The influence of season and of the application of lime on the botanical composition of grassland herbage

Summary. The botanical composition of the herbage of grassland under constant manurial treatment varies considerably from year to year. With complete fertilisers including nitrogen and minerals the relative proportions of the three main groups of species, i.e. grasses, leguminous and miscellaneous plants, are not usually much affected by season, though the individual species do vary, but with one-sided fertilisers and on unmanured areas wide fluctuations occur in the percentage of these groups. No correlation can be traced between the annual variations in the yield and the botanical composition of the herbage, except for some suggestion of association between high yield and high percentage of leguminous plants with long-continued mineral manuring. The variations of individual species occur on all plots. They may be caused by direct or indirect response to season and are much influenced by the type of manuring. It is often difficult to determine whether a marked increase or decrease of a species in any year is due to climatic conditions being beneficial or detrimental to that particular species. It may be that the real effect is on other constituents of the herbage which change so much that the proportion of the species under consideration is radically affected [cf. Alopecurus in 1922). In some cases, especially with organic fertilisers, the main groups and also certain species [as Alopecurus, Arrhenatherum, Dactylis] show a tendency to rhythmic changes with season, rising and falling over a period of years. In other cases the fluctuations are more abrupt and irregular, sometimes being exaggerated in the presence of lime. The application of lime to plots with long-established manurial treatment does not affect the balance of the three main groups with complete fertilisers, but with one-sided manures a definite bias in one direction appears sooner or later. Individual species usually respond to lime at once, showing a change of proportion at the first succeeding cut, but under certain soil conditions a delay may occur until a second dressing has been given. It would appear that the maximum effect of liming is reached within a few years from the first application, after which fluctuations with season may again become more obvious. Shade is also a factor which influences the balance of species in herbage. The available data is limited to a single plot, but indicates that certain species may be greatly increased or decreased as a result of shading, whereas the proportion of other species may not be affected.