DISC HARROWS.

King Country Chronicle, Volume XXXIII, Issue 4815, 26 July 1939, Page 3

DISC HARROWS.

SUBSTITUTE FOR PLOUGH. AN INCREASING PRACTICE. A practice which is receiving attention and increasing in popularity is the use of the disc harrows instead of the plough when cultivating a field previously in turnips or chou mollier for sowing out in grass, says the Otago Daily Times. By this method a variety of purposes is achieved. In the south the bulk of turnip crops are fed off where they are grown, with the result that valuable animal residues, are deposited at surface level, enriching the fertility of the surface layer of soil. Should ploughing be resorted to, this surface fertility is buried to such a depth that it is of no use in promoting quick pasture establishment, and of little use to the majority of surface-rooting grasses and clover.

Not only does this occur, but the ploughing also has the effect of removing from the surface soil any lime which has been applied before ridging swedes. Many farmers in the south now make a practice of applying a ton of ground limestone before sowing swedes or turnips, as this assists in the control of club-root, and, being slow-acting, it has sufficient time to be of use in promoting quick and vigorous establishment of clovers and grasses sown following the swede crop. Ploughing has the effect of removing the lime, which in any case has a natural tendency to percolate through the soil to a level at which it is of little use.

Further, in areas which are subject to grass grub attack, it is apparent that the degree of consolidaton of the soil is associated with the severity of attack. This contention is upheld by the fact that young pastures—i.e., those with the soil as yet unconsolidated—are more susceptible than older pastures, and that loose and open soils on the same farm and in the same district are more subject to grass grub attack than stiff clay soils.

Ploughing, followed by even the most effective cultivation, does not provide nearly as good consolidation as does the disc harrows, which merely penetrates the top two or three inches of the soil to provide a firm, fine seedbed with a firm subsoil. This is more prone to attack by subterranean caterpillar than to the grub of Odontria or "brown beetle."

In the cases of a crop of swedes being sown on a field ploughed out of old pasture, such as browntop, little decomposition of turf occurs in the period during which the swede crop is growing, with the result that ploughing subsequent to the swede crop often brings up this turf which is difficult to cope with satisfactorily. Swede and chou mollier crops are with the resultant germinating and killing of weed seeds in the surface soil, so that a fairly weed-free surface is present, which is retained largely by discing, whereas ploughing bring up a new supply of weed seeds to be dealt with.

Generally speaking, the requirements of a good seedbed are fineness, firmness and freedom from weeds, and these necessities can be adequately provided by disc harrowing after swedes, turnips or chou mollier.