442 



Journal of Agricultural Research 



Vol. V. No. 



The first observations were made on June 19, 191 2. The soil was very 

 friable at this time. Several showers had fallen since planting time, and 

 consequently the plots were in excellent tilth. 



A definite system was followed in locating places for compactness 

 determinations, similar to the plan for taking samples for analysis. This 

 eliminated any chance of duplicating a measurement of a given spot at 

 later times. Tests were made at least 18 inches apart to avoid further 

 any influence due to overlapping. In manip- 

 ulating the mechanical device (fig. 2) auger 

 plate E was placed squarely on the ground 

 and pin D was set in the aperture. Sheath F 

 was then slipped over pin D, and ram G was 

 dropped on the pin until it was driven into the 

 soil sufficiently deep for mark h on the ram to 

 be even with the top of sheath F. The ram 

 was raised each time to mark a and then 

 dropped freely by its own weight (7,445 gm.). 

 This operation was repeated, recording each 

 drop, until mark c on the ram was even with 

 the top of sheath F. Thus, the pin was driven 

 a distance of 4^2 inches in the ground each time 

 a test was made. The number of drops neces- 

 sary to produce this effect was the measure of 

 the relative compactness of soil in the various 

 plots. The results of these trials are given in 

 Table I. 



The fluctuation between the readings as seen 

 in Table I can not be accounted for other than 

 that it represents the normal variation of soil 

 friability over large areas. Increasing the 

 number of readings did not materially alter 

 the average secured. Therefore, the authentic 

 average compactness of the plowed and that of 

 the unplowed plots stand in the ratio of i to 4 

 at this time. Moisture determinations were made on the following day, 

 with no rain intervening, and were as follows: All plots — first foot, 26.2 

 per cent; second foot, 26.5 per cent; third foot, 29.3 per cent. 



On June 24 all plots were lightly cultivated with a hoe, in order to 

 remove the weeds which had begun to appear. At this time the cow- 

 peas were doing very well and stood about 4 inches high. Samples for 

 nitrate analysis showed the soil to contain at the beginning of the experi- 

 ment the amounts given in Table II. 



As might naturally be expected, there is most nitric nitrogen in the 

 surface foot, with a gradual decrease do^\Tiward. The analysis of indi- 



, — Device for testing the com- 

 pactness of the soil. 



