EFFECTS OF LIMING ON LAND.
The effect of liming in “softening” land or in rendering it more susceptible to poaching is well known for many years and there is a simple explanation for this effect. Liming improves soil fertility by rendering the major elements such as phosphate, potash and nitrogen more available. Nitrification resulting in the release of nitrogen will occur efficiently only in the presence of adequate lime which renders the soil reaction suitable for bacterial action resulting in the release of nitrogen.
The higher level of fertility resulting from liming and the direct effect of lime itself encourages the more superior leafy grasses which replace the more fibrous rough species which are less palatable and which tend to form a protective mat on the surface of the soil. When these rough species (agrostis and bent grasses) are replaced, the mat which they form is no longer available on the surface of the soil. The superior leafy grasses are less fibrous and normally are grazed bare (to surface of soil) leaving no protective fibrous mat and in consequence the soil surface is not protected and is cut up readily in winter by the hooves of cattle. The extent of this “cutting up” or “poaching” of the soil will of course depend on soil texture and drainage and will be worse on the heavier less well drained soils than on the higher free-draining soils. So obviously the extent of poaching will depend on the type of soil. It will also depend on the rate of stocking and the duration of stocking. Intensive stocking can lead to extreme poaching resulting in a condition similar to that achieved by cultivation or ploughing.
The effects described above are aggravated by the application of fertilisers, which add nitrogen, potash and phosphate directly to the soil resulting in a rapid build-up in fertility. Under the resulting more fertile conditions grass growth is more prolific and less fibrous and consequently poaching is more severe because the luscious growth is grazed more efficiently and there is less chance of a protective fibrous mat to protect the soil. Increased nitrogenous manuring in recent years has resulted in a much greater tendency to poaching. As high fertility is essential for maximum output it must be maintained. In these circumstances the only way to counteract poaching of the soil is by suitable management. This means controlled grazing and resting of fields and the provision of silage and suitable fodder for yarding of cattle during periods when severe poaching may occur.
M. J. BARRY
Department of Agriculture and Fisheries
22 Feabhra, 1973.