Mar. lo, 1919 Organic Matter and Water -Holding Capacity of Soil 273 



It is of interest that the differences in moisture content are as great as 

 would be computed on the assumption that the organic matter of this 

 silt loam has the same water-holding capacity as some of the most 

 absorbent peats, some of these, even when well drained, being able to 

 retain 300 to 400 parts of water to every 100 parts of dry peat. The 

 surface foot of plot 3 carries 1.37 per cent more organic matter than the 

 corresponding level on plot 4 (Table I), from which might be computed 

 a difference of about 5 per cent in water-holding capacity. 



Table VIII. — Hygroscopic coefficients of successive levels on plots j and 4 



Depth of section. 



I to 3 inches , . . 

 4 to 6 inches . . . 

 7 to 9 inches . . . 

 10 to 12 inches. 



First foot 



Second foot. .. . 

 Third foot 



INFLUENCE OF ORGANIC MATTER UPON PROPORTION OF USEFUL 



MOISTURE 



The nitrogen content of the surface foot of plot 3 is 138 per cent and 

 the organic matter 140 per cent of that on plot 4, while the hygroscopic 

 coefficient is only 5 per cent the higher on the former. As a consequence 

 the proportionate increase in free water is much greater than that in 

 total moisture content, and that in growth water still greater. Thus, 

 the average moisture content of the surface foot for the nine samplings 

 in May, June, and July was 26 per cent on plot 4 and 30.3 per cent on 

 plot 3, the free water 18.3 and 22.2, and the growth water 13.5 and 17. i, 

 respectively, corresponding to increases of 15, 21, and 27 per cent. 



Thus, the difference in organic-matter content, owing to differences 

 in the manuring and cropping of the two plots, caused a marked differ- 

 ence in the amounts of useful moisture during the season of 191 5 as is 

 well illustrated by a comparison of the ratios of the moisture content 

 to the hygroscopic coefficient (Table IX). The advantages of expressing 

 the moisture condition of soils by such ratios has been discussed in 

 several recent papers (3, p. 55; 4, p. 453; 5» P- 2^^)- The expression 

 "hygroscopic coefficient = lo.o; ratio = 1.7" indicates a moisture content 

 of 17.0 per cent, a wilting coefficient of 15.0^ {8, p. 65), 7 per cent of 

 free water, and 2 per cent of growth water. The ratios i.o, 1.5, and 

 2.0—2.5 appear to indicate, respectively, the minimum to which crop 



' The exact figure is 14.7. 



