266 
Journal of Agricultural Research 
Vot. IX, No. 8 
per cent of lime alone is added to the soil the conductivity is but slightly 
increased. The same amount of gypsum under the same conditions 
increases the conductivity about one-third. 
The net effect of the organic matter in increasing the conductivity of 
the soil when calcium carbonate was added was about the same as when 
gypsum was added. This is seen by deducting the conductivities of the 
soils to which calcium carbonate alone was added from the conduc¬ 
tivities of the soils to which both organic matter and calcium carbonate 
were added. Making similar subtraction of conductivities of the soils 
treated with gypsum, with and without organic matter, gives about equal 
conductivity results. 
The addition of sodium nitrate to soils increased the conductivity from 
2.5 to 3.5 times over the conductivities of soils receiving no treatments. 
However, when the conductivities of the soils receiving this salt alone are 
deducted from the conductivities of the soils receiving both organic 
matter and sodium nitrate it is seen that the solvent action of the organic 
substances in the presence of this salt is less than when the organic sub¬ 
stances alone are present. 
It is seen that the solvent action of 3 per cent of alfalfa mixed with 
the sandy-loam soil is almost as great as when the same soil is mixed 
with 0.2 per cent of sodium nitrate alone. The solvent action of 1 per 
cent of alfalfa mixed with the clay-loam soil was almost as great as when 
0.2 per cent of sodium nitrate was added alone, and 3 per cent of alfalfa 
mixed with the clay-loam soil produced a solvent effect 1.4 times greater 
than when 0.2 per cent of sodium nitrate alone was added to the soil. 
SUMMARY 
In southern California many Citrus groves are now being operated 
under the mulched-basin system. The principal substances employed 
as mulching material in the basins are stable manure, alfalfa hay, barley 
hay, sweet clover, and bean straw. These substances soon begin to 
decompose when wetted by rains or irrigation water, and the decom¬ 
position products leach into the soil. On certain soil types this method 
has produced very marked improvements in tree growth and fruit setting, 
especially when the mulches used have been alfalfa or bean straw. The 
present paper is concerned with an attempt to determine the extent to 
which the beneficial action of the decomposing organic mulches may be 
ascribed to a solvent action on the soil minerals, resulting in the libera¬ 
tion of plant food. 
Soil extracts were made with organic solvents obtained from freshly 
decomposing alfalfa hay, sweet clover, and barley hay. The same sample 
of organic matter was extracted four times at intervals of from three to 
six weeks, the sample being kept under conditions favorable to decom¬ 
position between the intervals of extraction. These organic solvents 
