145 
The action of natural meadows in enriching arable soils is of the 
same nature; here follow some curious results on this subject which 
I have borrowed from the works of Messrs. Lawes and Gilbert and 
those of Déhérain. 
In 1856 Messrs. Lawes and Gilbert transformed into meadow 
lands a portion of the domain of Rothamsted, which for a long 
series of years had been used only for raising grains. The soil con- 
tained then 1.52 grams per 1,000 of nitrogen; it was manured regu- 
larly and in what would be called excessive doses in such a way that 
the nitrogen of the fertilizers always exceeded that of the crop by 
about 15 kilograms every year. 
It is evident that they could not pretend with this small surplus to 
compensate entirely for the losses caused by the drainage; neverthe- 
less the soil, instead of becoming impoverished, was constantly 
enriched, and at the end of the year 1888 its proportion of nitrogen 
was 2.35 grams per 1,000—that is to say, 0.85 gram more than at the 
beginning. This difference corresponds to a total of 1,813 kilograms 
to the hectare for the entire time that the experiment lasted—that is 
to say, an annual gain of 50 kilograms per hectare. 
The phenomenon is moreover progressive, and nothing in its rate 
gives any reason for supposing that it is approaching its limit. 
At the experiment field of Grignon, my learned instructor, Déhé- 
rain, observed similar facts. From 1875 to 1879 he raised beets and 
maize for fodder upon a piece of land freshly cleared of lucerne 
grass and containing a proportion of 2.05 per 1,000 of nitrogen. In 
spite of the fertilizers given to it during that time, the land became 
rapidly impoverished, no doubt from excessive nitrification, and in 
1879 its fertility had declined to 1.50 grams—that is to say, to about 
three-quarters of its former value. 
The maize was then replaced by French grass |sainfoin] from 1879 
to 1883, then with a meadow of Graminex from 1884 to 1888, 
inclusive, this time, however, without giving it any kind of fer- 
tilizer. The soil then began g gradually to increase in fertility and has 
now returned to its former state of richness. 
Another experiment very similar to the preceding, but in which 
they had not manured the soil since 1875, gave nearly identical 
results. 
If we admit that at Grignon the soil of a hectare weighs on an 
average 4,000 tons, we see that in ten years, from 1879 to 1888, the 
soil gained under the influence of the prairie grass alone 1,920 kilo- 
grams of nitrogen, to which we must add 1,210 ‘kilog rams taken aw ay 
by the crops, or a total of 3,130 kilograms, or more than 300 kilograms 
a year per hectare. 
Here again the limit is far from being attained, and it can be 
easily understood that soils subjected to this treatment would in time 
come to contain 10 grams per 1,000, or a hundredth or more of nitro- 
gen, like the meadows mentioned by Messrs. Truchot and Joulie. 
It is clear that this natural phenomenon can not be owing to the 
contributions of nitric compounds brought by the rain w ater or by 
the atmosphere, for, even by attributing to these sources a power 
much beyond that which we have recognized as belonging to them, 
all plants should then behave in the same manner; whereas we have 
seen that we must distinguish between the cereals which impoverish 
the soil continually and the leguminous plants which always enrich it. 
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