22 THE MONTHLY BULLETIN. 



rapidly, and thus poor conditions for air penetration, and, therefore, for 

 deep root development must obtain. 



Why Are Deep Soils Superior to Shallow Soils? 



After being thus made acquainted with the causes contributing to 

 the formation of our deep soils, your next question doubtless will be 

 "Why do we val;ie deep soils so highly?" To reply simply, I must 

 saj-— for purposes of making possil)le a deep and large root development 

 on the part of the plant. I must also add that in its turn the deep and 

 large root development of a plant is advantageous because it places at 

 the disposal of the plant so much more area from which to draw its food 

 and water, and since so much more surface is available as a source of 

 food and water supply, the fertility of the soil is not only greater but 

 more lasting. To emphasize this point I must also say that plants can 

 only take their food up in solution from the water films surrounding 

 the soil particles, and it is only reasonable to expect that a plant which 

 has twice as many water films as another to draw on, because of its 

 superior root development, should obtain its food and water with greater 

 ease and have twice the amount at its disposal. A deep root develop- 

 ment, therefore, makes possible under our climatic conditions the 

 utility of the greater depth of the soils which we own as much as the 

 surface ; and by making the surface soil more lasting in its fertility and 

 placing a more adequate supply of food and Avater at the plant's dis- 

 posal, serves as one of the greatest blessings of him who grows crops 

 for profit. 



What Do the Foregoing Principles Teach for Soil Management? 



The six most important considerations in California soil fertility 

 which flow directly or indirectly from the principles just considered are : 



1 . Deep plowing of our soils. 



2. Prevention of formation or breaking up of plowsole. 



3. Irrigation in deep furrows. 



4. Deep incorporation of manure and fertilizers. 



5. Frequent summer cultivation. 



6. Green manuring and the maintenance of the humus and nitro- 



gen supply. 



I shall take up now a brief consideration of the first five factors and 

 consider the sixth by itself this evening. 



Deep Plowing. 



The functions of deep plowing in soils are : First, to aerate the soil 

 at greater depths, thus making it possible for weathering and bacterial 

 and root action to augment the supply of available plant food ; second, 

 to create a larger surface for catching and holding rain and irrigation 

 water. The importance of these two functions of deep plowing to the 

 maintenance of fertility in California soils can not be overestimated. 

 The second function named is of particular interest to us because of 

 the disastrously dry seasons of the past two years. There is doubtless 

 many an orchard in the State in which two inches of rain water saved 

 by a deeply plowed soil as against a like amount lost by a similar soil 

 plowed shallow has spelled the difference between profit and loss during 

 the past year. It is thus by throwing open a much larger surface of 



