BULLETIN 318 THE EFFECTS O p ALKALI ON CITRUS TREES 321 



every precaution should be taken to reduce evaporation to the lowest 

 point possible and thereby retard the rise of salts. 



It should be pointed out that a number of the soils studied, where 

 citrus trees have been severely injured by alkali, contain abundant 

 supplies of the usual plant foods. The soluble potassium, nitrate and 

 phosphate have been found to be present in abundance in a number 

 of those soils. It is highly improbable, therefore, that the lack of 

 plant food has contributed to the unhealthy condition of the trees, 

 or that the use of commercial fertilizers will effectively overcome the 

 injury. However, it should be stated that there is some evidence that 

 an abundant supply of plant food does enable citrus trees to overcome 

 small amounts of alkali. On the other hand, it is reasonably certain 

 that no amount of ordinary fertilizer will be able to rejuvenate the 

 trees where large amounts of alkali occur. 



THE EFFECTS OF SODIUM NITRATE 



Investigations at the Rothamsted Station in England, at the Penn- 

 sylvania Station in this country, and elsewhere, have been interpreted 

 to mean that the continued application of sodium nitrate contributes 

 to the formation of carbonates in soils. The presumption has been 

 that sodium carbonate is formed through the selective absorption of 

 the nitrate (NO,,) ion by the crop and the union of the sodium with 

 the ubiquitous carbon dioxide of soils. We are not aware that this 

 assumption has been conclusively proved, the published evidence being 

 more suggestive than conclusive. 



While we deem it to be highly desirable to know just what com- 

 pounds actually exist in a given soil, and recognize that dissimilar 

 effects are likely to be produced by different salts of the same base, 

 it is nevertheless true that any salt of sodium is an alkali salt. In view 

 of the possibility, as suggested above, that sodium nitrate may con- 

 tribute to the formation of sodium carbonate (black alkali) in soils, 

 a substance commonly regarded as injurious to plant life, and that 

 there is evidence that citrus trees ma.y be abnormally affected by 

 high concentrations of sodium, whatever its combination, it is of inter- 

 est in this co7inection to study the effects of sodium nitrate. 



Relatively large amounts of sodium nitrate have been applied to 

 citrus groves in different localities in California. The fertilizer plots 

 of the Citrus Experiment Station at Riverside afford material for the 

 study of the effects. One of these plots (H) has been fertilized 

 exclusively with sodium nitrate for the past twelve years. For the 

 past six years, approximately 900 pounds have been applied per acre 



