Nanuring.—The objeet of manuring is to supply to the plant those chemical constituents which the soil is deficient in. The sugar-grower's efforts must be direeted to the production, not of the tallest and stoutest canes, but of the greatest possible quantity of crystallizable sugar.
Therefore 1000 tons of cane take up from the soil rather more than 4 tons of mineral ingredients, and about 1 ton of nitrogen is required to form their albuminous matter. Manures deal only with the materials supplied through the soil, except in supplementing tbe amount of nitrogen. The nature and relative proportions of the mineral ingredients are ascertained by analysis of the ash of tbe full-grown entire cane. Much discrepancy exists in the analyses of csne-ash hitherto made, which is due in part to variety of soil, different ages of the plants, and omitting the leaves.
Subjoined are some analyses of cane-ash, by Dr. Stenhouse The first seven were all fine canes with the leaves ; No. 8 had no leaves; No. 9, but few ; No. 10 was in full blossom, and had been manured with pen-mauure ; No. 11, old ratoons, manured in the same way ; No. 12, young Mont Blanc canes, manured with pen-manure, guano, and marl.
The principal substances, therefore, required to be provided in an available state in a cane-soil are potash, silica, phosphoric acid, sulphuric acid, lime, and magnesia, besides a certain amount of nitrogen beyond what the plant can secure from the atmosphere. The oxides of iron and of manganese are, perhaps, also essential.
The relative importance of each substance is a difficult problem to solve. But the mineral ingredients are constantly found in the same relative proportions. It must not be forgotten, however, that the sugar-cane possesses a power of absorbing a quantity of salts from the soil, far in excess of its needs, and to the detriment of its juice. This is referred to under Soil (p. 1863), and is illustrated in Nos. 3, 7, 8, 9, and 11 of Dr. Stenhouse's samples.
Composition of Cane Soils.—The composition of cane soils may be illustrated by two analyses by Dr. Phipson, one (A), of a soil from an estate in Jamaica under canes for the first time ; the other (B), from a Demerara plantation worked for more tban 15 years consecutively :— While A possesses everything requisite to grow canes for a number of years, B is fast approaching exhaustion. Attention is called to the greater amount of organic matter (humus),
nitrogen, lime, and phosphoric acid in A, and to the important fact that the quantity of lime (0.08) in B is far below tbat of the magnesia (0.25). This last is a very bad sign, so much so that the degree of exhaustion which a soil has undergone can to a great extent be ascertained by comparing tbe relative amounts of lime and magnesia. The lime disappears by prolonged cultiva tion of tbe cane, whilst the magnesia remains as it was. When the lime has diminished so much as to be present to tbe extent of only 0.1 per cent,, and then amounts to but one-third of the tnagnesia (though originally the lime was higher than the magneeia), the crops of cane will fall off year by year, and most eareful ruanuring will be necessary to regenerate the soil.
Manures obtained froru Foreign Sourees.—The only manures fit to be used on a partially exhausted soil aro good stable-manure, well-fermented farmyard dung, or manure made frorn night soil. These are natural products, and not only contain all that the plant requires, but in the proper state for assimilation. Superphosphates have little beneficial effect upon graminaeenus plants (including the sugar-cane and the cereals); and though excellent special manures have been compounded, nothing ean equal dung and night-soil. Dung is precluded from wide use by reason of its bulk, but a, product is now prepared from night-soil and urine which well compares, in composition and fertilizing qualitiee, with concentrated farmyard mannre. It is got by evapo rating excreta as nearly as possible to the dry state ; as it holds only 12-16 per cent. of water, its transportation can be effected as easily and cheaply as with guano. Analysis shows it to eeetain all the ingredients of rich farmyard manure in a concentrated state, and in the same assimilable form. It is manufactured by the Urban Mauure Company, at Bloxwiteh and Churehbridge, and is eminently adapted for long-worked cane soils.