76 EXPERIMENTS UPON BARLEY 



twenty-year periods being very similar. This seems to show 

 that the decline in production on the manured plots in the 

 later periods in the Hoos field is due to season, and not 

 to the fact that barley has been grown continuously on 

 the same land. The unmanured plot, however, under con- 

 tinuous barley shows a much greater progressive decline 

 than the corresponding unmanured plot growing barley in 

 rotation, where the land is practically fallowed in alternate 

 seasons. On the whole, the results point to the probability 

 that unmanured land will become unable to grow barley con- 

 tinuously at a much earlier date than will be the case with 

 wheat, so comparatively restricted is the range of the barley 

 roots. 



B. Effect of Nitrogenous Manures. 



The effect of nitrogenous manures upon the barley crop is 

 best seen by comparing the yields of the various Plots 4, all of 

 which receive the same mineral manures ; the diagram Fig. 11 

 shows this comparison in a graphic form. Plot 4-0, receiving 

 no nitrogen, has only given an average crop of 20 4 bushels per 

 acre, and this has been more than doubled by the application 

 of 43 lb. of nitrogen per acre to the other three plots. But little 

 difference is seen in the return for this amount of nitrogen, 

 whether it be applied as ammonium- salts, nitrate of soda, or 

 rape cake. Over the whole period the nitrate of soda gives the 

 highest return by about 3 per cent., but during the last two 

 decades, the plot receiving ammonium- salts has been slightly 

 the best of the three. In the straw, again, the differences are 

 very small, though the superiority of nitrate of soda is rather 

 more pronounced with the straw than with the grain. The 

 fact that ammonium- salts answer better with barley than witli 

 wheat is due to their retention by the soil close to the surface ; 

 the comparatively shallow-rooted habit of Imrley and its growtli 

 during the warmer portion of tlie year when nitrification is 

 active, renders such a surface accumulation of nitrogen as 

 readily available to the plant as the nitrate of soda itself 



On the completely manured plots the rape cake, 4 C, is 



