1917] SOILS FERTILIZEBS. 623 



exposed to different conditions of temperature and moisture content. The dil- 

 ates C. ciicullus and B. elongatus in pure culture were detrimental to bacteria 

 in solutions but not in soil. Four types of active soil flagellates were not 

 capable of limiting the number of bacteria when acting In soil, but one culture 

 was Injurious to bacteria in soil extract. 



Treatment of soil with the ordinary amounts of volatile antiseptics (1 to 2 

 per cent) did not appear to simplify the protozoan fauna, and as much as 10 per 

 cent of carbon bisulphid or toluene failed to exterminate the protozoa entirely. 

 Within one month after treatment normal numbers of protozoa were again 

 present iu the soil. The maximum number of bacteria in partially sterilized 

 soil was not found while the protozoa were suppressed but after they had again 

 returned to their normal level. It appeared that the development of these two 

 classes of micro-organisms subsequent to treatment with volatile antiseptics ran 

 parallel. The reinoculation of partially sterilized soils with 1 per cent of 

 normal soil failed to decrease the number of bacteria. 



" The results of the foregoing experiments appears to establish quite defi- 

 nitely that protozoa in the soils which have been studied do not have a detri- 

 mental effect upon the bacterial flora." 



A list of 70 references to literature bearing on the subject is appended. 



The disinfection of soil, fi. Mi:§;ge (Assoc. Franc. Avanc. Sci., Coinptt. Rend., 

 JfS (1914), pp. 978-982) .—This is a summary of the results of the work of others 

 bearing on the subject. 



Rotation and manure experiments on the Wisconsin drift soil area, W. H. 

 Stevenson and P. E. Brown (Iowa Sta. Bid. 161 (1916), pp. 462-476, figs. 8).— 

 Six-year rotation and manuring experiments on Carrington loam soil are re- 

 ported. The rotation experiments were carried out on 13 1/10-acre plats and 

 the rotations were as follows : Continuous corn ; 2-year rotation, corn and oats ; 

 3-year rotation, com, oats, and clover; 2-year rotation, com and oats, clover 

 turned under ; 2-year rotation, corn and oats, covs^eas turned under ; 2-year 

 rotation, corn and oats, rye turned under ; and continuous clover. The manuring 

 experiments were conducted on 20 1/10-aere plats and the manure used at 

 rates of 8, 12, 16, and 20 tons per acre. 



It was found that the continuous growing of crops on this soil decreases its 

 fertility and leads to rapidly declining crop yields, while the rotation of crops 

 gives gi-eater profit than the continued growth of corn. "A 3-year rotation of 

 corn, oats, and clover is more profitable than a 2-year rotation of corn and oats, 

 or a 2-year rotation with clover, cowpeas, or rye used as a green manure crop. 

 The introduction of clover, cowT)eas, and rye into a 2-year rotation increases 

 the crop yields, but it can hardly be considered profitable except in the case 

 of the clover. The profit is less, however, in every case than in the 3 year 

 rotation. 



" The best amount of manure to apply to this tjrpe of soil appears to be 

 between 8 and 16 tons per acre, applied once in a 4-year rotation. Applications 

 of more than 16 tons of manure per acre are not profitable. Manure applied 

 in three equal amounts in the first, second, and fourth years of the 4-year rota- 

 tion proved of greater value on this soil than the same total amount applied 

 once in the rotation. Manure should not be applied to this soil after the corn 

 crop is up, as very much smaller effects are secured from its use than when 

 it is plowed under or disked in after plowing. On this soil type the latter 

 method seems to be slightly preferable." 



A modified method of green manvirlng, C. M. Hutchinson (Agr. Research 

 Inst. Pusa Bill. 6S (1916), pp. 12). — Field experiments are reported which con- 

 firm the conclusions from results of laboratory tests given in a previous bulle- 

 89684°— No. 7—17 3 



