1 144 THE BOOK OF GARDENING. 



the process of nitrification ; it increases the virtue of the soil 

 by retaining moisture, and helps some of the chemical processes 

 in the soil, which result in the more ready absorption of phos- 

 phoric acid, potash, and ammonia ; and it promotes early maturity, 

 favouring the vegetative property of plants. A good dressing is 

 from ten to twenty bushels to the acre in ordinary gardens, and 

 from two to three tons in sour soils. Lime may be broadcasted 

 and raked or harrowed in, as it has a tendency to sink into 

 the soil. 



Quicklime acts more energetically than carbonate of lime, 

 and is very good on soils especially rich in organic matter, and 

 on sour soils. 



Gas-lime contains small quantities of ammonia, also carbonate 

 of lime, sulphate of lime, and sulphites of lime (combinations of 

 quicklime and sulphuretted hydrogen), which are injurious to 

 all forms of life, whether vegetable or animal, and therefore gas- 

 lime must be exposed to the air before applying to the soil, in 

 order to oxidise these deleterious products and change them into 

 sulphate of lime or gypsum. When used as an insecticide, it 

 should be employed as fresh as possible. It will be found 

 exceedingly beneficial if applied to soils affected by the disease 

 known as Club-Root or Anbury, in root crops, and the 

 Brassica family. In this case, it may be spread on the land in 

 autumn and ploughed or dug in ; from thirty to fifty bushels per 

 acre may be used. 



Carbonate of Lime. — Chalk, shell-sand, and marls are all forms of 

 carbonate of lime. The marls also contain a certain proportion of 

 potash and of phosphoric acid. These forms of lime added to lands 

 deficient in this substance have proved of great value : they are 

 capable of neutralizing the organic acids contained in sour soils, 

 and form a valuable plant-food for many garden crops ; they 

 exert a decided beneficial mechanical influence upon stiff soils, 

 besides consolidating light, sandy soils, liberating the potash and 

 forming the valuable double silicates. Marls are particularly 

 useful in the cultivation of Roses. 



Green Manuring. 



This is one of the best and cheapest ways of adding humus or 

 organic matter, to poor sandy soils especially. The term is 

 applied to some quick-growing crop, such as mustard, which is 

 ploughed in green. Green manuring adds nothing to the 

 mineral matter of the soil. Its utility is due to its getting 

 organic matter from the carbonic acid of the air ; and also, as 

 in the case of leguminous plants, a certain amount of nitrogen 

 from the same source. The roots of green crops bring up 

 plant-food from the sub-soil to the surface for the ' use of 

 succeeding crops. Green manuring helps to smother weeds, and 

 it may in some cases destroy insects. Various crops are used 



