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This article in SSSAJ

  1. Vol. 60 No. 4, p. 1153-1159
     
    Received: Mar 13, 1995


    * Corresponding author(s): j.k.ladha@CGNET.COM
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doi:10.2136/sssaj1996.03615995006000040028x

Tillage Depth Influence on Soil Nitrogen Distribution and Availability in a Rice Lowland

  1. D. K. Kundu,
  2. J. K. Ladha  and
  3. E. Lapitan-de Guzman
  1. Soil and Water Sciences Division, International Rice Research Inst., P.O. Box 933, Manila 1099, Philippines

Abstract

Abstract

Previous studies using artificial barriers at selected depths have shown the importance of N supply from soil below 15 cm to rice (Oryza sativa L.). Subsoil N availability and its use by wetland rice, however, have not been evaluated under normal field conditions. We examined distribution and availability of 2 M KCl-extractable N in 0- to 15-, 15- to 30-, and 30- to 45-cm layers of a submerged Alfisol during three successive crop seasons, as influenced by the depth of tillage imposed at the outset of the experiment. Mineral N availability in the 0- to 45-cm profile and rice N uptake in the first season were significantly higher (20–25 kg ha−1 higher mineral N and 16–18 kg ha−1 higher crop N uptake) with tillage to a depth of 40 cm than to 15 or 25 cm, the increased N supply originating largely from the 15- to 30-cm layer. In two following seasons, tillage to 40 cm gave the highest mineral N in the subsoil layers, and increased rice N uptake by 12 to 14 kg ha−1, compared with tillage to 15 cm. The beneficial effects of deep tillage were attributed to the elimination of mechanical impedence to root proliferation, and lower susceptibility of subsoil N to various loss mechanisms. Initial and final analyses of Kjeldahl N in the soil profile indicated no adverse effect of practicing 40-cm-deep tillage once in three seasons on soil N fertility. Further study is needed to determine optimum depth and frequency of primary tillage for different soil types to enhance N use efficiency.

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