GREEN MANURING. 125 



handled somewhat differently. The density of the soil reduces the 

 ordinal y losses by drainage, so that there is less need of the green 

 manuring. The legumes found most useful on such lands are 

 lupins, seradella, yellow, red and crimson clover, field peas, horse 

 beans and vetches. Because of the density of the soil, decomposition 

 does not progress so freely; hence care must be taken not to overdo 

 the treatment by plowing in too much of the green plant. 



The extent of the utilization of the legume after growing, depends 

 upon the completeness of the decomposition and the eventual nitrifi- 

 cation of the material that is plowed under. It is possible to plow 

 under such a large quantity of vegetable matter that it will not 

 properly decay, either because the density of the soil prevents suffi- 

 cient aeration, or because too much acid forms, checking bacterial 

 activities. No value accrues from green manuring unless thorough 

 decomposition occurs. For this reason it is generally best to plow 

 in the leguminous crop before it has fully matured, for then it has 

 assimilated most of its nitrogen but has not become too bulky for 

 proper decay in the soil. Frequently it is best to reap the crop and 

 feed it to cattle, plowing in only the roots and stubble, this giving all 

 the organic matter that can be readily decomposed in the soil. If, 

 subsequently, the manure from the cattle that eat the crop is added 

 as a dressing, the greatest possible use will have been made of the 

 leguminous crop. 



The actual value of such green manuring has been demonstrated 

 many times. Sandy soils have been brought under fair cultivation, 

 and depleted farms have been reclaimed to cultivation by the skill- 

 ful use of this nitrogen-fixing power of legumes, aided by the tubercle 

 bacteria. A constant increase in nitrogen can be brought about 

 thus till the quantity is sufficient for large crops. In one extended 

 series of experiments and observations it was found possible to in- 

 crease the amount of nitrogen in a soil from .02 per cent, at the start, 

 to .17 per cent, at the end of about twenty-five years, equivalent to 

 5,000 pounds of nitrogen per acre. In another test the plowing in of 

 a crop of the velvet beans stubble upon a soil subsequently planted 

 with oats, increased the yield of oats from seven to thirty-eight 

 bushels per acre; and in this case the velvet bean crop was reaped 



