SOIL-NITROGEN ABSORPTION BY CORN AS AFFEC TED BY CROP RESIDUES ADDITION

Various levels of Canavalia brasiliensis and Panicum maximum (20, 40 a nd 60 t.ha(-1)) were incorporated into a red-yellow podzolic soil, whi ch was planted with corn. After 102 days in the greenhouse, the C, N, and organic matter fractions content of the soil and the N level dry m atter of the plants were measured. One ton of Canavalia brasiliensis o r Panicum maximum produced a linear increase of 0.088 or 0.068 mg C.g( -1) soil, respectively. The C content of the alkali-soluble soil fract ion of the humic fraction was unaltered, but was increased in the humi n and free organic material fractions, especially by Canavalia brasili ensis. Nitrogen content increased linearly with the application of one ton of Canavalia brasiliensis or Panicum maximum to 0.0103 or 0.004 m g N.g(-1) soil, respectively. There was a rise in the free fulvic acid fraction in soil treated with 40 and 60 t.ha(-1) of Canavalia brasili ensis, compared with the control. Canavalia brasiliensis increased the N content of the soil and enhanced the N content of the corn to a lev el equivalent to that obtained with the application of 560 kg.ha(-1) o f N.