Scientific Agriculture. 



136 



[February, 1912. 



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 pl<5cs 

 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 superphosphates or other 

 phosphatic manure. 



The question which was most before 

 Lawes and Gilbert when they laid out 

 their first experimental fields, the ques- 

 tion moreover which never ceased to 

 occupy their attention, was the sources 

 of the nitrogen of vegetation. Nitr ogen 

 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 imper- 

 fect 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 any- 

 thing else, led him to conclude that the 

 plant must need to draw this element 

 from the soil. The first set of field ex- 

 periments 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 of ammonia which were then begin- 

 ning to be available in commercial quan- 

 tities ; as the results became available he 

 entered the lists against Liebig. An 

 animated controversy followed which 

 lasted as long as Liebig lived, for though 

 the tide of opinion finally settled down 

 against Liebig's point of view, certain 



outstanding difficulties were never ex- 

 plained until after his death and he has 

 a few faithful adherents even at the 

 present time. The main problem is 

 solved, however. 



What the Rothamsted experiments 

 demonstrated was that for the cereals 

 and some of the other farm crops 

 growth up to a certain point was 

 proportional to the supply of nitro- 

 gen. The leguminous crops proved to 

 be an exception , they did not respond 

 to nitrogenous fertilizers to any great 

 extent and they proved exceptions in 

 another way, in that it was not possible 

 to maintain their growth year after year 

 upon the same land as with some of the 

 other crops. One of the most unex- 

 pected features revealed by the Rotham- 

 sted experiments has been the possibility 

 of dispensing to a large extent with a 

 rotation of crops, provided the supply 

 of fertilisers is kept up. One of the 

 cardinal principles in the old conser- 

 vative system of farming, a principle 

 embodied in the leases under which the 

 land was let, was that two corn crops 

 should never be taken in succession, and 

 it would have been considered impossi- 

 ble to grow wheat year after year with- 

 out any break. Yet the sixty-eighth suc- 

 cessive crop of wheat upon the Broad- 

 balk field has this year been harvested 

 and one of the plots has yielded more 

 than five quarters to the acre ; even the 

 plot which has had no manure of any 

 kind since 1839 has produced over twelve 

 bushels per acre. For various practical 

 reasons it is never desirable to attempt 

 such continuous cropping as this but one 

 immediate result of the Rothamsted ex- 

 periments has been to encourage a much 

 greater freedom of cropping, until to-day 

 it is a regular thing to take two or 

 three corn crops in succession ; a few 

 farmers have even adopted the plan of 

 continuous corn-growing, except in the 

 occasional years that have to be devoted 

 to cleaning and restoring the tilth of 

 the soil. 



It would be out of place here to discuss 

 in any detail the conclusions which 

 Lawes and Gilbert drew from their field 

 experiments after the results had been 

 confirmed by a few years' repetition, but 

 it is enough to say that the accepted 

 theory of the manures appropriate to 

 the different farm crops was established 

 by these experiments and that the 

 results have passed into the region of 

 traditional farming practice. 



But to return to the nitrogen question, 

 Lawes and Gilbert attacked it in another 

 fashion by repeating in the laboratory 



