816 EXPEBIMENT STATION EECOKO. 



which was to determine the influences of the physical properties of soil on the 

 yield of crops. 



The crops grew much faster and the yields were considerably greater on the 

 sand clay mixture than on the sand. With corn the best results were obtained 

 with a mixture of 5.4 kg. of sand and 0.9 kg. of clay. The Avheat, rye, oats, and 

 buckwheat yield on the sand-clay mixture were as large as in good loam soil. 

 When sand was treated with nitric acid and water allowed to percolate through 

 nearly all the nitric acid was washed out, while the sand-clay mixture 

 under the same circumstances retained a large part of the nitric acid. 



Experiments to explain the greater crop-producing power of the sand-clay 

 mixture on the basis of greater absorptive power for plant food, greater 

 moisture-retaining power, and greater capillarity were unsuccessful. Studies 

 of the root development of the crops and physical experiments with the two soils 

 led to the conclusion that the sand grains when wet offer considerable resistance 

 to the growth and spreading of plant roots, while when mixed with clay the 

 clay acts as a lubricant between the sand grains, thus permitting roots to spread 

 throughout the mixture, making a greater feeding area, and resulting in larger 

 crop yields. 



It is concluded from the results as a whole that the physical condition of a 

 soil determines in large measure the availability and extent of utilization of 

 plant food by plants and, therefore, exercises considerable influence on the 

 yield of crops. 



Unfavorable influence of too close a stand of trees on the water economy 

 of poor pine soils, Albert {Ztschr. Forst u. Jagdw., 47 (1915), No. 4> PP- 2^1-248, 

 figs. 2). — Investigations on the effect of thinning out the stand of pine trees on 

 the moisture content of light sand soil of relatively low fertility are reported. 



A pine tree thicket 20 to 25 years old was divided into three plats. The num- 

 ber of trees on two of the plats was reduced and the resulting brushw^ood 

 removed from one and allowed to remain on the other. Soil moisture observa- 

 tions made during two growing seasons thereafter show^ed that in the soil of 

 the thinned-out plats there was a noticeable and permanent increase in the 

 moisture content. The increase was greater for the plat on which the brush- 

 wood covering was allowed to remain. This is attributed to the decrease in 

 evaporation caused by the covering. It is also thought that the brush in- 

 creased the fertility of the soil. 



It is concluded that a proper thinning-out of pine tree growths on poor sand 

 soils, but allowing the brush to remain, is beneficial not only to the trees but to 

 the soil. 



A note on relative saturation, G. Brown {Jour. Ecology, 3 {1915), No. 1, 

 pp. SO, 31). — The author discusses and proposes as a general expression for the 

 condition of a soil with regard to its relative saturation, the formula {w-ni)/W, 

 in which w— the mass of a given quantity of soil with its contained moisture, 

 m = the mass, of same soil wiieu air dry, and W the maximum water capacity, 

 all being expressed in grams. 



For each natural habitat there will be a minimum, an optimum, and a maxi- 

 mum value of the ratio, the optimum indicating those edaphic conditions under 

 which the association or formation remains stable, the maximum and mini- 

 mum indicating the limiting conditions beyond which it can no longer be main- 

 tained as such, but will be replaced by a drier or wetter type. Relative satura- 

 tion as here indicated would, it is claimed, prove an efficient measure of the 

 soil water without taking into consideration the physical condition of the soil, 

 and would serve to differentiate edaphic conditions and to distinguish natural 

 habitats. 



