FROST AS A,FERTILISER.

Otago Witness, Issue 2416, 28 June 1900, Page 4

FROST AS A, FERTILISER.

All agricultural experience points to the value of frost a f s an agent whereby the fertility of the soil is increased. Hence the philosophy of early ploughing in such a climate as that of the south of- New Zealand, where the frosts are severe enough to jerfonn their valuable work. The forces of Nature operate by such imperceptible degrees in some directions that they are only detected by the accumulated result. Frost is one of these agencies, and it is only after the soil has been turned up in furrows by the plough for some time that the magic effect becomes apparent. Frost is far more effective in a climate subject to alternate freezing and thawing than Avhere the soil is frost-bound throughout the winter. Nowhere is that fact clearer brought out than when the different results are noted between Canada and the northern United States. Over the greater portion of die wheat-growing area in Canada the surface -soi] and deeper subsoil are frozen to a considerable depth for months at a time, and in the great North-west the subsoil never thaws even in the brief hot summer. A few inches of the surface thaw, and under the influence of the hot summer sun wheat grows and ripens admirably, the roots being kept watered by the thawing under soil. But, c'early, cultivation under such conditions cannot go on continuously, for the limited depth of soil brought into play will soon become exhausted, and future crops can only be grown at the expense of manure. The soil soon fails from the using up of its potash or phosphates, which hcive to bs made good by artificial means. In the milder States of the Union," however, the wheat lands are much more fertile in point of duration, if not so rich at the start. Alternate freezing and thawing has a marked effect upon the less yielding elements in the soil, which effect is accelerated when the soil is exposed, as in the upturned furrow, to the full force of the disintegrating influence. The combined force referred to is one of the most potent agencies in Nature, even the hardest rocks being shattered by it, and the " eternal hills ' rendered mutable. The evolution of soil shows the important part played by the disintegrating action of the elements. The firm rocks are shattered by frost, and the broken fragments soon undergo further comminution from the rending effects of the same agency. The finer particles carried down from the hilltops by rains and streams of water are distributed over the level lands to enrich the soil with potash and phosphates. The&e all-impor-tant elements in fertile soil have all been derived from that source, >and when the soil has originally come from some one of the older series of rocks, geologically speaking, the soil is correspondingly"rich in potash and phosphates. When the frost can get at the soil the elements of plant food contained therein are liberated. The tearing down effect of frost is due to well-known natural laws. As is generally known, just at the moment of freezing water expands, or at any rate a pound weight of ice occupies more space than a pound weight of water ; or, conversely, a cubic foot of ice crystals weigh, less than a cubic foot of water. The moist plough furrow is filled with ice crystals when the land freezes and is in consequence swelled to greater size. When a thaw; pomes the furrow;

shrinks again to its normal size. The alternate expanding and contracting thoroughly pulverises the soil until it becomes loose and friable, and the oftener the process is repeated the finer the soil becomes. From this circumstance the wheat lands in the milder temperate region of the United States retain their natural fertility much longer than similar lands in the colder north. The climate of Otago and Southland is an ideal one for frost to get in its work to the best advantage during winter. The only trouble is that some winters are so open that we do not get enough of frost. However, the present winter has mode a very good beginning, and any farmer who had his land turned over early will reap the benefit of his forethought noxt harvest. Where the frosts are good, with favourable thaws between, a partially-exhausted soil is often enriched by deep ploughing, even though the subsoil turned Up is cold tenacious clay. The latter generally holds imprisoned rich elements of plant food which are set free by ths frost. Even the etiffest clay will crumble to powder under the powerful influence of a winter's frosts, and when harrowed into the contiguous soil in spring-'-tims it paits with its fertilising agents. In some parts of the world burnt clay is used to enrich poor soil ; but frost does its work quite us effectively as fire when long enough in operation. The Canadian farmer is not able to take advantage of the fertilising power of frost, since he has to plough, sow, and reap his "corn all within the ppice of six months — between the timo when the land tiiaws in spring-time and when it is sealed up again in autumn. The real value of frost, is not appreciated as it oiiglit to be b^; our farmers, or eke more cf the land would be ploughed before the froKis properly set in. Our winters are usually so mild that the whole winter season is considered suitable for ploughing, and this all-important work- is as often as

not left over till the early spring-time. In Canterbury, where autumn wheat "'s sown the ploughing has t(\ba put in hand as soon after harvest a& possible ; but where spring wheat and oats aro grown there is no pressing need for early ploughing, and so the work is neglected. The advantages of e-°-rly I ploughing are so great that the farmer who [ fails to see its utility is quite behind the times. The finely-pulverised soil breaks readily under the horrows in spring-lime, and much time arid labour is saved ; but when the' ploughing is left over till ppringI time disc harrows and the grubber have to be brought into play, and even after all j the costly labour the soil is not nearly | so fine. When the soil- is exposed to the, frosts c± winter throughout its duration the farmer will find that less manure will I be required, so that early ploughing meaiis a great saving in time and money, both ■ of which are of prime import? ".ce. We • might employ plenty of other arguments, but sufficient has been written to establish the value of frcst as a fertilising agent.