Oct. i, 1920 



Cause of Lime-Induced Chlorosis 



39 



Since ferrous sulphate is, of course, immediately transformed into ferric 

 carbonate in a calcareous soil, it seems evident that calcium carbonate 

 renders ferric carbonate unavailable, or less available, to certain plants. 



It has been repeatedly demonstrated that the effectiveness of spraying 

 with ferrous sulphate is due only to the iron and that only soluble iron 

 salts are effective (12, 21, 25, 26, 27). 



Experiment I.— The results in Table I show the effect of an iron spray 

 upon chlorotic rice growing in a calcareous soil. The plants were grown in 

 the open from February 29 to July 13, 191 2, in small brick compartments 

 with 36 plants to each compartment. Each compartment held about 

 200 pounds of heavy loam soil and received 5 gm. nitrogen, 3.4 gm. 

 phosphoric acid, and 5 gm. potash, derived from various commercial 

 fertilizers. The plants sprayed with ferrous sulphate were given 4 appli- 

 cations of a 0.5 per cent solution and 12 applications of a 1 per cent 

 solution. 



Table I.— Effect of an iron spray upon chlorotic rice plants grown, on calcareous soils 



Treatment of plants. 



Unsprayed 



Sprayed with ferrous sulphate. 



Unsprayed 



Sprayed with ferrous sulphate. 



Unsprayed 



Sprayed with ferrous sulphate 



Green weight of plants per compart- 

 ment. 



Series A. Series B. Average. 



Gm. 



I, 022 

 1,088 



4 

 946 

 242 



874 



Gm. 

 I, 071 

 I, 040 

 (a) 



894 

 702 



893 



Gm. 

 1,047 

 I, 064 



920 



472 



a Some plants were eaten by mole cricket, but according to comparative growths of plants before any 

 were eaten, the weight would have been about 250 gm. 



Twenty-one days after planting, the plants in the calcareous soils were 

 markedly chlorotic, and spraying was begun at that time. Seven days 

 later, after nine sprayings, the sprayed plants in the calcareous soils were 

 much superior to the unsprayed in color and growth. All plants in the 

 noncalcareous soil had a good color at all times. (PI. 5, A.) 



The results obtained by treating the leaves and stems of chlorotic 

 plants with iron salts show clearly that a lack of iron in the plant is at 

 least one of the causes of lime-induced chlorosis. This conclusion is 

 substantiated by the results of ash analyses of the plants. But this work 

 does not show: (i) whether the lack of iron in the plant is due to a low 

 availability of iron in the soil or to reactions in the plant rendering 

 ineffective the iron absorbed; (2) whether an increased absorption of 

 lime is a contributory cause of chlorosis ; or (3) whether the reaction of 

 the soil has any effect on the appearance of chlorosis, aside from affecting 

 the iron supply. 



