1016 EXPEEIMEXT STATION RECOED. 



ing conclusious, among others, are drawn : The productiveness of a soil is 

 determined by the minimum factor. The soil should be so prepared as to be 

 adapted to the root growth peculiar to the siiecies of plants to be produced, 

 since the growth of the plant (other things being equal) is proportional to the 

 volume of soil traversed by the roots. A granular structure of the soil is espe- 

 cially necessary to root growth in forestry, this condition being dependent 

 upon the previous vegetation. The amount of rainfall and the capacity of the 

 soil for water are of prime importance and perhaps in the majority of cases 

 determine the growth obtained on a soil ; the conservation of the water in the 

 soil is regulated by the nature of the litter, the physical character of the soil, 

 the contents of humus, the depth of the surface soil, and the structure of the soil. 



It is pointed out that a forest soil is in large measure the work of the forest 

 itself and results from the reciprocal action of a large number of factors which 

 act slowly and through long periods. Sudden changes in forest conditions should 

 therefore be avoided, for such changes are likely to be followed by injurious 

 consefiuences. 



Maintenance of fertility with special reference to the Missouri loess, 

 W. H. Stevenson. A. H. Snyder, and I. O. Schaub (Iowa Sta. Bill 95, pp. 31, 

 figs. -}, dgms. .). map 1). — This bulletin discusses the general problems involved 

 in the maintenance of soil fertility, gives a brief account of field experiments 

 now in progress to test the effect of various carriers of plant food, manures, 

 green manures, and crop rotations upon the various types of soils upon which 

 they are located, and describes the soil of the Missouri loess area. 



The Missouri loess is described as " less clayey than the other types of loess 

 found in the State, but has all the characteristics of a wind-formed soil. . . . 

 It is buff, or yellow, in color, and is composed of fine particles of exceedingly 

 uniform size. Loess rarely, or never, contains large pebbles or stones, and but 

 very little coarse sand. ... It varies greatly in depth, being more than 100 ft. 

 thick in some places near the Missouri River, while it has only a depth of a few 

 feet in sections farther east. 



"This type of soil withstands both drought and excessive rainfall remarkably 

 well, and in general it may be said that it does not wash badly, considering 

 its rolling topography. Its porous nature allows large amounts of water to pass 

 into the soil readily. In localities where the loess is of great depth the water 

 may pass downward beyond the reach of plant roots, and may carry away the 

 soluble and readily available elements of plant-food from the plants. 



" The pf)rous nature of this soil permits of the free circulation of air and pro- 

 motes the rapid decomposition of organic matter. . . . 



" Owing to the rapid decomposition of the organic matter in the Missouri 

 loess, infertile tracts, varying from a few acres to as much as 50 acres in ex- 

 tent, are being develoi>ed where the loess is deep and the topography rolling. 

 Nearly every farm in the Missouri loess area is more or less affected in this 

 way, and, as the number and area of these tracts tend to increase, they form a 

 subject of much concern." 



The results are given of a field experiment with fertilizers on one of the in- 

 fertile hilltops of the loess area. No material benefit was derived from the 

 application of phosphoric acid in the form of steamed bone meal or of potash 

 in the form of sulphate. Apparently the best method of improving this soil is 

 the adoption of a system which economically maintains an adefpiate supply of 

 organic matter. '* Two methods have been mentioned for accomplishing this 

 end: First, the application of manure; and, second, crop rotation. This rota- 

 tion .should include the growing at frequent intervals of a crop which leaves 

 a large percentage of its material upon the laud." 



