Some Causes of Unproductiveness in Soils. 121 



Composition of a Soil impregnated with Salt and Nitrates. 



Moisture 10-86 



"Organic matter 4-84 



Oxides of iron and alumina 11'28 



')•?. 



ul) 



Phosphoric acid 



Equal to bone-earth (5-08) 



Carbonate of lime ['r21 



Nitrate oflimo 2-32 



Containing nitric acid (1-52G) 



Chloride of sodium 11-61 



Chloride of potassium 2-31 



Insoluble siliceous matter 49-22 



100-00 



*Coutaiuing nitrogen -24 



Equal to ammonia -29 



We have here a large proportion of common salt, and also 

 chloride of potassium and nitrate of lime, two salts still more 

 soluble in water than chloride of sodium. The nitrate of lime is 

 evidently a product of the oxydation of animal matter, the 

 presence of which in this curious soil, is distinctly evidenced by 

 the simultaneous occurrence of phosphate of lime (bone-earth) in 

 considerable quantities. We have here presented to us a true 

 nitre-eai'th, which, valuable as it is unquestionably when applied 

 as a manure, is far too rich in saline constituents to be cultivated 

 like an ordinary soil. 



In concluding this section of the subject, it may be well again 

 to mention briefly the various matters and conditions which render 

 some soils barren or unproductive. They are the following : — 



a. Superabundance of organic (humic) acids. 



b. Sulphate of iron (green vitriol), even when present in the 



soil in small quantities. 



c. Sulphide of iron (iron pyrites), and especially finely 



divided black sulphide of iron, which, in the smallest 

 proportions, is most pernicious to plants. 



d. Abundance of protoxide of iron, and absence of peroxide, 



indicating a bad physical condition of the land. 

 €. Chloride of sodium (common salt) in proportions of iVth 



per cent, and upwards. 

 f. Nitrates and all soluble saline matter, in quantities exceed- 

 ing small fractions of 1 per cent, of the whole mass of soil. 



2. Soils are unproductive wheri they are defcient in one or more 

 constituents found in the ashes of our cultivated plants. 



By far the greatest number of soils, as we find them in this and 

 other countries, are poor in phosphoric acid ; for which reason 

 phosphates in an available condition are generally useful as fer- 

 tilisers. In some soils this deficit is very marked. Thus in the 

 following analyses we have merely traces of phosphoric acid : — 



