[H] Gain of 6 lb. See p. 173. TABLE XVI.--ANNUAL ENERGY CHANGES IN SOIL: BROADBALK. APPROXIMATE VALUES ONLY. MILLIONS OF KILO CALORIES PER ACRE PER ANNUM. +---------------------------------+-------------+---------+ | | Farmyard |No Manure| | |Manure Added.| Added. | +---------------------------------+-------------+---------+ |Added in manure | 14 | nil | |Added in stubble | 2 | 0·3 | | +-------------+---------+ | Total added | 16 | 0·3 | |Taken from soil | nil | 0·5-1 | |Stored in soil | 0·5-1 | nil | | +-------------+---------+ | Dissipated per annum | 15 | 1 | +---------------------------------+-------------+---------+ |Per day: calories | 41,000 | 2700 | |Equivalent to | 12 men. | ¾ man. | |The human food grown provides for| 2 men. | ½ man. | +---------------------------------+-------------+---------+ These numbers are interesting when we reflect that the human food produced on the dunged land yields only 7000 calories per day, from which it is clear that our agricultural efforts so far provide more energy for the soil population, for which it was not intended, than for ourselves. The account is not complete; we have omitted all reference to the oxidation of ammonia and of elements other than carbon. Nature seems to be in an unexpectedly economical mood in the soil, and all compounds which can be oxidised with liberation of energy seem to have corresponding organisms capable of utilising them. Even phenol, benzene, hydrogen, and marsh gas can all be oxidised and utilised as energy sources by some of the soil population. Even with this remarkable power the soil population has insufficient energy to satisfy all its possibilities; our present knowledge indicates that energy supply is, in this country at any rate, the factor limiting the numbers of the population. Increases in the water supply or the temperature of the soil produce no consistent effect on the population, but directly the energy supply is increased the numbers at once rise. MATERIAL CHANGES.