Potash Salts are of the utmost service to plants. Carse or clay lands generally contain a sufficiency of potash, while medium and light soils require it to be added. Nitrate, sulphate, and muriate are all more or less employed in compounding potash manures (i.e. manures containing potash as one of their constituents), but kainit—an impure potash salt largely imported from Germany—is perhaps the most generally used when a dressing of potash only is desired.
Liquid Manure may be classed with farmyard manure, as it is now very commonly absorbed in the 'courts' by the straw, &c. Occasionally it is used in the liquid form on grass or stubble land.
Lime is one of the most necessary constituents of soils and manures. It is generally applied 'fresh burned' to newly-broken land, or where there is an excessive amount of peat or similar material. Lime is the great carrier into plants of other 'stuffs' which go to form their organic compounds, and during this elaboration organic acids are formed, many, if not all, of which would poison the plants themselves but for the presence of lime, with which these organic acids combine to form insoluble non-poisonous compounds.
The study of the subject—manures and manuring—can be most profitably followed in the works of Lawes and Gilbert. Yet most of our manurial—or agricultural—experiments are but gropings in the dark; they are most misleading and inconclusive, mainly because the experimentalists have known little or nothing of the changes going on in the plant itself, or of the variations in those changes caused by the amount and intensity of light and heat. Until we know more about the micro-organisms in the soil, their life-history and functions, but little progress can be made; and until we have experimentalists capable of demonstrating the functions, chemical and physical, of plants, and the variations in those functions with the ever-varying climatic conditions, so-called agricultural research must lead to disappointment. See AGRICULTURE, COMPOSTS, ROTATION, and SEWAGE.