422 NATURE AND PROPERTIES OF SOILS 



231. Influences of higher plants on nitrification.— It has 

 been known for some time that the nitrate content of a soil 

 varies with the crop that occupies the land. King and Whit- 

 son x reported in 1901 that the accumulation of nitrates was 

 greatest under maize, with potatoes next and alfalfa and 

 clover much lower. Stewart and Greaves, 2 in an experiment 

 covering several years, also found that maize allowed the great- 

 est accumulation, with potatoes, oats, and alfalfa following 

 in the order named. Brown and Maclntire 3 report forty 

 times more nitrates in a soil cropped to maize than when 

 planted to grass. As the moisture content was practically 

 the same in each case, the difference cannot be ascribed to 

 this influence. 



Perhaps the most extensive work along this line is that of 

 Lyon and Bizzell. 4 They noted a characteristic relationship 

 between the crop at different stages of growth and the cor- 

 responding nitrate content of the soil. During the most ac- 

 tive growing period of maize, although the crop was absorb- 

 ing nitrogen in large amounts, the nitrates were frequently 

 higher under the maize than in a contiguous fallow plat. Oat 

 land contained less nitrates, while grass seemed to retard 

 markedly the accumulation of nitrates. Whether the nitrate 

 organisms are stimulated by certain plants or whether nitrate 

 formation is merely depressed more by some plants than by 

 others is not known. It is clear, however, that the relation- 

 ship of crop to nitrification must be reckoned with in practical 



1 King, F. H., and Whitson, A. E., Development and Distribution of 

 Nitrates and Other Soluble Salts in Cultivated Soils; Wis. Agr. Exp. 

 Sta., Bui. 85, 1901. 



2 Stewart, E., and Greaves, J. E v The Production and Movement of 

 Nitric Nitrogen in Soil; Centbl. f. Bakt., II. Band 34, S. 115-147, 

 1912. ' ' ' ' 



'Brown, B. E., and Maclntire, W. H., Seasonal Nitrification, Soil 

 Moisture and Lime Requirement in Four Plats Receiving Sulfate of 

 Ammonia; Penn. Agr. Exp. Sta., Eep. 1909-1910, pp. 57-63. 



4 Lyon, T. L., and Bizzell, J. A., Some Relations of Certain Higher 

 Plants to the Formation of Nitrates in Soils; Cornell Agr. Exp. Sta., 

 Memoir 1, 1913. 6 * 



