1916] SOILS FERTILIZERS. 425 



oxygen absorption or carbon dioxid production, the rate of ammonification or 

 nitrification, and the changes in bacterial numbers in the soil. 



It is pointed out that, as a general rule, soil organisms are dependent upon 

 suitable temperature and water supply, and that they must have food and, in 

 many cases, calcium carbonate, but that " soil bacteria are subject to the opera- 

 tion of some limiting factor quite distinct from temperature, moisture content 

 or food supply." Curves for carbon dioxid and nitrate determination showed a 

 marked similarity except that the increases in nitrate came later, indicating 

 "that the curves both for nitrate and carbon dioxid are in the m:iin produc- 

 tion curves." 



The author disagrees with the bacterio-toxin theory as developed from labo- 

 ratory cultures, but produces some evidence showing that the growing plant 

 exerts a depressing effect on soil organisms. 



Th lespective values of organic and inorganic manures, H. B. P. Hodsoll 

 {Jour. Roy. Hart. .S'oc, 41 (1915), No. 2, pp. 211-226). — Cropping experiments 

 with orgnnic and inorganic manures and comparative studies of their mechani- 

 cal, chemical, and Ijiological actions in soil are reported. The results led to 

 the conclusion that organic manures should be used as a base to supply humus 

 and thus improve the texture of the soil, enable the obtaining of good tilth and 

 a good seed bed, permit the gradual feeding of the crop, and provide humus 

 to feed bacteria, and that mineral manures should be used as a top-dressing 

 to promote rapid growth and to act as a sterilizer to keep the bacterial flora in 

 balance. 



The influence of the time and depth of plowing under of stable and green 

 manure on yield, C. von Seelhorst (Jour. Landw., 63 (1915), No. 3, pp. 233- 

 260, fig. 1). — Field experiments begun in 1905 with rotations of winter barley, 

 beets, oats, beans, rye, potatoes, summer wheat, and peas ; and rye, beets, bar- 

 ley, beans, rye, potatoes, barley, and peas are reported. The manures were 

 applied in the fall and .spring to beet and potatoes, the green manure being 

 applied usually at the rate of 100 lbs, of vetch and 25 lbs. of horse beans per 

 acre, and the stable manure in amounts equivalent to about 100 lbs. of nitro- 

 gen per acre. The depth of plowing was from 5 to 6 in., from 7 to 8 in., and 

 9 in. 



It was found that with beets fall manuring was on the average more favor- 

 able than spring manuring. Roth manures when used in the fall gave on the 

 average practically the same results regardless of depth of plowing. Shallow 

 plowing in of green manure in the fall gave slightly better results than deep 

 plowing, but no difference was observed with stable manure. When plowed 

 under in the spring green manure gave better results than stable manure when 

 deep plowed, while better results were obtained with stable manure when 

 shallow plowed. 



Spring manuring was more favorable to potatoes than fall manuring. 

 Stable manure gave better results than green manure in both fall and spring 

 use, and deep plowing gave better results in both spring and fall than shallow 

 plowing. 



With barley following beets the time of manuring of the beet crop had no 

 effect on the barley crop. Shallow plowing under of the manures for beets gave 

 better results for barley in both spring and fall. The after-effect of green 

 manuring in both spring and fall was less than that of stable manure. With 

 barley following potatoes, fall manuring with both manures gave somewhat 

 better results than spring manuring. Deep plowing with one exception gave 

 better results than shallow plowing. The barley crop following potatoes was 

 always somewhat greater than the barley crop following beets. 



