188 LECTURES ON 



under what are, for nearly all agricultural plants, the most unfavor- 

 able conditions. Rye, for example, will grow well where wheat is 

 utterly unprofitable. Buckwheat yields a fair crop on exceedingly 

 poor soils; and the lupine is so extraordinary in this respect that by 

 its help the farmer may cover the most desolate blowing sands with 

 a luxuriant vegetation. 



On the other hand, some crops are easily spoiled by overfeeding. 

 Thus wheat, and the slender-stemmed grains generally, are unremu- 

 nerative on the newly broken up prairies of our west, while maize 

 flourishes even on the richest soils, being in practical language "a 

 rank feeder." 



It is plain that, other things being equal, a plant with long-branch- 

 ing numerous roots does not require so rich a soil as one with these 

 organs short and few, because it has a greater mass of earth at its 

 disposal out of which to collect its food. 



Again, those plants which expose to the air a large leaf surface 

 should, other things being equal, flourish better than the sparsely- 

 leaved plants in a soil poor in atmospheric elements. 



A plant which is of slow, regular, and protracted growth may, in 

 the same manner, organize more vegetable matter on a given soil 

 during a summer than one which quickly runs through all the stages 

 of its life, and therefore requires more rapid supplies of food — de- 

 mands more in a given time. 



In general, also, those crops which produce seed require a better 

 soil for their continuous production than such ;is yield only foliage. 



6. Different soils abound or are deficient, to « greater or less degree, in 

 one or more needful ingredients in assimilable farm. 



With the original differences of soils are to be likewise classed the 

 changes in condition which tillage and cropping arc perpetually 

 inducing. By the continued removal of crops the soil suffers a dimi- 

 nution of its resources, and often some one or a few of the nutritive 

 elements are soon brought to a minimum, while the others still remain 

 in quantity sufficient for hundreds of harvests. According to the 

 original composition of the soil, the failing ingredient may be potash 

 in one case, sulphuric acid in another, lime in another; and applica- 

 tion of these substances, respectively, may then form the most profit- 

 able manuring. 



1. It appears from experience that the ingredients which are rarest in 

 the soil — which are therefore most liable to exhaustion, and most needful 

 to be replaced — are, in general, phosphoric acid, assimilable nitrogen, (be it 

 in the form of ammonia or nitric acid,) and potash. 



The substances just named are therefore important ingredients in 

 all those manures by whose continued and exclusive use the soil is 

 kept fertile, and constitute the chief part of such fertilizers as bring 

 up exhausted lands to immediate and remarkable, though it be tem- 

 porary, productiveness. 



The above is intended as a very general statement, the truth of 

 which, as such, is not invalidated by the numerous and important 

 exceptions which occur. 



In examining the question of the direct action of manures, we have 

 first to notice the value of deductions from the composition of a sub- 



