Green-Manures on Light Soils 243 



having demonstrated that sUght dressings of barnyard 

 manure, too sUght in themselves to increase the yield 

 appreciably, are highly beneficial when spread over a 

 green-manuring crop before the latter is plowed under. 

 It seems that two or three tons of manure per acre, thus 

 applied, add to the soil millions of bacteria that hasten 

 the decay of the green crop and make it more quickly 

 available. 



The peculiar value of green-manures on light, sandy 

 soils is due chiefly to the open character of the latter. 

 In the presence of sufficient moisture, vegetable and ani- 

 mal substances decay very rapidly in them. It is fre- 

 quently next to impossible to accumulate any consider- 

 able quantity of humus in such soils. The various decay 

 bacteria work very rapidly under such conditions and, 

 in extreme cases, set free very considerable quantities 

 of nitrogen. In order, therefore, to maintain the humus 

 and moisture in these soils, green-manures must be 

 plowed under frequently. With a sufficient supply of 

 lime there is no danger of too great an accumulation 

 of acidity. The rapid and, at times, intense decomposi- 

 tion of the organic matter assures the ready availability 

 of the plant-food taken by the green crop from the soil. 

 There is, however, one serious drawback in the use of 

 green-manures on light soils, and that is the Hmited 

 amount of moisture available in them for the growing 

 of crops. 



Loss of moisture. — Careful experiments made in this 

 country and in Europe show that for every ton of dry 

 matter there are removed by evaporation from the 

 leaves and stems of the crop about three hundred tons 



