SOILS AND MANURES 365 



not well understood. Lime is not in itself a manure. It has chap. 

 a beneficial effect on the soil, and therefore on the crop. It 

 encourages nitrification, rendering nitrogenous matter in the 

 soil available to the growing plant. It also improves the soil 

 texture, making heavy adhesive soils more friable and granular, 

 and reducing their tendency to puddle, while it makes loose, 

 sandy soils more compact and retentive of organic matter. 

 Lime counteracts acidity of the soil, thus improving it for the 

 development of nitrifying organisms, and is useful for sweeten- 

 ing freshly drained swampy lands. Lime hastens the decom- 

 position of decaying matter, and may therefore be applied with 

 stable manure to advantage. But continuous application of 

 lime without the addition of real plant-food tends to impoverish 

 the soil ; there is a good old adage to the effect that " all lime 

 and no manure soon makes the farmer poor ". 



For soils deficient in lime, maize is a good crop with which 

 to apply it ; in the United States it is used with this crop to a 

 considerable extent, with apparently satisfactory results. 



326. Indication of Need of Lime. — Many South African 

 soils are deficient in lime, but others contain sufficient, and 

 where that is the case the application of more would only be 

 a waste of money. The farmer can tell whether lime will im- 

 prove his crops or not : (1 ) by chemical analysis, which will 

 show the percentage of lime (CaO) present ; for agricultural 

 crops CV2 per cent is usually considered the minimum require- 

 ment ; (2) by a test with neutral litmus paper which, if it 

 turns red, will indicate acidity in very sour soils and the con- 

 sequent need for lime ; (3) by the excessive adhesiveness of 

 clay soils ; (4) by the character of the native vegetation (e.g. 

 in South Africa theVaalbosch {T archonantlius carnphoratus) and 

 Salvia rugosa generally occur on soils rich in lime) ; (5) by 

 the persistent failure of certain crops, such as lucerne or sain- 

 foin ; (6) by experimental application — and this is probably 

 the most reliable test — of a good dressing of lime on say one 

 acre of a field of maize where the soil is uniform, and under 

 conditions which make it possible to tell whether there is any 

 increase of crop as a result of the application. 



327. Kinds of Lime. — Commercial lime is not always of 

 the same chemical composition. Two kinds are commonly 

 met with in South Africa, White and Blue lime. Blue lime 



