PRESIDENTIAL ADDRESS. 531 



not liable to the same ills as clover and turnips, so that if one set of troubles 

 intervened there would still be a reserve of food for the animals. 



These experiments had all been made on light land, but they slowly spread 

 to the heavier soils. It had early been found that some of the new crops could 

 be grown in such a way as to give all the benefits of a bare fallow without the 

 waste. Jethro Tull's drill enabled the seed to be sown in rows; he was not the 

 first to get the idea ; Piatt had already in 1600 made a wheat dibbler worked by 

 two men 'whereof the one maketh the holes and the other setteth the seed.' 

 Tull, however, was the first to make a machine that actually worked on a farm. 

 And along with the drill he introduced from the vineyards of the south of 

 France the idea of cultivating between the rows. Thus the necessity for bare 

 fallows disappeared, and by the end of the eighteenth century Young considered 

 himself justified in conducting a campaign in his usual vigorous way against 

 them. 



The process took a long time to develop, and it is not absolutely complete yet; 

 in 1915 there were still nearly 310,000 acres of bare fallow in England alone. 

 Usually this is on heavy land, where no way has yet been found for dispensing 

 entirely with the bare fallow. 



The introduction of clover had the immediate effect of providing more 

 food for the animals by increasing the stock of hay. But soon a new and 

 important effect became manifest. The clover actually benefited the succeeding 

 crops by that wonderful process of nitrogen fixation which took nearly fifty years 

 to discover and is not fully understood even yet. 



Thus, by the beginning of the nineteenth century a very much improved 

 system of agriculture was available to farmers. In place of the old medijeval 

 rotation (which some of them were still practising) in which only two-thirds of 

 the arable land was utilised, the remainder being fallow, they now had a rota- 

 tion enabling them to use all their land, giving them more cattle-food, more 

 farmyard manure, and con.sequently more human food; further, the clover crop 

 directly enriched the ground. 



In consequence the yields went up, and instead of the 10 bushels of wheat of 

 mediaeval times, it wa.=i not uncommon to get 25 or more bushels ; in Hertford- 

 shire, a great corn-raising district, the yields varied from 20 to 40 bushels.^ 



The yields might not have gone much higher, but for a new idea which came 

 in as a result of scientific investigations — an idea which developed till it led to 

 so vast an extension of agriculture and of industry that it may well rank as 

 one of the greatest ac]iievements of science. 



Up to 1840 it had always been supposed that crop production must necessarily 

 be limited by the amount of farmyard manure available, and the aim of the 

 agricultural improvers had therefore been to increase the quantity of farmyard 

 manure on the farm. 



It had long been known to chemists and physiologists that certain substances 

 were favourable to plant growth, but they were all expensive materials, pur- 

 chasable only by the ounce, and the observations were regarded as of academic 

 interest only. Thus, Francis Home in 1775 had made pot experiments showing 

 that saltpetre, Epsom salt, and ' vitriolated tartar ' {i.e. potassium sulphate) all 

 led to increased plant-growth. These and similar observations, though interest- 

 ing, must have seemed to the pundits of the day about as useless andill-assorted 

 a collection of material as could well have been got together. All these, how- 

 ever, were straightened out and systcmatised bv Liebig's brilliant generalisation 

 in 1840. 



Liebig declared that the need nf the plant was not farmyard manure, but 

 the mineral substances contained in its ash. If these were supplied it could 

 dispense with farmyard manure, and draw on the illimitab'e reserves of nitro- 

 gen, carbon dioxide, and oxygen of the air for all the rest of the materials it 

 wanted. A prodigious controversy arose, and although many of the details 

 proved to be wrong, there emerged the general truth, first demonstrated at 

 Rothamsted, that crops can be raised perfectly well without any farmyard 

 manure by supplying the necessary simple nutrients. Chemists speedily found 

 out what these were and the forms in which they were most easily given. The 



' Arthur Young, General View of the Agricnltiire of Hertfordshire, 1804. 



MM'..? 



