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Nitrogen and Organic Carbon of Soils as Affected by Crops and Cropping Systems 1
Author(s) -
Metzger W. H.
Publication year - 1936
Publication title -
agronomy journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.752
H-Index - 131
eISSN - 1435-0645
pISSN - 0002-1962
DOI - 10.2134/agronj1936.00021962002800030006x
Subject(s) - soil water , cropping , nitrogen , mathematics , agriculture , agronomy , citation , environmental science , political science , chemistry , geography , soil science , archaeology , law , biology , organic chemistry
T HE relative efficiencies of various crops and cropping systems in conserving soil nitrogen has been a matter of considerable interest to agronomists for many years. Many notable attempts have been made to measure such relative efficiencies. Only one of these attempts can be mentioned here. Salter and Green~ have determined the effect of the following crops and cropping systems on the soil’s supply of nitrogen and organic carbon: Corn, wheat, and oats each in continuous culture, a 5-year rotation containing a clover and timothy hay crop, and a 3-year rotation containing a clover hay crop. Furthermore, they have presented a means by which the efficiency of a rotation or an individual crop either in rotation or in continuous culture may be expressed mathematically. Assuming (a) that a given portion of the nitrogen and carbon of the soil, characteristic of the type of culture employed, is utilized in the production of each crop, and (b) that the gain in these constituents accounted for by the crop residues is roughly proportional to the size of the crop produced, the following equation was proposed by these workers: Nt = NoKt, ’ in which Nt is the nitrogen content of the soil after "t" years, No is the nitrogen content at the beginning, and K represents the fraction of the nitrogen remaining after growing the crop a single year. Using the "K" values obtained from experimental data for the nitrogen and carbon of soils continuously cropped with various crops, the corresponding value for a crop used in rotation but not in continuous cropping can be calculated. Determinations of nitrogen in the soil of many of the plats of the soil fertility project at the Kansas Agricultural Experiment Station were made in ~9~5, ~923, and again during the period of ~932 to ~934, and therefore an opportunity was afforded to test the assumptions involved in the formulation of the equation. The rates of change in the nitrogen content of the soil had probably become fairly well stabilized when the ~9x5 samples were taken, since six cropping seasons had elapsed after the establishment of the project before these samples were collected. For a series of ~2 plats in a 3-year rotation of corn, cowpeas (or soybeans), and wheat, a comparison the experimentally determined values with the values calculated