CLOSE GRAZING.

Manawatu Standard, Volume LVII, Issue 217, 13 August 1937, Page 5

CLOSE GRAZING.

EFECTS ON PASTURES.

The effects of rotational and continuous and close grazing on pastures were discussed by Mr W. A. Jacques, of Massey Agricultural College, during the course of a paper on tho effect of intensity of defoliation on tho root development and production of some pasture grass species, at the annual conference of the New Zealand Grassland Association at Dunedin, yesterr day.

Mr Jacques said that the effect of even one defoliation on the root system of plnnts was measurable. If the defoliation was continuous then the root was permanently starved and was unable even to mnitnain itself, so that a decrease in size took place, the reduction being in proportion to the rate of defoliation. Where the defoliation was severe and continuous the balance between root and .shoot was so upset, and the drain of food so strong in the direction of the leaves, that the plant died

In rotational grazing, though the amount of leafage and nutrients removed per acre was greater than that removed from a similar area where uncontrolled grazing was practised, yet there was abetter root system. The reason for this was that whilo the balance between root and shoot was upset at grazing, yet the rest period was sufficiently long to allow * ol ' recovery and replacement of the shoot, and the root was able to extend and collect food reserves. The balance between root and shoot weight was not a fixed one, but varied with the season and soil. However, undor any set of environmental conditions there was always an urge within the plant to revert to the most suitable balance whenever it became upset thus when the leaf area was reduced the root volume was also reduced. The vigour of the root systom was reflected in the increased vigour of the tops. With continuous and close grazing there was a continual reduction in photo-syn-thetic tissue, with the possible exception of short periods when the growth got awav from the stock. There was thus little food available, and no time between grazings to permit a strong root growth. The balance between root nnd shoot under the.se conditions was governed by the reduced shoot area. Furthermore, after such treatment had extended over a period, root food reserves were exhausted and the stunted root was unablo to maintain its rate of food supply to the leaves. Thus was set up a vicious circle, firstly, of un-der-nutrition of tho roots, which was lator reflected in a reduced supply of water and salts to. Hie shoot. Both parts of the plants suffered and were unable to produce to their fullest capacity under the existing soil fertility and climatic condi--1 There were many instances in pastoral farming in this country which pointed to the inability of tho grasses which had been sown' to withstand such rigorous crazing, and tlieso had died out to give place to weeds or low-produeUon grasses, of which Danthonia was tho best example. It was a starvation process which had been definitely unprofitable with stock and was equally unprofitable with pastures The fullest use could not bo madeof the soil when plants were kept with a restricted root system nor was it feasible that tho overgrazed plants would withstand drought conditions so well as under a more lenient system. ~ Further trials were needed beforo it was possible or safe to say which wore tho most suitable grazing conditions for the development of tho best root growth, but a rotational grazing system which permitted tho fullest leaf development consistent with good pasture control would appear to hold out tho greatest possibility for an improvement of pasture production.