Technique for Labelling Rice Straw wit

Abstract

The annual loss of nitrogen through the burning of rice straw in Thailand is estimated to range from about 5 to 50 kg N ha-1 depending on the kind and quantity of rice straw, and intensity and completeness of burning. The value of this loss has been estimated at several thousand million baht.
To facilitate research on rice straw N transformation and its subsequent availability to succeeding crops, this study was aimed at establishing a technique for labelling rice straw with 15N atom excess. The nutrient solution was maintained at pH 5.0 but its concentration was adjusted to 1/3 and 1/2 normal strength for the first and second weeks respectively; thereafter the normal concentration was maintained until the end of the experiment. The solution was renewed at 7 day intervals. The plants were harvested at 115 days, oven dried at 70 C for 72 hours, ground and anaylzed for 15N. The tagged rice straw contained 9.56% 15N atom excess as a result of isotope exchange and isotope dilution in the plants.