Arizona republican., 1907-01-15

narrowing may be applied with advan- tage. As elsewhere. the passage or hay making machinery and work ami mals tends to pack the surface soil thereby lessening the penetration Of air and water to the roots of the crop: and in addition. during our mild winter season. alfalfa fields are usually heavily pastured by cattle and horses some times for several months of the year.
 More peculiar. however. to South western irrigation conditions are the silt blankets resulting from the use of the muddy irrigating waters char acteristic of the region. These silt laden waters. when applied tO an irri- gated field. drop their load of detritus upon the surface of the soil in a layer decreasing in thickness from the head to the foot of the field. Inasmuch as alfalfa is perennial crop which can not be deeply cultivated these sediments accumulate from year to year in de- posits which frequently attain a thick ness of } 10 f inches. Since the sedi- ments composing these deposits are usually of a more or less plastic char acter, these blankets are often nOti- cably imperviOus to water and to air limiting the supply of these essentials to the deep root systems of the plants The result is a decreased yield. espec- ially at the heads of the fields. where accumulatiOns are thickest
 To measure the amount of depreci- ation. three representative fields of al- falfa near Yuma. Phoenix. and Solom- onville Were selected, dividing into plats from their upper to their lower ends, and the weight of alfalfa hay from each plat taken for one cutting Comparing these weights with the maximum yield at the lower ends of the fields. where the least sediment had accumulated. the percentage of de- preciation in yield due to the siIt-blan- ket was estimated as follows: Near Yuma. May 19. 1905. depre
 citation, in second cutting ...... 6.3Ts Near Phoenix. July 10. 1905. de-
 preciation. in third cutting .... 9.7cc Near SOlomOnville. June 23 1905.
 depreciation. in second cutting ZIG Z,
 A fourth field near Mesa. Ariz.. irri- gated with clear. pumped water pro duced it's heaviest crop next the ditch. where, sedimentary deposits being ab-
  cured.
 Cultivation, by means of disk and spring tooth harrows. is the best avail able means of handling these accumu latiOns in alfalfa. This treatment breaks up the blanket and allows bet ter penetration of water and air into the soil, thereby making their fertiliz- ing values available to the crop. which consequently realizes benefit instead of detriment from them.
 One man with an eight-fOOt disk and four horses will get over about ten acres of alfalfa in a day. This work may be done in winter when teams are more at leisure: but it is probable that in summer also, after cutting and before irrigating. an occasional disking to break up the sediment-blanket. may be well worth while, especially on the upper ends of alfalfa fields
 Summary: At trifling cost. there fore varying according to individual circumstances. the disk-harrow splits and spreads the crowns of alfalfa plants. causing them to develop addi- tiOnal tops; it destroys the egg de- posits and larvae of certain injurious insects; it breaks up the slit-blanket resulting from the use of muddy irri- gating water. allowing better penetra- ton of water and air to the roots of the crop; and to some extent it in cerporates beneficial sediments and fallen alfalfa leaves with the soil.
 It is quite probable, speaking con servatively, that for some or all of these reasons the average alfalfa crop in Arizona may be increased ten per cent by disking. But the cost of hand ling the increased crop is not greater in proportion; therefore, the net profit of disking. on the basis of the above estimate. may be somewhat more.
 R. H. FORBES.