil (except nitrates) are worked up and converted into a nitrate, so that the pknt can feed on it. The immediate effects of applications of nitrate of soda as contrasted with, the more tedious operation of other nitrogeneous manures — sulphate of ammonia, for example — sufficiently illustrate the importance of nitrification as promoted by lime. Nitrate of soda is quickly soluble, and is absorbed by plants unchanged. Now, soda, is not a plant essential, and, moreover, ifc cannot perform the functions of those things which are essential — lime, for example. When sulphate of ammonia is a,pplied to a soil, it comes in contact •nith lime, undergoes nitrification, and is converted into calcium nitrate — nitrate of limd

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> — a soluble and diffusible plant-food. Here, then, we have the nitrate for albuminoid construction, and we hare also the lime, whose presence in plants is of far more importance than has ever been dreamed of. One example will illustrate its importance. In. many groups of plants oxalic acid is elaborated in large quantity; that requires a base, and the lime earned into the plant by nitrified sulphate- of ammonia performs that function. The process described implies the formation of oxalate of lime in the plant — a salt of lime very abundant in the leaves of leguminous plants. The means by which nitrification takes place in the soil is owing to the agency of minute microscopic plants called bacteria or germs, -which are continually a-b -work wHererer the conditions are favourable making nitrate for the uEe of the plant. What are the conditions- necessary for the production of those nitrates? First of all there must bs fresh air : secondly, heat ; and, thirdly, moisture. The best temperature is summer heat, and this is the time when the most nitrate is produced in the soil. At a lower temperature the organisms become sluggish, and at a- still lower they cease work- altogether. When we consider how liable nitrates are to get washed out of the soil, we can see that this is a wise provision of Nature. If they were to continue producing nitrate during the winter, when there is no plant to take it up, it would all be washed out of the soil before the spring. Fourthly, there must be nitrogen in combination^ and fifthly we Lave lime. When we apply lime to the average of soils, we are starting a manufactory for the production of nitrates. Such soils are those containing organic matter, or- in other words, soils containing roots, dung, and decayed vegetable matter in an inert condition. From what has been said regarding the functions of lime, it is evident it can be applied to stiff soils to make them more easily worked, and also to sweeten land that is sour ; but before lime is applied for these purposes the land must • be thoroughly drained, because, as doctors j Bay, we must first remove the cause before ' we can cure the disease.