14 BULLETIN 42, U. S. DEPARTMENT OF AGRICULTURE. 



growth 3 per cent. With 30 parts per million, manganese oxidation 

 was increased 48 per cent and growth 19 per cent. With 50 parts 

 per million, manganese oxidation was increased 45 per cent and 

 growth 12 per cent. 



Subsequent experiments with other poor soils were made, the results 

 of which are similar to the one recorded above. One of these tests was 

 with a poor clay loam from Maryland. Manganese sulphate was 

 added to the soil extract in amounts of 10, 30, and 50 parts per 

 million. There was considerable improvement in growth and an 

 increase in the oxidizing power of the plants following the manganese 

 treatment. The relative growth was for the untreated 100; manga- 

 nese 10 parts per million, 132; manganese 30 parts per million, 111; 

 and manganese 50 parts per million, 105. The relative oxidation was, 

 respectively, 100, 133, 133, and 160. 



A similar test was made with a sample of poor Collington sandy 

 loam. The manganese was added at the rate of 20 parts per million, 

 manganese in the form of chloride, sulphate, nitrate, carbonate, and 

 dioxide being used. The results of the action of these various com- 

 pounds on this soil extract are shown in Table V. The experiment was 

 made from November 22 to December 6. 



Table V. — Effect of manganese (20 parts per million) on growth and oxidation of wheat 

 in extracts of poor Collington sandy loam. ( Untreated extract = 100.) 



Treatment. 



Relative 



Relative 



growth. 



oxidation. 



100 



100 



96 



•102 



102 



100 



110 



280 



108 



233 



110 



271 



Extract untreated 



Extract 4- MnCl 2 



Extract 4- MnS0 4 .... 

 Extract + Mn(N0 3 ) 2 . 

 Extract + MnC0 3 .... 

 Extract + Mn0 2 



The chloride and sulphate showed practically no increase in oxida- 

 tion or in growth in this soil solution. The other salts of manganese 

 increased oxidation considerably and also the growth. Where the 

 nitrate was used, oxidation was increased 180 per cent and growth 10 

 per cent. With the carbonate, oxidation was increased 133 per cent 

 and growth 8 per cent. With dioxide, oxidation was increased 171 

 per cent and growth 10 per cent. 



The effect of manganese on an extremely poor lawn soil is reported 

 in the next experiment. The soil used was very unproductive. The 

 natural vegetation is stunted and attempts at lawn making had failed. 

 The water extract of this soil is a poor medium for plant growth, but 

 is much improved by treatment with carbon black, which acts as an 

 absorbent. A chemical examination of the soil showed it to contain 

 dihydroxystearic acid and picoline carboxylic acid, both of which are 

 harmful to plants. 



