124 BIOLOGICAL PROBLEMS 



Of these Dock and Sheep Sorrel are frequently in- 

 troduced with the clovers, and when so introduced 

 adversely influence both grass and subsequent arable 

 land. Creeping Thistle is occasionally brought in 

 with the seeds, especially in Canadian and North 

 American clovers, but seldom to a serious extent. 

 The Creeping Thistle responds to manurial treatment, 

 and it becomes very plentiful on pastures that are 

 continually sheeped, and I more than suspect that 

 basic slag encourages its development; thus land full 

 of Creeping Thistle should be well cleaned before it 

 is allowed* to pass from arable to grass, or vice versa. 

 A cleaning crop should, therefore, always be taken 

 off a finished ley on being first ploughed up the 

 potato is perhaps the best crop for this purpose. 



An arable field foul with the above weeds should 

 not be put down to grass in a spring corn crop, as is 

 usually done; it would be better to take an early or 

 mid-season crop of potatoes and so thoroughly clean 

 the land and then sow down the grass under a plant 

 like rape if the potato crop can be removed in time, 

 or under rye sown in August or early in September. 



Bent, Creeping Buttercup, and Mint are perhaps 

 the worst weeds that are passed on from arable to 

 grass and from grass to arable. If a field has been 

 well cleaned before it is sown down to grass, they are 

 weeds which take time to establish themselves on a 

 ley, and, indeed, if a good mixture has been used and 

 the ley well cared for, they should not be much in 

 evidence until subsequent to the fourth year. It is 

 lack of appreciation on the part of farmers as to the 

 relationship between grass and arable that is respon- 

 sible for the trouble caused by Bent. The average 

 farmer has not the courage to plough down a ley 

 while it is full of clover he deems such a sward to 

 be too valuable from the herbage point of view; so 



