60 EErORT OF THE ACTING DIRECTOR AND ChEMIST OF THE 



and available forms wliich plants can readily take up and use. 

 This is probably the most important effect of plaster as an indirect 

 fertilizer. 



In whatever way gypsum may act, it is well established that it is 

 of value when applied on certain soils to certain crops, such as 

 clover, peas, lucern and similar plants. All forms of superphosphate 

 contain more or less gypsum, as will be explained later. 



Quicklime. — Quicklime or burnt lime or calcium oxide, com- 

 monly called lime, is known to be valuable as an indirect fertilizer. 

 It produces changes in both the physical and the chemical character 

 .of soils. It changes the mechanical condition of soils by loosening 

 heavy clay soils and also by holding together and giving body to 

 light sandy soils. Freshly burned lime acts chemically upon soils 

 by decomposing vegetable and mineral matter already present in the 

 soil and changing them into forms which are available as food for 

 the plant. Thus, lime acts upon insoluble mineral substances con- 

 taining potash, soda, etc., and converts them into soluble forms 

 which plants can use. Lime aids in the decomposition of animal 

 and vegetable matter, such as vegetable mold, stable manure, etc., 

 and tends to convert them into available plant-food. In this change 

 from insoluble to soluble forms, any food not taken up by plants 

 during the season may be washed away before another season and' 

 thus lost. In using lime, care should be taken not to use too large 

 quantities, and ordinarily it is best to use it in connection with 

 liberal applications of nutritive fertilizing substances. Lime can be 

 used to advantage on freshly drained swamp lands and also on lands 

 newly cleared. 



Common Salt has an indirect fertilizing value which is mainly 

 due to the fact that it has the power of changing unavailable forms 

 of plant-food, especially potash, into available forms. 



Danger in using Stimulant Fertilizers. — It should be kept 

 in mind that these stimulant fertilizers are not used for the plant- 

 food contained in them ; hence, as used, they do not furnish needed 

 plant-food. The chief value of their use lies in the fact that they 

 can change unavailable into available forms of plant-food. It can 

 readily be seen that, when stimulant fertilizers are used exclusively 

 for a term of years, the soil each year loses nitrogen, potassium and 

 phosphorus compounds, which are not replaced. The inevitable 

 result of such treatment is the exhaustion of these important food 

 constituents from the soil. This affords an explanation of the 



