FERTILIZERS AND PLANT PRODUCTS 171 



The Carbohydrate Producing Crops.— Wheat is 

 one of the most important plants grown in all countries of 

 advanced agriculture, as part of a system of rotation of 

 four or more years. Wheat is particularly suited to ploughed- 

 up land which has borne grass or clover, or mixtures of the 

 two. In such cases little fertilizer is necessary, a top 

 dressing of sulphate of ammonia, to the extent of half a 

 hundredweight per acre in the winter and spring, being 

 generally considered sufficient. When many white crops 

 are grown with a degree of frequency beyond that of once 

 in four years, some phosphatic manures will generally be 

 found necessary, and on the lighter soils some potash. 

 Oats also require comparatively little manure when grown 

 after a hay crop. Barley, when required for malting purposes, 

 should have comparatively little nitrogenous manure, 

 though when required for feeding purposes more may be 

 supplied. Phosphates are particularly desirable for purposes 

 of producing sound ripening, as alluded to below. Potatoes 

 are grown on such a great variety of soils that it is difficult 

 to lay down any particular rules, excepting that farmyard 

 manure is generally desirable, although in some districts 

 no farmyard manure is employed, potatoes being grown 

 after about two years clover. A good deal of the advantage 

 of using farmyard manure for potatoes is purely physical, 

 as the potato does not develop good root system unless the 

 soil is very open, and even actually hollow. Sulphate of 

 ammonia is gensrally preferable to nitrate of soda and 

 super-phosphate is often better than basic slag. I^ime is 

 also generally considered unsuited for potatoes. Excessive 

 nitrogenous manure causes the potatoes to produce less 

 starch, and more nitrogenous and fibrous tissue. In garden 

 cultivation of potatoes working the land so as to produce 

 a somewhat hollow structure is useful, as it induces the 

 roots to go down after water, and leaves the soil loose for the 

 development of the tubers. Sugar-producing crops are often 

 more exhaustive. Swedes and mangolds require much 

 nitrogenous as well as phosphatic mainire. A standard 

 dressing is used for mangolds at Cockle Park, containing 



