204 THE PRINCIPLES OF 



land, at least that is our experience. Some people say once 

 in a lifetime ; other people say once in a lease. Nature 

 clearly points out in the case of sainfoin the necessity of 

 change and of some form of rotation of crops. The same 

 rule holds good with flax; much land will grow flax, but 

 we must not grow this crop frequently, perhaps once in 

 twelve years will be found sufficiently often. Clover seeds 

 cannot be grown often on the same land. I could hardly 

 recommend you to grow clover seeds more than once in twelve 

 years. Potatoes are much the same. In field cultivation 

 land will often grow one good crop of potatoes, a bumper 

 crop, and it is in vain that we try to grow another, especially 

 on land of rather a weak character. Other examples could 

 be given, but these will suffice. Cereal crops are not open to 

 this objection ; they can be grown continuously on the same 

 land. 



When I was first introduced to the scientific aspect of 

 agriculture, the question of clover sickness was a very im- 

 portant one, and there was a great deal of controversy as to 

 the reasons why land becomes clover sick. I find the same 

 controversy going on now, and I am not aware that it has made 

 much advance. Want of food is perhaps the reason, but why 

 that should be the cause it is very difficult to understand, 

 because, after all, the requirements of clover, according to the 

 chemical analysis both of the ash and of the plant itself, ought, 

 we might imagine, to indicate the kind of food required, and 

 that kind of food could be added to the land. But all efforts 

 to do so up to the present time have been failures. The 

 Rothamsted experiments with regard to clover sickness will 

 well illustrate this point. In those experiments the land had 

 not only been liberally and completely manured for the first 

 nine inches in depth, but it had been manured for the second, 

 third, and fourth nine inches in depth successively and simul- 

 taneously. The ground having been manured by special 



