Management of Poaching Soils
By
C. WALKER,
Assistant Fields
Superintendent, Department of Agriculture, Palmerston North.
TN various parts of New Zealand "*■ the heavier and more fertile
soils, because of fairly-high rainfall, are subject to severe poaching during the wetter months. This is particularly the case during late winter and early spring, when the soils are normally well saturated with rainwater and appear incapable of discharging it at a sufficiently-rapid rate by normal means to maintain solidity near the surface.
SOILS that fall into this category are the various marine silts, the heavier meadow soils, and the stiffer clay loams, all of which absorb water freely and have the power to retain considerable quantities, but do. not possess those desirable features of drainage which enable other and lighter soils to discharge such surplus water. In districts of relatively-high rainfall where these soils occur it is not uncommon to find them poaching very severely. Poaching is a problem which is sufficiently widespread to warrant consideration not only of the causes, but also of the remedies. Each year quite large areas of good pasture in parts of North Auckland, on the Hauraki Plains, in parts of Manawatu,
and in Southland are badly mutilated by stock during periods when the land is excessively wet. Drainage the First Requirement Any reduction in the tendency of soils to break up badly under stocking is dependent almost entirely on the removal of sufficient water to enable the soil to remain firm enough to carry stock. This can be achieved by a suitable drainage system and drainage alone can do more in this respect than any other method or combination of methods which might be advanced as a means of overcoming the problem. To reduce soil soaking to a minimum it is of paramount importance that water should be disposed of as rapidly as possible after its precipitation as rain.
Drainage, then, should be the first consideration. Drains may be of several types to suit varying soils and conditions. In the main good underground systems of tile or mole drains, or a combination of both, will be more efficient on heavy soils which poach than will the open type of drain. The advantages may be summarised as follows: — 1. They provide more efficient drawoff of surplus water. 2. They do not interfere with cropping, cultivation, or stock movement. 3. They do not require double fencing and so do not provide a haven for weeds and pests. 4. Valuable land is not taken out of production. 5. Annual maintenance by cleaning, etc., is eliminated. Considerable areas of Manawatu and Southland country have been greatly improved - by underground drainage systems and it is fair to assume that even greater production could be expected from an intensification of this work on the same country. Despite the decided advantages of enclosed drains, it is not possible to dispense entirely with open systems. They are necessary usually as main drains for conveying the discharge from tile or mole drains, or they may be required as alternatives to these closed drains on country that is quite unsuited for the latter. Thus on the marine silts mole drains have an extremely short life and tiles tend to silt up within a year or so, so that the open drain is of first importance in removing surplus water. Because their sphere of influence will not extend very deeply into the fields, open drains should be placed so that they can receive minor feeder drains at short intervals.
In general 'the feeder drains within fields should not be very deep, nor should they be steep sided. Many areas are adequately served by gentlygraded depressions, not more than Sin. deep and about 4 to 6ft. wide at the top. Such channels grass over and do not impede the movement of implements.
Where steps have been taken to remedy any drainage problems that might be assisting poaching it can be expected that a material improvement will take place in the ability of the soil to withstand normal winter stocking. Nevertheless, even with the best of drainage, soils will tend to cut up under conditions of excessive rainfall and winter stocking. What, then, are the additional remedies?
Discing and Reseeding
Land that still poaches will. dry out with an extremely rough surface and a broken turf which will permit weeds to establish. The rough surface .will be difficult, to stock and extremely damaging to implements. A not uncommon method of handling these rough areas was to disc them down in spring as soon as they .were dry enough and sow them -over with a grass mixture to build up the sward, but the treatment had certain defects. Land which poaches easily will also dry out very rapidly, so that only a limited area on each farm can be treated before the soil is too hard'for discs to be effective. Further,.. the seedlings which germinate have to contend with hot, dry conditions that do not permit them to compete successfully with other plants such as the remaining grasses and clovers and the almost inevitable crop of buttercup, pennyroyal, etc., which follows the breaking of the turf.
On the whole, the discing and regrassing treatment cannot be recommended because the probability of success is so slight and the risk of weed invasion is too great.
Grading into Lands
An . alternative practice to . discing and resowing has been to grade fairlylevel areas into lands, thus providing a watershed and shallow channels for the disposal of rainwater. These lands may be established either by ploughing or by grading in shallow channels at intervals. The. material, moved to make the channels should be graded back to form a mid-line ridge between channels so that-water is turned into them. ■'' ■ ' . '
One of the chief defects of this system is that it limits the establishment of subsequent undergrounddrainage systems, particularly mole drainage, because the surface levels are destroyed. Further, cultivation of the surface almost invariably brings in the first year prolific development of buttercup, on the ridges while a few years later the depressions between lands become full of rushes and inferior grasses or water weeds.
On the whole grading into lands is not entirely satisfactory. Certainly it may give better run-off over most of the land, but it will lead to the proportion of a field taken up by depres-
sions being wet, low yielding, and still subject to poaching, even to an aggravated degree. Rolling of Swards Of more recent years, and principally because of the failure of discing and grading into lands to produce a remedy for poaching, consideration has been given to rolling as a means of restoring broken swards to a reasonable level of efficiency. Whether rolling coupled with good drainage can be the complete answer to the problem depends upon an appreciation by the operator of what rolling should aim to achieve and how that condition can be attained. Undoubtedly nothing more is required than the restoration of a continuous sward on the field sc
that every square foot is growing useful plants and there are no turf breakages which will permit weeds to flourish. To get this condition it has to be appreciated that the softer the soil the more readily will it come together. Further, by working when the soil is very soft only the lightest. of rollers will be required to bring about the desired condition. In practice many farmers in the past have done considerable damage to swards by using rollers of such a weight that they have simply buried the pasture.. In other cases those with excessively heavy rollers have been. unable to commence work until the land had dried out too much so that both the efficiency, and extent of their work have suffered. \
Judged by results it is obvious that on really wet country a light Cambridge roller will do an excellent job of restoring pasture and improving the surface. By “ironing out” the land all water lodged in hoof marks is brought to the surface, where wind and sun can do valuable work in removing it. Rolling should be followed by a spell from grazing of about three weeks to enable the surface to dry out and consolidate. The advantages of rolling in dealing with the problem of poaching are very apparent: A uniform sward is maintained, weeds have little opportunity of establishing, no reseeding is required, no grading or other disturbance of surface levels is necessary, and the work can proceed while the land is still very wet. - . While a case has been made for the rolling of poached areas on very heavy land, its usefulness is by no means restricted to these areas. Light, porous soils are also likely to cut up under winter and early-spring . stocking and while this takes place the rooting systems are disturbed and exposed. If these are left in this condition until dry weather sets in, affected plants will wither away and leave gaps , in the sward. If on the other ' hand the sward is rolled, the plants will be pressed back into position where they can root afresh and become useful constituents in the pasture. Summarised, then, the first essential on all poaching areas is a sound drainage system to reduce the water content of the soil. Whether this is an underground or an open system will depend upon circumstances, although the former, if practicable, is infinitely better for reasons already stated. Finally, provided drainage is efficient, and poaching has still to be offset, it is much more effectively handled by rolling the wet land than by discing a drying surface or by grading the country into lands.
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Bibliographic details
New Zealand Journal of Agriculture, Volume 78, Issue 4, 15 April 1949, Page 365
Word Count
1,602Management of Poaching Soils New Zealand Journal of Agriculture, Volume 78, Issue 4, 15 April 1949, Page 365
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