AGRICULTURAL EXPERIMENTS 245 



1843, when Lawes secured the co-operation of Dr. J. H. Gilbert, 

 a young chemist who had worked under Liebig at Giessen ; 

 the partnership thus entered into continued until Lawes' death 

 in 1900. With the advent of Gilbert, the experiments took 

 definite scientific form and it should be noticed that from the 

 outset they were never designed to demonstrate, still less to 

 advertise, Lawes' manufactures but were laid out to investigate 

 the nutrition of the plant on purely scientific lines. It is 

 interesting to find that though the plots showed the results 

 to be obtained from various sources of nitrogen, from potash 

 and other constituents of the plant, in only one case were they 

 so arranged as to afford a demonstration of the effect of super- 

 phosphate or other phosphatic manure. 



The question which was most before Lawes and Gilbert 

 when they laid out their first experimental fields, the question 

 moreover which never ceased to occupy their attention, was the 

 sources of the nitrogen of vegetation. Nitrogen is an invariable 

 constituent on the one hand of plants and on the other of the 

 soil but as plants live in an atmosphere of which four-fifths 

 consists of nitrogen, an atmosphere which also contains traces of 

 combined nitrogen in the form of nitrates and ammonia, it 

 naturally became a question of great interest whether the plants 

 derived their elements from the air or from the soil. Liebig very 

 definitely gave his verdict for the atmosphere, maintaining not 

 so much that the plant could bring into combination the free 

 nitrogen gas as that the ammonia which was brought down in 

 the rain-water was quite sufficient for the requirements of all 

 ordinary plants. He therefore advised farmers to restore to the 

 soil the mineral elements normally removed by the crop and 

 considered that there was no necessity to introduce a supply of 

 nitrogen. In forming this opinion, Liebig had been somewhat 

 misled by the exaggerated estimates which then prevailed, 

 owing to imperfect methods of analysis, of the amount of 

 ammonia contained in the rain. Lawes, however, did not agree ; 

 his experience as a practical farmer of the increased growth 

 which was produced by some of the fertilisers like dung, which 

 contains more nitrogen than anything else, led him to conclude 

 that the plant must need to draw this element from the soil. 

 The first set of field experiments were therefore laid out to test 

 on all the crops usually grown upon the farm the effects of 

 varying amounts of nitrogenous fertilisers, particularly the salts 



