SUBSOILING.

Waipa Post, Volume XXIV, Issue 1450, 15 January 1924, Page 3

SUBSOILING.

ITS ADVANTAGES EXPLAINED. Subs,oiling Jo conserve soil moisture is not very extensively practised in New Zealand. Yet in many classes of land subsoiling, or partial subsoiling, would prove highly beneficial. One reason for not practising subsoiling is the relatively heavy expense which it involves. Another rea- . son is that many farmers in possession of heavy land that is underlaid with a hard* retentive subsoil or land that has what is commonly called a pan, do not seem to realise the necessity for breaking up the lower layers of the soil. The former, however, is not very formidable, as an attachment can now be put on to any modern plough, so that the subsoiling and ploughing can be done in the one operation. ’i'his attachment is made in different styles, the choice of which is a matter of indifference, providing the subsoiler does efficient work. Two of the different types of subsoilers that have come under my notice are, first, one that is placed immediately behind the neck of each plough, whether a double or three furrow makes no difference. The other one is bolted across the main beam of the plough, and instead of subsoiling each furrow as it is ploughed, the subsoiler attached to the front plough loosens the bottom of the last furrow turned the round before. While the attachment on the back plough of a double furrow loosens the bottom of the front furrow, leaving the bottom of the last furrow not subsoiled, the latter method has this advantage that the horses walking in the furrow do not pack the stirred soil again as is the case with the former method. Therefore the attachment that leaves the bottom of the back furrow undisturbed is preferable to the one that loosens the subsoil immediately behind each furrow. Whichever of these two methods is adopted, however, they are much less expensive than the old time style ,of subsoiling, when each furrow had to be done separately and the subsoiling plough followed the single furrow. Practically the only extra expense incurred by subsoiling, beyond the cost and wear and tear of the subsoiler, is the upkeep of one or two extra horses according to the depth of work done.

Some argue that subsoiling does little, if any, good after the first season, unless there has been but little rain so that the ground has never been thoroughly saturated, permitting it to settle again together. But experience shows that this is not the case; on the contrary, it has been proved that on certain classes of land, at least, the improvement derived from subsoiling has been permanent. The main reason for this improvement may be attributed to the better regulation of the water supply in the soil. No matter how much plant food there may be in the soil, plants cannot grow without the presence of water. This water is needed for two 'purposes: to dissolve the plant food in the soil, and thereby enable it to enter the plant to contribute to the building of plant tissjie and to he mainenance of the life of the plant. A consideration of the amount of water required by plants in their growth shows why supplying plant food alone does not'" ensure the success of the crop. For instance, the amount of water used for a thirty bushel crop of oats in their development to maturity is approximately 11921 b of water per acre. It can be seen by this that the failure of crops is more frequently due to lack of moisure than to any other one cause, hence the importance of adopting any method that will deepen the reservoir for holding water. Subsoiling increases the percentage

capacity for water of the soil stirred, because when a soil is broken into lumps which lie loosely together and these lumps are saturated with water, the many lumps behave toward that water much as if each were a short column of soil which is in contact with standing water. The surface film of water which opens the pores at the surface of the saturated lump ,of soil has a definite strength, and if the lump is not too large can hold every cavity within that lump completely full of water just as a lump of sugar dipped into water and then withdrawn comes forth completely filled with fluid. But when the soil is compact so that each portion is part of one long and continuous mess extending downward several feet before water is reached, the surface tension of the water is not strong enough to maintain the soil cavities full of water, and a part drains away downwards. Subsoiling allows water to enter the soil more readily because it is only after the sub-soiling layer has become saturated that water begins to percolate through it, and so to store itself in the undisturbed layer below. But when rain enough has fallen to accomplish this result, then whatever else falls drops readily and rapidly through it, not only because there are wider channels for the water to move through under the stress of gravity, but because from an open soil the air escapes quickly and readily, thus making place for water which cannot enter until the space for it has been vacated. With all soils there is a certain amount of water they contain which it is impossible for the roots of plants to remove with sufficient rapidity to meet their needs, and this amount is relatively smaller in the coarse grained soils than it is in those having a finer texture. But wherever any soil has been subsoiled, and its water holding power thereby increased, this extra amount of water becomes wholly available to the plant. And if this amount would have been lost, either by downward percolation or by evaporation from the surface, then the subsoiling has been a decided gain.