Grass Productivity

Andre Voisin

• Éditeur: Island Press
• Année: 2013
• ISBN:
  9781610912730
• Sujet: Business
• Sous-sujet: Business General

Grass Productivity is a prodigiously documented textbook of scientific information concerning every aspect of management "where the cow and grass meet." Andre Voisin's "rational grazing" method maximizes productivity in both grass and cattle operations.

PART ONE

THE GRASS

Chapter 1

WHAT IS A HERBAGE PLANT?

Cutting and successive re-growth

A pasture plant must be capable of growing again after it has been cut either by the tooth of the animal or by the blade of the mower.

When this plant is cut it retains very little, and sometimes indeed hardly any of the green aerial part capable, by photosynthesis, of creating the elements necessary for the formation of new plant cells: that is, for the initial re-growth of the plant.

It is therefore indispensable that the plant, at the moment when it is cut, should have, in its roots or at the foot of its stalks, sufficient reserves to allow the formation of a certain green portion which, by photosynthesis, will then permit the normal growth of the plant.

Every new growth, that is to say every re-growth of our herbage plants, takes place at the expense of the organic substances elaborated previously (before cutting) in excess of what was necessary for the maintenance and growth of the plant. These substances have been stocked in the roots and lower aerial portions. If one cuts the plant before the roots and the part not cut have stored up sufficient reserves, re-growth will be difficult and may even not take place at all.

There is a period in which wheat can be grazed without being destroyed

This evolution of reserves in our herbage and forage plants is a question which, unfortunately, has been very insufficiently studied by plant physiologists until now. We know very well that there is a moment in the course of a plant’s development when the reserves in the roots are at their maximum and when, in consequence, the conditions for re-growth are optimum. Take our old graminaceous friend, wheat. Grazing wheat as it emerges from the soil destroys it. At harvest-time, when we cut the wheat with its grain formed and ripe, the stubbles of our fields do not produce re-growth. On the other hand, between these two extremes there is a period in which it is possible to graze the wheat and yet allow it to grow again and thus produce a reasonable harvest.

Definition of a herbage plant

We will therefore answer the question asked at the beginning of this chapter by stating that: A herbage plant is a plant which is capable, several times in the course of a year, of accumulating in its roots (and at the foot of its stalks) sufficient reserves to allow it to grow again after every cut.

Let us look quickly at a few points concerning the evolution and nature of these reserve substances which are indispensable to the re-growth of the grass, after cutting with the blade of the mower or shearing with the teeth of the animal.

Evolution of quantities of reserves in the plant

As Professor Klapp tells us (70, p. 350), the production of green matter by our herbage plants is not a continuous process throughout the period of vegetation; but accumulation and expenditure of substance alternate with each other. At the end of the summer and in the autumn the accumulation of reserve substances (as a result of the production of assimilation products by the leaves) permits re-growth in the ensuing spring, followed eventually by development up to flowering and the formation of seeds. An analogous phenomenon takes place after every cut, if the latter does not kill the plant.

Different plants differ enormously in the time and also in the speed of this assimilation and in the storing up in reserve of the substances assimilated.

Alternating rhythm of accumulation and exhaustion of the reserves

The Polish research worker Osieczanski (82, p. 65) has very clearly summarised this alternating rhythm of exhaustion and accumulation of reserves:

“Part of the products of photosynthesis is immediately utilised for the construction of the cells of those organs of the plant situated above and below the soil. Another part of these products of photosynthesis is used to satisfy the physiological requirements (respiration, metabolism). The remainder of these products is put into reserve for a time when there is no synthesis, or at least when the products of this synthesis are completely utilised to satisfy the needs of the plant organs. These reserves allow the plant to survive critical periods, such as, for example, the winter period, during which the balance of the phenomena of assimilation is negative.

“The reserve substances of grass are utilised for respiration, formation of stalks, leaves, seed, roots etc. and in particular for the respiratory processes at low temperatures (below 32° F. [0° C.]) and at high temperatures (above 85°-95° F. [30°-35° C.]); temperatures at which respiration uses up more energy than is supplied by the processes of assimilation. These reserves will also be utilised during periods when the plant is growing strongly as, for example, during tillering or the formation of seed. This will be the case in particular after cutting or grazing when the grass will have to re-create green surfaces supplying the products of assimilation. . . .”

Nature of the reserve substances

Under identical conditions as regards the quantities, or proportion, of reserve substances remaining after cutting, the re-growth of the same plant can vary greatly, concomitant with such other factors as day-length, soil moisture, amount of assimilable fertiliser elements present in the soil, rainfall, etc.

It would therefore be particularly desirable if we had better knowledge of the way in which the reserves are accumulated in our herbage plants: this would help us to use them more profitably.

At present, however, no firm conclusion has been reached even concerning the nature of the reserve substances. Sullivan and Sprague (102) have published a detailed review of the different theories put forward regarding these reserves. We refer the reader to these authors for this bibliographical review, and also for their study of the reserve carbohydrates of rye-grass (vide also Weinmann, 140).

Can grass build up a reserve of growth hormones?

In general, one considers as reserve substances all the fats and the nitrogen-free extract. As mentioned above, it is essential that the plant contains in its roots and the part not cut the maximum possible of these reserve substances. But these indispensable substances are probably not sufficient. Our herbage plants have also a stock of other substances which allow them to grow away again after being cut. Here, it is probably one or more hormones which allow the growth of the plant to be set in motion once more. R. O. Whyte (144), who is a plant physiologist, reminds us of this in well-chosen words:

“The physiologist studying herbage plants cannot fail to wonder at the remarkably small effect which repeated removal of leaves and damage to tender growing points of the plant has on the physiological behaviour of the plant and on its development.

“It does not appear out of place therefore to put forward a few hypotheses: is it not possible, when a plant goes to seed every year or every two years, that all (or almost all) the growth (or re-growth) hormone is removed in the seed? There would then be no more hormone left to revive the meristematic activity at the base and lead to formation of new tillers. Might it not be that in a h...