142 



THE GARDENER'S ASSISTANT. 



soil, it would seem essential to assume that a 

 large proportion of the nitrogen of crops growing 

 without any direct supply of it by manure must 

 be derived, in some way or other, from atmo- 

 spheric sources. 



The assumption which is most in favour with 

 some prominent writers is, that whilst some 

 plants derive most or all of their nitrogen from 

 the stores of the soil itself, or from manure 

 applied to it, others derive a large proportion 

 from the free nitrogen of the atmosphere. 

 Lawes and Gilbert, on the other hand, whilst 

 freely admitting that the facts of production are 

 not conclusively explained thereby, have main- 

 tained that such collateral evidence as the deter- 

 minations of nitrogen in our soils afford, are in 

 favour of the supposition that the soil may be 

 the source of the otherwise unexplained supply 

 of nitrogen. This latter conclusion has been 

 frequently stated in general terms, but until 

 recently there has not been published the 

 numerical results upon which it is based. 



If, then, the supply of mineral constituents in 

 the soil not being defective, the yield of our 

 crops is in the main dependent on the amount 

 of nitrogen which is available to them within 

 the period of their growth from the soil itself, 

 or from the manure applied to it, surely the 

 fertility of a soil must be largely measured by 

 the amount it contains, and the degree in which 

 it becomes available. And if this be so, it 

 proves that the soil is a "laboratory" in which 

 chemical food is being prepared for the use of 

 plants, as well as a "mine" in which this 

 prepared food is stored up. 



In reference to this point it may be stated, by 

 the analyses of some prairie soils from Illinois 

 and the North-west Territory of America, that 

 they were found to be about twice as rich in 

 nitrogen as the average of arable soils in Great 

 Britain. Indeed, they corresponded in their 

 amount of nitrogen very closely with the surface- 

 soils of our permanent pasture-land. As the 

 virgin prairie soils have their source of nitrogen 

 in the accumulation from ages of natural vegeta- 

 tion, with little or no removal, it has also been 

 found they are correspondingly rich in potash 

 and other mineral constituents, showing that 

 the soils of the " New World " as well as those 

 of the "Old World" are "mines" as well as 

 " laboratories ". If not, what, it may be asked, 

 is the meaning of the term & fertile soill 



The Sources of the Nitrogen of Crops. — We will 

 next consider whence comes the nitrogen of 

 crops, and especially whence comes the much 

 larger amount taken up by plants of the legu- 



minous, and some other families, than by the 

 Graminese, to which latter family belong the 

 grasses of our meadows and lawns; Wheat, 

 Barley, Oats, and Rye; Maize and Sugar-cane. 



Combined Nitrogen in Rain, &c. — It has been 

 assumed by some writers that the amount of 

 combined nitrogen annually coming down in 

 the measured aqueous deposits from the atmo- 

 sphere is sufficient for all the requirements of 

 annual growth. In Liebig's earlier writings he 

 assumed the probability of a much larger quan- 

 tity of ammonia coming down in rain than he 

 did subsequently; but even in his more recent 

 work, the Natural Laws of Husbandry, published 

 in 1863, he supposes that as much as 24 lbs. of 

 nitrogen per acre may be annually available to 

 vegetation from that source. Such an amount 

 would, it is obvious, do much towards meeting 

 the requirements of many of the crops grown in 

 the garden. 



The earliest considerable series of determina- 

 tions of the amount of ammonia coming down in 

 rain in the open country were by Boussingault, 

 in Alsace. He gives the amount of ammonia 

 per million of rain-water in each fall for a period 

 of between five and six months, May to October, 

 1852; but he does not calculate the amount so 

 coming down over a given area of land. 



His average amount of ammonia per million 

 of rain-water was, however, somewhat less than 

 that found in the Rothamsted rain-waters col- 

 lected in 1855 and 1856; which, calculated 

 according to the rainfall of the periods, gives 

 the following amounts of nitrogen so coming 

 down per acre. The amount of nitrogen as 

 nitric acid, and the amount of total combined 

 nitrogen as ammonia and nitric acid together, 

 are also given. 



Nitrogen, as Ammonia and Nitric Acid, in the Main/all of 

 three years, at Rothamsted, Hertfordshire, in, pounds per 

 acre. 





Rainfall. 



Nitrogen, per acre 



, as- 



Years. 



Ammonia. 



Nitric 

 Acid. 



Total 

 Nitrogen. 



1853-54, ... 



1855, 



1856, 



inches. 

 29-014 

 29-166 



27-215 



lbs. 

 5-20 

 5-82 

 7-28 



lbs. 

 0-74 

 0-72 

 0-76 



lbs. 



5-94 

 6-58 

 8-00 



Mean,... 



28-465 



6-10 



074 



6-84 



It will be seen that according to these results 

 an average of 6*54 pounds was contributed per 

 acre per annum in the rain in the form of am- 

 monia and nitric acid. More recently, however, 

 Dr. Faulklancl has determined the amount of 

 ammonia and nitric acid in numerous samples 



