145 



The action of natural meadows in enrichino: 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 Deherain. 



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- 

 Ici^s 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, 0.83 gram more than at the 

 beginning. This ditference 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, Dehe- 

 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 Graminew from 1884 to 1888, 

 inclusive, this time, however, without giving it any kind of fer- 

 tilizer. The soil then began 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 kik)granis taken away 

 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 untlerstood 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 comi)oun(ls brought by the rain water or by 

 the atmosphere, for, even l)y attributing to these sources a power 

 much beyond that which we have i-ecognized as belonging to them, 

 all plants should then behave in the same manner; whereas we liav'e 

 seen that we must distinguisli between the cereals Avhich impoverish 

 the soil continually and tlie leguminous plants which always enrich it. 

 2607—05 M 10 



