GRAZING ON PASTURES

Waikato Times, Volume 121, Issue 20284, 28 August 1937, Page 26 (Supplement)

GRAZING ON PASTURES

EFFECT OF DEFOLIATION. STARVATION OF ROOTS. f The effects of rotational and continuous and close grazing on pastures was discussed by Mr W. A. Jacques, of Massey Agricultural College, during the course of a paper on the effect of intensity of defoliation on the root development and production of some pasture grass species at the annual conference of the New Zealand Grassland Association at Dunedin. Mr Jacques said that the effect of even one defoliation on the root system of plants was measurable. If the defoliation was continuous then the root was permanently starved and was unable even to maintain 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 practiced, yet there was a better root system. The reason for this was that while the balance between root and shoot was upset at grazing, yet the rest period l' was sufficiently long to allow for recovery and replacement of the shoot, and the root was able to extend and food reserves. The balance between root and shoot weight was not a fixed one but varied with the season and soil. However, under 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 system was reflected in the increased vigour of the tops. Balance Between Shoot and Root. With continuous and close grazing there was a continual reduction in photo-synthetic tissue with the possible exception of short periods when I the growth got away from the stock. jThere was thus little food available, and no time between grazings to permit a strong root growth. The balance between root and shoot under these 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 unable to maintain its rate of food supply to the leaves. Thus was set up a vicious circle, firstly of under nutrition of the roots which was later reflected in a reduced supply of water and salts to the shoot. Both parts of the plants suffered and were unable to produce to their fullest capacity under the existing soil fertility and climatic conditions. 1 There were many instances in pastoral farming in this country which pointed to the inability of the grasses which had been sown to withstand such rigorous grazing, and these had died out to* give place to weeds or low production grasses of which Danthania was the 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 be made of the soil when plants were kept with a restricted root system nor was it feasible that the overgrazed plants would withstand drought conditions so well as under a more lenient system. 1 Further trials were needed before it was possible or safe to say which were the most suitable grazing conditions for the development of the best root growth, but a rotational grazing system which permitted the fullest leaf development consistent with good pasture control would appear to hold out the greatest possibility for an improvement of pasture production.