SOIL TREATMENTS AND SEED GERMINATION 29 



strengthened by the results of Zimmerman (103), who found that oxidizing agents 

 such as potassium permanganate improve the rooting of cuttings, but that aera- 

 tion alone may be even more effective. 



Charcoal 



Charcoal is mentioned at this point, for it too is occasionally recommended, 

 as by Macself (61), for a soil treatment to check the spread of damping-off, 

 although there seems to be little or no experimental evidence on which to base 

 such a recommendation. Chupp (19) observed that there was almost no damping- 

 off in a steamed soil with which a grower had mixed powdered charcoal, but the 

 steaming alone could, of course, account for that, and Chupp did not assert 

 otherwise. 



Powdered wood charcoal 1 to 4 ounces per square foot, worked into soil before 

 seeding, did not control damping-off or improve germination. Powdered charcoal 

 is sometimes used, as Taylor (84) says, with rooting media for cuttings; but when 

 the writer so used it, up to 3 ounces per square foot, there was no significant 

 effect on the rooting of cuttings (taken July 1) of Enkianthus subsessilis, Lonicera 

 syringantha, Rhododendron arbiitifolium and Persian yellow rose. 



Charcoal is said (2) to lessen the danger of injury to plants by a too acid soil; 

 but if so, it is not by changing soil reaction, for, in these experiments, 4 ounces 

 or less did not affect pH values of soil 54 days after soil treatment. 



Charcoal 1 to 4 ounces did not affect growth of seedlings of Aubrietia, heliotrope 

 or sweet pea, but did significantly improve the growth of nasturtium. This im- 

 provement was first evident 2 or 3 weeks after germination and continued for 

 5 to 10 weeks or as long as the plants were under observation, with most benefit 

 from applications of 2 to 4 ounces. 



Aluminum Sulfate 



Several investigators (97, 56, 52) have successfully used aluminum sulfate for 

 the protection of conifers against damping-off. Not much use has been made 

 of it with other species, although Weindling and Fawcett (95) found that 30 gm., 

 raked into soil before seeding, protected citrus seedlings against Rhizoctonia. 



Aluminum sulfate, in solution, was applied to soil before seeding. Damping-off 

 caused by Pythium and Rhizoctonia, more often by the latter, was not affected 

 by 10 or 15 gm., was less severe with 20 or 25 gm., but was never eliminated by 

 less than 30 gm. The exact quantities necessary would probably not be the same 

 in all soils, for Jackson (52) found that an application which lessened the severity 

 of damping-off of conifers at pH 3.5 was not as effective at pH 6.5. By preventing 

 some pre-emergence damping-off, 25 to 30 gm. improved the germination of 

 Calendula, China aster, several species of Dianthus (see Table 13), foxglove, 

 sweet pea, and Nicotiana. 



There was no injury to germination of any species by 28 gm., nor to Calendula, 

 China aster, and Nicotiana by 35 gm., while seeds of all species of Dianthus used 

 germinated without injur}- by 44 gm. 



, Soil pH values were lowered, in 8 weeks, from an initial value of pH 6.5 to 

 pH 6.0 by 20 gm. and to pH 5.7 by 25 gm. These effects might, of course, be 

 different in different soils. 



There was more injury to growth than to germination. Results are recorded in 

 Table 13. Seedlings of beet, a species which McLean and Gilbert (66) found 

 very subject to injury by aluminum, and China aster were injured by 20 gm., 



