328 Journal of Agricultural Research vo1.xv.no.6 



of soils is also increased in the presence of an excess of water, as indicated 

 from the results obtained with soil E. Drainage conditions will modify 

 the acidity of either an organic or inorganic soil, and this will have an 

 effect on soil fertiUty. Of course with soils well suppUed with calcium 

 and magnesium, poorly-drained soils would not become acid until a 

 part of the bases were dissolved and washed away. 



SUMMARY 



(i) Five different types of acid soils were kept under different moisture 

 conditions in pots in the greenhouse for one year. Portions of soil were 

 kept one-fourth saturated, one-half saturated, and fully saturated; also 

 in an air-dry condition. 



(2) Acidity determinations were made by the Hopkins potassium- 

 nitrate method, the C. H. Jones calcium-acetate method, and the ethyl- 

 acetate method. Samples of soil from each pot were tested for acidity 

 both in the moist and in the air-dried condition. The potassium-nitrate 

 extracts were analyzed. 



(3) The degree of soil acidity measured by the different methods 

 varied with different moisture conditions. 



(4) With each soil and each method used the samples which had been 

 kept half-saturated were higher in acidity than they were at the start 

 of the experiment. The acidity of the half- saturated soils was greater 

 than the acidity of the fourth-saturated soils. 



(5) The soils high in organic matter showed the greatest acidity when 

 kept fully saturated. The soils low in organic matter showed the 

 greatest acidity when kept half-saturated. 



(6). When the moist samples of soil taken at the close of the experi- 

 ment were air-dried, the fully-saturated samples showed loss of acidity. 

 The half- and fourth-saturated samples showed both gains and losses in 

 acidity when air-dried. 



(7) The potassium-nitrate extracts of the fully-saturated soils con- 

 tained much larger amounts of iron than extracts of other samples. 

 This soluble iron was in the ferrous form and was oxidized and made 

 insoluble when the soils were dried. 



(8) With the mineral soils the fully saturated soils had much greater 

 amounts of soluble manganese than the other samples. Drying the 

 soils did not render the manganese insoluble as it did the iron. 



(9) There was less soluble aluminium in the fully saturated minera 

 soils, but with the soils high in organic matter this was not true. There 

 was both increase and decrease of soluble aluminium on drying the soils. 



(10) Calcium, magnesium, and silica showed variations in solubiUty 

 owing to different moisture conditions, but the variations were not as 

 striking as those of iron, manganese, and aluminium. 



