1918] SOILS — FEETILIZERS. 727 



It was found that with sulphur plus barnyard manure there was a decreased 

 yield of grain and straw as well as a decreased nitrogen content of the crop. 

 Sulphur plus dried blood acted satisfactorily, but the exee^ of yield was not 

 very great. It is concluded that the application of sulphur either with barn- 

 yard manure or dried blood produced no particular effect in the crop. The 

 author is also of the opinion in this connection that the calculation of the prob- 

 able variation is an excellent method for forming an objective opinion on the 

 results of experiments. 



Former experiments by the author on the action of sulphur have been 

 previously noted (E. S. R., 34, p. 331). 



The use of iron in agriculture, A. Monnier and L. Kuczyaski (Arch. Sot. 

 Phys. et Nat. [Geneva], JfS (1917), No. 1, pp. 66-68; abs. in Internat. Inst. Agr. 

 [Rovie], Internat. Rev. Set. and Pract. Agr., 8 (1911), No. 5, pp. 693-695.)— Bx- 

 periments are reported to determine (1) the degree of solubility of the iron 

 already in the soil, and (2) the changes undergone by ferrous and ferric com- 

 pounds in arable land. 



Soils of normal composition showed no trace of iron when washed with 

 pure water or dilute solutions of alkaline carbonates and bicarbonates. A 

 soil containing 3.2 per cent of iron and 6 per cent of lime showed traces of 

 iron when treated with 5 per cent acetic acid. The solution by 1 per cent 

 citric acid and tartaric acid gave distinct iron reactions, and that by 1 per 

 cent oxalic acid gave' a strong iron reaction. " One hundred gm. of soil gave 

 0.02 gm. of iron when treated with the citric solution, and 0.06 gm. of iron 

 when treated with the oxalic solution. 



" Certain silicious soils entirely lacking in lime, as, for example, the soil of 

 Angers, give a fairly l«rge proportion of iron soluble in pure water. In these 

 soils pink hydrangeas give blue flowers ; but, if a small quantity of calcium 

 carbonate or magnesia is mixed with the soil it no longer gives up any iron 

 and the hydrangeas do not become blue. The compounds of soluble iron are, 

 therefore, precipitated by the lime. 



"A 1/1,000 solution of ferric chlorid was filtered through a layer of soil 20 

 cm. thick. All the iron was retained in the upper part which turned red- 

 brown. Calcium carbonate precipitates the iron in the form of a basic car- 

 bonate which gradually becomes a hydrate. The line of separation is clearly 

 marked, and the filtered liquid contains no iron, but a large proportion of 

 chlorin and calcium. This experiment was repeated with many samples of 

 soil containing different quantities of lime. The colored layer increases in 

 thickness in proportion as the lime content of the soil decreases. The thick- 

 ness of the colored layer does not exceed 2 cm. in soU containing 5 per cent 

 of calcium carbonate. If ferrous sulphate is used instead of ferric chlorid, 

 the salt is oxidized and precipitated, and a mixture of basic sulphate and 

 hydrate is formed, which colors the superficial layer red-brown, as in the 

 case of ferric chlorid. 



" The results of these experiments show that the iron contained In soils of 

 normal composition is present in a form very difficult to assimilate, which 

 explains the increased yield when vei*y small amounts of soluble iron are 

 added. The manure can have no favorable effect unless it is placed directly 

 within reach of the roots. This condition is found in pot cultures or when 

 the manure is added at the beginning of growth, but it is no longer present 

 when the roots have entered the soil to a certain depth where they receive 

 no trace of the ferric manure, which has been held up and made insoluble in 

 the surface layers of the soil. 



" Tests were also made with potassium ferrocyanid as a source of iron. 

 The results showed that the compound Is not rendered insoluble in the soil. 



