82 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



soil texture. Its power of holding water may be improved ; its- 

 supply of available plant food increased ; and then by a suitable 

 manurial treatment it may be brought into condition to yield 

 bountiful returns for all that is done to it. 



The next question very naturally is, What ingredients of 

 plant-food are most frequently deficient in horticultural soils ? 



I think we may take it as a pretty-well established fact that 

 the only constituents of plant food which need be supplied to 

 garden soils are potash, phosphoric acid, lime, and nitrogen. 

 When we say these ingredients are lacking, we do not mean that 

 the soil does not contain them, but that it does not supply the 

 growing plants with as much as they need. It is not so much 

 because horticultural soils have been worn out of plant food, but 

 rather because the food is locked up in such combinations that 

 the roots cannot get at and use it, that an artificial supply of 

 soluble food in manure becomes necessary. 



Conclusion. 



In conclusion, a few practical remarks may be made upon the 

 three main constituents of plant food in horticultural soils — 

 namely, nitrogen, potash, and phosphoric acid. 



Nitrogen. — Although the nitrification in rich garden soils, 

 leaf-moulds, and peat-moulds may be sufficiently active for the 

 gardener to dispense with artificial nitrogenous manures in most 

 cases, yet there are certain species of plants which rapidly 

 develop a large mass of foliage, and these cause a rapid and 

 extensive demand upon the available nitrogen of the soil. For 

 such plants it will always be advisable to use nitrate of soda, 

 sulphate of ammonia, guano, soot, or similar materials as manure ; 

 and also for growing very early crops, or plants out of season. 



Phosphoric Acid. — Assimilable phosphoric acid occurs in 

 very small actual quantities in most soils, however rich ; this 

 has been fully illustrated in the tables. It is therefore necessary 

 to add this ingredient by a manurial application if full crops are 

 to be obtained. The best form in which phosphoric acid may be 

 added to horticultural soils is by bone phosphate, bone meal, 

 double superphosphate, or basic slag. Superphosphate of lime 

 yields a certain proportion of phosphoric acid soluble in water. 

 But in rich moulds cheap mineral superphosphates are not to be 



