MANAGEMENT OF NURSERIES. 159 



After the crop of nursery-trees is removed from the ground 

 another one should not be planted in the same place until the 

 soil has fully recovered from the exhaustion of the first. An 

 intermediate crop of clover turned under for manure is found 

 useful. There should be an interval of at least two or three 

 years before occupying the ground again with nursery; al- 

 though a less time is often given in connection with heavy 

 manuring. 



The reasons for the failure of trees to grow well on " treed " 

 land has been the subject of much discussion. By many it 

 has been supposed that the first crop of nursery trees exhausts 

 the land of some element which trees need. This notion is 

 mostly given up. It is no doiibt true that the trees use first 

 that part of the plant-food which is most readily available, 

 hut the amount of nitrogen, potash, and phosphoric acid which 

 they consume is small as compared with that required by 

 wheat. Probably the largest factor in the matter is the loss 

 of humus in the soil consequent upon three to five years of 

 clean tillage without the addition of manure or the turning 

 under of green material. It has been found that a thorough 

 dressing of manure will sometimes make it possible to follow 

 trees with trees at a profit. 



