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This article in SSSAJ

  1. Vol. 52 No. 4, p. 1114-1117
     
    Received: July 27, 1987
    Published: July, 1988


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doi:10.2136/sssaj1988.03615995005200040041x

Long-term Tillage and Nitrogen Fertilization Effects on Organic Nitrogen and Carbon in a Semiarid Soil

  1. P. E. Rasmussen and
  2. C. R. Rohde
  1. USDA-ARS, Columbia Plateau Conserv. Res. Ctr., P.O. Box 370, Pendleton, OR 97801
    Columbia Basin Agric. Res. Ctr., P.O. Box 370, Pendleton, OR 97801

Abstract

Abstract

Maintaining or improving soil organic matter has high priority in agriculture because of its beneficial effect on soil physical, chemical, and biological properties. Soil organic N and C were measured 44 yr after establishment of a long-term experiment to evaluate tillage and fertilizer effects in a winter wheat (Triticum aestivum L.)-fallow rotation on a coarse-silty mixed mesic Typic Haploxeroll. Main treatments consisted of three primary tillage systems, one conventional (moldboard plow) and two stubble mulch (offset disc, subsurface sweeps). Subplots consisted of six N treatments, 493, 728, 986, 1221, 1714, and 2207 kg N ha−1 applied over 44 yr. Organic N and C in the top 75 mm of soil were 26 and 32% higher, respectively, in the two stubble mulch systems than in conventional tillage, and equal below 75 mm. Stubble mulch plots contained 245 kg more N ha−1 than conventionally tilled plots, representing the conservation of 5.7 kg N ha−1 yr−1. Nitrogen fertilization increased soil N linearly in all tillage treatments, with 18% of the applied N incorporated into the soil organic fraction. Applied N also increased soil C linearly on plots with previous S application. Soil C was higher on plots with no previous S than on comparable plots with previous S, however, which suggests an S deficiency that altered S, but not N, transformations in soil. Identical N fertilization effects on soil organic N and C in both stubble mulch and conventional tillage suggests that N transformations were the same in both systems.

Contribution of USDA-ARS and Oregon State Univ. Agric. Exp. Stn. Tech. Paper no. 8259.

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