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Book: Determinants of Soil Loss Tolerance
Published by: American Society of Agronomy and Soil Science Society of America

 

This chapter in DETERMINANTS OF SOIL LOSS TOLERANCE

  1.  p. 75-86
    asa special publication 45.
    Determinants of Soil Loss Tolerance

    B.L. Schmidt (ed.)

    ISBN: 978-0-89118-311-2

     
    Published: 1982


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doi:10.2134/asaspecpub45.c7

Technology Masks the Effects of Soil Erosion on Wheat Yields — A Case Study in Whiteman County, Washington1

  1. H. A. Krauss and
  2. R. R. Allmaras2

Abstract

Sustained productivity of an eroding soil cannot be determined unless yield increases from technology advances are separated from soil productivity changes due to erosion. This concern is especially paramount in the Palouse landscape of Whitman County where serious erosion occurs under an intensive dryland wheat production, that has also had significant technology advances. The separation of technology and soil productivity involved the use of long-term wheat yields, measured wheat response to remaining epipedon, historical soil erosion rates, and landscape-distributed soil erosion rates. Current wheat yield in Whitman County increased approximately 36.1 kg/ha (0.54 bu/acre) per year as an average for the whole landscape; meanwhile annual soil erosion losses average 21.1 metric tons/ha (9.4 tons/acre) on a cropland base of 421,200 ha (1,040,000 acres). The soil productivity decrease from an average epipedon loss of 13.4 cm (5.3 in) in a 90-year period was 725 kg wheat/ha (10.8 bu/acre). An average erosion rate, however, does not reveal the true impact on productivity. Isolation of the soil productivity change component by land capability subclass showed that the net increase in yield on lie and IIIe land (67% of the cultivated cropland) has masked a significant decline in productivity of subclasses IVe and VIe land (18% of the cultivated cropland) in the 90-year period of intensive cultivation. The average soil erosion rate in Whitman County over the 1940 to 1978 period has been nearly twice the tolerance value of 11.2 metric tons/ha (5 tons/acre) per year. Average annual soil erosion at the soil-loss tolerance (T value) level is expected to expose the subsoil of IVe land (about 12% of the cultivated cropland) in about 128 years.

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Copyright © 1982. Copyright 1982 by the American Society of Agronomy and Soil Science Society of America, Inc., 5585 Guilford Rd., Madison, WI 53711 USA