SOILS OF ILLINOIS. 789 



States Department of Agriculture, on the Maryland soils indicate that the 

 texture and physical conditions of the soils are of even more importance 

 than the chemical composition. On this matter Professor Whitney has 

 written as follows: 1 



The prevailing- ideas of plant nutrition have been based maiuly upon the chemical 

 composition of soils. When it was found that the chemical composition of a soil and 

 plant did not show what was lacking in the soil for a large crop, it was held that only 

 a small part of the plant food in the soil is at any one time in a form of combination 

 which is available to plants; that the available plant food never accumulates as such 

 in the soil, but quickly reverts to more insoluble forms, which are unavailable to 

 plants. According to this idea the exhaustion of soils by continued cropping is due 

 to the actual loss of available plant food removed by the crop or converted into an 

 unavailable form by chemical changes iu the soil. The chief use of fertilizers is to 

 supply the plant with food which the soil fails to furnish. The reason certain plants 

 do better on certain kinds of soil is assumed to be due to the fact that plants vary 

 greatly in their powers of gathering their food from the soil and air, and that thus a 

 rye plant would do well on a soil too poor to give a good yield of wheat. 



Our investigations on the Maryland soils seem to show, however, that the 

 texture and the physical conditions of the soil are of more importance than the 

 chemical composition. It appears that under favorable couditions of moisture and 

 temperature plants can readily gather sufficient food material from nearly all soils; 

 but if these conditions of moisture and heat are changed, the development of the 

 plant will be greatly changed and it will take up more or less food from the soil. 

 Soils differ greatly in their texture— that is, in the amount of sand and clay which 

 they contain— and, as we have seen, this controls very largely the supply of moisture 

 which they can maintain for the crop Avith a given amount of rainfall. If there are 

 4 inches of rainfall a month, the coarse sandy soil will allow most of this to run 

 through very quickly, so that there may not be more than 5 or per cent of water 

 held in the soil for the crop, or, say, about 100 tons of water per acre 1 foot deep; and 

 when this water is used up, the soil has comparatively little power to draw up more 

 water from below for the use of the crops. With a compact clay soil, on the other 

 hand, the water passes downward very slowly, and the soil will maintain about IS or 

 20 per cent of its weight of water for the crop, or about 400 or 500 tons of water per 

 acre 1 foot deep. In the dry season, also, the clay soil has more power of drawing up 

 water from below, and maintaining this supply. If a florist should give a plant four 

 times as much water as he gives another plant of the same kind, the two plants would 

 develop very differently, and he uses this constantly to produce any kind of develop- 

 ment he desires. If it is desired to have the. plant flower or fruit, the soil is kept 

 rather dry and cool. If it is desired to produce large leafy plants, the soil is kept 

 much wetter and warmer. To have equal success with different kinds of plants the 

 amount of water must be carefully regulated according to the needs of the plant. 

 Some plants require a much more abundant supply of water than others. This con- 

 trol of moisture and temperature is far more important than the mere chemical com- 

 position of the soil. 



' Kept. Illinois Board of World's Fair Commissioners. 1895. pr>. 94-96. 



