SOILS — FERTILIZERS. 19 



Sterilization of water on a large scale by means of ultraviolet rays {Lari- 

 cct [London], 1010, II, No. 25, pp. nS)-nS6, fig. 1). — The results of experiments 

 with apparatus recently proposed for this purpose are summarized in" this 

 article. 



SOILS— FERTILIZERS. 



The gumbo soils of Iowa, W. H. Stevenson and J. F. Barker {Iowa Sta. 

 Bui. 119, pp. 28^-305, figs. 2, map 1). — The work here reported consisted of 

 drainage, cultural, and fertilizer tests, and of physical and chemical analyses 

 of Iowa gumbo soils. " The term ' gumbo ' as used in this bulletin refers to 

 heavy, black clay surface soil, and not to the almost impervious gray or yellow 

 clay subsurface soil which geologists refer to as gumbo and which is locally 

 often called hardpan." 



The soils are classed with the heaviest clays, based on analyses which showed 

 90 to 97 per cent of silt and clay, the remainder being very fine sand. The clay 

 content ran from 25 to 50 per cent, and is believed to be a water deposit of 

 recent origin, the rock flour being carried down from melting glaciers. 



Chemical analyses of the soil showed an average of only 0.3 per cent of nitro- 

 gen, 0.049 per cent of phosphoric acid, and 2.06 per cent of lime, but only a 

 trifling amount of the lime was present as carbonate. The percentage of 

 organic matter was found to be relatively low. 



Tile draining was successful wherever a good outlet could be had. The soil 

 was improved by fall plowing, and the use of clover or some green manure. The 

 use of lime, even in large amounts, did not seem to improve the physical proper- 

 ties of the soil. 



The management of heavy clay soils, A. R. Whitson and E. J, Delwiche 

 {Wisconsin Sta. Bui. 202, pp. 3-11, figs. 6). — This bulletin is based upon obser- 

 vations and experiments made at the Superior and Ashland substations and 

 elsewhere in the State. 



" Thg most extensive class of clay soils which is at all heavy is that known 

 as the heavy red clay, which occurs along the southern shores of Lake Superior, 

 iu the valley of the Fox River, and to a much less extent along the shore of 

 Lake Michigan. The total area of this type is estimated at .3,000,000 acres. 

 Smaller areas of moderately heavy clay soils occur in other sections of the 

 State. When properly managed, these soils are very productive, their very 

 fineness giving them a large water-holding capacity which adapts them espe- 

 cially to small grains and grasses. The largest areas of this clay are located 

 where there are climatic conditions favorable to these crops." 



The principal defect of these soils is the tendency to pack and thus become 

 flifiicult to cultivate. The means suggested for overcoming this difficulty in- 

 clude the exercise of gi-eat care to plow only when the soil is in proper moisture 

 condition, to drain, and to practice a 4 or 5 year rotation, including clovers, 

 small grains, and tilled crops such as corn, potatoes, and rutabagas. It is also 

 considered "necessary to add considerable vegetable matter by turning under 

 an occasional second crop of clover or other legume as well as by using all 

 available manure. Clay soils rarely contain much humus even in the natural 

 state. The supply of phosphorus is also limited and should be increased by 

 the addition of phosphate fertilizer supplementing farm manure." 



The improvement of sandy soils, A. R. Whitson and F. J. Sievers {Wis- 

 consin Sta. Bui. 20.'f, pp. 25, figs. 6). — It is stated that "Wisconsin contains be- 

 tween four and five million acres of soil which farmers generally classify as 

 ' sandy.' Approximately three million acres of these lands lie in the central 

 and southern portions of the State and are already settled and in farms. The 

 remaining area, between one and two million acres in extent, occurs chiefly in 



