26 STATE BOARD OF AGRICULTUEE. 



green manuring give all the results of growth which lend any measure- 

 of green material to that which is plowed under. Furthermore, to make 

 green manuring possible we must assume that the soils are to remain 

 idle for a portion of the time, that is, that they will not be continually 

 employed in the growing of commercial crops. 



The very nature of the soil as to its liability to waste during idleness, 

 as a man spends his money while his time is not emploj^ed, demand that 

 the soil be kept occupied all the time. The solvent action of the acids 

 secreted from the roots of plants indicate to us that if we would make 

 the most of that large store of mineral plant food possessed by our 

 ordinary soils we must encourage the continual growth of food storing 

 plants during the periods separating the growth of commercial crops. 

 A glance at the history of soil formation suggests at once to us the 

 wisdom of this practice. It is reasonable to suppose that the agencies 

 which wrought to transform the solid rocks into our fertile soils are 

 still as actively at work, and are encouraged in this activity by the 

 presence of developing organisms. Some of this plant food is digested 

 or dissolved by bacterial growth within the soil, and if not assimilated 

 by a growing crop will be converted into a gas, and escape into the air 

 or be leached away by drainage water. The presence of a growing crop 

 not only utilizes the products of bacterial development but it is found 

 that the growing plants secrete at the extremities of their roots an acid 

 which serves to digest the food materials in the soil. These facts, 

 together with the silent influence of shade in holding moisture, protect- 

 ing the humus from the burning action of the sun, and the encourage- 

 ment it offers in the friendly microbe in the improving of the soil under 

 its protection warrants the intelligent farmer in keeping his soil continu- 

 ually in the shade of a growing crop. 



Green manuring, however, is a slow process, and it has no claims to 

 the panacea for all the existing ills that obtain in our wornout soils. 

 And while theoretical agriculture may support it as a scheme for re- 

 claiming an exhausted soil, it is a process too slow, uncertain and 

 expensive. 



What does green manuring do? It utilizes available plant food pro- 

 duced in the soil which would otherwise be wasted. It sends down 

 its roots into the deep sub-soil and brings to the surface for succeeding 

 crops large quantities of plant food in the form of mineral matter from 

 the lower strata and soluble materials which have been carried below in 

 the drainage water. 



LEGUillXOUS PLANTS. 



In the case of legumes, it adds large stores of organic nitrogen to 

 the surface soil, thereby increasing the available plant food, though 

 with regard to the mineral elements no green manuring plants have the 

 power of adding them to the soil. ^lineral elements, however, are dis- 

 solved and made available to succeeding crops by the process of green 

 manuring. 



Where then shall green manuring be practiced and what are some of 

 the agricultural plants valuable for this purpose? In ge'neral, the intel- 

 ligent farmer will practice green manuring only as a catch crop, that is,, 

 between the commercial crops grown upon the farm. With the grain 

 farmer, or on the farm where only a small quantity of live stock is kept, 

 a crop grown solely for the purpose of improving the soil may well con- 



