THE ROTATION OF CROPS. 67 



years of continuous maize growing is due in large part to the 

 destruction of the more active decaying organic matter, result- 

 ing ultimately in insufficient liberation of plant food within the 

 feeding range of the maize roots. "^ 



Yield of Maize at Missouri University (after 17 years). 



Maize continuously ... 11.8 bushels. 



Maize, wheat, clover ... 50.7 ,, 



Maize, wheat, clover, manure ... 77.6 ,, 

 Here again the rotation alone showed to great advantage 

 over the maize grown continuously. However, only when 

 manure was added was yield maintained. 



Extensive experiments at Indiana showed conclusively 

 that in a rotation experiment when only grain crops were em- 

 ployed, and even when fertilised, the yield was not maintained. 

 The addition of organic matter through the use of humus adding 

 crops (clover and grass), when fertilised, increased the original 

 productivity of the land. 



The following South African ex[)eriments show the effect 

 of previous crops on those following : — 



Potchefstroom School of Agriculture. 



Yield of wheat in pounds. 

 1916. 1917. 1918. 



Velvet beans cut for fodder, wheat 



following 1,240 1,080 1,040 



Cowpeas cut for fodder, wheat 



following 1,400 1,380 1,240 



Maize, summer crop, wheat winter 



crop 800 520 540 



Sunflowers, summer crop, wheat 



winter crop 400 600 600 



Not only is there a consistent and marked difference 

 between the residual effect of the legumes, but an enormous 

 reduction is apparent when w;heat follows non-leguminous cul- 

 tivated crops. 



Cedara School of Agriculture. 



Average of Results from three farms: 



Maize in pounds. 



First year after Second year after 



Check Plots. Cowpeas. Cowpeas. 



(1) 1,329.0 1,876.0 1,589.0 



In this experiment the legume was cut for hay, conse- 

 quently this marked effect is due chiefly to the residual effect 

 of the roots. 



