MANTJRIKG IN THEOEY AND PRACTICE. 



39 



the atmosphere they obtain, through the action of 

 their leaves, nearly the whole of their volatile matter 

 —the carbon, with small quantities of nitrogen and 

 water. 



It was at one time believed that a complete 

 restoration to the soil of the mineral constituents 

 taken out of it by plants would enable them to 

 assimilate or gather in their necessary supplies of 

 nitrogen from the air ; hut this has been proved by 

 Sir J. B. Lawes and Dr. J. H. Gilbert, in their 

 experiments at Eothamsted, Hertfordshire, to be 

 entirely fallacious. 



The following table gives a summary of some 

 of the Eothamsted experiments, which will assist 

 us iu understanding this part of the subject : — 



AVEBAGE PkODUCE PER AcKE OF EoOT-CbOPS, 



Grow>,' Te.ib. after Year on the sajie Lank. 



Description of 

 Crop. 



How 

 Treated.* 



Norfolk White ( 

 Tomips (4 years, i 

 1815—1848) (. 



Swedish Tnx- 

 nips (4 yearSj 

 1838—1852). 



Swedish Tur- 

 nips (15 years, .J 

 1856—1870) . (. 



IVIangel Wnrzel ( 

 4 years, 1881— J 

 1S84) . ' 



n 



Without Manure 



Mineral Manure > 



I ouly . . f 



Without Manure 



Mineral Manure \ 



only . . f 



Without Manure 



Mineral Manure ") 



, only . .S 



Without Manure 



Mineral Manure ) 



only . . / 





■as 



S3 i 

 OHO 

 4 17 



12 15 



6^0 6 



17:0 10 



2 

 7 



ujo 

 2 e'o 



4 



3 



e'o 8 



17 18 



lei 



Increase 

 by the 

 lUannre* 



Balhleat. 



3 -"In — 



& I o s 

 H o >< o 



6 171 18 



5 lljO 4 



1 15i0 5 



mo 2 



Average Produce per Acre of Cereal Crops 

 Grown Year after Year ox the same Laxd. 



These results show that while a certain amount of 

 increase in growth is obtained by the annual appli- 

 cation of a manure composed exclusively of mineral 

 constituents, it is entirely inadequate to force a full 



• Mineral ipanure always composed of sulphate of potash, 

 soda, magnesia, and superphosphate ot lime. 



average crop of either roots or grain, and that in the 

 case of the root-crops, which were all grown upon 

 the same land, the accumulation of minerals in the 

 SOU by the yearlj- dressing did not assist the succeed- 

 ing crops iu obtaining a larger supply of nitrogenous 

 constituents, either from the soil or from the atmos- 

 phere, for in each succeeding stage of the experiment 

 the increase obtained over and above that yielded 

 without manure was less than in the preceding 

 period. 



In the foregoing experiments phosphoric acid 

 was apphed in the form of superphosphate of 

 lime, and Ville says that ' ' phosphates fill two dis- 

 tinct functions in plant-growth — they aid themselves 

 in the nutrition of the plant, and determine the 

 beneficial action of the other mineral ingredients. 

 Their function is therefore more important than 

 that of the other mineral constituents, since to their 

 own peculiar action is added a secondary derived 

 effect, that of determining the assimilation of all the 

 other mineral ingredients." 



As all crops taken from the land remove a 

 greater or less amount of plant-food, it is clear 

 that, if healthy plant-growth is to be maintained, 

 soils must be provided with available mineral con- 

 stituents from external sources ; for as each species 

 of plant requires a certain amount of minersil matter 

 for its development, it follows that unless a soil is 

 capable of furnishing this supply the plants will 

 either not flourish, or will refuse to grow at all. 



"We now come to the combustible or volatile con- 

 stituents of plants. These are made up of five 

 chemical elements, and comprise carbon, oxygen, 

 hydrogen, nitrogen, and sulphur. Without these five 

 important elements no plant is ever produced ; they 

 are, however, distributed in very different propor- 

 tions. Thus, plants dried at a temperature of 212" 

 Fahrenheit yield of — 



Carbon, nearly one-half by weight. 



Oxygen, rather more than one-third. 



Hydrogen, little more than 5 per cent. 



Nitrogen, from ^ to 4 per cent. 



Sulphur, from 1 to 5 per cent. 



This is further illustrated by the following', 

 table:— 



