78 CHEMICAL FERTILIZERS ; AND LIME 



becomes intensely brown after standing for some hours, and especially 

 if it becomes black, the probable presence of acid vegetable matter is 

 indicated. 



When a soil test indicates only slight acidity, lime may not be needed 

 for most plants. 



Application oj lime. 



On sandy soils, 500 lb. of lime to the acre may be sufficient. On soils 

 very rich in acid organic matter, as much as 5000 to 6000 lb. may be 

 needed. Under usual conditions, about one ton to the acre is a good 

 dressing (20 to 40 bu., with 30 bu. perhaps the average). The legal 

 weight per bushel of lime is 70 lb. in some states and 80 lb. in 

 others. 



Some persons apply lime after plowing and mix it into the soil 

 with the harrow ; others apply in fall and follow by spring plowing. 



Forms of lime (Fippin). 



In a pure form, the calcium equivalent in 100 lb. of lime is about a? 

 follows (Ca is calcium ; 0, oxygen ; H, hydrogen) : — 



r*T/^TTT« TAi EQUIVALE>fT IN 



inn^» Composition to 



lUU LB. jQQ j^g L^j^p Ljj^^ 



(a) CaO, Lump lime, freshly burned lime, 



quirklime 71 100 



(6) Ca(OH;j, Hydrated lime, water-slaked 



lime 54 132 



(c) CaCOj, Lime carbonates, air-slaked lime, 



ground limestone, marl 40 180 



id) CaSO^ + 2H2O, Gypsum, land plaster . . 23 310 



(e) Ca3(P04)i, Lime phosphate, ground phos- 38 Pure 187 



phato rork 39 25% CaCOa 181 



CO CaH«(P04), + CaSO*. Acid phosphate 



(15% PjOr.) 23 310 



ia) (CaO)4Pj06, Basic slag, Tomas phosphate 



powder 43 165 



{h) Ashes (containing quicklime) 15 to 30 450 



Strictly speaking, the lime manufacturers are concerned with only 

 the first three fonns, but these must compete to some extent with other 

 forms. Phosphate fertilizers may sometimes owe their benefits to 

 their lime contents. The same result might then be secured at much 

 less cost from lime. 



