MEASUREMENT OF THE AMOUNT OF WATER THAT 

 SEEDS CAUSE TO BECOME UNFREE AND THEIR 

 WATER-SOLUBLE MATERIAL 



By George J. Bouyoucos and M. M. McCool 



Michigan Agricultural Experiment Station 



INTRODUCTION 



It has been shown that soils cause water to become inactive or unfree, 

 as is indicated by its refusal to freeze or to function as a solvent. The 

 magnitude of this unfree water has been measured by means of the 

 dilatometer method, 1 which has proved most convenient, appropriate, 

 and unique for this purpose. The principle of this method is based 

 upon the fact that water expands upon freezing. If the amount of 

 expansion that a certain amount of water (i gm.) produces upon freezing 

 is known, then the quantity of water that freezes in the soil can be cal- 

 culated from the magnitude of expansion produced. On the basis of 

 this dilatometer method the water in the soil has been classified anew 

 as follows : 



i. Gravitational water, unsuitable to plants. 



2. Free water, readily available to plants. 



I Capillary, adsorbed, very slightly available to plants. 

 | water of hydration 1 very unavailable to 

 1 water of solid solution J plants. 



The free water is that which freezes very readily at the supercooling 

 of —1.5 C. ; the capillary, adsorbed water is that which freezes from 

 the temperature of — 1.5 to — 78 ; while the combined water is that 

 which does not freeze at all, even at the extreme temperature of — 78 . 



AMOUNT OF WATER THAT SEEDS CAUSE TO BECOME UNFREE 



It is, of course, very well known that seeds absorb large quantities of 

 water and with a considerable force. Seeds like the lima bean, cowpea, 

 soybean, clover, and alfalfa absorb over 100 per cent of their dry weight 

 of water; while seeds like the wheat, rye, and corn absorb about 50 

 per cent of their dry weight of water. The great attraction that seeds 

 have for water is best realized by the fact that they will abstract the 

 moisture from the soils even down to the point of air-dryness. Whitney 



1 Bouyoucos, George J. measurement of the inactive, or unfree, moisture in the sou, by 

 means of the dilatometer method. In Jour. Agr. Research, v. 8, no. 6, p. 195-217, 1 fig. 1917. Litera- 

 ture cited, p. 217. 



classification and measurement of the different forms of water in the soil by means 



of the dilatometer method. Mich. Agr. Exp. Sta. Tech. Bui. 36, 48 p., 5 fig. 1917- 



and McCool, M. M. further studies on the freezing point lowering of soils. Mich. Agr. 



Exp. Sta. Tech. Bui. 31, 51 p. 1916. 



Journal of Agricultural Research, Vol. XX, No. 7 



Washington, D. C Jan. 3, 1921 



wi Key No. Mich.-i2 



(387) 



