IRRIGATION AND ROTATION OF CROPS. 11 



nels, such as tile or other drains. It works best in sandy 

 soils. In clayey soil the water runs too slowly through the 

 sides of the tiles. Land tiles make as good channels as any 

 for this purpose. They should be buried a few inches below 

 the plants to be watered, being laid level with open joints. 

 Some experiments seem to show that it is a very wasteful way 

 of using water, while others have shown this system to be 

 economical. As practiced for watering plants in greenhouse 

 benches it has given excellent results. 



ROTATION OF CROPS. 



By rotation is meant the special succession of crops 

 growing upon the land for a series of years. This is very 

 desirable even on land in the highest state of cultivation, but 

 it is very difficult to lay down exact rules to be followed. 



Reasons for Rotating Crops. — We rotate crops: (1) to avoid 

 insect enemies, as in the case of onions and turnips, which 

 are often liable to serious insect injuries when grown 

 more than one year on the same land, turnips being es- 

 pecially liable to injury from insects when grown in the same 

 place successively; (2) to avoid injuries from fungous dis- 

 eases, i. e., in case of potato and beet scab, onion and melon 

 rust, corn smut, etc.: (3) to increase the amount of humus in 

 the soil, as when land is seeded down to grass or clover; (4) 

 to deepen the soil and add nitrogen to it as well as humus, 

 as when clover is grown on the land; (5) to get rid of weed 

 seeds in the soil: (6) to use the plant food in the land to best 

 advantage, since crops vary very much in the amount of the 

 different elements which enter into their composition. Legu- 

 minous crops, like clover, peas, beans, etc., improve the land 

 on which they grow, while most other crops exhaust the soil. 

 Some plants excel others in their power to search for plant 

 food, or to take plant food from the soil. Some plants feed 

 near the surface largely, while others take their food mostly 

 from a lower level. Root crops should not follow root crops, 

 nor should vines follow vines for many years in succession 

 on the same land. 



