May, 1909.] 



Scientific Agriculture. 



any growth already made at the time, 

 and provided also that the estimates 

 as to the water-requirements ;derived 

 from tbe experience of the countries 

 of summer rains (the humid regions) 

 hold good for the arid region also. 

 Wic'.hor or not this can be assumed, 

 is among the points our experiments 

 are designed to determine. The sur- 

 prisingly successful growth and bearing 

 especially of deciduous trees, without 

 irrigation, despite a drought of five or 

 six: months in the "Franciscan climate,"* 

 has led to an impression that a less 

 amount of water may suffice under 

 arid conditions. For in the East, as 

 many weeks of drought and intense 

 heat would frequently suffice to destroy 

 the crop. 



Probable causes of this endurance of 

 drought.— Doubtless the main cause <~>f 

 this remarkable endurance is to be 

 found in the much deeper rooting of all 

 plants in arid climates; whereby not 

 only a mush larger bulk of moist soil is 

 at their command, but the roots are 

 withdrawn from the injurious effects 

 of hot, dry surface and air. 



This deeper range of the roots is not 

 the result of foresight on the part of the 

 plant. It could not occur on Eastern 

 soils, because of the intervention, in 

 the great majority of cases, of difficultly 

 penetrable subsoils ; from which, more- 

 over, plants could draw but little 

 nourishment on account of their " raw- 

 ness." In the arid region, as a rule, 

 subsoils in the Eastern sense do not 

 exist ; the soil mass is practically the 

 same for several feet, and in the pre- 

 valent soils is very readily penetrable to 

 great depths. This, summaiily speak- 

 ing, is due to the slight formation of 

 clay, and the rarity of heavy rains in 

 the arid region. And this easy pene- 

 trability of the soils implies, moreover, 

 that being well aerated, the depths of 

 the soil are not " raw," as in the East ; 

 and therefore that the " subsoil " such 

 as it is, may fearlessly be turned up as 

 deeply as the farmer is willing to go 

 with the plough, without danger of injur- 

 ing the next season's crop, in all lands 

 that are well drained ; as, by reason 

 of their depth and perviousness, is the 

 case with most California soils. 



The accompanying plate illustrates 

 from Nature the deep penetration of a 

 peach root developing in a normally 



* This name has been felicitously applied by 

 Powell to the climate of middle imd southern Cali- 

 fornia, which is characterized by the concentra- 

 tion of rains within a winter which is mild enough 

 to constitute a growing season, while the summer 

 is practically rainless, 



deep, well serated "bench" soil, in a 

 manner quite impossible to the same 

 root when growing in land underlaid, 

 as are most Eastern ones, by a subsoil 

 which either is too dense or too wet to 

 be penetrated and utilized by the tree. 



A glance at the figures suffices to 

 show that, while a root system like 

 plate 1, a typical Eastern tree root will 

 stand in absolute need of frequent 

 rains or irrigation to sustain its vitality, 

 such a one as plate 2 may brave pro- 

 longed drought with impunity, being 

 independent of surface conditions, and 

 able to perform all its functions out of 

 reach of stress from lack of moisture.* 

 It is equally clear that it is to the 

 farmer s interest to favour, to the 

 utmost, this deep penetration of the 

 roots, both in the preparation and tillage 

 of the ground, and in the use of irri- 

 gation water. For if the latter is used 

 too frequently or too abundantly, the 

 salutary habit of deep rooting will be 

 abandoned by the plant, and it will, 

 as in the East, be dependent upon fre- 

 quent rain or irrigation ; and also, owing 

 to the small bulk of soil upon which 

 it can draw for its nourishment, upon 

 frequent and abundant fertilization. 



Eastern immigrants as well as a large 

 proportion of California farmers do not 

 realize the privilege they possess of 

 having a triple and quadruple acreage 

 of arable soil under their feet, over and 

 above the area for which their deeds call ; 

 and they tenaciously continue to adhere 

 to precautions and practices which, 

 however salutary and necessary in the 

 region of summer rains, do not apply 

 to this climate. The shallow ploughing 

 so persistently practised results in the 

 formation of a "plowsole" that plays 

 the part of the Eastern subsoil in pre- 

 venting root penetration ; limiting their 

 range for moisture and plant food and 

 thus naturally causing crops to succumb 

 to a slight stress of season which ought 

 to have passed without injury, had the 

 natural conditions been taken into 

 proper consideration. 



Roots follow moisture. -Very striking 

 examples of deep rooting as the result 

 of vertical moisture penetration can be 

 observed in some of our native trees, 

 which, while naturally at home on moist 

 ground, are nevertheless sometimes 

 found forming luxurieut clumps on the 

 slopes and even summits of our coast 

 ranges and foothills. If we examine 

 the ground where this occurs in the 

 case of California laurel, we will gener- 



*The moisture determination under this tree 

 gave, to the depth of eight feet, an aggregate amount 

 of water of 1,058 tons per aore. 



