816 EXPEEIMENT STATION RECORD. 



uesium carbonate for silicon dioxid, hydrated silicates, and titanium oxid is 

 thought to account for the decomposition and rapid disappearance of mag- 

 nesium carbonate in the pot and field experiments. 



The general conclusion is reached that " except for the minute quantities in 

 soil moisture, resulting from hydrolyzation of silicates, or immediately after ■ 

 carbonate treatment, before decomposition has been effected, magnesium is not 

 to be found in the carbonate form in surface soils." 



While it is shown that the large applications of magnesium carbonate were 

 decidedly toxic to wheat, it is thought " that ground dolomite might be used 

 even in excessive amounts without any immediate toxic effect upon plant 

 growth. However, the greater loss of lime by leaching of carbonate and hydro- 

 lyzed silicates would produce at some future time conditions which would 

 necessitate extensive liming to overcome magnesia poisoning." 

 A bibliography of 55 references to literature bearing on the subject is given. 

 The effect of strongly calcareous soils on the growth and ash composition 

 of certain plants, P. L. Gile and C. X. Ageton (Porto Rico Sta. Bui. 16 (1914), 

 pp. 45, pis. 4). — The plan of the investigations reported in this bulletin was 

 to grow several species of plants in adjacent field plats containing varying 

 amounts (5, 18, and 35 per cent) of calcium carbonate and then measure the 

 yield and determine the composition of the ash of the plants from the different 

 plats. 



The plats were prepared by digging holes 10 ft. wide by 20 ft. long and 2 ft. 

 deep in a clay soil, leaving a bank 3 ft wide between each plat. These holes 

 were filled with clay, sand, and disintegrated limestone in proportions to fur- 

 nish soils of the desired texture and composition. Eight species of plants rep- 

 resenting six families were grown in the plats, namely, rice, soy beans, bush 

 beans, radishes, sunflowers, sweet cassava, sugar cane, and pineapples. 



The results showed that " the growths of bush beans and radishes were un- 

 affected even by 35 per cent of CaCOn. The growths of sunflowers, soy beans, 

 and sugar cane were somewhat depressed by 18 per cent of CaCOs; the growth 

 of sweet cassava was somewhat depressed by 5 per cent of CaCOj and markedly 

 by 35 per cent of CaCOs; the growths of rice and pineapples were markedly 

 depressed with the appearance of chlorosis, by 5. 18, and 35 per cent of CaCOs. 

 " The carbonate of lime apparently had no effect on the amount of nitrogen, 

 potash, and phosphoric acid contained in the various plants, but did increase 

 slightly the total carbon-free ash in all the plants except rice, and modified 

 either the amount of lime, magnesia, or iron in the ash of all the plants. 



" On the calcareous soils the lime in the ash of bush beans was not increased, 

 but there was a slight increase in the amount of lime in the ash of soy beans, 

 sunflowers, and sugar cane. On the plat with 5 per cent of carbonate of lime, 

 the lime in the ash of radishes was increased about 17 per cent, but on the plats 

 with 18 and 35 per cent of carbonate of lime the increases of lime in the ash 

 of this plant were progressively less. On the plat with 35 per cent of carbonate 

 of lime the amount of lime in the ash and dry substance of sweet cassava was 

 markedly increased. On all the calcareous soils the amount of lime in the ash 

 and dry substance of rice and pineapples was greatly increased. 



" Some plants whose growth was little affected by the carbonate of lime 

 (bush beans, soy beans, radishes, and sunflowers) showed marked decreases in 

 the amount of iron or noticeable decreases in the amount of magnesia in the 

 ash, when grown on the calcareous soils. 



" The plants whose growths were most depressed on the calcareous soils 

 (rice and pineapples) showed the greatest increases in the amount of lime in 

 the ash and dry sub.stance of the plant, and also a marked decrease in the 

 amount of iron in the ash." 



