COMMERCIAL FERTILISERS.

Auckland Star, Volume LXI, Issue 33, 8 February 1930, Page 17

COMMERCIAL FERTILISERS.

THE EFFECT OF NITROGEN.

COMPARISON OF NITROGENOUS

MANURES.

(By SUNDOWNER.)

In previous articles dealing with commercial fertilisers, their composition and effect on plant growth; it has been necessary once or twice to touch on nitrogen and its effect, for in' many instances the application of one type of chemical maure has chemical reactions on the soil, or produces a type of growth which encourages the liberation of an entirely different element. Thus phosphates applied to dryish §oils having abundant humus encourage the rapid decomposition of this humus, resulting in the liberation of nitrogen. Phosphates also encourage the growth of clovers and other leguminous plants which gather nitrogen from the air by means of nitro-gen-gathering bacteria which make their home on the roots. These bacteria supply nitrogen to the soil in a form available to plants, hence phosphates indirectly increase the supply of nitrogen by two methods, and to a considerable extent, it is this nitrogen-increasing effect of phosphates which is responsible for the added growth noticed on pastures topdressed with superphosphate only. When pastures that have been top-dressed with superphosphate show a marked increase in the quantity of leaf grown, as apart from the number of plants to the square yard, or the palatability of the grazing it is fairly sure evidence that the land is lacking in available nitrogen. Nitrogen Affects Bulk of Growth.

■ Nitrogen has no appreciable effect on the nutritive value of the fodder, but it does increase the growth of leaf, stem and roots, and is therefore of very considerable interest to the farmer, for, provided he can get quality—i.e., nutritive value —in his grass by applying phosphates, it is important to get greater quantity of this superior fodder by applying nitrogen. As stated in the previous article of this series, a shortage of nitrogen is indicated" by stunted growth, a yellowing of the leaves, and sometimes a pink or reddish tint on the leaves of the grass plants. An excess of nitrogen, on the other hand, causes a rank growth, such as that which grows on old stack butts or around cattle droppings. This is sour and unpalatable to stock. Further, whereas phosphates hasten the ripening of plants and increase the quantity of seed or grain, nitrogen has the reverse effect, lengthening the growing period and reducing the amount of seed. It must therefore be obvious that the application of the correct proportions of both nitrogen and phosphate to a pasture where either or both is lacking is of the utmost importance in securing an increased period of growth, greater quantity of feed, and superior nutritive value.

Commercial Forms of Nitrogenous Manures. Where observation has convinced the farmer that available nitrogen is lacking ill the soil, the most important consideration; which presents itself to him is in what form should it be applied to secure the best results? I have already dealt with Peruvian guanos and blood manure, both of which contain organic nitrogen; which- becomes slowly, available to the crop or pasture over an extended period, and where these are suited to the class of soil, they are undoubtedly the best form in which nitrogen can be supplied. Farmyard manure, when properly saved, is aiiother' form in which nitrates are liberated slowly and regularly, and as this also contains phosphate and potasli in suitable-quantities, it is usually considered the perfect or. complete manure for any land. With our system of open air farming in New Zealand, however, farmyard manure is not a commercial article. Nitrate of Soda. In contrast to these organic manures nitrate of soda, one of the chief forms in which this element can be purchased, gives a quick, concentrated, but brief

stimulation. It should therefore be used principally where rapid growth over a short period only is desired, as when it is wished to'force the growth of turnips, rape and similar crops beyond a Stage when the fly will seriously damage them, or when top-dressing pasture in late autumn or early spring to get a growth out of the normal growing season to supply the wants of early calving dairy cows, .ewes, lambing abnormally early to Southdown rams, etc. Nitrate of soda is, however, one of "the most expensive of the nitrogenous manures, and for top-dressing pastures the cheaper though slightly slower acting sulphate of ammonia will be found to give equally good, if not better results.

Njtrate of soda contains about 15 per cent of nitrogen, and because of its extreme solubility it should be applied in several small dressings rather than all at one time. If used to. excess it tends to destroy* the tilth of heavy soils.

One valuable characteristic-of nitrate of soda is that it has a chemical action on potash compounds already in the soil, making, these soluble, arid thus it largely does away, with the necessity of applying potash. , Calcium Nitrate. Nitrate of lime, or calchim nitrate, is similarly quick in its action, although it contains only about 13 per cent or nitrogen. Because of the amount of lime forming the body of this manure, it can be used without risk of the soil becoming acid, and also for the same reason calcium nitrate has no had effect on soil tilth-

The Popular Sulphate of Ammonia. The most popular nitrogenous manure in New Zealand is at present undoubtedly sulphate of ammonia. ; It is not quite so quick-acting as nitrate of soda, as it has to be changed into nitrates m the soil, but this is rather an advantage where it is applied to pastures, as it gives a longer period over which , it stimulates growth.

Sulphate of ammonia, being less soluble than nitrate of soda, is a better application for light, porous soils and in districts of high rainfall. Also it does not affect soil tilth as does nitrate of soda, but it should never be used on soil deficient in lime, for it creates acidity, and lime encourages the growth of sorrel and the repression of clovers On naturally acid soils it should be used only after the land has been heavily limed. It contains from 18 to 20 por cent of nitrogen. When to Apply Nitrogen. Nitrogenous manures promise to beof most value to New Zealand in prolonging the growing season in response to applications in late winter or early spring, and. again in late autumn. Broadly speaking; whereas phosphates give befit results in dry, sunshiny cliinates, nitrogenous manures, especially when coin' bined with potash, give greatest returns where there ib considerable rainfall and clouded, ekies. It will therefore be seen why in pasture topdressing in the North Island phosphatic manures should bo applied in spring and nitrogenous manures in autumn. .