254 A VISIT TO EOTHAMSTED. 



Ill goiiig over Bioadbalk Field we felt we were treading on 

 what might be called classic ground, for it was the experiments 

 conducted there which furnished Lawes and Gilbert with the 

 materials for carrying on the great controversy with Baron Liebig 

 regarding the employment of nitrogenous manures. 



Liebig, enamoured of what is known as the " mmeral theory 

 of plant nutrition," which exalts into the first rank the applica- 

 tion of mineral manures (such as constitute the ash of plants) 

 for the maintenance of the fertility of the soil, and the contiimous 

 j)roduction of full crops, viewed the application of nitrogenous 

 manures, if not as an unnecessary, at least as an unimportant con- 

 dition of good farming, and considered that the supply of nitrogen 

 present in the soil, and being continually Ijrought thither by 

 natural processes from the atmosphere, was sutiicient for the 

 wants of agriculture. The experiments conducted by Lawes 

 and Gilbert led them to an entirely opposite conclusion, and they 

 did not hesitate to join issue with the great German chemist on 

 this subject. 



Accustomed to universal deference on all matters regardinL!,' 

 the chemistry of agriculture, Liebig was naturally impatient of 

 the criticism of the English experimenters, and resented their 

 strictures with characteristic vigour and eloquence. Into the 

 history of the now famous controversy it is unnecessary here to 

 enter. It was a strife between theory and practice, and the 

 practical lesults oljtained on Broadbalk Field at Bothamsted 

 conclusively settled the question of the relative importance to 

 agriculture of mineral and nitrogenous manures. 



If the mineral or ash food of plants were sufficient to produce 

 fertility in a soil, then plot 5 should have shown it ; Ijut the 

 crop there is not much over that of the unmanured plot. On 

 plot 0, which received a threefold application of superphosphate, 

 and plot 1, which received a double application of alkaline salts, 

 there was no corresponding increase of crop. It is plain then 

 tliat the large yield on plot 3, wliicli , received annually 14 tons 

 farm-yard manure, cannot be explained on the supposition that 

 the mineral matters contained in it were the only effective con- 

 stituents. A glance at the produce of plots 5 to 8 shows unmis- 

 takablv where the increase came from. Wlien to the mineral 

 manures were added a small dressing of ammonia salts, only 200 lbs. 

 per acre (plot 6), on an average of twenty- four years about 10 

 bushels per acre were added to the produce. When an additional 

 200 lbs. ammonia salts were added (plot 7), a further increase of 

 about 10 bushels of wheat per acre w\as the result. Wlieii a 

 further addition of 200 lbs. ammonia salts was applied (plot 8), 

 there w^as again an increase of crop, but it amounted only to an 

 average of o^ Inishels per acre over the twenty-four years. 



The lesson taught by the produce of these four plots, if we 



