258 SEEDING AND PLANTING 



Mineral phosphates are derived chiefly from phosphate rock of 

 several varieties and from Thomas slag, a by-product in the manu- 

 facture of steel. When applied in the raw state phosphate rock 

 is very slow in becoming available as plant food. It is usually 

 chemically treated to produce the so-called superphosphates in 

 which the phosphorus is in available form for plant food. Raw 

 phosphate rock, Thomas slag, and the superphosphates are rarely 

 used in nursery practice except in mixture with other materials. 

 Phosphate rock and Thomas slag are usually mixed with com- 

 posts of vegetable origin, while superphosphate is one of the 

 principal ingredients of standard mixed commercial fertilizers 

 which are sometimes used as a top dressing. 



If the soil is not of the proper consistency when the permanent 

 nursery is first established, it is usually advisable to improve it by 

 adding sand to a heavy stiff soil and loam to a very loose, light 

 soil. Although this procedure entails considerable expense, it will 

 usually pay in the end. Wherever muck can be obtained at little 

 cost for transportation, it is an excellent amendment for sandy 

 soils as well as tenacious clays. The actual plant food content, 

 however, can be much more economically secured from other 

 sources. Its value depends upon the large content of organic 

 matter which has the same physical effect upon the soil as humus. 

 Large quantities are necessary in order to improve materially the 

 physical condition of the soil. At least 40 to 50 tons of dry 

 muck per acre should be used. Its effect is lasting, and it can be 

 gradually applied through a series of years. When used on soils 

 deficient in plant food, lime and commercial fertilizers rich in the 

 deficient nutrients should also be applied. 



30. The Quantity of Fertilizer Required. The quantity of 

 fertilizer necessary depends not only upon the kind of soil, but 

 also upon the species and the length of time that the plants 

 remain in the beds. The quantity, therefore, can be stated only 

 in a general way. The condition of the stock invariably indicates 

 whether we are using adequate fertilizer for acceptable results. 



Heavy applications of farm manures and commercial fertilizers 

 are usually expensive. A part of this outlay can be recovered by 

 growing a field crop immediately after applying the manure or 

 other fertilizer. This procedure gives a change of crops, permits 

 a thorough working of the soil, and removes all danger of over- 

 stimulation of growth in the nursery stock. A common practice 



