602 
Rotation of Crops. 
as every fourth year ; and in many cases it is not attempted to 
grow it more than once in eight years. The difficulty of 
growing red clover or beans frequently on ordinary arable land 
has been very fully illustrated in our experiments on the growth 
of leguminous crops. On the other hand, it has been found that 
red clover may be grown for many years in succession on rich 
garden soil ; and, further, that on ordinary arable land where 
clover had entirely failed, some other Leguminosae, having more 
extended root range, or more powerful root habit, grew luxu- 
riantly, and yielded large crops, containing large amounts of 
nitrogen, for a number of years in succession. Lastly, in another 
field, where beans had frequently failed, red clover was after- 
wards sown, and gave unusually large crops. 
Referring to the results in Table III. it is seen that when 
clover was grown in 1850, that is in the first course, and when 
it had not been grown on the same land for many years, large 
crops were obtained on all the plots ; though the larger where 
the mixed manure including potash, and also nitrogen, had 
been applied for the root-crop three years previously. For 
the second, third, and fourth courses, clover was sown with the 
preceding barley, but in all three it failed in the winter, and 
beans were grown instead; that is, in 1854, 1858, and 1862. 
After these repeated failures,- clover was not sown for the fifth 
and sixth courses, but beans were taken instead, in 1866 and 
in 1870. In the seventh course, clover was sown again, with 
the barley, and gave three cuttings in 1874 ; that is, twenty-four 
years since the last good crop. Without manure, the produce 
was, however, not much more than one ton per acre ; with 
superphosphate it was much more ; and with the mixed manure, 
including potash, much more still— corresponding to about 
34 tons of clover hay. For the eighth course clover was not 
sown, but beans were taken in 1878. For the ninth and tenth 
courses, however, clover was again sown, yielding in the ninth 
(1882) even more than in 1874 ; but in the tenth (1886) very 
much smaller crops, though more with mineral manure alone, 
now including potash, than with the mixed manure containing 
nitrogen also. Lastly, for the eleventh course, clover was again 
sown with the barley, but failed, and in 1890 beans were grown 
instead ; the crops, as in the case of the clover in the tenth 
course, being greater with mineral manure alone (now including 
potash) than with the mixed manure containing nitrogen 
also. 
Thus, in only four out of the eleven years in which clover 
should have been grown, was any crop obtained, and beans had 
to be taken in the other seven. The produce of clover is given 
