Fertilizing the Orchard 75 



tion of plant food contained in the soil was evidently 

 existing in a form that was readily available to the 

 roots of the plants. 



Again, some soils such as heavy clays, appear to 

 contain a considerable amount of potash, the greater 

 portion of which is in a form that is not easily taken 

 up by the plants, and so vegetation does not thrive. 

 Experience has shown that soils such as these are 

 rendered more fertile by applications of gypsum, 

 which liberates a portion of this potash, and make it 

 available for plant growth. 



The more a soil comes under the direct influence 

 of sun, air, frost, and rain the more will its ingredi- 

 ents be broken up, and be made more readily avail- 

 able to plant roots. Hence the value of ploughing 

 and cultivating land lies not only in the general 

 loosening effects resulting therefrom, but from the 

 exposure of the soil to the elements, more of the 

 plant food contained in the soil being available to 

 the plants. 



The beneficial effects often following a few sea- 

 sons of bare fallow on wheat-sick lands appear to be 

 greatly due to these causes, but other influences, 

 such as the stimulation of the soil bacteria, have 

 also to be taken into consideration. Therefore 

 ploughing, or other methods of land cultivation, 

 although not adding to the ingredients contained in 

 the soil, have nevertheless, by making the sub- 

 stances already in the land more available to plants, 

 become factors controlling soil fertility. 



HUMUS. 



Besides their mineral ingredients practically all 

 soils contain an amount of decayed vegetable matter 

 or humus. When in their natural state they are 

 covered with forest, shrubs, or grasses, and all lands 

 are continually receiving fresh deposits of humus, 



