3IO SYSTEMS OF MANURING CROPS [chap. 



whatever the tilth it seems desirable to give this crop 

 about 3 cwts. per acre of superphosphate, or its equivalent 

 in steamed bone flour or phosphatic guano on light soils 

 poor in carbonate of lime. The question of potash is 

 more doubtful ; while potash manures have been found 

 to stiffen the straw and increase the size of the berry- 

 by promoting starch-formation, they also prolong the 

 maturity of the barley and darken its colour slightly. 

 Hence, potash manures must be used carefully and are 

 only likely to be valuable on light sandy or gravelly 

 soils. We thus arrive at the following mixture for a 

 barley manure, when barley follows one or more white 

 straw crops and the land is no longer in high condi- 

 tion : — 



Sulphate of ammonia ^ to i| cwts., or rape dust 4 to 

 6 cwts. per acre. 



Superphosphate 3 cwts. per acre, or steamed bone 

 flour 2 cwts. 



Sulphate of potash \ cwt. per acre, on light soils 

 only. 



The superphosphate and sulphate of ammonia or 

 rape dust should be mixed and sown broadcast before 

 the seed is drilled ; it is impossible to distribute small 

 quantities like a | to i cwt. as a top dressing evenly 

 unless they are mixed with a much larger bulk of 

 ashes. 



A mixture of this kind would also serve for the rare 

 case of barley following roots which have been grown 

 without farmyard manure and then carted off the land. 



When barley follows roots which have been highly 

 manured with farmyard manure, still more so when the 

 roots have been folded off by sheep, the land is already 

 too rich in readily available nitrogen to grow barley of 

 the highest quality, the more so as the roots are often 

 left so late on the ground that a good seed-bed cannot 



