INVESTIGATIONS ON THE PRODUCTION OF PLANT FOOD. 197 



much bacterial action the chances are that it has dried too much. 

 It is therefore necessary to wait for rain to supply the needful water 

 and renew the dissolved oxygen in the water round the soil particles. 

 It is this combination of temperature, moisture, and oxygen supply, 

 following on the beneficent changes effected in the winter months in 

 the soil organic matter and the soil population, that causes the great 

 outburst of soil life in the spring. 



The explanation is new, but the facts have long been known to all 

 observers. 



Spring has always been recognized as the great time for life in the 

 soil. " It is then," says Virgil, " that Aether, the Almighty Father of 

 Nature, penetrates the womb of earth with his fruitful showers and, 

 blending his mighty frame with hers, gives life to all the embryos 

 within." * 



The summer minimum may be attributed to dryness, and the 

 autumn maximum to a repetition of the spring effects. In a moist 

 warm summer, however, continued activity may occur right up to the 

 point when " sickness " sets in, and the autumn maximum may not 

 then arise. 



In consequence of these various activities the soil is left pretty 

 rich in nitrates at the end of the autumn provided the summer has 

 been reasonably dry. If these remain they form a good supply for 

 the young plants of the following season. But in a wet winter part is 

 washed out and the young plant is deprived of some of its food. We thus 

 have part of the explanation of the harmful effect of a wet winter, and 

 one of the reasons why the husbandman in all ages has hoped for dry 

 winters. " A wet summer and a fine winter," to quote again from 

 the Georgics, " should be the farmer's prayer. From winter dust comes 

 great joy to the corn, joy to the land. No tillage gives Mysia such 

 cause for boasting, or Gargarus for wondering at his own harvest." f 

 English farmers would ask for the wet spring instead of the wet 

 summer, but they would agree entirely as to the winter, and out of 

 their experience they have evolved a variety of similar expressions. 

 Again the man of science has annotated the poet, and Sir William 

 Shaw has worked out a mathematical expression showing how much 

 damage is done on an average by winter rain. 



The trouble can be met by a system of green manuring, whereby 

 plants are grown in the autumn to take up the nitrates and are then 

 ploughed into the land ready for the operation of the soil organisms 

 in spring. The system is very sound, and as soon as it is sufficiently 



* " Vere tument terrae et genitalia semina poscunt. 

 Turn pater omnipotens fecundis imbribus Aether 

 Coniugis in gremium laetae descendit, et omnis 

 Magnus alit magno commixtus corpore fetus." 



Georgics, Bk. II. 11. 324-327. 



f " Umida solstitia atque hiemes orate serenas, 

 Agricolae ; hiberno laetissima pulvere farra, 

 Laetus ager : nullo tantum se Mysia cultu 

 Iactat et ipsa suas mirantur Gargara messes." 



Georgics, Bk. I. 11. 100-103. 



