192 
ordinary agricultural soil weighs about 80lbs. per cubic foot, so that 
the total weight of one acre of dry soil, one foot deep, would be 
3,484,800lbs., or, say, 3,500,0001bs. This being so, a rich soil con- 
taining one per cent. of potash or phosphoric acid would contain 
35,000lbs. 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 3,500lbs. and a crop removing, say, 5lbs. or 50lbs. 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 svil 
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 . ele wit anh aes 8-0200 
Organic Matter a as ae .» 13-9900 
*Phosphoric Acid a i es ss 0-0255 
*Potash . . ass eee 0:0848 
Oxide of Tron ‘and Alumina se oy 1-7165 
Carbonate of Calcium Be sine on 0- 6400 
Soluble Silica oe en an siece 0- 3660 
Insoluble Silica ane ons Mi w.  73+9260 
*Nitrogen sa ang 2a wed sibs 0-420 
Equal to Ammonia eas ee obs ane 0-510 
sedi Chloride ies Se 2a Sea 0-3714 
Magnesia Chloride... ee Sie sits 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 ... 3 .. 350 x 85 = 2,975lbs. 
Of Phosphoric ‘Acid .. 850 x 25 = 812lbs. 
Of Nitrogen ... .. 850 x 42 = 14,700lbs. 
Of Salt (Sodium Chloride) .. 850 x 37 = 12,9501bs. 
Of Magnesium Chloride ... 350 x 15 = 5,250lbs. 
Supposing this land was cropped annually, and the erop re- 
moved from the ground 50lbs. each of potash, phosphoric acid, 
