PURCHASE: AND USE OF FERTILIZERS 325 



Root crops (beets, mangels, turnips, carrots, Irish and sweet 

 potatoes) cannot make ready use of the mineral constituents of 

 the soil. Phosphates are especially useful for turnips, while beets 

 and carrots require more nitrogen. Potash is particularly useful 

 to potatoes. 



Market garden crops have a high commercial value with a low 

 fertility content. Hence they can be profitably supplied with an 

 abundance of plant food. This supply also increases rapidity of 

 growth, which is desirable, as the price is often in proportion to 

 their earliness. 



Fruit crops have a longer season of preparation and growth, 

 and require a constant transfer of food from the tree to the fruit 

 during the growing season. Food that will encourage a slow and 

 continuous growth, rather than a quick one, is required. 



The Kind of Rotation. The order in which the crops 

 follow one another in rotation, the kind of crop previously grown, 

 and the treatment given it, are factors in intelligent fertilization. 

 If the previous crop is a legume, and has left considerable 

 residues, the succeeding crop stands less in need of nitrogenous 

 fertilizers. A crop succeeding an exhaustive crop not liberally 

 fertilized, may require liberal applications of plant food. The 

 further removed the crop is from the legume crop, the greater 

 its probable needs of nitrogenous fertilization. 



Effect of Phosphoric Agid, Potash and Nitrogen on Plant 

 Growth. While the entire plant requires all forms of plant food, 

 it may be said that nitrogen and potash stimulate the growth of 

 leaves and stem, and phosphoric acid stimulates ripening of the 

 fruit. An excess of nitrogen tends towards a large development 

 of leaf and late maturity. Thus at Rothamsted, on the wheat 

 plots which receive nitrogen and potash but no phosphoric acid, 

 the grain hardly ripens at all. The use of phosphoric acid, how- 

 ever, hastens the maturity of the plant. 



Fertilizer Experiments. A great number of fertilizer experi- 

 ments have been carried out by Experiment Stations, and other 

 investigating agencies. The plans of the experiments vary a great 

 deal, according to the crop to be tested, the information desired, 



