Agriculture, Dainging., &c.

Taranaki Herald, Volume XLIV, Issue 10477, 30 November 1895, Page 4

Agriculture, Dainging., &c.

HINTS TO FARMERS. ELEMENT OF PLANT FOOD IN SOILS.

Soil to be fertile must contain the elements ef plant food in such forms that they can be readily used for the nutrition of vegetation. At the same time its condition must not be too loose, else a firm hold will not be afforded to the roots of plants, and there will be too much drainage and evaporation. Nor must it be too heavy and plastic, for then air and water could not freely permeate it nor the roots extend themselves beyond a very limited area. Generally speaking, light loose soils are not so rich in plant food as those in which clay predominates ; yet, on account of their excellent condition of tilth, they often yield in favorable seasons heavier crops than the latter. Stiff heavy clays, though rich in inorganic plant food (potash and phosphoric acid), are often poor ia nitrogen, while their condition is such as to prevent thorough aeration and the penetration of tho roots. It is these soils especially that are benefited by drainage. By a system of drainage the water which saturates the surface soil i 3 carried off, air allowed to permeate, the whole rendered more friable and easily worked, and much plant food is converted into assimilable forms. Where sand largely predominates the soil is not retentive of moisture and fertilising material especially if the subsoil be light, and though easily worked is not so desirable in dry seasons as a heavier soil. A proper proportion of sand and clay, therefore, for many reasons makes the best soil. With the clay and Band varying amounts of peaty matter or humus (derived from the decomposition of vegetable matter) and of calcareous matter (principally carbonate of lime), are usually associated, and aright proportion of the two latter exerts a beneficial influence upon the tilth of a soil. The moat important in organic constituents of a seil are potash and phosphoric acid. These, together with nitrogen, are known as the essential elements of plant food. Potash — derived principally from tha decomposition of granite rocks — exists chiefly in combination with' •ilica in a more or less soluble condition. The limits of pofash in a soil lie between a mere trace and about 2 per cent. A good agricultural soil contains between 0.25 and 1 per cent. Clay soils usually are the richest in potash. PotasK as a fertiliser is of special value to clover, peas and other leguminous crops ; potatoes, beets, cabbage, grasses, and leafy plants in general, are also benefited by it. It should form a large part of manures for orchards and all fruit tree. Phosphoric acid, combined principally with lime, is found in all fertile soils. Like potash it has been derived from the rock that originated the soil, and consequently is not constant in quality. It never exceeds 1 per cent, even in the richest soils, and the average in good soils is about 0.2 per cent. It benefits chiefly root crops, and in conjunction with nitrogenous manures is very effective for the cereals, promoting an early maturity and an increased yield. Of the inorganic elements of minor importance lime is the principal. It affords food directly to the plant, and liberates in the soil potash and nitrogen, pre-existent in insoluble forms. Many consider that less than 1 per cent, shows a soil to be deficient in lime, and, <calcareons soils are almost invariably fertile. Nitrogen is the clement of value in the organic portion of a soil. It there exists, for the most part, in forms from which it can be but slowly absorbed by plants. By a process of fermentation, known as nitrification, it is rendered assimilable. The presence of lime appears to assist in this useful operation, especially when the ground ia sufficiently open for the ajr to permeate it. Moisture and warmth are also necessary to encourage the growth of the macroscopic ferment, which causes the formation of nitrates from nitrogenous material. Very rich soils contain from ).6 to 1 per cent, of nitrogen j good fertile soils possess on an average from 0.15 per cent, to 0.25 per percent. An excess of nitrogen, however, promotes undue rankness of growth.