PLANT -FOOD REMOVED BY CROPS 



281 



144. Amounts of plant-food material removed by 

 crops. The utilization of mineral substances by crops 

 is a source of loss of fertility to agricultural soils. In 

 a state of nature, the loss in this way is comparatively 

 small, as the native vegetation falls upon the ground, 

 and in the process of decomposition the ash is almost 

 entirely returned to the soil. Under natural conditions, 

 soil usually increases in fertility; for, while there is some 

 loss through drainage and other sources, this is more 

 than counterbalanced by the action of the natural 

 agencies of disintegration and decomposition, and the 

 fixation of atmospheric nitrogen affords a constant, 

 although small supply, of that important soil ingredient. 



Fig. 98. A collection of hand-tillage implements. From left to right: 

 1. Field and garden hoe. 2. Mattock. 3. Weeding -hoe. 4. Stone-hooks. 

 5. iinger-weeder. 6. Grub-hoe, 7. Scuffle-hoe. 8. Garden rake. 9. Spading- 

 fork. 10. Garden trowel. 



