250 



FORESTRY AND IRRIGATION. 



June, 



lary action, comes to the surface and 

 evaporates, the sohible salts are left at 

 or near the top of the ground. A shal- 

 low wetting of the soil also leads to the 

 development of tree and plant roots near 

 the surface, for plant roots also must 

 develop best where requisite amounts of 

 water are accessible. As a result of 

 shallow irrigation and insufficient cul- 

 tivation, therefore, the orange orchards 

 (which were more particularl)^ studied) 

 of this district were found with root 

 systems in considerable part developed 

 within a foot of the surface in direct 

 contact with accumulated alkali salts 

 left by evaporation. 



Flooding, where water is available 

 and drainage good, is the best means to 

 dispose of alkali. The occasional river 

 floods could be utihzed for this purpose, 

 such water being least salty ( as low as 

 52 parts in 100,000 observed) and abun- 

 dant for a little time. Deep borders and 

 six or eight inches depth of water will 

 be found more effective than operations 

 of less determined nature. After the 

 salts are leached down into the lower 

 soil, the ground must be deeply and 

 thoroughly cultivated to prevent surface 

 evaporation and consequent return of 

 alkali. 



Deep irrigation in subsoiler furrows 

 has the merit that a scanty head of 



water is made to penetrate quicklj^ and 

 deeply into the soil, leading to a deeper 

 establishment of root systems and allow- 

 ing less surface evaporation. The em- 

 ployment of the subsoiler, however, does 

 not do away with the advisability of 

 distributing surface accumulations of 

 salts downward through the soil by 

 flooding, as soon as the water supply will 

 permit. These measures have proved 

 entirely effective in certain of the orange 

 orchards of southern California. 



The shading of the soil, especiall}^ in 

 summer, by heat and drouth-resisting 

 crops, checks surface evaporation to a 

 useful extent and lessens the rise of 

 alkali in proportion. German and com- 

 mon millets are probably suitable for 

 this purpose in Arizona. 



To some extent, also, such crops as 

 sour clover, barley, or millet take up 

 alkali salts, which are removed with the 

 crops from the soil. A heavy crop of 

 sour clover, for instance, weighing 

 50,000 pounds, green, will contain about 

 1,000 pounds of ash, largely composed 

 of alkali salts from the soil. This, how- 

 ever, is approximately onl}- one-third of 

 what would be added in an acre foot of 

 concentrated summer water. Moreover, 

 if plowed under as green manuring, the 

 salts taken up by the crop are returned 

 to the soil from which they were taken. 



AN ELM TREE STRUCK BY LIGHTNING. 



By L. H. Pammel, 

 Professor of Botany, Iowa State College of Agriculture and Mechanic Arts. 



IT is a well-known fact that man}- 

 kinds of trees are frequently struck 

 by lightning. The writer has ob.served 

 among the deciduous trees the follow- 

 ing : White Oak {Querciis alba), the 

 Red Oak [Quercus rubra), Bur Oak 

 ( Quercus macrocarpa) , Black Oak ( (^/^i?;-- 

 cus vehdiua) , the Hickory {Hicoria 

 ovata), and the American Elm. Of the 

 conifers which have come under the 

 writer's observation, theEodgepole Pine 

 ( Piniis niurrayana) and the Rockj' 

 Mountain Balsam {Abies lasiocarpa) 

 may be mentioned. Many other trees 



are frequently struck by lightning, as 

 numerous observers attest. In western 

 Wisconsin, where the writer spent his 

 boyhood, it was not an uncommon thing 

 to find a score of trees struck by light- 

 ning on my father's farm every season. 

 It is a general belief among country 

 people there that the oak is much more 

 frequently struck by lightning than 

 any other species. This opinion is 

 probabl}" not well founded. However, 

 for this reason, few people in that vicin- 

 ity will plant the oak for a shade tree. 

 The oaks would naturally be struck 



