144 THE MONTHLY BULLETIN. 



used to fill the furrows and leave a shallow mulch until the under soil 

 is dry enough for deeper work. I have used satisfactorily the Acme 

 cultivator, or harrow, as it is sometimes called and prefer this to the 

 spike tooth harrow or drag, in use by many. A tool similar in many 

 ways to the Acme is the Killifer weed cutter, which is giving satisfac- 

 tion in several groves. 



There is a great deal of discussion just now as to the proper depth 

 to cultivate a citrus orchard. Some favor shallow frequent cultivation, 

 while others are convinced that it pays to cultivate deeply as well as 

 frequently between irrigations. The experiments of Professors Fortier 

 and Beckett show that when water was applied uniformly over all 

 plots they were able to save 5 per cent more of the water applied when 

 a four-inch mulch was maintained than with a two-inch mulch, and 

 that a six-inch mulch saved nearly 7 per cent more than the two-inch 

 mulch. As this work was done in Northern California these gains due 

 to deep mulches would undoubtedly be increased under the warmer, 

 drier conditions existing in our citrus orchards of the south. Thus 

 on soils where the roots have not been allowed to come too close to tlie 

 surface, deep cultivation to establish a heavy mulch is undoubtedly an 

 important factor in water conservation. 



Another point in favor of a deep mulch is the fact that the larger 

 the loss of water by evaporation, the greater is the concentration of 

 the soluble salts in the surface soil. This means not only that consider- 

 able of the soluble plant foods are removed from the deeper soil to the 

 surface layers where the roots can not get at them ; but also that such 

 soluble salts as sodium carbonate (black alkali) and sodium sulphate 

 (white alkali) are also deposited in this upper area of soil. These 

 two may not be laid down in quantities so great as to be toxic to plants, 

 but very small amounts of such salts are necessary to defloculate the 

 soil and cause a cementing together of soil after irrigation, a condition 

 commonly known as ''plow sole" or "irrigation hardpan." 



In this connection I wish to mention what I believe to be an even 

 more common cause of this so-called "irrigation hardpan"; that is 

 working the soil when it is too wet, whether from rain or irrigation. 

 The fact that this will puddle heavy soils to such an extent that several 

 years are often required to overcome the bad effects of even one such 

 wrong practice makes it very evident that a continuation of this prac- 

 tice can not but seriously impair the physical structure of the soil. 



To sum up briefly the following points are of prime importance in 

 the irrigation of citrus orchards : 



First — Lay of the land so that the furrows will not be too long or too 

 steep, that is, not longer than 400 or 500 feet or with a fall of more 

 than six inches to the 100 feet. 



Second — If land is comparatively level use pipe line and standpipes 

 as a distributing system, otherwise use the cement flume. 



Third — Furrow deeply, that is, at least six inches deep. 



Fourth — "When starting the water run it as rapidly from flume to 

 lower end of furrow as grade will permit without washing, then cut 

 the head down to prevent waste from end. 



