828 EXPEEIMENT STATION RECORD. [Vol. 37 



meters (17.7 to 20.1 in.), and in the following 2 weeks, which form the pre- 

 flowering period and actual growing period itself, the root growth was very 

 intense, attaining a length at the age of 3 months of from 103 to 110 centimeters. 

 Such gi'eat fluctuations in root growth were not observed previous to or follow- 

 ing this period, and the author believes this fact to be the essential point in his 

 investigations. 



These observations are said to confirm those of Rotmistrov, but better specify 

 the process of root growth by establishing the period of most intense develop- 

 ment. 



The effect of phosphorus on alfalfa and alfalfa bacteria, H. W. Truesdell 

 (Soil Sci., 3 (1911), No. 1, pp. 77-98, pis. 2). — Investigations are reported in an 

 effort to discover the reason for the beneficial influence of phosphorus upon 

 alfalfa and other legumes, as simple nutrition (shown by chemical analysis) 

 is deemed insuflScient to account for this phenomenon. The hypothe.sis is ad- 

 vanced that phosphorus fertilization may cause greater growth and activity 

 of the root bacteria, re.sulting in greater nitrogen fixation and more rapid 

 growth of the leguminous host. This theory has been tested experimentally 

 in these investigations. The experiments fall into two parts, (1) those which 

 treat of the influence of phosphorus upon the growth of the alfalfa organism 

 {Bacillus radidcola) as shown by numerical counts, and (2) those which treat 

 of the influence of phosphorus upon alfalfa as regards nodule formation, rate 

 of growth, dry weight of plants, and percentage and absolute content of nitro- 

 gen. The secondary phosphates* of potassium, sodium, and calcium were used 

 in quantities sufficient to supply a phosphorus equivalent of 0.1, 0.02, and 0.002 

 per cent. The studies were made at the University of Wisconsin. 



The treatment of pure cultures of D. radidcola from alfalfa with phosphates 

 resulted In large increases In the number of organisms, varying with the charac- 

 ter and solubility of the salt. The highest counts were obtained from treat- 

 ments supplying a phosphorus equivalent of 0.02 per cent, and disodium phos- 

 phate gave the highest increase after seven days' incubation, with dipotassium 

 phos-phate next. 



Pot culture experiments were conducted under greenhouse conditions to study 

 the effect of dicalcium phosphate upon alfalfa. Alfalfa grown on unsterilized 

 soil was inoculated, treated with phosphates and phosphorus plus nitrogen, and 

 the results in nodule formation, dry weight, and percentage and absolute nitro- 

 gen content compared with all possible control combinations. Percentages of 

 phosphorus of 0.005, 0.015, and 0.045, equivalent tu field applications of 700. 

 2,100, and 6,300 lbs. per acre of rock phosphate, respectively, were employed, 

 and urea equivalent to 0.014 per cent used as a nitrogenous fertilizer. 



The results of phosphorus fertilization of alfalfa may be briefly summarized 

 as follows: The seedlings made a much more rapid growth, and increased 

 nodule formation, dry weight, and total nitrogen content was observed. The 

 third cutting (much more representative of normal average conditions) showed 

 not only an increase in total nitrogen, but also an increase In the percentage 

 of nitroTen associated with the addition of phosphorus fertilizer. 



The author concludes that the early Increas-e noted in the growth of phos- 

 phorus-treated seedlings may be a result of nutrition of the plant and the 

 slanulatlon frequently associated with cell reproduction and to the quickening 

 of bacterial processes in the soil. The ultimate increases in growth resulting 

 from phosphorus treatments may be due to increased infection with alfalfa 

 organisms, increased growth and proliferation of the organism within the 

 nodule, and consequently iucrea.scd nitrogen fixation. 



