Rotation of Crops. 
641 
mental investigation into the mineral composition of leguminous 
crops, it may be observed — that clover at any rate grows more 
favourably on land that has recently been chalked or limed ; that 
chalking or liming of the mixed herbage of grass land also 
favours the development of the leguminous herbage ; and that 
the application of gypsum to clover has been found very effective 
on some lands, especially in America, though it has not proved 
to be at all generally useful when it has been so applied in this 
country. Indeed, the direct application of potash as manure is 
certainly more frequent, and is more generally recognised as 
effective for leguminous crops, than is that of lime, notwith- 
standing its obvious importance, and its great influence on the 
luxuriance of growth of such crops. This may perhaps be 
partly explained by the fact that, in many, if not in most, 
soils, the immediately available supply of potash within the 
root-range of the plant will probably be sooner exhausted 
than will that of lime. 
Summary and General Conclusions. 
It remains, in conclusion, very briefly to summarise the facts 
brought out in this extended inquiry on the subject of rotation, 
and to endeavour to draw from them an explanation of the 
benefits arising from the practice of it. 
At the commencement it was pointed out, that although 
many different rotations are adopted, they may for the most 
part be considered as little more than local adaptations of the 
system of alternating root-crops and leguminous crops with the 
cereals. Thus, there are rotations of five, six, seven, or more 
years. But these variations are, in most cases, only adap- 
tations of the principle to variations of soil, altitude, aspect, 
climate, markets, and other local conditions ; and they consist 
chiefly in the variation in the description of the root-crop, and 
perhaps the introduction of potatoes ; in growing a different 
cereal, or it may be more than one cereal consecutively ; in the 
growth of some other leguminous crop than clover ; or the inter- 
mixture with the clover of grass seeds ; and perhaps the exten- 
sion of the period allotted to this element of the rotation to two 
or more years. 
It is true, also, that, under any specific rotation, there may 
be deviations from the plan of retaining the whole of the root- 
crop, the straw of the grain crops, and the leguminous fodder- 
crops, on the farm, for the production of meat or milk, and, coin- 
cidently, for that of manure to be returned to the land. But it 
is also true that, when under the influence of special local, or 
