964 



Journal of Agricultural Research 



Vol. VI, No. 24 



Here, again, the marked effect of manure, particularly in the case of 

 corn and wheat, is evident. These two plots rank at the bottom of the 

 series when untreated, but by the addition of manure they are moved 

 from ninth and tenth places to first and second, manure having a much 

 greater influence on these than on any other plots studied. The effect 

 of manure is quite marked on the timothy and rotation plots, though not 

 nearly so great as in the case of corn and wheat. Considering both 

 seasons, we find the percentage of increase caused by the application of 

 manure to be as follows: 



Corn percent. . 217 



Wheat per cent. . 150 



Timothy percent. . 47 



Rotation percent. . 28 



1913 

 160 



44 



3 2 



The increases due to the application of chemicals w^ere as follows: 

 Wheat, 103 per cent; rotation, 30 per cent. 



These figures are from the average of those samples receiving no 

 calcium carbonate. Considering the same phenomenon when calcium 

 carbonate was added to the test samples, we find entirely different data : 

 Corn, 39 per cent; wheat, 21 per cent; timothy, no increase; rotation, 

 9 per cent. When chemicals were added the increase of wheat was 9 

 per cent; that of the rotation plot, 4 per cent. 



The application of calcium carbonate to the soil from different plots 

 in 1 914 gives some equally interesting data: 



Plot No. 



17 



18 



9- 



10 

 2 . 



23 



22 



13 

 1. 



3- 



Cropping system. 



Continuous corn 



Continuous corn, with the addition of manure. . . . 



Continuous wheat 



Continuous wheat, with the addition of manure. . . 

 Continuous wheat, with the addition of chemicals 



Continuous timothy 



Continuous timothy, with the addition of manure. 



Six-year rotation 



Six-year rotation, with the addition of manure . . . 

 Six-year rotation, with the addition of chemicals. 



Percentage 

 of increase 

 due to cal- 

 cium car- 

 bonate. 



162 



IS 



187 



40 



54 

 102 



37 

 89 

 61 

 5° 



Calculating from the 1914 tests the percentage increase in the nitrate 

 formation of manured soil with the addition of calcium carbonate over 

 the untreated in the absence of calcium carbonate, we approximate the 

 combined influence of both factors. Estimating the theoretical effect of 

 the two factors by adding the increases resulting from manure alone and 

 from calcium carbonate alone, very different results are obtained. 



From these data and those given above it is evident that in only one 

 case of the series studied is it possible to replace entirely the calcium 

 carbonate by manure or the manure by calcium carbonate. However, 

 this may be done to a very large extent. In the case of timothy it is not 



