CHAPTER IV 



EXPERIMENTS UPON WHEAT 



I. The Continuous Growth of Wheat, Bioadbalk Fit-Id : 



A. Maintenance of the yield under Continuous Wlioat fri-owlnj^r ,,,, the 



same land. 



B. Effect of Nitrogenous Manures. 



t'. Effect of the Mineral Constituents. 

 D. Retention of Manures by the Soil. 



K. Character of the Crop as affected by Mainn-ing and Season. 

 II. Wheat after Fallow and in Rotation. 

 III. Trials of Varieties of Wheat. 



Practical Conclusions and References. 



I.— The Continuous Growth of Wheat, Broadbalk Field. 

 The experiments on the continuous growth of wheat were 

 begun in the Broadbalk field in 1843, but for tlie first eight 

 years the manuring was of a varied description, so that only 

 three of the plots have received the same treatment during the 

 whole period of sixty years. The plots as seen to-day began in 

 1852, since wliicli time the few changes in manuring have been 

 matters of detail and not of principle ; thus the results repre- 

 sent a continuous trial of wheat grown with the same manures 

 upon the same land year after year for more than half a 

 century. 



The Broadbalk field has an area uf about 11 acres, and 

 slopes somewhat to the east ; the plots are each half an acre in 

 area, and consist of strips 351 yards long by about 7 yards 

 wide, running down the slojje for the whole lengtli of tlie field, 

 and separated by paths which are not cropped. Previous to 

 1843 the land had been cropped on a five-course system : 

 manure was last applied to the turnips in 1839, and two white 



