4 8 



Journal of Agricultural Research 



Vol. XX, No. i 



however, it was found necessary to apply a small amount of nitrogen, 

 phosphoric acid, and potash to the sand in the sieve in order that the 

 plants might develop sufficiently for their roots to penetrate the soil 

 below. 



The intention was that the plants should absorb practically all their 

 nutrients from the soil in the buckets (a calcareous soil except in control 

 buckets i to 4), but that in some cases the plants should be able to absorb 

 iron from a lime-free medium in the sieve. If carbonate of lime affected 

 the plants in any way except through depressing the absorption of iron, 

 all plants should make equally poor growth; but if, on the other hand, 

 the only action of the carbonate of lime lay in decreasing the availability 

 of the iron, those plants that could draw iron from a medium containing 

 no carbonate of lime should do much better than the others. 



A preliminary test was run with two pots, No. 1 containing silica sand 

 in the sieve and a calcareous soil in the bucket, and No. 2 containing 

 silica sand plus carbonate of lime in the sieve and the same calcareous 

 soil in the bucket as No. 1. Four gm. of ferrous sulphate were applied 

 to both sieves (PI. 6, A). The yields from pots No. 1 and 2 were respec- 

 tively 169 gm. and 97 gm. of air-dried plants, the plants in No. 1 being 

 green in color and those in No. 2 chlorotic. 



Experiment VII. — The results of a more extended test are given in 

 Table X. The plants were grown from October 22, 191 2, to March 3, 

 1913. A large number of seeds were planted, but the plants in each pot 

 were thinned to eight. The sieve of each pot contained 10 pounds of 

 silica sand to which were added 0.45 gm. ammonium nitrate, 0.1 gm. 

 acid potassium phosphate, and 0.2 gm. potassium sulphate. The 

 bucket of each pot contained 23 pounds of soil and received 12 gm. 

 ammonium nitrate, 3 gm. acid potassium phosphate, and 5.5 gm. potas- 

 sium sulphate, in two applications. The moisture content of the soil 

 was maintained at 31 per cent of the dry weight. 



Table X. — Effect of carbonate of lime in the soil on the availability of iron 



