156 HARNESSING THE EARTHWORM 



REVIEW OF LITERATURE 



Although several workers have investigated the activities 

 and the benefits of earthworms, only a few data on the compo- 

 sition of the casts have been published. Darwin (2) devoted a 

 whole book to the subject of earthworms but did not include any 

 such data. Hensen(3) found that loss on ignition of worm 

 excrement lining the burrows was 3.3 to 5 per cent, compared 

 with 2.3 per cent for the unworked soil. He also mentioned that 

 Miiller reported 24 to 30 per cent loss on ignition for worm ex- 

 crement in contrast to about 8 per cent for soil. Salisbury (9) 

 found that worm casts had a higher organic matter content than 

 the soil in six cases out of eight. He also reported that the re- 

 action of the casts was usually more nearly neutral than was that 

 of the original soil. Similar findings have been reported by 

 Robertson (7) and are shown in the data of Puh given below. 

 Blanck and Giescke (1) found a marked increase in the nitrify- 

 ing power of three different soil types as the result of earthworm 

 activity. Earthworm casts collected from cut-over land on two 

 soil types had higher base-exchange capacities, organic matter, 

 and nitrogen contents than did the unworked soil mass, according 

 to Powers and Bollen (5). They discovered that barley grown 

 in pots produced much higher yields when earthworms were 

 present than when the soil was free of worms. 



Robertson (7) has shown that earthworms secrete calcium 

 carbonate concretions in their calciferous glands. Secretion can 

 take place under acid, neutral, or alkaline conditions, provided 

 the worms have access to material containing calcium. He points 

 out, however, that these concretions, which are excreted in the 

 casts, do not affect the reaction of the casts in the least; it is 

 rather the secretions of the gut wall which are responsible for 

 changes in the reaction of the casts. When worms were kept on 

 filter paper or in acid peat, formation of calcite concretions ceased 

 after a week or 10 days. 



