INDIVIDUAL ELEMENTS 151 



investigations would indicate that this condition holds for a great many 

 soils. Thus the sulphur content of Illinois soils has been reported as 

 ranging from 280 to 750 pounds per acre in the top %% inches. ^^'^ Since 

 the average growing crop removes only 4 to 10 pounds of this element per 

 acre and losses through seepage arc likely to be nearly offset by additions 

 through rainfall, it would appear that the application of sulphur as fer- 

 tilizer to such soils does not offer much promise of increased crop returns. 

 However alfalfa removes 40 pounds per acre per year and cabbage nearly 

 as much. Moreover there are many soils not so well supplied with 

 sulphur and Shull^^^ is authority for the statement that "the normal 

 sulphur content of soils is sufficient for from 15 to 70 crops, provided 

 there are no additions from outside sources as from rainfall. Even if we 

 count in the rainfall sulphur, it is probable that sulphur is just as often a 

 limiting factor as is phosphorus, or nitrogen, or potassium." The soils 

 poor in sulphur and applications of compounds containing this element 

 of the Rogue River valley in southern Oregon have been found very 

 have greatly increased jdelds of leguminous crops. ^^^ In some instances 

 these increases have amounted to 500 to 1,000 per cent. Without doubt 

 these conditions are very exceptional; nevertheless the results suggest 

 that sulphur may be a much more important Hmiting factor in soil pro- 

 ductivity than has been considered generally. Recent investigations 

 indicate that sulphates have a special influence on root development.^^ 

 This is particularly marked with red clover and rape, where sulphate 

 applications resulted in root elongation and consequently in an extension 

 of the feeding area and a greater ability to withstand drought. Little is 

 known regarding the direct effect of sulphur-carrying fertilizers on 

 deciduous fruits. However, the application of 178 pounds of sulphur per 

 acre to certain vineyard soils has resulted in increases in yield of 19.2 to 

 32.7 per cent, and in increases of 25.03 to 27.3 per cent, when applied with 

 14 tons of stable manure.-^ Though no direct influence of sulphur- 

 carrying fertilizers upon tree growth or production was reported in the 

 Rogue River valley experiments the crops so greatly benefited by their 

 application were those commonly grown as intercrops and cover crops in 

 the orchard. Through them the trees might be greatly benefited in 

 later years. 



These facts taken with the lack of data on the distribution of sulphur 

 in plants accentuate the importance of more analytical and experimental 

 work on this element. Sulphur has been neglected because it was 

 thought to occur in relatively small amounts, but the small amounts 

 found were due to faulty methods of analysis and sulphur is just as 

 essential to plants and as worthy of consideration as phosphorus. 



IRON 



Iron occurs in plants in even smaller amounts than sulphur. It is 

 found in organic combination in some nucleic acids. ^"^^ 



