SOILS OP MASSACHUSETTS AND CONNECTICUT. 39 
its best possible condition for plant growth — varies widely with soils 
of different textures. In other words, from a given amount of rain- 
fall one soil is more capable than another of furnishing optimum 
moisture to a given crop. Frear x states that — 
Equally essential with the proper food supply for the growth of a crop are 
fitting temperature, moisture, and looseness of the soil for the root of the plant. 
While the soil temperature and moisture are strikingly affected by local climate, 
they depend also in very large measure upon the structure of the soil itself. 
If we could determine the structure of the soil accurately, we would probably 
be able ere long to make quite exact predictions as to the kinds and qualities of 
crops any soil whose structure was known could produce. * * * While no 
satisfactory means have been devised for determining soil structure with pre- 
cision, the size of the particles of which it is composed affords valuable indica- 
tions of its physical properties and especially of its moisture relations. Another 
important function must be added: The soil largely modifies the climate to 
which the plant is exposed. We are accustomed to regard atmospheric condi- 
tions as most largely influencing the life activities of plants, but careful ob- 
servation has shown that within a wide range of temperature the warmth of 
the soil far more than the air determines the vigor of plant development. 
With tillage conditions equal, the thickness of the film of moisture 
around each grain of soil depends, on the one hand, upon the supply 
of ground water at any particular time, and on the other, upon the 
rapidity with which the film of moisture is being removed by plant 
rootlets. Amendments may be added to the soil in the form of lime 
and humus, which also affect in varying degree the amount of film 
water in the soil which is available to plant rootlets. But the plant 
food in the soil is obtained by growing plants only as it is dissolved 
in the soil film moisture, hence it is apparent that the distribution 
and consequent availability of the moisture is a matter of the utmost 
importance. 
Jeffery 2 found in his work on the water-holding capacity of soils 
that of water that was passed — 
Through 100 ounces of air-dry clay soil, 56 ounces were retained. 
Through 100 ounces of air-dry loam soil, 49 ounces were retained. 
Through 100 ounces of air-dry sandy soil, 36 ounces were retained. 
Through 100 ounces of air-dry muck soil, 170 ounces were retained. 
In the first three cases the differences are due largely to the size of 
the soil grains. In the fourth case the great capacity of the soil for 
water is due to the large amount of organic matter present, which in 
this particular soil was over 69 per cent. It is thus apparent 
that any marked increase in the water-holding capacity of any one 
of the three first grades of soil in the above experiment would re- 
quire some amendment, and for this purpose humus is the most 
efficient. In the case of the sandy soil, however, decayed organic 
1 Bol. 20, Pa. Agr. Expt. Sta. 
- Bui. 219, Mich. Agr. Expt. Sta. 
