SOIL NITROGEN 13 



Early spring in 1924 was wetter than normal and the soil was too sticky to 

 be sampled until June. Fertilizers had been applied before this date and the 

 plots with nitrogen were superior in the growth of crops on them. Only the 

 plots without nitrogen were sampled in June. The plots with nitrogen were 

 left until November when the samples might represent more or less exhaustion 

 of the fertilizer nitrogen. 



The June samples were drawn from three depths, (a) surface to 8 inches; 

 (b) 8 to 20 inches; (c) 20 to 32 inches. The last depth was difficult to secure 

 with the soil auger because an irregular layer of pebbles interfered with its 

 penetration. There was very little organic matter visible and this sample was 

 omitted in all later work. Fragments of vegetable matter on the surface were 

 avoided with the auger. Roots within the soil were included in the sample 

 when it was prepared for analysis. 



In 1927 the samples were collected in October after the crop of sweet corn 

 had been harvested. The samples in 1931 were taken in August after the 

 removal of the oats and peas. In 1934 the soil was too dry for sampling when 

 the Hungarian millet was cut, and samples were taken the last of August, 

 after showers had moistened the soil sufficiently to allow the use of the auger. 

 Nitrogen had been withheld from Plots 5, 8, and 10 in each of these years, 

 and the comparatively small effect of residual nitrogen on crops indicated that 

 fertilizer nitrogen had been exhausted before the soils were sampled. 



Each sample was dried in the air and then a subsample was separated by 

 quartering. The subsample was dried in the oven and ground in an iron 

 mortar until all of it passed through a half-millimeter sieve. This material 

 was used for the determination of total nitrogen and organic matter. Total 

 nitrogen was determined by the Kjeldahl-Gunning method modified for ni- 

 trates. The distillates from the subsoil samples were Nesslerized instead of 

 titrated. 



Analyses made at intervals of three and four years may be subjected to 

 variations in reagents used at the different periods. To check this possible 

 variation, several samples from 1924 and 1927 were analyzed simultaneously 

 with the samples of 1931. Samples of 1924 were increased by the proportion of 

 100:110, but those of 1927 were unchanged. Samples from 1931 were repeated 

 in 1934, with no appreciable change. 



All the work of taking and preparing samples of the soils and of the chemical 

 analyses were performed by the writer, which may have lessened the probable 

 variations in manipulation from period to period. 



Organic matter was determined in the samples of 1924, 1927, and 1931 by 

 the method described in Soil Science by Schollenberger. An electric heater 

 was substituted for a gas burner because it could be more easily regulated to 

 a uniform heat. 



Comparisons of the numerical data by plots and subplots and by years fail 

 to bring out any positive accumulation of nitrogen in the soils of Plots 5, 8, 

 and 10, which received nitrogen fertilizers, and do not show any loss of nitro- 

 gen from Plots 6, 7, and 9, which did not receive any nitrogen throughout the 

 experiment. 



Organic matter in soils may be expected to vary with the root systems of 

 the crops grown upon them. The clovers and grasses of 1924 appear to have 

 developed the highest percentages of organic matter by a small margin over 

 the corn crop of 1927 and the oats and peas of 1931. The percentages in 

 1927 are the lowest. 



Comparison of legume subplots with nonlegume subplots reveals a positive 



