This section is from the book "Commercial Gardening Vol4", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
The results of the most recent experiments go to show that the best crops are obtained from a moderate quantity of stable manure, supplemented by a judicious combination of chemicals. Near large centres of population, where stable manure can be obtained readily at moderate price, little else is needed. Where, however, it is scarce and dear, organic manures in some other form and chemical manures must be brought in. In this matter, again, it is impossible to generalize. One knows highly successful market gardeners who hardly ever have used anything but stable manure; and others who, beyond what little is made in the place, have depended entirely on what are called "waste-product" manures and chemicals. No one who has studied the matter will deny that, apart from the fertilizing agents it brings to the soil, there is a physical effect exerted by stable manure on the texture of the soil, which is most valuable and can hardly be supplied by anything else. Nitrates, either in the form of nitrate of soda or sulphate of ammonia to give a filip in the spring, or in the form of crushed hoofs in the autumn; phosphates in the form of basic slag or crushed bones in the autumn, or superphosphate or dissolved bones in the spring; potash, either in the form of kainit in the autumn or sulphate of potash in the spring, are the manures the market gardener who wants to supplement stable manure must consider.
A great difficulty is created for the market gardener by the heavy manurings his constant cropping with crops requiring high conditions of fertility necessitate. The land gets into a condition analogous to that of the gourmand. Another source of difficulty is the close family relationship which exists between many of the crops which he must grow. The beneficial change secured for the land by the farmers' four-course rotation is difficult to obtain in a market garden that is not partly farmed.
Hence the market gardener is flogged by that scourge called "club", common to all plants of what botanists call the "Cruciferas". Scientific research has failed to discover a remedy, though there are palliatives. As a correction both to the overfeeding of the land and to the conditions resulting in attacks of "club", frequent applications of fresh slaked lime have been found valuable. The usual manner of application is to deposit the lumps of unslaked lime in small heaps to the amount of 3 or 4 tons per acre, then to cover these heaps with a light covering of soil and leave them to slake, which in normal weather will occur in four or five days. Then as much may be spread each morning as can be ploughed or dug in during the day.
Lime must not be applied at the same time as manure, because its chemical action will be to dissipate too readily the nitrates contained in the manure. Market gardeners going on the market to purchase manures should make themselves master of the principle of unit value. A knowledge of this will prevent their being rooked by vendors of manures that are practically worthless. The Board of Agriculture Leaflet No. 72 is an excellent one for this purpose. (See also Vol. I, p. 162.) [w. g. l].