Water content and soil nitrification in unsaturated zone
Answers
In considering water in unsaturated soils, Edgar Buckingham, at the beginning of the century, had postulated that water was held in the interstices between solid particles by means of surface tension forces, and had defined the capillary potential dependent on the water content. A gradient of this capillary potential would produce movement of the water. L.A. Richards, in 1931, argued that Darcy's law would be obeyed in unsaturated soils because the air-filled pores could be regarded as the same as the solid soil particles as far as water conduction was concerned. However, the hydraulic conductivity would decrease with the water content, since the pathways for water movement would be more tortuous, fewer, and narrower, with the larger pores draining first. The work of W.B. Haines at this time on the physics of hysteresis in the relationship between water content and soil-water pressure in unsaturated soils was a complicating factor. Childs saw that these basic physics concepts were of little use to agriculture unless they could be applied to practical situations.