July 1, 1898.] 



KNOWLEDGE. 



149 



soil growing legaminous plants a small quantity of the 

 watery extract of a soil containing the appropriate organ- 

 isms, a marked development of the ao-called leguminous 

 nodules on the roots is induced ; and that there is, coin- 

 cidently, increased growth and gain of nitrogen. For 

 example, in growing peas, there was limited growth in pot 1 

 (see figure) with sand without soil extract, and also an 

 entire absence of nodule formation on the roots. The 

 increased growth in pots 2 and 3, with soil extract, was 

 coincident with a very great development of nodules. 

 In pot 4, with garden soil, itself supplying abundance 

 of combined nitrogen and doubtless micro-organisms as 

 well, there was also a considerable development of nodules, 

 bat distinctly less than in either pot 2 or pot 3 with 

 sand and soil extraci only. Further, without soil extract 

 and without nodules there was no gain of nitrogen, but with 

 soil extract and with nodule formation there was much 

 gain of nitrogen. Experimental results, iu fact, clearly 

 prove that there is immense gain of nitrogen under some 



Peas grown in Experiments on the Fixation of Free Nitrogen. 



conditions. It has also been conclusively shown that due 

 infection of the soil and of the plant is an essential to 

 success. The available evidence at the same time points 

 to the conclusion that the soU may be duly infected for 

 the growth of some descriptions of plants, but not for some 

 other descriptions. Moreover, land which is, so to speak, 

 quite exhausted so far as the growth of one leguminous 

 crop is concerned, may still grow very luxuriant crops of 

 another description of the same order, but of different 

 habits of growth, and especially of unlike character and 

 range of roots. 



Not only the facts ascertained iu the Eothamsted ex- 

 periments and in other investigations, but also the history 

 of agriculture throughout the world, so far as it is known, 

 clearly show that a fertile soil is one which has accumulated 



within it the residue of long periods of previous vegetation, 

 and that it bscomss infertile as this residue is removed. 

 That this exhaustion proceeds slowly miy be gathered 

 from the fact that wheat ha3 baen grown at Rotham3ted 

 for more than fifty years in succession oa the sama land, 

 and, setting aside fluctuations due to season, the produce 

 has only bean reduced by an average of about one-sixth 

 bushel per acre per annum, due to exhaustion. Without 

 any manure whatever, the average annual produce for 

 over fifty years was thirteen and a half bushels — a yield 

 exceeding the average of the United States under ordinary 

 cultivation, including their rich prairie lands, and about 

 the average of the whole world. The accompanying table 



8 years, 

 8 years, 

 8 years, 

 8 years, 

 8 years, 

 20 years, 

 20 years, 

 40 years, 

 50 years, 



1852-59 

 1860-67 

 1868-75 

 1876-83 

 188-1-91 

 1852-71 

 1872-91 

 1852-91 

 1844-93 



U Tons 



Faruiyiird 



Mumire 



every 



Bushels. 

 34t 

 35^ 



39i 

 351 

 33| 

 341 

 33J 



Year. 



Bushels. 

 16^ 

 13J 

 12i 



lot 



125 



14i 



IU 



13 



13i 



Mixed Ammo- 



Miueral | uium 

 Manure Salts 



aloue. < aloue. 



BusKels. Bushels. 



19 



15i 



14 



121 



13i 



17 



32i 

 3U 

 28^ 

 27i 

 32^ 

 31S 

 29i 

 30i 



shows that with farmyard manure the average annual 

 produce over the fifty years of continuous growth was 

 thirty-three and a half bushels — a result not far short of 

 three times the average produce of the United States, and 

 more than two and a half times the average of the whole 

 of the wheat lands of the world. Artificially manured plots 

 show that mineral manures alone gave very Uttle mcrease of 

 produce ; that nitrogenous manures alone gave consider- 

 ably more than mineral manures alone; but that mixtures 

 of the two gave very much more than either separately. 

 An inspection of the following table of results, as indicating 

 the amounts of produce in the best and in the worst 

 seasons of the forty years, will show how easy it is to form 

 wrong conclusions as to the effects of different manures 

 if experiments are conducted for one season only, or in 

 only a few seasons, and if the characters of the seasons are 

 not studied and due allowance made accordingly in drawing 



Wheat Year aft^-r Year on the Same Land. — Produce of the Best 

 Season, 1863; of the Worst Season, 1879; and the Average of 

 Forty Years, 1852-1891. 



Dressed Grain (per Acre). 



Descriptiou of Manures 

 (Quantities per Acre). 



Unmannred 



Farmyard manure 



Mixed mineral manure alone 

 Mixed mineral manure and 200 



pounds ammonium salts =^ 43 



pounds nitrogen 



Mixed mineral manure and 40O 



pounds ammonium salts = 86 



pounds nitrogen ... 

 Mixed mineral manure and 550 



pounds nitrate soda ^ 86 pounds 



nitrogen 



Mixed mineral manure and 600 



poimds ammonium salts — 129 



pounds nitrogen 



55} 



inferences from results obtained. Thus it will be seen 

 that all the plats suffered severely in the bad season. 

 Compare columns <( and b. In most cases (see columns 



