440 Journal of Agricultural Research 



Vol. V. No. lo 



Wollny ^ reports that the shade of crops on land has little or no tendency 

 to increase the looseness of a soil, but his data show that a crop, either 

 cereal or legume, partially prevents the land from becoming compact. 

 He has proved that not alone is this effect due to the elimination of the 

 effects of beating rains and sunlight thereafter but to a greatly increased 

 bacterial activity on cropped land. The bacteria thrive better in the 

 moderate shade afforded by the plants, produce more humus, and thus 

 improve the soil structure. The author gives definite experimental data 

 to substantiate his conclusions. 



Stewart,^ in experiments with the effect of shading on soil condi- 

 tions, where tobacco under tents and in the open was grown for com- 

 parison, reports the following conclusions from his investigation. The 

 soil under the tent remains more moist than the uncovered soil, a condi- 

 tion which is especially important during the dry growing period. For 

 this reason the shaded soil is always closer to the optimum water con- 

 tent. Because the soil is not subject to the packing due to alternate 

 wetting and drying, it remains in better physical condition. 



PLAN OF THE WORK 



The soil of the Missouri Experiment Station field, upon which this 

 experiment was performed, analyzed as a silt loam. The surface soil 

 to a depth of 8 inches is a grayish to brownish silt loam; from 8 to 21 

 inches it grades heavier and is dark red in color, and from 24 to 48 inches 

 it becomes more granular, contains some sand, and is of a light yellowish 

 tinge. The mechanical analysis is as follows: Fine gravel, 0.26; coarse 

 sand, 0.37; medium sand, 10.77; ^^ sand, 0.77; very fine sand, 29.37; 

 silt, 49.55; clay, 8.88; total, 99.97; volatile matter, 4.91. 



This soil might be termed the Shelby silt loam, according to the classi- 

 fication of the United States Bureau of Soils 



Work was actively begun on the preliminary part of this investi- 

 gation in 191 1. The number of samples of soil to be taken from the 

 plots for analyses in order to eliminate the errors of sampling was deter- 

 mined by careful trials. Again, it was necessary to experiment with a 

 mechanical device for measuring the compactness of the soil under 

 different treatments. 



A systematic plan for sampling the plots and for making tests for 

 compactness at periodic times was arranged so as to avoid all chance 

 of dupHcation of trials on the same piece of ground. 



Experimental work was necessary upon a shade device that would 

 permit rain to pass through without much hindrance and would shut 

 out eft'ectively the direct rays of the sun, thus providing the desired 

 shade effect. 



' WoIIny, Ewald. Der Einflussder Pflanz'endeckeund Beschattung . . . p. 165. Berlin, 1S77. 

 ^Stewart, J. B. Effects of shading on soil conditions. U. S. Dept. Agr. Bur. Soils Bui. 39, 19 p., 7 

 fig., 4 pi. 1907. 



