FERTILIZATION AND FERTILIZERS 141 



This is a dreadful waste of valuable plant food. Both 

 should first be allowed to rot in piles kept moist, before being 

 plowed into the land. The soil will then be enriched with 

 humus without making it too "open." 



Soil bacteria. But stable manure and compost 

 aid crops, not alone by the plant food and humus they 

 bring into the soil. One of their greatest advantages 

 is that they carry with them j^great^ultitude of 

 bacteria^which act very favorably on the soil. Much 

 of their immediate effect is due to these minute plants, 

 which greatly help the soil-nutrition of plants. 



Some of these bacteriaTlake nitrogen, a very valuable 

 plant food, from the air and store it so that the plant 

 can use it. These are called n^rogei^jcing._bacteria. 

 Some of them live in the soil, others live in tubercles 

 on the roots of legumes. Read wliatTs said about them 

 on page 263. 



Greenmanure. When we can get no stable manure, 

 or not enough, we can with great benefit use green 

 plants for plowing in. Such plants are best grown on 

 the land itself. A crop of weeds will do some good, 

 but it is better to grow legumes such as clover, peas, 

 beans, or vetches. The reason for using these particu- 

 lar plants for greenmanuring is that by means of 

 bacteria in tubercles on their roots (figure 75) they take 

 nitrogen from the air (page 128 and figures 75 and 76). 

 Grasses are not able to do this, and are not nearly as 

 good for greenmanuring. 



