SOILS — FERTILIZERS. 823 



The investigations were made by means of the paraffiu-pot method described 

 in earlier bulletins (E. S. R., 17, p. 227) and were confined to "high- 

 grade, standard fertilizing materials, consisting of nitrate of soda, snlphate of 

 potash, and acid pliosphate, together with air-slalied lime, well-decomposed 

 stable manure, and green cowpea vines. These ingredients were ai)plied to 

 the soil separately and in various combinations." The relative effects of "the 

 different fertilizers were measured by the transpiration as well as by the green 

 growth of wheat during the first IS to 21 days of the life of the plants. 



Some of the more important conclusions drawn by the author are substan- 

 tially as follows: 



The paraffin-pot method is a useful means of determining the fertilizer re- 

 quirements of soils, giving results differing in degree but not in kind from those 

 obtained in the field. 



The green weights show more pronounced variations than transpiration. 

 "The green weight of plants grown for about 25 days in the pots occasionally 

 equals or exceeds 1 per cent of the weight of the soil in which they grew. 

 Such plants contain about 85 per cent of water and transpire aitprc^ximately 

 100 gm. of water for each gram of green matter produced. The dry matter 

 of such plants is richer in mineral constituents and niti-ogen than that of the 

 same plants if matured. The draft on the water and mineral constituents of 

 the soil under these conditions is greater than that occasioned by the removal 

 of a large and matured crop under field conditions." 



Soils vary greatly in crop-producing capacity and in the degree to which they 

 respond to commercial fertilizers, lime, manure, and green manures. " In gen- 

 eral, the degree of response varies inversely as the crop-yielding capacity and 

 ranges from zero to several hundred per cent. The soils of the Atlantic and 

 Gulf Coast States are much more responsive than those of the Central and 

 Northern States. . . . With few exceptions the character of fertilizer re- 

 quired for soils depends more upon local conditions and practices than It does 

 upon the type of soil or the geological formation to which It belongs. The muck 

 soils are an exception and show a universal response to potash salts." 



The organic manures were as a rule more effective than the chemical ferti- 

 lizers. Barnyard manure and cowpeas with lime were the most effective 

 manures. With the chemical fertilizers used individually the order of effi- 

 ciency was first nitrate of soda, then lime, potash, and acid phosphate. 



In 00 per cent of the soils tested each fertilizer salt appeared to have a special 

 function In plant growth which was not materially modified by adding or with- 

 holding other salts. In the pot experiments the aggregate efficiency of the 

 several salts used separately was slightly gi'eater than that of the same salts 

 used in combination. 



" The character of fertilizer indicated for a specific soil type as it occurs in 

 widely separated localities usually varies more than that for very different 

 types when In the same locality and subjected to similar environment. ... In 

 general, the finer the texture of soils the less responsive are they to fertilizers, 

 although the character of fertilizer indicated remains the same." 



It is believed that "the condition of the soil is of greater importance than 

 its chemical composition [for] without materially changing the composition of 

 the soil, poor soils by proper manipulation and suitable applications can be 

 made to produce as large crops in the pots as can be grown on the best soils by 

 the same or other treatments." 



It is held that " while manure and fertilizers may often increase crop yields 

 as a result of a direct supply of plant food or as a stimulant to the plants, there 

 is now abundant evidence that their effect is rather the result of a direct action 

 upon the soil, thereby changing its relation to plants. Complex and imper- 



