77 



STIMULANT MANURES. 



Stimulant manures are those whose addition to the soil 

 does not supply directly any plant food of value, but whose 

 presence there brings about the decomposition of other 

 forms of plant nutriment not otherwise available for plant 

 use. Among the more important and more commonly em- 

 ployed manures of this class are lime and gypsum (land 

 plaster), and in some countries, salt also finds some employ- 

 ment as an auxiliary stimulant manure. 



Lime is, itself, an important mineral ingredient of plant 

 life, and some scientists and investigators (notably Yille) 

 have classed it along with the three essential constituents 

 of complete manures above alluded to. It so happens, how- 

 ever, that lime is present in sufficient quantities in almost 

 all soils to meet the actual requirements of the plant itself 

 for this particular element, and when it or its compounds are 

 supplied to the soil it is almost invariably with a view to the 

 fulfilment of its functions as a stimulant manure. One of 

 the most important offices performed by the lime consists in 

 the decomposition or breaking up of certain, mineral forms 

 of potash, whereby the latter becomes readily soluble and 

 available for plant food, while in its original state of combi- 

 nation it was practically of no nutritive value. 



Lime also corrects the acidity of so-called "sour soils" 

 and checks in a marked degree the tendency of "running to 

 weed" commonly exhibited by cotton and other crops 

 grown on such soils. 



The more important uses and efi^ects of lime upon soils 

 are very appropriately given by Dr. Hilgard in one of the 

 Tenth Census Reports on Cotton Production, and his conclu- 

 sions are reproduced herewith : 



(a.) "A more rapid transformation of the vegetable matter 

 into active humus. 



(b.) The retention of such humus against the oxidizing in- 

 fluences of hot climates. 



(c.) It renders adequate for more profitable culture per 



