Fertilizing the Commercial Apple Orchard 199 



usually respond to moderate applications of nitrate of 

 soda, even though they may have no clear indication of the 

 need. In such cases, the amounts to he applied should 

 be reduced. , < 



NEEDS OF IRRIGATED REGIONS 



The importance of nitrogen as the limiting element of 

 plant-food is emphasized under western irrigated condi- 

 tions where the nitrogen-content of the soil is soon 

 exhausted unless replenished by the growing of legumes or 

 by application of manure or commercial fertilizer. The 

 system of clean culture with irrigation, practiced so exten- 

 sively at one time in the Northwest, caused more or less 

 rapid depletion of humus and nitrogen. The results of 

 this harmful practice became very evident, in the famous 

 Hood Eiver Valley of Oregon. In about 1915, the 

 orchards of this well-known region were producing rather 

 small annual crops; the foliage was beginning to take on 

 a yellow appearance, particularly in the non-irrigated 

 orchards where no leguminous shade-crops were grown. 

 It beicame apparent that some change in orchard manage- 

 ment was necessary to bring back the yields and vigor of 

 the trees to normal. It was in these circumstances that the 

 value of nitrate of soda was demonstrated. While the 

 importance of nitrates as commercial fertilizers is recog- 

 nized in the Pacific Northwest, and particularly in Ore- 

 gon, the value of acid phosphate and potash commonly 

 recommended in the East in conjunction with nitrates has 

 not been established in the irrigated regions. In other 

 words, eastern orchards' more commonly require general 

 fertilization, while northwestern plantings are not likely 



