HILLSIDE IRRIGATION 



191 



greater the distance that can be left between the connections, and 

 vice versa. In this way the water is taken slowly down a grade 

 where it would flow too rapidly were it admitted to furrows in the 

 direction of its flow. 



Another combination of the check and furrow system is found 

 where the lowest spaces of a slope irrigated by furrows are laid off 

 in checks to catch the overflow from the furrows and compel its 

 percolation at a point which would otherwise receive too little 

 water. The parts of a furrow system which lie farthest from the 

 source of supply are obviously least supplied, because long flow 

 can not be maintained there without much loss from overflow. 

 Holding the water in checks at the lower end usually for two 

 rows of trees is quite a help toward even distribution. 



The Basin System. The term basin should be restricted to 

 inclosures which do not aim at covering the whole surface, but 

 only a small area immediately surrounding the tree. The check 

 system is clearly a more rational and perfect method of flooding. 

 When basins were used on ground capable of irrigation by the 

 check or furrow systems, it was probably due to a misconception 

 which has prevailed also in the practice of fertilization, that the 

 tree derived its chief benefit from the soil immediately surround- 

 ing and beneath its bole, and that distant applications were likely 

 to be wasted. Years ago it was held that the lateral root exten- 

 sion of a tree was equal to the spread of its branches, but recent 

 investigations have shown that under favorable soil conditions the 

 root extension is vastly greater. It is not reasonable then to restrict 

 water or other plant food to the region chiefly occupied with 

 the stay roots and not the feeding roots of the tree, and it is a 

 frequent observation that basined trees do not do so well and that 

 they show distress sooner than those under systems which secure 

 more complete water distribution. 



To the basin system may, however, be conceded these possibili- 

 ties : (1) Trees may be grown on hillsides too steep for other means 

 of irrigation unless the hillside be previously terraced; (2) the 

 basins afford 'an opportunity to use a very small stream of water 

 by allowing it to run for a long time in each basin, thus making 

 a miniature reservoir at the base of each tree ; (3) for young trees 

 a small amount of water may sustain growth, while with other 

 methods the same amount of water would be almost wholly lost 

 by evaporation or percolation, or both ; (4) the expense of wider 

 application of water and the necessary after cultivation is obviated. 



In planting on hillsides, terracing is the foundation of the basin 

 system. Terraces are plowed and scraped out until they have 

 width enough to accommodate a line of basins and a ditch at the 

 foot of each bank to supply them. The terraces are given a little 

 fall, alternating in direction so that the water, starting from the 



