18 VEGETABLE GROWING IX NEIV SOUTH WALES, 



propounds the theory that their use tends to exhaust the soil. On the con- 

 trary, it is certain that any ordinary soil becomes impoverished by the 

 constant removal of plant food by the crop, unless some means are adopted 

 of maintaining fertility. 



The materials required to keep the soil in fertile condition may be broadly 

 classified thus : (1) Manures that contain the necessary plant-food (princi- 

 pally potash, phosphoric acid, and nitrogen) ; and (2), vegetable matter and 

 lime, which, besides containing plant-food, are of considerable value iii 

 improving the mechanical condition of the soil, and which thereby have a 

 material effect in rendering available certain ingredients previously present 

 in the soil, though not in a form in which" plants could make use of them. 



Manures that Supply Plant-food. 



(a) Phosphoric Acid. Manures containing phosphoric acid may be applied 

 in the forms of bone manures (bonedust, bonemeal, &c.), superphosphate, and 

 Thomas' phosphate. 



Phosphoric acid is undoubtedly the plant food that can be most profitably 

 added to the soils of the State at any rate it is the particular plant-food 

 that, when supplied in the form of a fertiliser, produces the most profitable 

 response under our conditions. It is most commonly added to the soil here 

 as superphosphate, that being the form in which phosphoric acid is most 

 available to plants, and in which they can therefore soonest make use of it. 

 Hence it is of special use where a rapid return is required, as in the case of 

 spring-sown crops. 



Superphosphate is usually applied at the rate of from 56 Ib. to 3 cwt. per 

 acre, the amount varying with the nature of the soil and with the quantities 

 of other manures used in conjunction with it. This manure generally forms 

 the basis of the "general manures," "special manures," " mixed manures," 

 Ac., on the local market ; such mixtures are usually prepared by the addition 

 of sulphate of ammonia or nitrate of soda, and some potash salt. 



Bonedust, another source of phosphoric acid supply, is also valuable for its 

 nitrogen content. In place of superphosphate it may be used as a base for 

 mixtures. It is, however, somewhat slower in its action. 



(6) Potash. Muriate of potash and wood ashes are the only forms in 

 which potash manures are now obtainable. The former is a concentrated 

 fertiliser and is chiefly used in mixtures. Until recently the main sources of 

 supply of this particular plant-food were sulphate of potash and kainit, both 

 of which are now unobtainable. The results from potash manures are not 

 seen in our soils on the same scale as are frequently reported from other 

 parts of the world, in fact, the present writers have never yet seen an 

 instance of increased production from the use of potash manure alone, and 

 therefore can only recommend its use as part of a complete fertiliser. 



