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Effects of Manure, Vetch, and Commercial Nitrogen on Crop Yields and Carbon and Nitrogen Contents of a Fine Sandy Loam Over a 30-Year Period¹

ABSTRACT

Annual per-acre treatments of 5 tons of manure, 52 pounds of N as NaNO₃, and vetch grown annually in a 2-year rotation of cotton and corn were compared during the 17-year period of 1925–41.

Corn yields from the manure, commercial N, vetch, and check plots were 44.0, 40.2, 35.1, and 7.3 bushels, respectively. The yields of seed cotton were 1,773, 1,488, 1,418, and 433 pounds respectively.

During 5 years after these treatments were discontinued, residual effects of manure exceeded those of commercial N or vetch by about 14 bushels of corn and 475 pounds of seed cotton. From 1948 through 1955, all plots were in corn and received 80 pounds of commercial N. Yields from all plots were 50 to 60 bushels the first year of this period. Manure increased yields for at least 8 years after the last application.

Total C and N determinations were made on soil samples taken at intervals throughout the 30-year period. C and N levels were maintained about constant on the commercial N and vetch plots, increased on the manure plots, and decreased on the check plots. Levels of C and N in all except the former check plots decreased during the residual study. Eighty pounds of commercial N did not stop the loss of C and N from the manure plots.

¹ Contribution from the Department of Agronomy and Soils, Agr. Exp. Sta. of the Alabama Polytechnic Inst., Auburn. Presented before Div. III, Soil Science Society of America, Nov. 13, 1956, at Cincinnati, Ohio.

² Associate Agronomist, Agronomist, and Associate Soil Microbiologist, respectively.

Received for publication March 28, 1958. Accepted for publication May 15, 1958.