AVAILABLE NITROGEN OF THE SOIL. 281 
than the most barren sand. In eight distinct trials the 
crops weighed (dry) but 3 to 5 times, in one case 8 times 
(average 4 times), as much as the seed; while in sand, 
pumice, or burned soil, containing no nitrogen, Boussin- 
gault several times realized a crop weighing 6 times as 
much as the seed, though the average crop of 38 experi- 
ments was but 3 times, and the lowest result 14 times the 
weight of the seed. 
The fact that the nitrogen of this garden soil was for 
the most part inert is strikingly shown on a comparison 
of the crops yielded by it to those obtained in barren 
soil with aid of known quantities of nitrates. 
In a series of experiments with the Sunflower, Boussin- 
gault (Agronomie, etc., I, p. 233) obtained in a soil desti- 
tute of nitrogen a crop weighing (dry) 4.6 times as much 
as the seeds, the latter furnishing the plants 0.0033 grm. of 
nitrogen. In a second pot, with same weight of seeds, in 
which the nitrogen was doubled by adding 0.0033 grm. in 
form of nitrate of soda, the weight of crop was nearly 
doubled—was 7.6 times that of seeds. In a third pot the 
nitrogen was trebled by adding 0.0066 grm. in form of ni- 
trate, and the crop was nearly trebled also—was 11.3 
times the weight of the seeds. 
In another experiment (p. 271) the addition of 0.194 
grm. of nitrogen as nitrate of potash to barren sand with 
needful mineral matters, gave a crop weighing 198 times 
as much as the seeds. But in the garden soil, which con- 
tained, when 40 grms. were employed 0.104 grm., and when 
130 grms. were used 0.338 grm. of nitrogen, the result of 
growth was often not greater than in a soil that contained 
‘no nitrogen, and only in a single instance surpassed that 
of a soil to which was added but 0.0033 grm. The fact 
is thus demonstrated that but a very small proportion of 
the nitrogen of this soil was assimilable to vegetation. 
From these beautiful investigations Boussingault deems 
it highly probable that in this garden soil, and in soils 
