The Healthy Soil 



15 



ash in the soil, forming potassium nitrate which is 

 a form available for plants. 



As a result of the activity of soil bacteria, hydro- 

 gen sulphate is evolved from the decomposition of 

 proteids. The sulphur may be further changed into 

 sulphur dioxide, and when combining wdth water 

 and oxygen, into free sulphuric acid. The latter 

 readily combines with calcium or magnesium, form- 

 ing calcium or magnesium sulphate, from which the 

 plant obtains sulphur for the construction of its 

 proteids. 



