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weight of average agricultural land gives a relative idea a.s to its 

 richness or deficiency in any of the manurial constituents. One 

 acre contains 43,560 square feet of surface, and a depth of one foot 

 of that area therefore contains 43,560 cubic feet of soil. The weight 

 of one cubic foot of soil varies greatly from the heaviest rocky and 

 and sandy soils to the lightest peaty and clayey soils. The average 

 ordinary agricultural soil weighs about SOlbs. per cubic, foot, so that 

 the total weight of one acre of dry soil, one foot deep, would be 

 3,484,8001bs, or, say, 3,500,0001bs. ' This being so, a rich soil con- 

 taining one per cent, of potash or phosphoric acid would contain 

 35,0001bs. of such plant food on an acre one foot deep. Similarly 

 should the analysis disclose '1 per cent, the amount on that area 

 would be 3,5001bs. and a crop removing, say, 501bs. of potash or of 

 phosphoric acid a year would thus take 700 or 70 years, as the case 

 may be, to exhaust such a soil absolutely of either of the substances 

 referred to. 



Although theoretically that lapse of time would be necessary 

 for the crops to entirely drain that soil of its potash or some of 

 the phosphates, it is nevertheless found that beyond a limit the soil 

 tenaciously holds up and refuses to part in favour of the crop with 

 the whole of its elements. It then becomes imperative to either 

 restore to the ground those elements of plant food which have been 

 removed or by fallowing and spelling provide fresh supplies from 

 the deeper strata and from the upper layer itself by the process of 

 weathering. It is fortunate that the future is thus protected against 

 the rapacity of the present. An examination of one of our own 

 soils, a free dark chocolate loam, on the bank of a brook, will serve 

 as an example of the teachings which soil analysis conveys to the 

 mind. The land in question is under black wattle, flooded gum, and 

 blackboys, and looks very fertile. Its analysis is as follows : 



Moisture '. 8'0200 



Organic Matter 13'9900 



* Phosphoric Acid 0'0255 



*Potash Q'0848 



Oxide of Iron and Alumina ... ... ... 17165 



Carbonate of Calcium ... ... ... ... 0'6400 



Soluble Silica 0'3660 



Insoluble Silica 73-9260 



* Nitrogen ... ... ... ... ... ... - 420 



Equal to Ammonia ... ... ... ... O'SIO 



*Sodium Chloride 0-3714 



Magnesia Chloride... ... ... ... ... 0'1504 



This analysis shows that the land in question is a free dark 

 loam. It contains 74 per cent, of sand and is also rich in humus. 



Approximately, one acre of that soil, one foot deep, contains : 



Of Potash 350X85= 2,9751bs. 



Of Phosphoric Acid 350x25= 8121bs. 



Of Nitrogen 350 x 42 = 14,700lbs. 



Of Salt (Sodium Chloride) ... 350 x 37 = 12,9501bs. 



Of Magnesium Chloride ... ... 350X15= 5,2501bs. 



