NURSERIES. 155 



contain or contains in too slight a proportion, or to restore to it 

 those elements which have been removed from it by the plants 

 raised therein; and (3) to render harmless or inert certain injurious 

 constituents present in it. A nursery is rarely started any where 

 except in virgin forest land that has been fertilized by generations 

 of tree-growth; but it is seldom that such land possesses uniformly 

 all the requisite physical characters, and even as regards the ele- 

 ments of plant-food, there is nearly always advantage in adding, 

 howsoever little it may be, to what is already present to the soil. 

 Hence, as a rule, in preparing soil for the first time we have to put 

 into it manures which chiefly modify and improve its physical 

 characters, and only secondarily increase its nourishing power for 

 plant-growth. 



On the other hand, in a nursery that is already in working order, 

 the physical characters of the soil have been already more or less 

 permanentlyiinodified in accordance with all requirements by means 

 of the first manuring; whereas, howsoever great the proportion of 

 the elements of plant-food may be which we give to the soil in the 

 shape of manures, those elements are constantly being exhausted 

 by the planting material raised therein. Indeed the soil of a nur- 

 sery exhausts itself just as rapidly as soil under wheat cultivation : 

 on the whole, if loses less phosphoric acid but much more potash 

 and lime than the latter. As compared with trees of the same 

 species about eighty years old, nursery seedlings only a year old 

 take up annually from the soil six times as much phosphoric acid, 

 seven times as much potash and nearly twice as much lime and 

 magnesia; and whereas those large trees return to the soil, in their 

 fallen leaves, fruit and small twigs, almost more than what they 

 have taken up through their roots, the seedlings are carried away 

 bodily, and consequently whatever they may have appropriated 

 from the soil is lost to it for ever. Hence, in a nursery that is al- 

 ready in full working order, we must put into the soil manures 

 that affect little, or not at all, its physical characters, but supply to 

 it, in a very large measure, the direct elements of plant-food. 



Thus, according as we require chieflv to modify the phvsical 

 qualities of the soil or to supply it with useful compounds of nitrogen 

 anb phosphorus, and of potash, lime and magnesia we have, for the 

 purposes of a forest nursery, two broad classes of manures, which 

 we may designate respectively (a) WEAK MANURES and (b) STRONG 

 MANURES. 



