io Mineral Nutrition of Plants 



scientific research over the last 150 years. On no other great soil group 

 has a comparable amount of research been clone and on no other can 

 we find similar, widespread increases in production, although there are 

 important advances in other areas that point to the potentialities. 



Scientists and farmers alike, on the Gray-Brown Podzolic soils of 

 Europe and the United States, know how to overcome the handicaps 

 of relatively low fertility by liming, fertilization, growing legumes, and 

 so on. The question of what yields to strive for is, within limits, an 

 economic matter of input-output relationships of the various factors 

 involved, including fertilizers. Yet, even now, only a part of the farm- 

 ers on these soils are really efficient. If all of them followed the prac- 

 tices of the most efficient one-quarter or one-third, production could 

 probably be increased another 25 to 35 per cent, to say nothing of 

 possible contributions of entirely new technology. 



Ch 



ernozems 



The Chernozems are the great wheat-producing black soils of the 

 United States, Canada, Argentina, and the. Soviet Union. Unlike the 

 Gray-Brown Podzolic soils, the Chernozems are highly fertile at the 

 start. They have abundant organic matter and an excellent granular 

 structure. They are rich in nitrogen, calcium, potassium, and most other 

 plant nutrients. 



In spite of this storehouse of nutrients, yields on Chernozems are not 

 especially high, on the average. Rainfall on these soils is erratic and 

 often low. So far, science has had conspicuously less success in over- 

 coming the limitations set by drought than those set by low fertility. 

 Still, a lot has been done recently to increase yields on Chernozems, 

 especially through improvement in varieties of grains and through 

 better and more timely tillage with powerful machines. 



Yet, there are fertility problems with Chernozems. Under the pre- 

 vailing practice of continuous grain production, the nitrogen supply 

 declines. The growing of legumes, like alfalfa and sweet clover, tends 

 to offset this loss, but it also tends to deplete the moisture supply for 

 the following grain crop. Thus, yields following legumes are sometimes 

 lower than they are following the previous grain crop and especially 

 following fallow. No doubt, we shall see more nitrogen fertilizer used 



