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 of lime. 



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

 very rich in acid organic matter, as much as 5000 to 6000 Ib. 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 Ib. in some states and 80 Ib. 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 Ib. of lime is about as 

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



EQUIVALENT IN 

 COMPOSITION TO 

 100 LB. LUMP LIME 



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



quicklime ........... 71 100 



(6) Ca(OH) 2 , Hydrated lime, water-slaked 



lime . . ........... 54 132 



(c) CaCO2, Lime carbonates, air-slaked lime, 



ground limestone, marl ...... 40 180 



(d) CaSO 4 + 2H 2 O, Gypsum, land plaster . . 23 310 



(e) Ca3(PO4)2, Lime phosphate, ground phos- 38 Pure 187 



phate rock ........... 39 25% CaCO 3 181 



(/) CaH 4 (PO 4 ) 2 + CaSO 4 , Acid phosphate 



(15% P 2 O 5 ) .......... 23 310 



(g) (CaO) 4 P 2 O5, 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 forms, 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. 





