MANURES AND MANURING (from OF. manorrcr, Fr. mamerrcr, to manage, work by hand, from OF. manourre, manorre, from \l L. munaopera, manopera, a working with the hand, from Lat. matins, hand opera, work). In a broad sense, the term manure is applied to any substance used to increase the productive ness of soil. The word is commonly used in a more restricted sense to mean the excreta (solid and liquid) of farm animals. either mixed or umnixed with litter, and more or less fermented. In this article the term is used in its broader sense. Manures may be direct or indirect in their effect. The former supply plant food which is lacking in the soil, the latter render active the insoluble fertilizing constituents already present and improve the chemical, physical, and bio logical conditions in the soil. The first class in cludes the so-called commercial or artificial fer tilizers, such as superphosphatcs, nitrate of soda, etc.; the second embraces natural manures, such as the green manures, sea-weed (q.v.), and ani mal manures, and the soil amendments or soil improvers, such as lime, gypsum. salt, etc. Under certain conditions all these manures may be both direct and indirect in their action.
Plants derive the bulk of their food directly or indirectly from the atmosphere. A small but very essential portion. however, is drawn from the soil. This includes the inorganic or ash constituents and nitrogen, which, however, is in certain cases derived indirectly from the air. These substances, being soluble, are transported by water, which is not considered a food. Of the
soil constituents which plants need only four are likely to be exhausted by ordinary systems of cropping, viz. nitrogen, phosphoric acid, potash, and, in some cases, lime. Direct manures supply one or more of these constituents, which are known as the essential fertilizing elements. The fertility of the soil would remain practically unchanged if all the ingredients removed in the various farm products were restored to the land. This may he accomplished to a large extent by feeding the crops grown on the farm to animals, carefully saving the manure and returning it to the soil, and when practicable combining a ju dicious use of green manures with a system of stock feeding in which those farm products comparatively poor in fertilizing constituents are exchanged for feeding stuffs rich in these substances. Under such practice the loss of soil fertility may be reduced to a minimum or there may even be an actual gain in fertility. Under ordinary conditions of farming, however. the ma nure produced on the farm is not sufficient to maintain its fertility. Roberts estimates that in ordinary mixed husbandry only about one-half of the fertility taken from the soil by crops is re stored in farm manures. Hence the necessity for supplying the deficiency from other sources, resulting in the wide use of artificial or com mereial fertilizers of various kinds.