SOILS — FERTILIZEES. 819 



Among the general conclusions reached from this investigation are that 

 while the distribution of rainfall varies widely in different parts of the country 

 from year to year and month to month and in proportion to the distance from 

 the coast, tlie available evidence goes to show that there has been no definite 

 diminution in the total rainfall of South Africa during historic times. There 

 is, however, some evidence of cyclic or periodic variations. While denudation 

 of the forested and grassed areas has not appreciably affected the total rain- 

 fall, it has been an important factor in increasing soil erosion. Other important 

 factors are the making of roads, tracks, or paths, and the grazing of stock. 

 It is stated that the combined effect of these various agencies " has been 

 calamitous in the extreme." 



T^ie conditions which favor soil erosion have also been responsible for the 

 drying up of the lands in certain parts of the country. Increased surface 

 run-off has been accompanied by less penetration of moisture into the soil, and 

 the formation of numerous gullies and drainage channels has resulted in the 

 lowering of the underground water. The evidence appeai'ed to be unanimous 

 and conclusive " that many parts of the Union, in spite of the apparent con- 

 stancy of the total amount of the rainfall, have been slowly but surely drying 

 up, the rate of desiccation varying with the differences of locality, soil, and 

 gradients ; and that such parts must sooner or later become useless and un- 

 inhabitable if the process proceeds unchecked." 



Among the remedial measures proposed are conservation of water by means 

 of dams and irrigation works, encouragement of fencing, the increase of vege- 

 tation, control of veld burning, afforestation and reseeding to grass, and more 

 attention to drainage in the construction of roads and railways. 



The pTsvention. and control of erosion in North Carolina, with special 

 reference to terracing', F. R. Baker {North Carolina Sta, Bui. 236 (1916), pp. 

 27, figs. 25). — This bulletin, prepared in cooperation with this Department, 

 states that the area in which soil erosion is especially active in North Carolina 

 is almost wholly within the Piedmont region, but that a considerable amount 

 of the western Coastal Plain is subject to erosion, the whole area so affected 

 covering over 10,000,000' acres. Methods discussed for the prevention of erosion 

 are (1) proper cultivation, (2) tile drainage, (3) hillside ditches, and (4) ter- 

 racing. The falling and level terraces are given the most attention. 



" Of the two terraces the broad, level terrace is more ideal, but its use 

 is limited to soils in good physical condition. The falling terrace can be more 

 generally used and is probably best adapted to the conditions found generally 

 in North Carolina. The fall of the terrace varies with the state of cultivation 

 between 6 in. in 100 ft. and a dead level. The level terraces should be spaced 

 three or four feet apart (vertical distance) ; and the falling terraces four or 

 five feet apart (vertical distance). A broad mound should be maintained 

 whether a level or fa^iiing terrace is used." 



Useful accessories, including levels and terrace drags, are also described. 



The increase of the ecolog'ical value of light soils by intermixing clay 

 (Betonung-), C. Schneider (FiihUng's Landio. Ztg., 64 {1915), No 13-14, PP- 

 352-366). — The author enumerates and discusses the factors influencing the 

 ecological value of a soil, and, considering light sandy soils and heavy clay 

 soils as representing practically the limits of soil texture, points out how a 

 proper mixture of clay or clay soil with a light soil will indirectly increase the 

 ecological value of the latter by favorably influencing the factors mentioned 

 and resulting in a normal soil. A general classification of soils on the basis of 

 their content of sand and clay is given, and the relations between the different 

 classes and normal soils for different crops is discussed. 



