Browsing by Author "Kandasamy, O S"

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    Natural and predicted time course behaviour of ammonium nitrogen release in lowland rice soils
    (Kerala Agricultural University, 2000) Johnkutty, I; Kandasamy, O S; Palaniappan, S P
    An experiment was conducted on Typic Haplustall" soil at the Tamil Nadu Agricultural University, Coimbatore to study the effects of green manuring and N timings on soil ammonium-N release pattern under lowland flooded rice soils. The main-plot treatments consisted of three green manures viz., sesbania (Sesbania rostrata), cowpea (Vigna imguiciilnta) and parthenium (Parthenium hysterophoms L.) to supply 54 kg N ha"1 and one non-green-manure treatment. Application of 150 kg N ha"' as urea at varying quantities, at different growth stages of the crop along with one control formed the sub-plot treatments. Incorporation of green manures increased soil ammonium-N content. The effect was more pronounced during the peak period of soil ammonium-N release, which occurred between the second and fourth week after transplanting rice. Application of N fertilizer resulted in an immediate spurt in soil ammonium-N, but it declined within a few days. Due to faster N uptake by the crop, the decline was rapid during late growth stages. Continued splits (150 kg N ha'1 in six equal splits) ensured a steady ammonium-N supply throughout the growth period. Similarly, skipping of basal N and application of 150 kg N in three equal splits starting from early tillering stage onwards also adequately met the crop N demand for high yield. Mathematical models were developed on the ammonium-N release pattern from green manures and they predicted similar ammonium-N release pattern as observed in the experiments.
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    Time course leaf n concentration in rice under different nitrogen application strategies and development of simulation models
    (Kerala Agricultural University, 1999) Johnkutty, I; Kandasamy, O S
    An experiment was conducted at the Tamil Nadu Agricultural University. Coimbalore dunn£ the kharif and rahi seasons of l'J'M-"96. lu study the time CIHIISC leaf N cmicetnraiion in lowland ria under diilercntN timings. Application of I 50 kg N ha"1 m six staggered sPllts/rom planting to heading or m tnree splits Irom early tillering Ul heading suslamed the leal'N eoncenlration at increased levels for higher grain yields. Early N application and limitation of N supply at later stages decreased the plant N con contrail on during grain filling stages and reduced the grain yield. Continued application ol Fertilizer N until heading stage favoured maintenance of N concentration in leaves during ilic posl-anlnests period, resulting in high grain yields. Based on the natural behaviour of time course leat'N concentration, simulation models «cre evolved based on the prediction ability and test of significance