EFFECT OF MANURES ON HERBAGE.

Otago Witness, Issue 3403, 4 June 1919, Page 10

EFFECT OF MANURES ON HERBAGE.

Comparatively little has been done in New Zealand in the way of fertilising pasture lands. The customary method in a new country is to go on delivering the products —wool, meat, and milk —until there is a marked diminution in the land's carrying capacity. Less wool, in spite of better breeding, smaller sheep and cattle, a lower . output of dairy products per acre, arid so on, is the tale of far too many areas. So, too, with our arable lands, object-lessons of the dire need of agricultural education, and generous expenditure on experimental farms. Certain definite practical conclusions have been deducted from work of an experimental nature in other lands. For instance, _in respect to permanent pasture, the important constituents, nitrogen and phospheric acid, can be supplied in larger quantities than they are removed by crops; the application of dung not only compensates for much of the exhaustion from the removal of hay, but it has a beneficial influence on the botanical character of the herbage, when grass is not mown, but fed the exhaustion is much, less, but it is greater when consumed for the production of milk than for that of store or fattening increase, etc. Under the heading, " Pasture Problems: ,the Response of Individual Species Under Manures," Mr R. S. Stapleton, M.A., contributed to the Journal of Agricultural Science an article containing information which gives some valuable hints on the use of fertilisers on grass lands. For instance, it is pointed out that perennial ryegrass and cocksfoot have strong avidities for inorganic nitrogen, bent has a considerable avidity for ammonium sulphate, erect brome has an avidity for potashsalts. Rough stalked meadow grass and smooth stalked meadow grass have very strong avidities for nitrate and ammonium salts respectively. The remarkable avidity of the leguminosae for phosphatic manures, especially of Dutch clover for basic slag, is somewhat exceptional. This suggests a twofold action on the part of basic slag (on those soils where it is specially successful). In the first place the clover responds on account of a marked avidity for phosphates; _in the second place the slag, in its capacity as ef soil-controller, modifies the habitat in a direction even more favourable to this plant. Reductions of species under manures are more often to be explained by indirect than direct influences. It has been shown that reduction of perennial rye is directly due to interspecific competition. Large reductions of bent under basic slag (which are not universal) are almost certianly due to the combined influences of interspecific competition and soil control. Inorganic nitrogen, however, would seem to have a depressing influence on clovers (which may be reduced even -when standing at their minima). The most striking effect is that of ammonium sulphate—especially with mineral dressings—on certain -weeds, such as ribgrass, buttercups, daisies, etc., which it reduces even when near their minima. On the application of the dressing the comparatively few species, which may have a marked avidity, or the reverse, for the substances added, will rapidly increase or decrease, as the .case may be. Interspecific competition is thus awakened, -with the result that the far larger number of species, Avithout any marked wartiality towards the substances added, will readiust themselves in relation to their cardinal figures rather than in relation to the "altered availability of any particular plant food or plant foods.