Green-Manures on Heavij Lands 



255 



hence the decomposi- 

 tion processes do not 

 run their course as 

 rapidly here, and the 

 green- manures and 

 animal manures last 

 longer. In other words, 

 the soil -humus needs 

 to be replenished on 

 heavier soils less fre- 

 quently than on light 

 soils. Similarly, the 

 losses of nitrogen are 

 usually smaller from 

 heavier soils than they 

 are from light soils, be- 

 cause the nitrates are 

 not as readily leached 

 from the former, nor 

 are the decay processes 

 in them sufficiently in- 

 tense to lead to the 

 setting free of gaseous 

 nitrogen. One excep- 

 tion is found in heavy 

 soils that are apt to 

 become water -logged. 

 Under such conditions, 

 the soil-nitrates may be 

 reduced with the evolu- 

 tion of nitrogen gas. 



Fig. 48. Young alfalfa plants. Tha few 

 tubercles are, for the most part, larg^. 



