3o8 SYSTEAfS OF AfANURING CROPS [chap. 



the extra price of organic manures like the guanos will 

 rarely be repaid by any increased yield. 



Barley is grown under two very different conditions 

 of tilth. In the first place, it may follow wheat and 

 form the second or even the third white straw crop after 

 roots or a clover ley; in the Isle of Thanet three, four, 

 or even five barley crops may be taken in succession 

 after an old lucerne or sainfoin ley has been broken up. 

 In such cases the high condition will have been taken 

 out of the soil by the first crop of wheat, there will no 

 longer be any excess of readily available nitrogen, and 

 as there is a good opportunity of getting the soil early 

 into tilth, barley of high quality may be expected. 

 Good malting barley contains a low percentage of 

 nitrogen, hence the soil on which it grows must not be 

 too rich, nor must any large quantity of nitrogenous 

 manure be employed. On the other hand, however, it 

 is a mistake to suppose that impoverished soil alone 

 will yield good barley ; unless a reasonable amount of 

 nitrogen be available not only will the yield be small 

 but the size of the berry will fall away. This may be 

 illustrated from the Rothamstcd experiments on the 

 Agdell field, where the barley follows Swede turnips in 

 the rotation. On this field the plots are manured for 

 the root crop but not for the barley which follows, and 

 on three of the plots the following average results were 

 obtained (Table XC). 



The soil of the first plot was in a very impoverished 

 condition because a crop of roots had been grown 

 without nitrogenous manure and had been wholly 

 removed from the soil ; the grain in consequence was 

 poorly developed for want of nitrogen, as is shown by 

 its low weight per bushel and per looo grains; its value 

 was, in consequence, low in spite of the small percentage 

 of nitrogen it contained. The second plot, on which a 



