Oct. i, i 920 Cause of Lime-Induced Chlorosis 49 



At 1 5 days after sowing the seed all plants were chlorotic except those 

 in pots 13 to 16, and many died because of their inability to establish 

 roots in the soil in the bucket. At 121 days the plants of pots 1 to 4 

 and 9 to 12 were green, while those of No. 5 to 8 and 13 to 16 were strongly 

 chlorotic. 



The plants encountered some difficulty in establishing their roots in 

 the soil in the buckets; the roots after passing through the sieve often 

 grew for a time on the surface of the soil. This retarded growth con- 

 siderably, but when the roots once penetrated the soil, growth became 

 normal. At the end of the experiment the greater part of the roots were 

 in the soil in the bucket, where practically all the fertilizer was located. 



The final yields of the plants and the chlorotic appearance of certain 

 plants during the latter stages of growth confirm the idea that the only 

 effect of carbonate of lime in inducing chlorosis lies in depressing the 

 availability of iron. The plants in pots No. 9 to 12 and those in No. 

 13 to 16 were exposed to the same conditions except that the plants in 

 No. 9 to 1 2 were able to draw part of their iron from a medium containing 

 no carbonate of lime; this difference was sufficient to double the growth 

 of plants. The plants of No. 9 to 12 had to assimilate practically all 

 their mineral nutrients, except iron, from the same calcareous soil as 

 the plants of No. 13 to 16; hence, if the carbonate of lime induced chlorosis 

 by depressing the availability of any nutrients other than iron, or if 

 an increased assimilation of lime were a contributory cause of chlorosis, 

 the yield from pots No. 9 to 12 should have been practically the same 

 as from No. 13 to 16. 



The only apparent contradiction in this demonstration of the cause of 

 lime-induced chlorosis lies in the fact pots No. 5 to 8 yielded more than 

 No. 13 to 16. Plants in pots No. 5 to 8 evidently secured less iron than 

 those in No. 9 to 12, for they made less growth; but if the sand in the 

 sieve had been really iron-free they should have made no more growth 

 than plants No. 13 to 16. Later work showed that, although no iron 

 was added to the sieves of No. 5 to 8, doubtless the silica sand contained 

 enough iron to cause the unanticipated growth. In work with nutrient 

 solutions it was found that rice practically satisfied its iron requirements 

 in a solution containing no more than 1 part of truly soluble iron in 

 10,000,000 parts of solution (17, p. 5). 



On repeating this experiment the same difficulties were encountered, 

 but the relative growths made by the differently treated plants were 

 similar to those in the preceding test. 



AVAILABILITY OF IRON IN THE SOIL 

 INTRODUCTION 



Since the preceding summary of facts and experiments seems to indi- 

 cate that lime-induced chlorosis is simply the result of insufficient avail- 

 able iron in the soil, evidently a knowledge of conditions affecting the 



