280 
Mineral Manures and Manuring. 
land by such application enormous quantities of manure would 
have to be employed. Thus Liebig asserted that in order to 
obtain a good crop from land deficient in phosphoric acid 
or potash, it was necessary to add to the soil 100 times as much 
of these substances as is contained in an average crop. This 
erroneous view rested upon theoretical conclusions, drawn from 
the natural fertility of soils and the quantity of mineral food they 
contained. If it were correct it would be impossible to improve 
profitably the condition of the soil by artificial manuring, or to 
raise larger crops than those which are the result of its natural 
fertility. But whilst only small portions of the natural con- 
stituents of the soil can be taken up by the roots of plants, 
nearly everything which is applied as manure can be easily 
absorbed. For in artificial manuring we use potash in the 
form of easily soluble salts, such as the sulphate, carbonate, or 
chloride ; and phosphoric acid in the form of guano, bone-meal, 
or superphosphate. 
The fallacy of the supposed necessity of excessive quantities 
of manure has been demonstrated by experiments. There are 
soils exceedingly poor in phosphoric acid, which upon the 
application of a few hundredweights of superphosphate and 
ammonia-salts, or of guano and common salt, yield tolerably 
large crops. 
Mr. Mechi possessed a soil which had been notorious for its 
sterility, and which contained, according to Dr. Voelcker's 
analysis, only 0*04 to 0"06 per cent, of phosphoric acid. By 
the application of 2 cwt. of Peruvian guano and 1 cwt. of salt 
he obtained a yield of 6 quarters of wheat per acre. 
Mr. Lawes has obtained equally striking results. He has 
shown how two or three hundredweights of superphosphate and 
alkalies once applied to the land continue to exert their influence 
for many years. Two adjacent experimental plots, 10 a and 10 ft, 
received, the one 420 lbs. potash, 200 lbs. sulphate of magnesia, 
and 400 lbs. of bone-ash dissolved in 300 lbs. of sulphuric acid, 
the other double this quantity. From the year 1852 to the year 
1865 each plot received 400 lbs. of ammonia-salts annually. 
On an average, plot 10 a yielded 22 bushels of wheat, and plot 
10 ft, 26j bushels. Thus double the quantity of manure increased 
the yield by 228 lbs. of wheat per acre per annum, for a period 
of 12 years. For the next 14 years the increase in yield of plot 
10 ft was 120 lbs. of wheat per annum. Thus the influence of 
the manure was felt over a period of 26 years. 
Whilst these experiments prove not merely the utility, but 
the necessity, of applying minerals to the soil, they also prove 
that excessive quantities are not necessary. 
The cultivators of poor light soils must make use of a judicious 
