52 Journal of Agricultural Research vol. xx.No. i 



In the noncalcareous soil none of the special compounds affected 

 growth significantly, and in the calcareous soil none of the iron com- 

 pounds proved efficient sources of iron, although possibly the ferric 

 tartrate and benzoate increased growth slightly. 



Molasses alone and molasses followed by ferrous sulphate depressed 

 growth markedly and intensified the chlorosis of plants in the calcareous 

 soil, but the "ferric molasses" had no effect. Probably the molasses 

 that had not been treated with iron still further depressed the availa- 

 bility of iron in the calcareous soils by promoting the formation of in- 

 soluble organic iron compounds. 



Experiment IX. — Later a second test was conducted with pure 

 organic iron compounds and organic materials containing iron in cal- 

 careous and noncalcareous soils. The pure iron compounds were applied 

 so as to furnish 0.75 gm. or 1.50 gm. of iron per pot, the smaller applica- 

 tion being at approximately the same rate as in the preceding experiment, 

 if the sizes of the pots and quantities of soil used in the two experiments 

 are considered. In the tests with ferric citrate and ferric tartrate, a 

 comparison was made between the results obtained by mixing all the 

 material with the soil before planting and those obtained by applying 

 the material in small doses in solution during the growth of the plants. 

 This was done to see if the materials might not be available for a short 

 time in the soil although rendered unavailable in the course of time by 

 bacterial or other action. 



The "ferric humate," which, it was thought, might contain some iron 

 compounds similar to those existing in a natural soil, was prepared by 

 extracting leaf mold with 4 per cent ammonia, acidifying with hydro- 

 chloric acid, washing the precipitate free from chlorids, and evaporating 

 the precipitate to dryness with sufficient ferric chlorid solution to furnish 

 25 per cent as much iron as dry matter. The "mixture" used per pot 

 was composed of 4 gm. dried blood, 40 gm. Stizolobium vines, 40 gm. 

 tobacco stems, and 0.90 gm. iron from equal parts of ferric citrate, 

 tartrate, "humate," tannate, oxalate, and benzoate. Velvet beans 

 (Stizolobium) were tested because they are extensively grow r n as a green 

 manure crop. Both Stizolobium vines and tobacco stems were cut up 

 before mixing with the soil. Citric and tartaric acids were tried to see 

 whether an organic radical alone would have any effect in maintaining 

 available iron in the soil. The test was conducted from December 8, 

 1916, to February 19, 1917, with eight rice plants in each pot. The 

 pots contained 42 pounds of sandy loam soil, or 47 pounds of sandy soil 

 containing 10 per cent carbonate of lime. The moisture contents of 

 both soils were maintained at 18 per cent of the dry weight. The ferti- 

 lizer for each pot was given in two applications and consisted of 15 gm. 

 ammonium sulphate, 19.5 gm. acid phosphate, and 6 gm. potassium 

 sulphate. The special additions were mixed with the top 4 inches of 

 soil before the rice was planted, except the solutions of ferric citrate 



