166 THE ROTHAMSTED EXPERIMENTS. 



rotations, will not be attained without having recourse to 

 a considerable variation in the description grown. Other 

 essential conditions of success will generally be the liberal 

 application of potash and phosphatic manures, and some- 

 times chalking or liming, for the leguminous crop. Then 

 the questions would arise, How long the leguminous crop 

 should occupy the land ; to what extent it should be con- 

 sumed on the land, or the manure from its consumption be 

 returned ; or under what conditions the whole, or part, of it 

 should be ploughed in ? Lastly, it is probable that more 

 benefit would accrue to the lighter and poorer than to the 

 heavier or richer soils by any such extended growth of 

 leguminous crops. 



SECTION IV. — EXPERIMENTS ON THE GROWTH OF 

 WHEAT FOR MORE THAN FIFTY YEARS IN SUC- 

 CESSION ON THE SAME LAND; BROADBALK FIELD, 

 ROTHAMSTED. 



Introduction. 



Wheat and It has been already pointed out, that although wheat and 

 barley com- k ar i ev are closely allied botanically, and they have in some 

 respects very similar requirements, yet that there are dis- 

 tinctions as well as similarities which have to be borne in 

 mind. Thus, whilst in our country and climate barley is 

 generally sown in the spring, wheat is almost always sown in 

 the autumn, and thus has four or five months for root-devel- 

 opment, and for gaining possession of range of soil, before 

 barley is sown. In the United States, on the other hand, 

 wheat is to a great extent both a spring and an autumn sown 

 crop ; whilst in some other exporting countries it is in some 

 cases a spring and in others an autumn sown crop. At any 

 rate, it is so important a crop in many countries of the 

 world that results relating to its growth, even under widely 

 different conditions, can hardly fail to be of interest to foreign 

 as well as to home growers. 



The Field Experiments on Wheat. 



Plan of the The experiments on the continuous growth of wheat at 



W erlments Rothamsted were commenced in the autumn of 1843, the first 



experimental crop being harvested in 1844 ; so that the crop of 



1894 was the fifty-first grown in succession on the same land — 



1. Without manure. 



2. With farmyard manure. 



3. With a great variety of chemical manures. 



