PROGRESS OF NITRIFICATION.

King Country Chronicle, Volume VI, Issue 432, 20 January 1912, Page 3

PROGRESS OF NITRIFICATION.

Nitrogen in the form of nitrates is generally regarded as the best kind of nitrogenous food for plants. They obtain this food from four sources already present in the soil; (2) from those that are carried down to the soil from the air by rain and dew; (3) from those that are applied artificially in manures; and (4) from the nitrates which are formed in the soil from the ammonia of other substances.

As is well known, nitrogen applied to the soil for manurial purposes, especially farmyard dung or vegetable composts, is not in the form of nitrates, and before it can be taken up and used by the growing plant, the organic nitrogen must be changed first into the form of ammonia gas, and then into nitric acid. These changes all take place through the agency of micro-organisms, and that particular process in which the nitrogen of the ammonia is changed to nitric is called nitrification. This change is accomplished by the joint action of two separate organisms, one of which changes the nitrogen of ammonia into nitrous acid, while the other changes the nitrous acid into nitric acid.

The conditions that are required for the developments of nitrifying organisms are the presence of certain food and other elements—heat, moisture, air, and some mineral basis, such as lime, or potash—to neutralise the nitric acid as it is formed. The nitrifying organisms require certain substances as food, among which phosphoric acid is the most important. It has been found that without phosphoric acid there can be no nitrification. This may be one of the reasons why phosphates show such beneficial results when applied to some soils, besides which they furnish plant food directly. The three conditions which exert a marked influence on nitrification are heat, air, and moisture. Here, then, is one of the reasons why thorough tillage is so essential to successful farming The loosening and pulverising of the soil allow the admission of the necessary air, and regulates the supply of moisture. If the soil is either very dry or saturated with water to the exclusion of air, nitrification is retarded, and may be riermanently stopped. Tho final product of nitrification is nitric acid, but the nitrifying organisms cannot develop in the presence of a free acid, hence the beneficial result of liming sour soils and peaty soil. The application of lime corrects the sourness of the soil by neutralising the free acid, and then if the other conditions of heat, air, moisture, and food are available, nitrification may proceed. There must be an excess of lime applied over and above the amount necessary to correct the acidity of the soil, in order to neutralise -the nitric acid a sit is formed. Basic slag has also been found of great value in the aid of nitricfiation. The caustic lime of the slag may have at first a retarding effect on the nitrifying organisms by rendering the soil too alkaline, but it soon gets converted into a mild form, and then acts most beneficially. The organisms found in the tubecles in the roots of leguminous plants, such as clovers, peas, beans, etc., are not the organisms that produce nitric acid These are what are called bacteria, whose office it is to seize or fix upon the free nitrogen of the air, or the nitric acid of the soil, and store it for the use of the host plant..