696 
Journal of Agricultural Research 
Vol. XI, No. 13 
that is, in pieces not over % inch in length—can not be said to represent 
conditions exactly comparable to field practice, yet it is believed that 
the rate of decomposition would have been approximately the same if 
they had been added in larger pieces. The results found here confirm 
those of Boltz already referred to. What shall we say, therefore, con¬ 
cerning the use of green manures in building up the organic matter of 
the soil? In the first place, it is to be remembered that neither in our 
experiments nor in those of others have the roots of the plants been 
used. Parts of the roots would probably decompose somewhat more 
slowly because of their toughness. However, it is doubtful if this would 
radically change the results. As Pieters (6) concludes from his review 
of the subject, the use of green manures generally gives greater crop 
yields to crops immediately following. This increase of crop would 
usually, if properly handled, give greater crop residues to plow under, 
which in turn would tend to enrich the soil. Then it must not be for¬ 
gotten that the green manure would of itself add available plant food 
to the soil, taken partly or largely from the unavailable supply. And, 
of course, in the case of leguminous green manures, nitrogen would be 
added also. Then its decomposition would render an additional amount 
of plant food available. 
In practice it is often observed that, where insufficient time is allowed 
between the plowing under of the green manure and the planting of a 
crop, in a dry season the crop suffers from lack of moisture. This prob¬ 
ably is due to the turning under of the green manure in large bunches. 
From the results of this experiment it is seen that if some practical plan 
could be found to mix the material thoroughly with the soil, most of it 
would be decomposed in a short time. This must be left, of course, to 
field experiments. 
When results for total organic matter are considered, it is observed 
from column 11 (Table IX) that the limed soils showed a greater per¬ 
centage of decomposition than the unlimed. In some instances, how¬ 
ever, the differences are so small as not to be significant. 
In the twelfth column (Table IX) the carbon coming from the green 
manure alone is shown. In the case of the unlimed soils, it is less by 
nearly one-half than the corresponding amount from the green manure 
applied to the soil s alone. From the limed soils, however, it is seen that 
the stable manure apparently quite appreciably increases the rate of de¬ 
composition of green manures. We are not prepared to give an expla¬ 
nation of these facts. However, we believe that the results of this exper¬ 
iment and the one preceding warrant the conclusion that green manures 
under most conditions will be decomposed sufficiently rapidly in the soil 
without the addition of stable manure. 
