EFFECT OF SOIL TEMPERATURE UPON THE DEVELOP- 

 MENT OF NODULES ON THE ROOTS OF CERTAIN 



LEGUMES 



By Fred Reuel Jones, Pathologist, Office of Cotton, Truck, and Forage Crop Disease 

 Investigations, Bureau of Plant Industry, United States Department of Agriculture, 

 and W. B. Tisdale, Instructor in Plant Pathology, University of Wisconsin 



INTRODUCTION 



During a search for the cause of a diseased condition of alfalfa under 

 observation in 191 7 and 19 18 the senior writer was led by observations 

 contributed by H. L. Westover, of the Office of Forage Crop Investiga- 

 tions, to believe it likely that soil temperature, within the range which 

 occurs in cultivated fields, affects the initiation and the development of 

 nodules on the roots of alfalfa and perhaps all other legumes to such a 

 degree that the assimilation of nitrogen by these plants is greatly modi- 

 fied by this lactor during the summer. The probable importance of such 

 an effect of temperature, should it be demonstrated, upon the develop- 

 ment of alfalfa and other legumes and especially its possible relation to 

 the disease in question seemed adequate reasons for making a beginning 

 at the experimental determination of the facts. Experimental methods 

 suitable for the performance of this work had already been highly devel- 

 oped in the course of the study of soil-inhabiting plant parasites at the 

 University of Wisconsin. Thus it came about that the collection of the 

 following data was begun at Madison by the junior author in 191 7 and 

 continued by both authors in 191 9 and 1920. A temporary suspension 

 of the work is the immediate reason for the publication of this prelimi- 

 nary report. 



In the beginning, interest was centered upon ascertaining to what 

 extent soil temperature determined the number of nodules which any of 

 a selected group of legumes might develop. Later the size and composi- 

 tion of the nudoles appeared more significant than the number. Finally, 

 it is seen that soil temperature probably affects profoundly the rate of 

 nitrogen fixation within the nodules of the legumes studied and its 

 assimilation by the plants. A complete demonstration of such an effect 

 and a quantitative determination of its amount remains for the future. 

 During the progress of the work certain striking effects of soil temperature 

 upon the development of the plants quite apart from any relation to 

 nodule formation have been noted. 



Journal of Agricultural Research, Vol. XXII, No. i 



Washington, D. C. Oct. i, 1921 



zo Key No. G-24S 



54817°— 21 2 



(17) 



