12 BULLETIN" 42, U. S. DEPARTMENT OF AGRICULTURE. 



In each treatment two cultures containing 20 wheat plants were 

 used. Comparison was made with an equal number of plants growing 

 in an untreated portion of the soil extract under the same conditions. 

 At the end of two weeks the green weight of each culture was taken. 

 In addition the oxidizing power of the plants subjected to various 

 treatments was determined. 



The method used to determine the oxidizing power of the roots 

 in these solutions is the one described by Schreiner and Reed in 

 Bulletin 56 of the Bureau of Soils. One hundred milligrams of aloin 

 were added to each 250 c. c. culture jar. Aloin is a yellow powder and 

 when dissolved in water gives a pale yellow solution, which is changed 

 by oxidation to a deep red wine color. The aloin was added to 

 the solution the last day of the cultural experiment; that is, after 

 the plant had grown for two weeks. It remained in the solution and 

 was subjected to oxidation by the plant roots for 12 hours before a 

 comparison of the various treatments was made. The intensity of 

 color of the solution was estimated by means of a Schreiner colori- 

 meter. The untreated soil solution was used as the standard for 

 comparison. It is sometimes difficult to make comparisons where 

 there is a wide difference in the degree of oxidation. When this 

 was the case the solutions were arranged in the order of their apparent 

 color intensity, and the weakest colored solution was used first as 

 a standard, being compared with the second weakest. Number 2 

 was then compared with the third weakest. In turn the third solu- 

 tion can be used as a standard against the next strongest, and so on. 

 In this way the necessity of comparing a solution strongly tinged 

 with yellow against a solution which has a deep red color is avoided. 

 Finally, all readings were reduced to the basis of the untreated soil 

 solution as the standard. 



EFFECT OF MANGANESE IN EXTRACTS OF UNPRODUCTIVE SOILS. 



The first experiments were made with the poor sandy loam soil, 

 which responded to manganese when tested in pots. Extracts were 

 made of the soil, in the manner described above, and wheat plants 

 were grown in the extracts with additions of manganese in several 

 forms. The manganese was added at the rate of 50 parts permillion 

 of the element Mn. The chloride, sulphate, nitrate, and carbonate 

 were used. The plants grew from May 11 to May 22. Two cultures 

 were run with each treatment. Aloin was added to the solution the 

 last day of the experiment and the oxidizing power of the plants 

 taken. The comparative growth and oxidation is given in Table III. 



