1919] SOILS — FERTILIZERS. 215 



A search for the active factor then being made among the inorganic con- 

 stituents, aluminum was found to be responsible for the different intluence upon 

 the plants. AMien equivalent amoimts of aluminum sulphate and sulphuric acid 

 were added to an optimum nutrient solution, both produced the same depression 

 on the growth of barley. Sulphuric acid caused a similar depression of rye, 

 but aluminum sulphate had very little effect. Since the nutrient solution con- 

 taining the acid possessed about four time the H-iou concentration of that con- 

 taining aluminum sulphate, the toxic effect of the latter on barley was attrib- 

 uted lai-gely to the aluminum. 



Finally, it is stated that " treatment of an acid soil with eitlier phosphoric 

 osid or acid phosphate reduced the amount of active aluminum in the soil. 

 Unusually large additions of acid phosphate caused remarkable growths of 

 plants so sensitive to an untreated acid soil that previously no growtla was pos- 

 sible, and this was in spite of the fact that the acidity of the soil was very 

 much Increased by the acid phosphate. The active aluminum, however, was 

 much decreased by the treatment. Tlie results indicate that the practical ad- 

 vantage of pliosphating and liming may often prove to be due to the precipita- 

 tion of active aluminum quite as much as to supplying phosphorus as a nutrient 

 and lime as a reducer of acidity." 



The influence of heated soils on seed germination and plant growth, J. 

 Johnson {Soil ScL, 7 {1919), No. 1, pp. 1-103, flgs. J 6). —Supplementing work 

 previously noted (E. S. K., 35, p. 722), the author describes a series of investi- 

 gations conducted at the Wisconsin Exiieriment Station to ascertain primarily 

 the nature of the action of sterilized soils upon plant growth. 



The evidence is held to demonstrate the importance of microorganisms in the 

 loss of toxicity in the soil and that reduced toxicity is due to biological action 

 upon ammonium carbonate, resulting in the liberation of gaseous ammonia or 

 its fixation in the soil. Tne soils employed in tlie study included Waukesha 

 silt loam, Miami silt loam, Norfolk sand, virgin sandy loam, fine sandy loam, 

 red clay, muck, and peat, and were subjected to widely varying treatments and 

 conditions, and their action on numerous seeds and plants determined. The 

 data are presented in tabular form and fully discussed, together with con- 

 firmatory evidence found in the Uterature bearing on some of the conclusions 

 presented in this paper. The results secured may be summai'ized as follows : 



Heating soil to dilferent temperatures usually resulted in a gradual increase 

 in toxicity to seed germination and to early plant growth which reached its 

 maximum at approximately 250° C, but gradually decreased to practically no 

 toxicity on soils heated to 350° or above. The time required for recovery from 

 this toxic action was usually directly proportional to the intensity of toxicity 

 produced, but the final beneficial action was often greatest on soils exhibiting 

 the gi-eatest injurious action on early plant growth. Different soils varied 

 markedly in their behavior upon heating to the same temperature both in 

 toxicity and in beneficial action to seeds and plants, this apparently not being 

 correlated with any single distinguishing character in the soil but rather with 

 the balance of all the factors concerned. 



Seeds varied greatly in their sensitiveness to the toxic action, the degree of 

 sensitiveness being roughly characteristic of their genetic relationship. The 

 Graminse and the Cucurbitaceae were usually resistant, and the Leguminoseaj 

 and Solanaceie were, so far as determined, more susceptible. 



With seeds resistant to the toxic action, marked acceleration of the rate of 

 germination may occur on even highly heated soils, this being regarded as 

 another expression of the same sulwtances that cause retardation in more 

 susceptible seeds. Seeds classed as susceptible may, on the other hand, show 



