446 



Journal of Agricultural Research 



Vol. V, No. 10 



of the data given in Table III with those secured at the beginning of the 

 experiment (Table I) can be made, for on October 15 the moisture in the 

 first foot of every plot except H was within the limit of variation, where 

 by preliminary tests the effects due to water can be appreciated by our 

 means of measurement. Therefore, disregarding water as a factor, it is 

 apparent that cowpeas possibly have a tendency to maintain the friability 

 of either plowed or unplowed land. The data also show that the plot G, 

 plowed and artificially shaded, was almost as compact as the adjoining 

 plowed plot (H) which was not shaded. This may be interpreted either 

 that the shade was inefficient or that the loosening of the soil is due to 

 some other factor. From the conclusions of Wollny ^ on this point and 

 from the experimental data to be presented below it seems probable that 

 this preservation of soil structure is due to increased bacterial activity, 

 resulting in the formation of humus. This was actually demonstrated 

 by Wollny. 



The nitrate analysis of the plots at the close of the experiment, together 

 with the bacterial count and the nitrifying and ammonifying efficiency, 

 is given in Table VI. 



Table VI. — Nitrate analysis, bacterial count, and nitrifying and arnmonifying efficiency 

 of soil on October 15, IQ12 



« The determination of ammonia i 

 and titration method. 



the ammonifying-efficiency studies was made by the distillation 



The amounts of nitric nitrogen in the soil in the fall, as shown by the 

 data of Table VI, reveal the fact that all plots are going into winter with 

 more available nitrogen in the soil than they contained in the early 

 spring, as shown in Table II. It is also seen that cultivated plots, either 

 cropped or uncropped, are richer in nitric nitrogen at the end of the 

 season than are the plots not plowed. The low nitrate content of the 

 first foot of the plot artificially shaded can not be explained. Lastly, 

 the results check with previous investigations in the fact that under even 

 a legume treatment there exists less nitrate in the soil in the fall than 



Wollny, Ewald. Op. cit. 



