136 FIELD CROPS 



is followed, about the only element that must be supplied by 

 means of commercial fertilizer is phosphorus. 



Experiments have shown that during the first half of 

 its growth wheat appropriates about 85 per cent of its 

 mineral constituents, while during the subsequent period 

 of its growth it is developing its starch and cellulose ingredi- 

 ents which are taken largety from the air. These facts have 

 bearing on the problem of its fertihzation. 



In the East and South, where the soils have become worn 

 by long continued cropping, commercial fertilizers are usually 

 applied for each crop. Likewise, in some of the Central 

 states the appUcation of commercial fertilizers is becoming 

 necessary in many localities to insure profitable yields. 

 The kind and amount of fertilizer most profitable to apply 

 can be determined only by careful trials in each locaUty and 

 on each type of soil. A very common practice is to apply at 

 seeding time from 200 to 300 pounds of fertilizer to the acre, 

 containing about 2 per cent available nitrogen, 8 per cent 

 available phosphoric acid, and 2 per cent potash. In many 

 localities, where a supply of vegetable matter and nitrogen 

 is maintained by growing clover and by applying stable 

 manure, the application of either raw or treated rock phos- 

 phate is sufficient to provide for satisfactory yields. 



GROWING THE CROP 



175. Preparation of the Land. The preparation of the 

 land does not differ materially for winter or spring wheat, 

 though the crops are seeded at different seasons of the year. 

 The main object in the preparation of the soil for wheat is to 

 produce a mellow, firm seed bed with sufficient loose soil on 

 the surface to check the rapid evaporation of moisture, and to 

 provide a hospitable place for the plants to grow. Where 

 possible, land is plowed for wheat, though sometimes the crop 

 is seeded on disked corn or stubble land. The better practice 

 is to plow the land. To prepare newly plowed land for 



