The proper time of application depends upon the age, the texture and the kind of manure, the crops to be grown, and the systems and the rotations to be followed. In the growing of truck crops in rotation with general field crops, perhaps, the manure should be applied at any convenient time previous to planting, and preferably upon grass land. If the manure is fine and the supply limited, it may be an advantage to use it as a top dressing after plowing, thoroughly incorporating it with the soil by harrowing. This is unquestionably the best method for hen, sheep and hog manures. In intensive gardening a crop may be removed, the manure applied, and the land plowed, harrowed and planted the same day. If 50 tons of manure to the acre are available annually and several crops are to be grown during the season, it is considered preferable to apportion the manure for each crop as may seem desirable rather than to use the entire amount at any one time.
As indicated in the previous paragraph, coarse manures should be plowed under, while those of fine texture will be most beneficial when used as a top dressing after plowing, especially upon heavy soils of moderate fertility. Surface applications after plowing certainly have a marked effect in improving physical conditions, in making soils warmer, more friable, and less subject to baking and washing.
A common practice in soils of rather low fertility is to use stable manures in hills or drills. This plan is seldom practiced by gardeners cultivating soils of high fertility, but it is without doubt an advantage in the thinner soils, because it secures greater concentration of plant food in the immediate region of the roots and results in a more economical use of the manure applied.
The spreading of stable manures on truck farms and on market gardens is generally done with an ordinary four-tine manure fork. This is the most economical method when the manure is spread from the wagon as hauled from livery stables. Manure spreaders, however, should be in more general use among commercial vegetable growers, because they save labor and secure a much more even distribution than is possible by hand spreading.
The rate of application varies with the character and the supply of available manure, the character of the soil and the kinds of crops to be grown. In field trucking with such crops as sweet corn and cabbage the applications often do not exceed 10 tons an acre, while in market gardening the amount varies from 25 to 100 tons an acre. More than 50 tons to the acre is regarded by some as wasteful, or at least not economical. Twenty-five tons is a medium application in market gardening, while many claim that maximum profits cannot be obtained with less than 50 tons an acre applied annually. In the most intensive garden operations manure is often spread to the depth of 3 inches. When supplementing with commercial fertilizers it is possible to succeed with less manure, although the land may suffer in its physical composition. By using commercial fertilizers and a good system of irrigation the grower can unquestionably economize in the amount of manure.
Night Soil is a term applied to the human excrements, used extensively in the gardens near Philadelphia and for truck crops near Baltimore. At Baltimore it is taken from vaults and transported on barges to truck farms and there pumped into large reservoirs, which are provided with double gates. When loading on the wagons, which are backed up to the spouts of the reservoirs, the outer gate is first closed and the inner gate opened. The space between the two gates holds a wagon load. When this space is filled, the inner gate is closed and the outer gate opened and the material is then conducted into the wagons, provided with tanks that are closed tightly when the wagon is in motion. In distributing over the field the end gate to the tank is raised by a lever operated by the driver, and the watery material is then spread over the slanting tail-board. Figure 10 shows the style of wagon used on the Patapsco Neck near Baltimore. An analysis shows that the Baltimore night soil contains 0.28 per cent phosphoric acid, 0.2 per cent potash and 0.43 per cent ammonia and is worth about $1.50 a ton. It is secured at a nominal cost, but if the unpleasant character of the material is taken into account, gardeners should be well paid for accepting and using it. In Philadelphia County considerable night soil is hauled in barrels with tight covers to market gardens providing dumping reservoirs. No charge is made for the material and no bonus is paid the gardeners.