The Temuka Leader THURSDAY, MARCH 13, 1884. WHAT FARMERS OUGHT TO KNOW.

Temuka Leader, Issue 1150, 13 March 1884, Page 2

The Temuka Leader THURSDAY, MARCH 13, 1884. WHAT FARMERS OUGHT TO KNOW.

AGRICULTURAL CHEMISTRY. 1 ( Written specially for this Paper.) v. THE COMMON METHODS OF RE-FERTILISING SOIL. Having, in our fonner articles, run over the chemistry of the atmosphere, the soil, and the plant, we are now in a position to understand more clearly the immediate benefits of the ordinary methods employed to fertilise land. A.nd first cf all, we must thoroughly understand bow land becomes exhausted by cultivatior. We have seen how plants take up mineral matter ; how they absorb, through the agency of water, lime, potash,

soda, salt, silica, phosphoric acid, sulphur, chlorine, etc. We, have seen how plantlife is able to decompose carbonic acid, reserving the carbon to build up their structures and rejecting the oxygen. We have seen how plants absorb ammonia (nitrogen and hydrogen), and are capable of producing organic compounds containing these constituents. We seen how all these materials —inorganic, as sulphur, silica, soda ; and organic, as the pro tern compounds are wonderfully adapted to the growth and nourishment of animal life.

Mineral matters are obtained solely from the soil ; organic matters from the atmosphere and the soil. And this fact must be noted, that the requirements of vegetable growth contained in the atmosphere are being constantly supplied to it by the means of animals, and that the necessary Inorganic constituents contained in the soil are not being constantly replenished. In the air we have floating about us gases, nitrogen, oxygen, carbonic acid, and water. These, the plant can lay hold of, and apply to its own uses in building up complex organic compounds ; mineral substances, as lime, soda, phosphoric acid, we have not in the air, but in a fixed state in the soil. Plants, it has been already explained, absorb these inorganic constituents present in the soil by means of their solution in water. The compounds present in the air they absorb by their leaves and other means. Now, when a large crop is grown each individual plant thereof contains so much organic and inorganic material, the former gained partly from the air, partly from the land ; the latter obtained from the soil alone. Hence it is, that in the application of manures, it is chiefly with mineral or inorganic compounds we have to deal. We say advisedly, “ chiefly,” All the compounds used by plant* in their growth are not got from the air but many are absorbed, like the mineral matters, by solution in water. Thus, we have seen that ammonia produced in the atmosphere meeting with the nitric acid also produced there, gives rise to the salt, nitrate of ammonia, and that, this being washed down by the rain, is carried into the soil, there to be re-cissolved in water, and absorbed for use by the plant. Ammonia itself is obtained by plants through solution in watei. Thus, we can only say that organic mateaial is afforded vegetable growth by the air and soil, and that inorganic or mineral matter is obtained from the soil alone.

Now, in all cases where crops are grown and removed from the land it is evident that the land so cropped must be impoverished. To supply the deficiency so created we resort to various means. “ On comparing the constituents of a soil with the ingredients obtained by incineration from the ashes of plants, it is found that plants withdraw from the soil chiefly its alkaline, mineral acid, and earthy ingredients ; and if all these were not essential to the .very existence of plants, they would not, of course, be taken up by them ; and as the plants constituting our cultivated crops withdraw those ingredients in a varied amount, it follows that unless the soils we cultivate contain them in ample amount and variety it will be imposible for the plants placed upon them to arrive at a perfect state of development of all their parts ; for, chemically speaking, and rationally speaking, too, soils cannot be expected to produce crops abundantly, unless they contain a sufficient supply of every ingredient which all the crops wo wish to raise require from them.” (Johnston’s Lecture Agricultural Chemistry.) The following table shows the quantity “ of the more essential constituents of the soil removed from it per acre by a crop of wheat.” The table is extracted from Sibson: Wheat (grain) of 25 bushels. lbs Nitrogen 27.90 Mineral substance, containing Phosphoric acid ... ... 12.07 Potash ... 7.86 Magnesia ... ... ... 3.22 Lim e 89 Other less important mineral substances ... ... ... 1.39 Total matters removed ... 53.33 From these figures some idea may be got of the impoverishment of land consequent on a wheat crop. To replenish this diminution many and great agencies must be brought to bear on the land. Rotation 01? Crops. From what has been said of the removal of various ingredients in the soil by means of crops, it may have been seen that different mineral constituents preponderate in different crops. Thus, if we grow one crop on land year after year, the soil is bound to become exhausted, for the inorganic matters that that crop draws most heavily cn are sure to run out. But suppose that instead of growing the same crop annually on the same piece of land, we raise a different one, then the preponderating inorganic constituents will be different, and the great draw will be on another set of materials altogether. Hence, we have a rotation of crops. This, however, is not the only benefit to be derived from a change of crops. While one crop is being produced the mineral or inorganic ingredients are being augmented ; thus the land drained of one particular class of mineral, may in course of years contain as good a store as ever. Many inorganic materials are present in the soil, but are unfit for use through their insolubility in water, The action of the weather, rain, frost, etc., soon, however, produce a change, and convert the insoluble into soluble compounds, and hence the land is fertilised by nature, and tbe soil may be gaining in fertility between the growth of the same crop. It is due to these facts, that a crop of a different nature from the one preceding can be generally grown on land ; and that the land becomes more fertile for a particular crop, if between several growths, other crops be produced. As an example of an insoluble compound changing through course of lime to a soluble one, phosphate of lime might be cited. As bones (crushed bones) it is insoluble. However, when put on in fine division it becomes soluble, this, however, takes time. The famous superphosphate of lime is readily soluble and thus speedily benefits the land. Another important fact must be noted in connection with this subject. “But apart from the character of the materials a crop extracts from the soil during its growth, its place in a series of crops or a rotation, is regulated by the capabilities and habits of plants composing it, it being well-known that different kinds of plants ere very unlike in their ability to ,

seek their food from the soil and provide for themselves ; soma plants are helpless, so to speak, and languish for want of food, unless it is placed immediately within their reach. Others, again, are indefatigable and industrious in shifting for themselves even under difficulties, and if food is at all to be had, they will search it out and appropriate it. These latter plants are highly useful for collecting together the small quantities of valuable materials scattered throughout a large bulk of soil. Wo may distinguish these as industrious plants, since they are noted for sending out roots to great depths and great distances in the soil in search of the materials required for the fabrication of the seeds and other parts of their structure at the surface. To this tribe of plants belong the clovers and grasses ; hence the improvement in the surface soil that may be effected by laying it down in grass, and the advantage that is gained by the introduction of a grass crop in the aeries of crops of a rotation.” As an example of the inert or lazy class of plants—in contradistinction to the industrious clover and grasses—we might cite turnips and Swedes. Thus these crops—with many other roots—require a well fertilised and conditioned soil in order that they may flourish. These roots need during growth a considerable quantity of phosphoric acid, that they may mature, and hence the great benefit to be derived from manuring land with the very soluble superphosphate of lime. And now a few remarks as to the . Natural -Renovation of Soil.

Soil, when let lie after having been cropped, is well-known to become more fertile than directly after the removal of the crop. Now this fertilisation is accomplished in three different ways ; the first by the accession of nutritive materials from the atmosphere ; the second, by the decay of vegetable matter in the soil ; and the third, by the improvement of the condition of mineral constituents already present. It has been pointed out several times how ammonia is obtained from the air. It is washed down by the rain and carried into the soil, where it becomes fixed. Again humus and clay have the power of absorbing it. This may represent the first method nature employs for renovating land. The roots of the removed crop contain quantities of organic matter, which on decay, affords valuable food for the next crop. As to the third method. We have already seen that mineral matters may be present in the soil and yet be useless, owing to their nonsolubility in water. Should supplies of these useless substances exist, then, rain, frost, and the action of weathering, in course of time, effect changes in them, and they become soluble and thus useful. In thia way stores of plant food may be present iu a soil but yet unobtainable by the plant. The natural course of things brings about changes and the supplies are unlocked. But suppose land has been cropped and cropped till these mineral matters have been all removed ; what is the consequence ? The land is totally unfit for cultivation, and the only remedy is—manures. In our next we pass to the mechanical means of improving land. (To be Continued.)