Effects of Nitrogen Application on Leaf Chlorophyll Content in Post-transplanting Growing Stages of Medium Hybrid Rice in Winter Water Logged Fields

Using 18 medium hybrid rice varieties as the materials,the sensitive stages and leaf positions of leaf chlorophyll content to nitrogen application were studied in growing stages after transplanting of medium hybrid rice in winter water logged fields in Sichuan.In the experimental design,the nitrogen fertilizer containing 150 kg/hm~2 of pure nitrogen was applied before transplanting for the treatment of nitrogen application(AN),while no nitrogen fertilizer was applied for the control(NN).The results showed that the leaf chlorophyll contents(SPAD) of AN were significantly higher than those of NN in the periods from the 7~th to 28~th days after transplanting(DAT)(tillering stage),from the 63~rd to 77~th DAT(jointing to heading stages) and from 98~th to 112~th DAT(mid to late grain filling stage),indicating these stages were sensitive to nitrogen application.In these periods,the difference of leaf chlorophyll content between AN and NN had a highest value from 9~th to 11~th DAT,indicating that it is the optimum time to determine the amount of nitrogen to be applied by measuring seedlings.Moreover,the lower leaves had a bigger difference between AN and NN in chlorophyll content than the higher leaves.The 4~th leaf from the top had the highest difference value between AN and NN,so it can be the best marker leaf for the nitrogen nutrition of rice plants.