74 
Field Experiments on Clover-Seeds 
results obtained in several trials showed that even in a drv season 
like that of 1864: the application of potash-salts in conjunction 
with superphosphate of lime to clover-seeds was attended with 
considerable benefit on land naturally li^ht in texture, and de- 
ficient in available potash — a characteristic constituent of all the 
better descriptions of agricultural clays and clay-marls. In most 
cases, however, in which I employed potash-manures, they did 
not produce the effects which at one time I anticipated they would. 
As potash is an expensive manuring element, it is of much im- 
portance to the agriculturist to be able to determine with some 
degree of certainty, before he goes to the expense of buying 
potash-manures, whether money laid out in this way is likely to 
be a profitable investment. The questions, therefore, naturally 
suggest themselves, under what circumstances is it advisable to 
spend money in the purchase of such manures, and upon what 
soils or for what crops are they altogether useless, or not likely 
to give a good result in an economical point of view. 
Every one who has given attention to agricultural chemistry 
must be struck with the rapid progress which has been made of 
late years with regard to our knowledge of the manner in which 
plants derive nourishment from the soil and the atmosphere. We 
are at present in a much better position than our forefathers were 
to explain rationally the fact that some fertilising matters produce 
a much more marked effect upon vegetation than others : in many 
instances we can account satisfactorily why a manure, which 
when applied to one soil has a powerful effect on a particular 
crop, does not show the same effect upon another ; numerous 
systematic field experiments have taught us when and how to 
use fertilisers in which ammoniacal salts, or nitrates, or phos- 
phates, are the preponderating or characteristic manurial con- 
stituents. Again in many instances the causes of the sterility 
which characterise some land have been clearly traced to a de- 
ficiency of one or more of those soil-constituents, without which 
our farm-crops cannot grow luxuriantly nor come to perfection ; 
and by supplying the deficiency in the soil of fertilising matters, 
such as lime, potash, phosphoric acid, &c., the intelligent farmer 
has succeeded in many instances in transforming all but barren 
land into useful and fairly productive soils. 
Great as has been the progress during the last ten years with 
regard to the theory and practice of manuring, an extensive field 
for inquiry is still left open to the man of science as well to the 
advanced agriculturist ; and much pains-taking labour will have 
to be expended by both before our knowledge of the action of 
fertilising matters and our practice of manuring become thoroughly 
satisfactory. 
The conditions under which ammonia, lime, or phosphates 
