Soils and fertilizers . inpoorly drained ones. It is, however, from the furrow sHcethat plants derive most of their nourishment. Subsoils sometimes contain more and sometimes lessplant-food materials than do the surface soils. Nitrogenis almost always present in greater quantity in the surfacesoil, because it is a constituent of material that has beenplowed into the furrow shce. Table 18 contains a statementof the analyses, expressed in percentage composition, of twosoils to a depth of four feet, each foot of which was analyzedseparately. Table 18. — Ultimate Analyses op Two Soils to a Depth o
Soils and fertilizers . inpoorly drained ones. It is, however, from the furrow sHcethat plants derive most of their nourishment. Subsoils sometimes contain more and sometimes lessplant-food materials than do the surface soils. Nitrogenis almost always present in greater quantity in the surfacesoil, because it is a constituent of material that has beenplowed into the furrow shce. Table 18 contains a statementof the analyses, expressed in percentage composition, of twosoils to a depth of four feet, each foot of which was analyzedseparately. Table 18. — Ultimate Analyses op Two Soils to a Depth opFour Feet, Expressed in Percentage Composition DuNKiRS Clat Loam VoLUBiA Silt Loah 1st ft. 2nd ft. 3rd ft. 4th ft. l8t ft. 2nd ft. 3rd ft. 4th ft. Nitrogen . .126 .067 .064 .064 ..143 .052 .059 .050 Phosphoric acid . .084 .066 .103 .125 .081 .039 .018 .071 Lime . . .330 .270 .520 .230 .160 .260 .360 Magnesia .160 .150 .150 .320 .560 .390 .290 .400 Potash . Plate XI. Surface Soil and Subsoil. — Note the differencebetween the top soil and the subsoil in the upper figure ; also the abun-dant growth of plant roots in the top soil as compared with the subsoil inthe lower figure. PLANT-FOOD MATERIALS IN SOILS 93 These analyses show in some cases more, and in othersless, of the various constituents below the surface foot,with the exception of nitrogen, which is always less in thesubsoil. The fact that the greater part of the roots ofmost plants is in the surface soil makes the draft greateron that layer, but the total volume to a depth of four feet,or even more, may be considered to be the feeding groundof crops. 107. Upward movement of plant-food materials. — Thereis another way in which the soil to a considerable depthmay contribute to the nourishment of crops. This is byfurnishing plant-food materials that are carried upwardby ascending currents of moisture, or that are absorbed byroots from the lower depths and deposite
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