1905.] 



On the Retention of Bases by the Soil. 



31 



gases has been exhausted, any calcium carbonate re-formed in this way would 

 not appear in the analyses set out, which only extend to the depth, of 

 27 inches. 



It is, however, clear that manuring with organic manures, the growth of 

 clover and other leguminous plants which leave behind a considerable residue 

 of roots and stubble particularly rich in calcium oxalate, the debris of plant 

 tissues which accumulates in the soil of grass land, all go to maintain the 

 stock of calcium carbonate, which in its turn is being as constantly drawn 

 upon for nitrification and for the neutralisation of the other acids produced 

 during the bacterial decay of the carbon compounds the soil receives. 



Doubtless in all soils containing only a minimal amount of calcium 

 carbonate under natural conditions these various actions have reached an 

 equilibrium, since the increase of any one only tends to bring into play the 

 factor which limits it (the rate of nitrification, for example, will be slowed 

 down as the available base in the soil becomes scarce), but also accelerates 

 the operation of some action in the opposite sense ; even the one irrevocable 

 loss by drainage and removal of crop will probably be balanced by the 

 calcium salts coming into solution through the continued weathering of the 

 soil particles. In the main, however, the original stock of calcium carbonate 

 in the soil circulates continually between plant and soil without suffering: 

 appreciable loss. It is only under particular conditions, such as the use of 

 ammoniacal manures, or the setting up of anaerobic conditions through lack 

 of drainage, thus allowing the formation of organic decay acids but not their 

 final oxidation to carbonates, that the soil will develop an acid reaction and 

 become infertile. 



Summary. 



The chief points brought out in the course of the investigation are as 

 follows : — 



(1) Arable soils which contain upwards of 1 per cent, of calcium carbonate 

 are subject to a normal loss of that constituent in the drainage water 

 amounting to about 800 lbs. to 1000 lbs. per acre per annum. 



(2) The loss is increased by the use of ammoniacal manures by an amount 

 equivalent to the combined acid of the manure. The loss is diminished by 

 the use of sodium nitrate or organic dSbris like farmyard manure. 



(3) The growth of plants normally returns to the soil a large proportion of 

 the bases in the neutral salts which the soil provides for the nutrition of 

 plants. 



(4) The calcium oxalate and other organic salts of calcium present in 



