50 



On Plats 2 and 3, which received excessive quantities of the spray 

 material, no injurious effect of iron sulfate in the soil was detected. 

 In searching for an explanation of this matter, the writer is inclined 

 to accept the view recently advanced by Longyear (1918), namely 

 that iron sulfate is unlikely to produce an injurious effect on the roots 

 of the plants since the chemical oxidizes very readily and, upon reach- 

 ing the soil, is combined with soil constituents, and becomes insoluble 

 and inert. 



In this connection it is interesting to consider the killing of the 

 clover by the sulfate in the light of the work of Ruprecht (1915), who 

 found that sulfate of iron has a very harmful effect upon the roots of 

 clover plants when used in excess of four parts per million in culture 

 solutions. 



At the Indiana Experiment Station, Arthur (1914, p. 35) did some 

 work with red clover which led him to the conclusion that, when 

 mixed with the soil, 400 pounds of iron sulfate per acre is the largest 

 quantity which can be used without danger of injury to the clover. 



RELATION OF WEATHER CONDITIONS TO EXTENT OF INJURY TO 

 GRASS AND WEEDS. 



Most experimenters recommend that the spraying be done on 

 bright, dry days. In general, this appears to be true. However, 

 according to our observation, there are certain exceptions to that 

 rule. Apparently, the weather conditions preceding spraying and 

 the condition of the lawn soil, whether wet or dry, are important fac- 

 tors. During eight years of observation we have found that serious 

 injury to the grass may result if it is sprayed when the soil is dry. In 

 such cases liberal spraying (drenching) materially increases the 

 amount of injury which follows. Heavy dew following spraying was 

 found to facilitate materially the action of the chemical and conse- 

 quently increase the injury to the dandelions. It was found that, 

 in certain instances, when the lawn was sprayed on a damp, cloudy 

 day following a period of dry weather (Plat 4 sprayed July 28; and 

 Plat 5, the Robinson lawn), the dandelion foliage was quickly and 

 very effectively killed .and the grass also displayed an unusual 

 amount of discoloration. It was observed, too, that young seedlings 

 of grass suffered more than older lawns. Bolley (1908, p. 551) has 

 discussed a similar set of conditions encountered in his work in North 

 Dakota on the eradication of weeds in grain fields. 



