568 IOWA DEPARTMENT OF AGRICULTURE 



ture, they are quite retentive, and drainage water passes through them 

 slowly. In such cases drains of less than four feet are of greater value 

 for agricultural purposes. It may he said that for farm lands lateral 

 drains should be about three feet, unless the compact and retentive soil 

 indicates that less depth should he used. When it is attempted to follow 

 any general depth the necessity of obtaining suitable grades for the drains 

 will often make some parts of the drain deeper or shallower than desired. 

 A nice and economical adjustment of the depths of the several drains of a 

 system can be learned only by practical work. 



A practical knowledge of the field, coupled with the facts on the field 

 book, form the key to the dormant resources of the soil. 



The frequency of drains is also a question upon which there is a wide 

 difference of opinion and consequently a difference of practice. 



It would be a waste of labor and material to place drains 40 feet apart 

 in some of our soils, while, on the other hand, to place drains at inter- 

 vals of 150 feet would come far short of accomplishing thorough drain- 

 age. Generally drains are placed about every 100 feet, but this feature 

 of the work should be very carefully studied before deciding upon their 

 frequency. 



No set rules can be given in regard to how many acres a given tile 

 will carry, for the grade had much to do with amount of water a given 

 size tile will carry. On ordinary flat lands I would not recommend using 

 any tile smaller than five inch. 



THE ERADICATION OF BINDWEED, OR WILD MORNING-GLORY. 



U. S. Department of Agriculture, Farmers' Bulletin 368. 



INTRODUCTIOX. 



The terms "bindweed" and "wild morning-glory" are rather indis- 

 criminately applied to the various species of the genus of plants known 

 by botanists as Convolvulus that are of importance as weeds. In cer- 

 tain limited sections other common names are used to refer to these 

 species, such as gopher vine, pea vine, and wild sweet potato. By far the 

 larger number of these plants are classified under the two species 

 Convolvulus sepium and C arvensis, the former a native of this coun- 

 try and the latter an introduction from Europe. There are a few other 

 species, principally Convolvulus sepium repens and C. californicus, that 

 occur as weeds in certain regions. The former is a variety of Convolvulus 

 sepium, but is often referred to as C. repens. 



In many parts of the country these species rank among the worst of 

 all the weeds that trouble the farmer, and in some regions they are by 

 far the worst. Being perennials, they propagate not only "by their seeds, 

 but also by their underground parts. It is the latter character especially 

 that makes them such formidable enemies to the tiller of the soil. The 

 common or cultivated morning-glory, with the large, bell-shaped flowers 

 of various colors, is sometimes found in fields where it has escaped from 

 cultivation. This is an annual not difficult to control and should not be 

 mistaken for a species of Convolvulus. 



