A COMPARISON BETWEEN THE EFFECTS OF AMMONIUM SULPHATE AND OTHER FORMS OF NITROGEN ON THE BOTANICAL COMPOSITION OF CLOSELY CUT TURF
Authors: BLACKMAN G. E. 
Published: February 2008

In a previous investigation it was shown that the periodic application of ammonium sulphete to closely cut turf could bring about a reduction in the weeds (plants other than members of the Gramineae) without producing significant changes in the soil reaction. Evidence is produced in this investigation that such reduction is due to the direct action of the ammonium ion.

A number of small plots were laid out on a uniform piece of turf and treated, respective1 y, with ammonium dihydrogen phosphate, sodium nitrate, urea, dilute sulphuric acid, and ferrous sulphate alone and in combination with ammonium sulphate. The rate of application of the nitrogenous fertilisers was the equivalenk of the nitrogen in 3 Ib. ammonium sulphate per 1000 sq. ft. (1.2 cwt. per acre). Ferrous sulphate (FeSO,. 7 q O) was applied at 4 Ib. per 1006 sq. ft. and sulphuric acid at the equivalent of the sulphate radicle in the ammonium sulphate. The dressings were made weekly fiom May to September and the applications were “wateredin,” in order to prevent damage by solutions of high osmotic concentration

By botanical analyses made initially and afterwards at monthly intervals the changes in the percentage area covered by each species were followed. It was found that a statistically significant reduction in the “total weeds,”i.e. the sum of the areas covered by all the different weeds, was brought about ody by the ammonium compounds. Although urea and sodium nitrate did not produce changes significantly different from the control, the slight increase brought about by urea was significantly different from. the decrease with sodium nitrate.

The weeds in the sward varied in their behaviow to ammonium compounck. The majority of species, such as Achillea Millefolium, were reduced. On the other hand, Cermtium vulgare increased significantly, but the addition of ferrous sulphate inhibited this increase.

All the nitrogenous treatments produced the same changes in the grasses, the Poa spp. increasing at the partial expense of Fmtuca ovim. With the remaining treatments the grasses did not change.

Determinations of the pH of the soil were made at the beginning and end of the experiment. The figures showed that owing to the high chalk content there were no significant changes apart from a small increase of alkalinity caused by the sodium nitrate.

Since the ammonium compounds have alone produced significant weed diminutions, it seems evident that such reductions must be ascribed to a toxic action of the aqunonium ion. There is evidence from the results of earlier workers that the absorbed ammonium ions combine with carbohydrates or with organic acids. The suggestion is therefore put forward that the differences in the response to ammonium salts of the plants of the turf may be related to differences in the content of such substances. In this view the plants resistant to the injurious action of the ammonium ions, i.e. the grasses and a few of the weeds, should show a high content of available carbohydrate or of organic acid or both. The susceptible planks‐the majority of the weeds– the other hand should show a low content.