EEMOVAL OF NUTRIENTS FROM THE SOIL 299 



soil particles and the plant, as well as between the soil-water 

 and the plant. Such a condition complicates in no small 

 degree the practical questions of soil management and plant 

 nutrition. 



158. Why crops vary in their ability to thrive on dif- 

 ferent soUs. — It is very commonly recognized that crops of 

 different kinds vary in their ability to obtain nourishment 

 from the soil. The difference between the nitrogen, phosphoric 

 acid, potash, and lime taken up by an average corn crop and 

 a wheat crop of average size is striking. The terms '*weak 

 feeders" and '* strong feeders," so often heard, indicate the 

 practical field relationships. Aside from the fact that crops 

 do not all need the same quantities of nutrients these differ- 

 ences in ability to grow normally on different soils may be 

 due either to (1) a larger absorbing system or (2) a more 

 active absorptive capacity. 



Plants with large root systems may be expected to absorb 

 greater amounts, not only of water but of nutrients also.^ 

 Such a development is especially important in time of drought 

 and in addition gives the plant a greater area from which to 

 draw nutrients. Water, as well as nutrients, does not move 

 through any great distance towards the imbibing and ab- 

 sorbing surfaces. Root development, while of some impor- 

 tance in explaining the differences in the feeding capacities 

 of plants, is probably by no means as important as differences 

 in the absorption activity. 



The absorptive activity of a plant under any given condi- 

 tion of soil, climate, and stage of growth depends on: (1) the 

 concentration and composition of the cell-sap; (2) the char- 

 acter of the cell-wall; (3) the activity of the cell in elabo- 

 rating and removing from solution the materials absorbed; 

 (4) the extent to which exudates — whether these be carbon 



* Gile, P, L., and Carrero, P. L., Ahsorption of Nutnents as Affected^ 

 hy the IsFumber of Boots Supphed with the Nidrient; Jour. Agr. Bea., 

 Vol. IX, No. 3, pp. 73-95, 1917, 



