444 



Journal of Agricultural Research 



Vol. V, No. lo 



Obsen^ations taken on August 21 showed that the cowpeas on the 

 plowed plot were only a little heavier than those on the adjacent unplowed 

 plot. Blossoms had already begun to appear, and runners measured 

 from I to 2 feet in length. Some crab-grass had sprung up, but only a 

 few other weeds were noticed. The shade devices were in very good 

 condition and the soil beneath seemed normal except that it was covered 

 with a growth of green alga. This was also true of the soil of the cow- 

 pea plots, but to a less marked extent. 



Great care was given to details, such as freeing from weeds, renewing 

 the covering of the shade device, etc., throughout the season. Just 

 before frost, compactness tests were again made on all plots after remov- 

 ing the cowpea vines. The vines were cut Avith a scythe and the strip 

 walked on by the operator was eliminated from the test areas. The 

 data on soil compactness secured for October 15 are given in Table III. 



Table III. — Relative compactness {number of drops of ratn) of soil on the various plots, 

 as measured on October 75, igi2 



Plot D 



(unplowed ; 



clean). 



PIotE 

 (unplowed ; 

 cowpeas). 



PIotF 

 (plowed ; 

 cowpeas). 



Plot G Plot H 



(plowed; arti-, (plowed; 

 ficial shade). clean). 



3 



4 



5 



6 



7 



8 



9 



10 



II 



12 



13 



14 



15 



16 



17 



18 



^9 



Averasre 



The relative compactness as shown in Table III was duplicated, using 

 a modification of the method which originated with Wollny ^ — i. e., the 

 apparent specific gravity of the soil in each plot was determined. A 

 metallic brass tube 7.8 cm. in diameter was driven to a depth of 23.2 

 cm. in the soil. The tube was then dug out and the contact below 

 broken. Duplicate cores of soil from each plot were thus secured, taken 

 to the laboratory, dried, and weighed. The dry weight of the soil divided 

 by the volume of the cylinder (i ,465 c. c.) is the apparent specific gravity 



» Wollny, Ewald. Der Einfluss der Pflanzendecke und Bcschattung . . . 197 p., lo pi. Berlin, 1877. 



