THE MONTHLY BLLLETIX. 23 



soil particles for catching rain and irrigation water that deep plowing 

 acts as one of the most potent methods of moisture conservation which 

 we can employ. And it accomplishes this great service for us in addi- 

 tion to making possible the more active bacterial development at great 

 depths in the soil, the more rapid Aveathering of the soil minerals, there- 

 fore increasing the availa])le plant food supply, and the much deeper 

 root development of plants — the paramount importance of which, espe- 

 cially in our soils, has already been duly emphasized. Who can say 

 truthfully, in view of these arguments, that it is possible to over-em- 

 phasize the importance of deeply plowing California soils? 



As to the proper depth to plow under different conditions, I want to 

 say that in the orchard it may vary from eight to ten inches, depending 

 on the nature of the soil and other circumstances regulating tillage 

 operations on the ranch. The greater depth is to be preferred. There 

 is no necessity for changing suddenly from a shallow to a deep plow 

 depth. It will suffice gradually to attain to that condition recom- 

 mended by plowing an inch or two deeper every succeeding season. 

 IMoreover, with such methods of plowing pursued, but one plowing a 

 year will suffice to render the soil one of proper air and moisture con- 

 ditions. 



The Prevention of the Formation of Plowsole. 



Plowsole in soils is produced thi-ough either plowing at the same 

 depth year after year or through the washing of fine clay and silt into the 

 soil by irrigation water or rain. When it is due to the silting up of 

 irrigation furrows, it is known as an irrigation hardpjui. but it produces 

 the same effects as plowsole. The latter is thus a hardened, more or 

 less impervious layer of varying thickness found between four and 

 eight inches in depth below the surface of the soil. If in an old orchard 

 in which poor methods have been employed it may attain a thickness of 

 six or more inches. Air passes through the plowsole layer only with 

 the greatest difficulty and water likewise can percolate but slowly 

 through it. If this condition is allowed to continue for any length of 

 time in a soil, the roots of plants will soon find conditions in the soil 

 depths uncongenial to their development and so will the beneficial soil 

 bacteria. The result will be that the roots will tend to come to the 

 surface for more air, Avarmth, and available plant food, and we grad- 

 ually produce from a naturally deep soil an artificially shallow one. 



Plowsole should be broken up Avitli a subsoil plow if it is already 

 formed. Three or four furrows betAveen tAvo roAws of trees Avill improve 

 conditions markedly. If the ploAvsole is thin it may be broken up by 

 means of an ordinary deep ploAving Avith a moldboard ploAV. To pre- 

 vent the formation of ploAAsole change the ploAv depth from year to 

 year, and break up the compacted and silted bottoms of irrigation 

 furroAvs instead of merely covering them Avith loose diy soil. 



Irrigation in Deep Furrows. 



The foregoing remarks anent the prevention and breaking up of 

 ploAA'sole and irrigation hardpan haA^e for their principal purpose the 

 more adecpiate aeration of the deeper soil layers so as to make in them 

 more congenial conditions for the deA^lopment of plants' roots, and to 

 prevent the massing of the feeding roots at the surface of the soil AA^here 

 both the food and Avater supply may soon become insufficient to 



