84 



6. Laying Out Furrows: Number, Length, Depth and Slope. 



The number of furrows varies greatly with the opinion and judgment of 

 the irrigator. For young orchards frequently only two furrows are used 

 for each row of trees, one on each side of the trees. For older orchards 

 usually at least three furrows are used, one on each side of the tree rows 

 and one in the center between tree rows. To obtain a more uniform dis- 

 tribution of moisture, as many as six or eight furrows to each row of trees 

 are used. The present tendency is to use deeper furrows and space them 

 farther apart (Fig. 71). A depth of 8 inches is frequently used. In 

 southern California orchards are usually furrowed with plows attached to 

 the frames of wheeled cultivators in the place of the cultivator teeth (Fig. 

 72). Furrows 9 inches deep have a bottom width of 10 inches and a top 

 width of 15 inches. 



The experiments described under the distribution of water in furrow 

 irrigation gave some interesting results which should guide the orchard- 

 ist in adopting the best arrangement of furrows. These experiments 

 showed that for a sandy soil with furrows 4 feet apart it took about 24 

 hours for the water to spread sideways and meet between the furrows; for 

 a clay loam about 12 hours was sufficient. These experiments also showed 

 that for a deep furrow the sideways spread was greater than for a shallow 

 furrow. The sideways spread for sandy loam was limited to about 2 feet 

 on each side of the furrow and for clay loam about 3 feet; this would indi- 

 cate that the distance apart of furrows should be not over four feet for 

 sandy loam and six feet for clay loam. The furrows on either side of the 

 row of trees should be placed as near as possible to the tree to moisten the 

 soil directly under the tree. 



Fig. 73. Method of laying out zigzag furrows. 



(O. E. S. Bulletin 236, U. S. Dept. Agr.) 



