THE MONTHLY BULLETIN. 141 



the varying soil types. As a general rule, however, sandy soils, and 

 especially those having a gravel subsoil, will require that the furrows 

 be made quite close together — in other words from two to three feet 

 apart. As the soil type becomes heavier the distance between the 

 furrows should be increased. On heavy adobe land furrows five to 

 six feet apart seem to give the best results. This difference is due to 

 the fact that the water soaks vertically much more rapidly than later- 

 ally in sandy soils, Avhile on the heavy lands the lateral seepage takes 

 place nearly as fast as does the percolation vertically. Thus in sandy 

 soils when furrows are made too distant much water is lost by perco- 

 lation below the reach of the roots before the soil between the furrows 

 is wet ])y the slow lateral movement of the water. 



The opposite, however, is true in the case of very heavy soils, and 

 the danger of having the furrows too close together is imminent, for 

 in this ease lateral seepage from the furrow is so rapid that the surface 

 soil is frequently wet before the water has percolated deep enough 

 for best results. Once the lateral seepage has filled the pores of the 

 upper layer of soil with water the vertical percolation goes on very 

 slowly, much as takes place when land is flooded. 



Another mooted question comes up in regard to the proper depth of 

 the furrow which results in the greatest conservation of the water 

 applied. Many believe in the deep furrow, some advocating a depth 

 of even 12 inches. The deeper the furrow the less of the upper soil is 

 wet. and as this surface layer is used as a mulch between irrigations 

 the water in this upper four or five inches of soil is entirely lost by 

 evaporation. Thus it would certainly seem that furrows deep enough 

 to leave most of this mulch in a dry condition would conserve the 

 water to the greatest extent. 



Experiments along this line are reported 1)y Professors Fortier and 

 .Beckett in bulletin 248 of the United States Department of Agricul- 

 ture. In this work water was applied in furrows of various depths and 

 cultivated to establish a mulch as soon as soil was dry enough to work. 

 In the case of three inch furrows it was found necessary to wait two 

 days after the application of water before cultivations could begin, 

 while with the six and nine inch furrows the soil was in shape to cul- 

 tivate one day after irrigation. This day's difference means a large 

 saving of water, as the evaporation is very rapid from a saturated 

 soil surface. 



In this work it was also found that the total losses for the thirty 

 davs between irrigations from soils irrigated with three inch, six inch 

 and nine inch furrows were as follows : 



Three inch — 18 per cent of water applied was lost. 

 Six inch — Ifi per cent of water applied was lost. 

 Nine inch — 1.5 per cent of water applied was lost. 



Thus it would certainly seem wise to use furrows at least six inches 

 in depth, if a maximum duty of the water applied is to be obtained. 

 The soil type also becomes a factor governing the optimum depth of 

 the furrow. The sandy soils require a more shallow furrow than the 

 heavier types, since the lateral seepage which causes the loss through 

 wetting of the mulch is much less rapid than in the heavy soils. 



The practice of running the furrows in and out among the trees in 

 a zigzag fashion is an attempt to keep all of the soil in the orchard 

 4—15979 



