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This article in AJ

  1. Vol. 83 No. 5, p. 926-928
     
    Received: June 22, 1990
    Published: Sept, 1991


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doi:10.2134/agronj1991.00021962008300050029x

Chlorophyll Meter to Predict Nitrogen Topdress Requirement for Semidwarf Rice

  1. Fred T. Turner  and
  2. Michael F. Jund
  1. Texas A&M Univ. Agri. Res. and Ext. Center, Route 7 Box 999, Beaumont, Texas 77713

Abstract

Abstract

Semidwarf rice (Oryza sativa L.) tolerates excessive N fertilizer without lodging. In fact, it is difficult to maximize semidwarf rice yield without applying excessive N fertilizer since most farmers have not found a quick, unbiased, reliable method for assessing the N requirement for rice plants. A portable chlorophyll meter that instantly provides a measure of leaf chlorophyll may quickly monitor the need for additional N fertilizer. The Minolta model SPAD 502 chlorophyll meter was evaluated during a 3-yr period for its potential to determine the need for N fertilizer by semidwarf ‘Lemont’ rice grown in research plots on several soils and locations in Texas. Preplant N rates ranging from 56 to 280 kg N ha−1 were applied to paired plots to develop plots with a range in leaf chlorophyll. At one of four plant growth stages, one of the pair of plots was topdressed with 50 kg N ha−1 after measuring leaf chlorophyll. At the prepanicle initiation and panicle differentiation stages, the rice yield increase due to N topdressing dropped from about 1600 to 100 kg ha−1 as the chlorophyll meter readings of the most recently matured leaf increased from 24 to 42, respectively. As chlorophyll readings exceeded 40, N fertilizer did not increase yield. However, at the tillering and heading growth stages chlorophyll readings were not well correlated with N fertilizer needs. These data provide evidence that the chlorophyll meter can be used to determine topdress N needs of semidwarf rice at pre-panicle initiation and panicle differentiation.

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