CHAPTER 



6 



The Effect of Soil Phys- 

 ical Properties on 

 Nutrient Availability 



J. 6. PAGE and G. B. BODMAN 



S. 



ince the beginnings of plant science the major emphasis 

 has been placed upon the chemical properties of the soil and plant nu- 

 trients. Liebig stated in 1840: "The crops on a field diminish or increase 

 in exact proportion to the diminution or increase of the mineral sub- 

 stances conveyed to it in manures." This view has been widely accepted, 

 and can easily be understood in light of the very favorable yield in- 

 creases usually obtained when fertilizers are applied to the soil. The 

 proper use of fertilizers has become an accepted and necessary part of 

 farm operations. There are, however, other factors of importance in 

 crop production. This has long been recognized but comparatively little 

 attention has been paid to the physical properties of the soil, particularly 

 as they affect plant growth and fertilizer response. Studies in soil fertility 

 and soil physics have proceeded concurrently with but little appreciation 

 of the significance of the interaction of soil physical properties upon the 

 better understood and more intensely studied chemical properties of 

 the soil. Many accept the physical properties of a soil as being extremely 

 important but apparently feel that little or nothing can be done to effect 

 changes or improvements in such properties. With some soils, particu- 

 larly the well-drained sandy soils, such a view may be partly justified 

 since they have a textural porosity which permits favorable water and 

 air movement. For a great many very important agricultural soils, how- 

 ever, the physical behavior is dependent upon structure and aggregation 

 and these not only play a very important role in crop production but 



