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Soil Productivity and Erosion of Iowa Loess Soils

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASAE. 25 (5): 1295-1299. (doi: 10.13031/2013.33716) @1982
Authors:   R. G. Spomer, R. F. Piest

ABSTRACT SOIL and plant nutrients are being rapidly removed from inadequately-protected rowcrop fields in Iowa (Spomer et al., 1981), but increased use of fertilizer and adoption of other technology have masked the effect of erosion on crop yields. Prior to the adoption of hybrid seed corn in 1932 and increased use of commercial fer-tilizer beginning in the early 40's, Iowa average corn yields (1866-1931) remained nearly constant at 2.3 t/ha (37 bu/ac). Pottawattamie County corn yields averaged 2.9 t/ha (45.6 bu/ac), 1929 through 1953, with a small but steady annual increase of 0.037 t/ha (0.59 bu/ac). The most rapid increase in corn yields, highly correlated with fertilizer use, occurred during the decade of the 60's. Concurrently, we show that soil erosion rates from unprotected cornfields in the region greatly exceeded ac-ceptable soil loss tolerances. Measured sediment yields from a 33.6 ha (83 ac) research watershed since 1964 were 30.4 t/ha/yr (13.6 t/ac/yr), and the effective denudation of the watershed is occurring at a minimum rate of 40 cm (16 in.) per century. Average annual nitrogen and phosphorus movement during a recent 5-year period of minimal runoff and erosion was 20 kg/ha (18 Ib/ac) and 3.0 kg/ha (2.7 Ib/ac), respectively.

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