SOIL TREATMENTS AND SEED GERMINATION 27 



Calcium Hypochlorite 



Calcium hypochlorite, chlorinated lime, or bleaching powder, often called 

 chloride of lime, has fungicidal properties (14, 91). That used by the writer con- 

 tained 26 to 30 percent available chlorine and was applied, dry, to soil some days 

 or weeks before seeding. 



Germination was not injured so much as was growth and in some cases was 

 even improved by the treatments named in Table 12. The severity of damping-off 

 was in some cases lessened also, but this disease was not consistently prevented 

 and there was too much chemical injury (see Table 12) to most species of plants 

 the seeds of which were sown 1 to 3 weeks after soil treatment. 



Gratz (39) made the similar observation that enough of this chemical to kill 

 plants (cabbage) was not enough to prevent their infection by Rhizoctonia, and 

 a heavy application used by Small (81) did not protect tomato seedlings against 

 this fungus. 



This is not a chemical which, in effective amounts, may be used safely with 

 most species immediately before seeding, and the time interval between soil 

 treatment and seeding with safety is not likely to be short. It is, of course, less 

 injurious to some species than to others, and the one least injured in these ex- 

 periments (see Table 12) was ten-weeks stock. According to Loew (59), the 

 length of time which is necessary between soil treatment with calcium hypo- 

 chlorite and seeding, may be affected by the character of the soil, with the interval 

 shorter in soils rich in humus and low in clay. He used about 19 gm. per square 

 foot without injury to cabbage and beet, but these were not planted until 2 

 months after soil treatment — a delay which many growers would consider as 

 undesirable as the risk of damping-off without any treatment. 



Other Calcium Salts 



As was discussed earlier, it does not appear that damping-off is ordinarily 

 controllable by the use of calcium in the form of lime. Albrecht and Jenny (4) 

 observed less damping-off of soybean, however, when they used calcium acetate 

 and calcium chloride and they concluded that calcium concentration is more 

 important than H-ion concentration in affecting damping-off. They made no 

 observations as to infecting fungi, and their seedlings often damped-off in spite 

 of sterilization of soil and seeds by other means. It is, therefore, at least possible 

 that fungi may not have been the cause at all, for plant ailments of very different 

 origin may be much alike in symptoms. 



The calcium salts here named were applied by the writer to soil inoculated 

 with Pythium and this fungus was isolated from seedlings which damped-off. 

 The disease was not controlled by calcium chloride in amounts sufficient to injure 

 Ageratum, Myosotis, and mignonette. Calcium acetate was less injurious, but 

 heavy applications, up to 30 gm., did not control damping-off. 



Calcium sulfate, gypsum, even 50 gm. per square foot, also failed to control 

 damping-off, although 20 to 35 gm. did improve the growth of seedlings of sweet 

 pea, but not of lavender and Delphinium. It is occasionally recommended in 

 horticultural literature for the control of root rots of pea, and the growth of 

 legumes in some soils has, according to Cubbon (24), been benefited by it; but 

 the results in this work were not such as to warrant its recommendation as a 

 soil fungicide. 



Riviere and Richard (77) concluaed that calcium sulfite has a temporarily 

 antiseptic action in soil. Apparently it is not very pronounced, however, for 10 

 to 25 gm., used in these experiments, did not control damping-off satisfactorily. 



