814 EXPERIMENT STATION RECORD. 



treatment of water containing large numbers of germs, and the authors are 

 of the opinion that this method of treatment as at present developed is not 

 practically applicable except under special conditions. 



SOILS— FERTILIZERS. 



The fixation of nitrogen in some Colorado soils, W. P. Headden {Colorado 

 Sta. Bui. 178, pp. 3-96, pis 6). — Further investigations on the injurious nitrates 

 in Colorado orchard soils (E. S. R., 23, p. 523) are reported, including additional 

 analyses of the water-soluble portion of a number of soils from barren spots 

 and tests of the rate of nitrogen fixation and nitrification in the soils. 



The author states that the spread of the trouble during 1910 was very 

 marked and that the intensity of the attacks has increased rather than abated. 

 Areas of several hundred acres on which fruit trees are dead or dying as a 

 result of nitrate injury are involved. " In one 14-year-old orchard not less 

 than 12 acres of trees, apple, plum, pear, and cherry, together with currant 

 bushes and other small fruit, have been killed in less than a year. The water 

 table in this land was not, at any time, near enough to the surface to do any 

 damage. 



" No single instance of the death or eradication of a brown area, a niter 

 spot, has been observed ; but the interior of such areas has been found so 

 excessively rich in salts that the ground has become barren, even of the 

 Azotobacter flora. 



" This deportment of the bacteria suggests the probability that the land 

 may again become fertile after a few years, in fact, varieties of Atriplex, salt- 

 bushes, are already taking possession of land which has been devoid of vegeta- 

 tion for several years. 



" The drainage in several of the cases given is excellent, in other cases drains 

 have been laid for periods of from one to five years without preventing the 

 formation of niter areas, 



" Trees badly affected by this trouble show almost no recuperative power, 

 probably due to the continued excessive supply of nitrates in the soil, possibly 

 to the severe toxic action of the nitrates. So far as our observation goes both 

 factors seem to be involved. Slightly affected trees may recover but no badly 

 affected tree has been observed to do so. 



" The generally observed change in the soil, indicating danger to the trees, 

 is a turning brown of the surface which is expressed by the statement that ' the 

 soil turned brown or black and the trees died.' 



" The samples of brown soil have, without exception, contained excessive 

 quantities of nitrates. 



" The color is not due to the nitrates nor to sodic carbonate or black alkali 

 proper but to the development of pigments by the Azotobacter. This applies 

 to the soils here described. Some soils may have a brown color due to other 

 causes. 



" This condition is usually preceded and accompanied by a mealiness of the 

 soil, often described as ashy. There is usually but little or no efflorescence on 

 such soils though it sometimes occurs. 



" The time required for the killing of a tree varies with the virulence of the 

 attack, in bad cases from four days to two weeks. Slightly affected trees may 

 linger a long time. 



" These areas may occur in perfectly drained land, situated in the midst of 

 land which shows no abnormal quantities of nitrates. 



