IQQ CALIFORNIA FRUITS: HOW TO GROW THEM 



which means that if twelve inches of such water were used on 

 the ground during the season, each acre would receive therefrom 

 about twenty pounds of fully available potash. At Riverside a 

 crop of oranges requires about forty-two pounds of potash per 

 acre, of which the amount of irrigation water used in that case 

 contained thirty-five pounds, beside other matters required by 

 plants. These things have a definite cash value in the market; and 

 this value the irrigator gets as a free gift in addition to the water. 

 Even in the case of the Nile, the sediment is only part of the sum 

 of fertility conveyed by the river. 



GREEN MANURING OR COVER CROPS 



Green manuring consists in plowing under a growth of weeds 

 or a sown crop to secure by its decay a contribution of humus 

 to the soil. Plants grown for this purpose are currently called 

 ''cover crops" because they cover the soil instead of allowing it 

 to remain bare in "clean culture" of orchard or "bare fallow" of 

 grain fields. 



All plants by their decay in the soil add organic matter to it, 

 and this matter is of nitrogenous character, but leguminous 

 plants do this and a great deal more, through their exclusive ability 

 to use atmospheric nitrogen gathered by the bacteria which cause 

 nodules upon their roots. There is also special value in deep- 

 rooting legume in soil amelioration. There is now reason to 

 believe, as has already been stated, that where moisture is ample 

 for both alfalfa and trees we shall come to using this plant for 

 a permanent cover of orchard ground as a substitute for apart 

 of the clean culture which is now observed. This is, in fact, 

 already being done to some extent. It is also probable that alfalfa 

 can be used for a certain time even where its permanent stand 

 is not desirable, for it is not difficult to destroy alfalfa with a 

 well-sharpened plow although the roots may have attained con- 

 siderable thickness. Of course this, as already stated, depends 

 upon moisture supply ; where that is n6t abundant, clean culture 

 for moisture conservation is unavoidable. But where moisture in 

 excess of the needs of the trees is available it will be used in future 

 indirectly for their benefit in ways we are only just beginning to 

 discern, and one of these is likely to be the summer growth of 

 legumes in the orchard. Cow peas on moist or irrigated lands may 

 be used in this way. 



A summer cover crop in California is, however, largely a matter 

 for future determination, and under ordinary conditions may never 

 be practicable. The wider problem is to secure the best legumi- 

 nous plant which will make a heavy growth during the winter 

 months, so that it can be plowed in early in spring, and the ground 

 put in shape for the thorough surface pulverization to prevent 



