COVER-CROPS OF GREEN MANURES 151 



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, however, except where irriga- 

 tion water is cheap, may never be practicable. The wider problem 

 is to secure the best leguminous 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 evaporation of moisture during our long, dry summer. 

 For this reason we can not use many plants which are used for green- 

 manuring in humid climates. Crimson clover, cow peas, etc., do not 

 make good winter growth unless the temperature is relatively high 

 and frosts few and light. They make exuberant growth for a time in 

 the spring when heat is adequate and moisture abundant, but at that 

 time it is too late to grow crops for plowing under because the soil is 

 too dry for their decay and their presence tends otherwise to the loss 

 of moisture and makes it very difficult to secure a good surface tilth. 

 The greatest care must be had not to allow a growth either of cover 

 crop or of weeds to stand too long or its covering will do more harm 

 than good. Hardy legumes are therefore the desideratum both for 

 winter forage and green-manuring. The common "burr clover" 

 (Medicago denticulate,) is proving very satisfactory in some parts of 

 the State, the "Canadian field pea," the winter vetch, the hairy vetch 

 and fenugreek are coming into quite wide use in orchards in different 

 parts of the State. Which plant is best in any locality must be deter- 

 mined by its local behavior. In some places native lupines make a 

 good natural cover crop. If local conditions do not favor growth of 

 legumes, a good winter cover of rye or other hardy grain may be 

 grown. It will serve the same purposes, though, perhaps, to a less 

 degree. 



A Matter of Local Study. The recourse to cover crops in the 

 orchard or vineyard should be approached with a disposition to careful 

 study and experiment. Unless it is done in the right way it is likely 

 to be disappointing and the right way involves both the selection of 

 the best legumes and the best ways to grow them. Scant growth, 

 cloddy soil, loss of moisture and condemnation of the practice are likely 

 to result from ill-considered methods. On the other hand, success 

 with cover crops results in such numerous and important advantages 

 that the wide introduction of them must be looked upon as one of the 

 most important advances in California horticulture during the last 

 decade. 



Nothing more emphatic can be stated in support of green manuring 

 under the proper conditions than a description of the role played by 

 organic matter in soils. Professor C. B. Lipman, of the University of 

 California, prepares such a description as follows : 



1. By its binding action on the soil particles and by its sponge-like 

 absorptive power, organic matter makes sandy soils more retentive of 

 moisture. 



