89 



Steenbjerg: Microelements from a Practical Point of View 



from the manganic oxides which are reduced during the growth 

 of the plants. There is the possibihty that the manganic oxides 

 are stored as more active higher oxides in loams or clay soils than 

 in the light sandy soil. There is perhaps, so to say, no "aging" of 

 the manganic oxides in heavy soils. 



In a series of field experiments performed mosdy on sandy 

 soils some years ago in which increasing amounts of manganese 

 sulphate were added we found that the amount of exchangeable 

 manganese in the manganese fertilized plots had decreased to the 



Table 16: Experiments with manganese sulphate, 50 kgs per ha: — 



same order of magnitude as in the untreated plots within a month 

 after the addition of MnS04 (also laboratory experiments have 

 shown this fact) and still the effect was good the first year; more- 

 over, the residual effect was not zero in the following years. This 

 seems to show that manganic oxides are reactive and available the 

 first, second and third years. But the availability decreases pro- 

 gressively from the first to the third year. 



