Taller Pasture Plants To Yield More In Droughts

Press, Volume CII, Issue 30289, 15 November 1963, Page 22

Taller Pasture Plants To Yield More In Droughts

(New Zealand Preu Association) PALMERSTON NORTH, November 13. Some revolutionary suggestions for the future development of New Zealand’s pastoral industry were made by Dr. K. J. Mitchell, director of the Plant Physiology Division, at the annual conference of the Institute of Agricultural Science in Palmerston North today. He suggested the replacement of present pasture species with taller-growing, higher-yielding plants; the use of tall, possibly twining legumes, or even cheap electric energy from Te Anau, to fix nitrogen in the soil; and “cut-and-carry” feeding of stock instead of direct grazing of paddocks.

'Tor several decades,” said Dr. Mitchell, "this country has developed an extremely efficient system of pasture production and utilisation, but as ever-increasing calls are made on it for higher production, its limitations are becoming increasingly apparent. No doubt our maximum economic effort in the years ahead should go toward realising the potential from the pastures we have. But we would be very wise to look closely at the possibilities of alternative systems for turning our climatic resources into feed for livestock, or, for that matter, into other saleable products.” Particularly in the North Island, there was a trend toward management procedures which were, in effect, creating a Mediterranean type of climate for pastures. In winter, there was adequate moisture, but in summer, the considerable heating which could occur during sunny days accelerated the creation of a hot dry surface, and as pastures generally were not very efficient at drawing moisture from a considerable depth, extended periods of moisture shortage in summer and autumn quickly developed. This meant a large part of the year’s potential production was thrown away by encouraging drought restriction on pasture growth in summer.

Current Practice Where low-cost, year-round feed for stock in the paddocks was the prime objective, this would generally be of little consequence. Under these circumstances, it became more important to get a small percentage of extra growth in winter than it was to be further embarrassed by an excessive growth in late spring and possibly summer. “However, I would seriously suggest that we are within sight of a time when the gains from this approach may be out-weighed by the losses we suffer by, in effect, deliberately throwing away a high proportion of our total annual growth potential,’’ he said.

With present information, it was becoming practicable to define the types of growth form which had good potential for maximum efficiency in converting New Zealand's climate into the greatest quantity of utilisable, good quality plant material. A structure of vegetation which would appear to meet the various requirements would be one in which moderately small leaves were distributed over a wide zone of height—preferably several feet. Vegetation of this form would be adapted to make efficient use of the light by spreading it as evenly as practicable and a larger leaf area. It should give relatively good ventilation around the leaves from which would come reliability of supply of carbon dioxide, and the minimising of the build-up of excessive humidity around the leaves after rain during the summer months. Both its wide spread of light-intercep-tion and satisfactory ventilation should largely eliminate the rapid rises of temperature above the surrounding air, which have very unfavourable effects on the efficiency of utilisation of moisture. It would also be expected to have bigger and deeper penetrating roots which would lessen the resistance involved in drawing moisture

from deeper layers of soil, and, in effect, make a considerably larger reserve of soil moisture available to it. Yield Estimated "Present evidence which includes measurements of yields achieved in the field in New Zealand, indicates that a stand of vegetation with this type of structure and with the same temperature response characteristics as those of perennial ryegrass can be expected to give a ceiling potential for growth of over 40,000 lbs of dry matter an acre a year,” said Dr. Mitchell. “That is approximately double the ceiling potential which we can estimate for a pasture made up of the conventional species.” Discussing the question of where suitable plant species could be sought. Dr. Mitchell said: “A very considerable proportion of the North Island was originally clothed, not in a Mediterranean type of vegetation nor in a north-west European type of vegetation, the areas from which our present economic plants largely originate. It was clothed in sub-tropical rain forest with close generic connexions to the flora of the Indonesian and Malaysian area.

“The presence of such flora indicates that its structure is in large measure achieving efficient utilisation of moisture during the summer, and the many other advantages that flow from that. "We are thus left with the thought that it may pay us to turn to such areas in the east, not only as new markets for our animal produce, but also as sources for the plant material which we could be using in the future for producing that animal produce.”