PLANT FOOD.

Manawatu Standard, Volume LX, Issue 96, 21 March 1940, Page 12

PLANT FOOD.

IMPORTANCE OK NITROGEN. (Written for the “Standard.”) From the standpoint of plant food material, by far Hie greatest benefit from the addition of organic matter to the soil is the increase in the available important plant food, nitrogen. The soil cannot be increased in its total phosphate or potash content- by the growing of any crop, but part ot the value ot green manuring or rotation crops is that some of them, being more deep-rooting than the usual main crops, draw these plant foods from greater depths and leave them in the surface soil on their decay, so that there is an actual small increase in some cases of the available phosphates and potash in the surface soil for the benefit of the succeeding main crops. The same action takes place to some extent in the case of nitrogen, and this is, of course, accentuated by the growing of leguminous crops, which, by means of bacteria in the nodules on their roots, draw on the nitrogen of the air usually more than on the nitrates of the soil and thus, if they are totally returned to the soil, actually increase both the total and available nitrogen in the soil. Where the nodules are scanty or absent, such plants obtain the greater proportion of tlieir nitrogen from the soil, just as other plants do. On rich soils containing an abundance of nitrogen, legumes are often poorly proviued with nodules and thus obtain most of their nitrogen from the soil, but on such soils these legumes do not need to be grown for soil improvement, though they may be for their high feeding value for stock. On poor soils the paucity of nodules may be due to the comparative absence of the necessary bacteria or organisms in the soil, and if this is the case the soil does not become greatly enriched in nitrogen, nor so much in humus either, on account of the scantier growth. Practically every legume has its own strain of nodule bacteria, and such a crop grown for the first time does not usually do as well as on the same soil when it is properly inoculated with the specific organisms. Artificial inoculation of the soil or seed is now generally advised in most parts of the world. There are some soils in which artificial inoculation does not seem to be of much benefit. This may be because some of the native plants or natural leguminous herbage j belong to the same group of plants I and carry the necessary organisms. It I is generally accepted that leguminous crops, well supplied with root nodules, obtain about two-thirds of their nitrogen from the air and the remainder lrom the soil. As in many cases, the amount of material produced in the top growth is about twice that in the roots, it may be assumed that when the top growth of such crops is removed from the land, and only the roots ploughed in, there is practically no increase in the nitrogen content of the soil; and that only when portion or all of the top growth of the crop, or its equivalent, is returned to the j soil is there any increase in the soil nitrogen. That increased yields of the subsequent crops after legumes are obtained, when practically all the top growth is removed, is accounted lor by the fact that the nitrogen content is about maintained in the soil, whereas 'by the growth of other crops it would bo diminished. A turther contributing cause would be, perhaps, the increase in the availability of the nitrogen in the soil from the growth of a leguminous crop. 'This system does not conduce io any permanence in the improvement of the soil fertility, and farmers should beware of being misled into a sense of security in growing and removing leguminous crops (particularly short-season crops) by a comparative increase in the sillisequent crop the first season. Only when the whole or portion of the top growth of the leguminous crop or its equivalent in animal manure (which is partlv obtained from grazing) is returned to the soil can there be expected to be a sufficient increase in tlic nitrogen and the organic matter of the soil to greatly benefit the yields of subsequent crops, or to have anv lasting value. And this is what should be aimed at. for it may not be economically sound practice in some districts to introduce a soil-improving crop (which is not usually a cash crop) into the. rotation more often than every three or four years.

NITROGEN AND THE PASTURE. Hitherto the opinion has been held that, besides good grasses, a good pasture should contain a goodly percentage of leguminous plants. As a manure, phosphoric acid and polasli were recommended exclusively. The use of these plant foods served in the lirst place to stimulate the growth ol leguminous plants, the plentuul development of which was intended to influence favourably the quantity and the quality of the herbage and indirectly to help in feeding the grasses with nitrogen. Experience has shown that manuring with potash and phosphates always cause an increased yield, as compared with, _ unmanured land, but the one-sided stimulation of leguminous plants prevents the grasses from attaining their full development. The conclusion is that, unless the soil is naturally rich in assimilable nitrogen compounds, it is not possible to obtain the maximum yield from pastures by the use of potash and phosphate fertilisers only. During recent years the theory that pasture lands must be manured not only with potash and phosphates, but also with nitrogen, has gained considerable support. Good pasture consists of approximately 75 per cent, good grasses, and at the most 2.3 per cent of . all other plants, amongst which leguminous plants arc predominant. Experience has shown that yields sufficient in quality and quantity cannot be obtained from pasture if manuring, is made favourable only for that portion which forms at most one-quarter of the surface. In that case, three quarters of the surface remains underfed, as the indirect feeding of the grasses with nitrogen by the leguminous plants seems to take place only to a very limited extent.

More of the flesh-forming element is formed by manuring grasses directly with nitrogen than by encouraging clovers. Jt seems evident that a pasture of which three-quarters is being suitably fed, and the remaining quarter is not being fed suitably, must vield a better result than if a method be followed which from the outset renounces the suitable feeding of three-quarters of the plants.

Cows Fed On Apples. Increased production is claimed by a Jersey breeder, Mr H. J. Forneau. of Fako.vhai, •as the result of feeding apples to his dairy herds. He mixes a suitable concentrate, such as bran, and lie lias not had any trouble with feed flavours in cream.