ORGANIC CONSTITUENTS OF SOILS 



149 



loam and black clay loam by leaching with dilute ammonia, the 

 power to granulate is lost. 



Figure 78 shows the effect of removal of humus upon the granu- 

 lation of black clay loam and drab clay. The silt loams granulated 

 very little even with organic matter. Each soil has been wet and 

 dried several times. Cropping with the continued removal of 

 organic matter will ultimately bring about a condition of poor 

 granulation and consequently poor tilth. 



3. Retaining Moisture. There is no better method of increas- 

 ing the moisture holding capacity of soils than by adding organic 



Fio. 78. The effect of the removal of humus and of wetting and drying upon granula- 

 tion. Drab clay is the only one that shows any tendency to granulate when humus is re- 

 moved. (University of Illinois.) 



matter. It acts as a sponge itself, and when mixed with the mineral 

 part of the soil gives higher porosity and consequently reater water 

 capacity. Jt retards capillary movement in soils, as \\oll as aids in 

 the production of a better mulch, both of which help in retaining 

 moisture by reducing evaporation. Sand permits of rapid percola- 

 tion with comparatively small amounts of water retained. I f organic 

 matter is added to sand, the retentive power of sand will be greatly 

 increased. This table shows the effect. 



Effect of Organic Matter on Retention of Moisture in Sand 8 



