THE MONTHLY BULLETIN. 457 



The taprooted plants through decay improve the subdrainage of the 

 heavier soils and bring the subsoil to the surface ; they separate the fine 

 particles of these heavier clay soils, improving its aeration, while the 

 binding action of the root systems makes the light soil more retentive 

 of moisture. This organic matter is the laboratory in which soil bac- 

 teria manufacture available plant food. Finally, the cessation of soil 

 cultivation for the months during which the cover crop is growing 

 makes for economy in labor and for the conservation of the soil — as a 

 too continuous cultivation uses up the nitrates of the soil. 



Now as California soils especially need organic matter and also nitro- 

 gen, it would seem that the leguminous cover crop deserved the attention 

 of every citrus grower. Bear in mind the bigness of this citrus industry. 

 In seven of the counties of southern California — not counting Tulare 

 with its three million trees — 150,000 acres are under citrus culture, 

 112,000 of which are in bearing. These groves produced last year over 

 40,000 cars of fruit. Such an industry, with its prospective increase, 

 with its ever threatening liabilities, and the current prices of fruit, 

 make it evident that the grower should study economy in citrus culture. 



There was published in the April University of California Journal of 

 Agriculture a legume cover crop balance sheet, a summary of which will 

 indicate the saving per acre through use of cover crops as compared with 

 the cost of other forms of nitrogen : cost of seed, $3.00 ; plowing, $2.00 ; 

 seeding, $1.00; inoculation, $2.00; total, $8. This crop is estimated to 

 produce 200 pounds of nitrogen at a cost of four cents per pound. In 

 other forms this nitrogen would have cost some sixteen cents per pound, 

 or $32.00 per acre — a saving by use of cover crop of three-fourths in cost 

 of this fertilization. 



Although the cover crop may demand extra water and cost of added 

 inconvenience there is as an offset to this : more organic matter, better 

 physical and bacterial condition of the soil, with the liberating of other 

 elements of fertilization, besides the protection of the soil itself from 

 flood and freeze and, with the added humus, probably a permanent im- 

 provement of the soil, 



KINDS OF COVER CROP IN USE. 



While it would be of interest to study the history of the use of cover 

 crops from early ages in Asia and in Egypt, to follow the spread of 

 legumes around the Mediterranean, the use of such green manuring in 

 Roman Italy, and its increasing use in Germany and France in more 

 recent times, still it is enough to note that there is nothing new under 

 the sun ; and it is well for farmers to rediscover some truths and to learn 

 wnsdom from the experiences of the past. We confine our observations 

 to southern California and to the near present. 



Winter cover crops have had some years of testing, although not with 

 the thoroughness that could be wished. Opinions vary in regard to the 

 relative value of this and that kind of legume. Only by gathering data 

 from wide observation and through special experiments will satisfactory 

 conclusions be reached as to the best variety for the different kinds of 

 soil. Certain kinds of legumes have proved of special worth and the 

 grower should watch for further discoveries. Considerations which go 

 to determine the plant selected will include cost and purity of seed, care 

 and disposal of the crop, the tonnage and the amount of nitrogen made 



2—19452 



