io Commercial Gardening 



will give some idea as to the various mineral foods taken out of the soil by 

 different fruit and vegetable crops. These foods must be all soluble in 

 water, and the temperature of the soil must be favourable, otherwise the 

 roots would be unable to absorb them. It will be noticed that the same 

 food is taken up by different crops in different proportions, and there is 

 often a great difference in the composition of the wood and the fruit on 

 the same plant. It should also be stated that the results obtained by 

 different chemists vary greatly, probably owing to the plants tested being 

 taken from different soils and at different times. 



The quantity of these foods to an acre may be seen from the follow- 

 ing analysis of Broadbalk Field, Rothamsted. The soil had not been 

 manured for fiity years, and at 9 in. deep the weight of an acre was 

 2,500,000 Ib. containing 



Carbon ............ 22,250 Ib. 



Nitrogen ...... ... 2,500 



Soda ............ 1,500 



Potash ............ 6,750 



Magnesia ......... 9,000 



Lime ............ 62,250 



Alumina ......... 112,250 



Oxide of iron ......... 85,000 



Phosphoric acid ... ... 2,750 



Sulphuric acid ... ... ... 1,250 



Carbonic acid ... ... ... 32,500 



Total ... 338,000 



This particular soil lost about 4'20 per cent, or 105,000 Ib., on ignition; 

 12'53 per cent, or 313,250 Ib., was soluble in hydrochloric acid; and the 

 undissolved siliceous matters were 83'27 per cent, or 2,081,750 Ib. 



These figures would indicate that there is an inexhaustible supply of 

 food in the soil far more than could be absorbed by many crops in the 

 course of several years. 



It has been estimated that an acre of fruit trees would require each 

 year about 200 Ib. lime, 150 Ib. potash, 75 Ib. nitrates, 50 Ib. phosphoric 

 acid. It would thus take over 311 years to exhaust all the lime in the 

 Broadbalk Field at Rothamsted, 45 years to exhaust all the potash, 33 

 years to exhaust all the nitrogen, and 55 years to exhaust all the phos- 

 phoric acid. And it must be remembered that these quantities are given 

 for an acre of ground unmanured for 50 years, and taken from only 9 in. 

 deep. 



In an American experiment, soil at 1 ft. deep (not 9 in.) gave 

 3,225,000 Ib. weight to the acre, and was estimated to contain 



Phosphoric acid ... ... 6,772 Ib. per acre. 



Potash I... ....... 32,897 



Lime ......... ... 47,407 



