Of late years the old custom of liming the land has been revived. It is now found that lime, or other alkali, is needed to neutralize the acidity of certain soils.

To determine whether a soil is acid, and therefore probably in need of lime (Wheeler).

By litmus paper (to be secured at drug store). - To half a cup of soil add water until it is like thick porridge, and then insert blue litmus paper without handling the end introduced into the soil. After an hour or two, remove and rinse only the lower end. If this end is intensely reddened, liming is probably desirable. The color is pinkish if much acid vegetable matter is present; but if it is not present, the color may be brick-red.

By ammonia water. - To a tablespoonful of soil in half a glass of water add a teaspoonful or more of dilute ammonia water; if the liquid 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 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 as follows (Ca is calcium; O, oxygen; H, hydrogen): —

 

Calcium in

100 LB.

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) CaC02, Lime carbonates, air-slaked lime, ground limestone marl..........................

40

 

180

(d) CaSO4 + 2H20, Gypsum, land plaster . .

23

 

310

(e) Ca3(PO4)2, Lime phosphate, ground phosphate rock....................

38

Pure 25% CaCO3

187

39

181

(f) CaH4(P04)2 + CaSO4, Acid phosphate (15% P2O5)..........

23

-

310

(g) (CaO)4P2O5, 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.