Manures and Commercial Fertilizers 107 



than they take and make what is called a symbiosis, or 

 living together. 



Many of our heavy soils, particularly those in which 

 the clay is the result of the decomposition of granite rocks 

 containing large percentages of feldspar, have in them 

 large amounts of potash in the form of an insoluble 

 silicate. On these soils it has been found that the use of 

 lime has the effect of releasing potash in such a shape 

 that plant roots can get it. In some soils the first use of 

 lime has such a marked effect from this releasing of pot- 

 ash that farmers often jump to the conclusion that all 

 they need to keep their land rich is to continue applying 

 Hme as a manure. But you understand by this time that 

 the lime has only helped them to get at what was already 

 in their soil and has depleted instead of enriched it. While 

 the ordinary commercial fertilizers are merely the means for 

 supplying plant food that may be deficient in the soil, lime is 

 therefore to be regarded more as a stimulant. It has also a 

 mechanical effect about which you have already learned. 



Lime and ashes, remember, should never be mixed with 

 the farm manures, since the effect will be to form the vola- 

 tile carbonate of ammonia, which will escape into the air, 

 for wood ashes contain a large percentage of lime. Neither 

 should Hme be mixed with phosphatic fertilizers as it will 

 tend to revert the phosphoric acid in them into a less avail- 

 able form or condition. But there is another form of lime\ 

 that can be used with benefit with the manure. This is j 

 the sulphate of lime commonly known as plaster. When / 

 this is mixed with the manure it tends to retain the ammo- / 

 nia in a less volatile form. Plaster also has the effect of/ 

 releasing potash in the same way that lime does. 



