Studies On Carbon Phyto-fixation In Rice As Affected By Different Fertilization

Carbon dioxide (CO2) is the main greenhouse gas (GHG). The increase in global temperatures due to radiative forcing by CO2and other GHGs in the atmosphere has been estimated at0.7℃during the20th century, and is predicted to be1.5-6.3℃by2100relative to1990. Agricultural production process plays an important role to fix CO2and reduce CO2in the atmosphere.The carbon sequestrations of pasture、corn and wheat were4.0t/ha,6.0t/ha,2.3t/ha respectively. But the carbon sequestration of rice is not clear yet and the impact of the rice carbon sequestration by different agronomic measures is rarely reported. In this study, a serious of field experiments were conducted to investigate the effects of nitrogen, phosphorus and potassium fertilization on biomass of and carbon accumulation in rice plants. The feasibility of estimating carbon fixation based on rice grain yield was also discussed. The results were as follows:1. The results of the field experiment showed that total biomass of the whole plant (except only potassium treatment), carbon contents in root and in unfilled grain, carbon accumulated in straw and in brown rice and total carbon accumulated in the whole plant (except only potassium treatment) of fertilizer treatments were significantly higher than that of no-fertilizer treatments (P<0.05). Under the same phosphorus and potassium condition, total biomass of grain, carbon contents in straw and in unfilled grain, carbon accumulated in straw, rice husk, unfilled grain and total carbon accumulated in the whole plant with nitrogen application were significantly higher than that of no-nitrogen fertilizer treatments (P<0.05). Under the same nitrogen and potassium condition, biomass of brown rice and husk, carbon contents in root and in unfilled grain, carbon accumulated in brown rice of phosphorus fertilizer treatments were significantly higher than that of no-phosphorus fertilizer treatments (P<0.05). Carbon contents in root and in brown rice, carbon accumulated in straw and in brown rice and total carbon accumulated in the whole plant of PPN treatments (PPN, POU1:POU2:Normal urea=0.3:0.4:0.3) were significantly higher than that of NU treatments (P<0.05). The ratio of total carbon accumulation (TCA) to air-dried grain yield (ADGY) of fertilizer treatments ranged from1.12to1.20, with the average as1.15±0.06.2. The results of the field experiment with different potassium treatments showed that grain yield and biomass of the treatments with potassium applied were significantly higher than that of the no-potassium treatment (P<0.05). Potassium contents in straw and husk, phosphorus contents in straw, carbon contents in root and brown rice of potassium treatments were significantly higher than that of no-potassium treatments (P<0.05). Nitrogen accumulated in unfilled grain and rice husk, phosphorus accumulated in aboveground organs, potassium accumulated in straw, rice husk and unfilled grain, carbon accumulated in unfilled grain, as well as total nitrogen, total phosphorus, total potassium accumulated in shoots of potassium treatments were significantly higher than that of no-potassium treatments (P<0.05). The ratio of total carbon accumulation (TCA) to air-dried grain yield (ADGY) with approperate nitrogen and phosphorus ranged from0.98to1.04with the average as1.01±0.05.3. The results of the field experiment showed that total biomass, carbon contents in root and in brown rice, carbon accumulated in straw and in unfilled grain and total carbon accumulated in the whole plant of rice of fertilizer treatments were significantly higher than that of no-fertilizer treatments (P<0.05). Under the same phosphorus and potassium condition, carbon accumulated in straw, filled grain and unfilled grain and total carbon accumulated in the whole plant of nitrogen fertilizer treatments were significantly higher than that of no-nitrogen fertilizer treatments (P<0.05). Under the same nitrogen and potassium condition, biomass of straw, filled grain and total biomass of the whole plant of phosphorus fertilizer treatments were significantly higher than that of no-phosphorus fertilizer treatments (P<0.05). The ratio of total carbon accumulation (TCA) to air-dried grain yield (ADGY) of fertilizer treatments ranged from0.93to1.10, with the average as1.01±0.06.From the results obtained in the three experiments, the ratio of total carbon accumulation (TCA) to air-dried grain yield (ADGY) varied slightly, it can be used as an index to estimate the capacity of carbon phyto-fixation in rice cropping system.