Studies On Water And Nitrogen Use Effiency Of Rice Seedlings Under Different Nitrogen Forms By Isotope Technique

Rice is the most important cereal food crop in China, and consumes a large amount of water usedin agricultural production. However, in dee production system, more than 80％of the total waterirrigated is lost through evaporation and leakage, less than 20％is transpired by rice plants themselves.This so-called ecological water waste in the rice production system is obtaining more andmore concerns. In China, some field experiments and demonstrations were conducted toexamine the effects of non-flooded mulching cultivation on rice yield, aiming to developthe water-saving irrigation system in rice production system. After planting under thenon-flooded condition, two conditions have been changed; plentiful water supply is shiftedto relative water stress, and nitrogen form absorbed by rice plants is inevitably shifted to theratio of less ammonium to more nitrate in the soil due to the increased nitrification innon-flooded condition. Therefore the effects of different nitrogen form on the growth, waterand nitrogen uptake and utilization by rice plants under simulated water stress were studiedin a hydroponics experiment by adding polyethylene glycol 6000 to solution.Under non-water stress, the bio-mass of rice plants were about 49.63％and 63.25％higher under the supply of mixture of NO₃^--N and NH₄⁺-N than either sole supply ofNO₃^--N or NH₄⁺-N, respectively. However, under water stress, the bio-mass of rice plantswere about 5.76％and 484.01％higher under sole ammonium supply than the other twotreatments, WUE of rice plants were also 11.36％and 81.63％higher than them, and12.39％higher than the same nitrogen form supply under non-water stress.Rice seedlings prefer NH₄⁺-N than NO₃^--N. Under water stress, the differences of 15Nabundance in rice seedlings between 15ANP and A15NP were higher than under non-waterstress, demonstrated that water stress stimulated the absorption of NH₄⁺-N. 15N abundancewere the highest in stem, than in root and leaves in A 15N and A15 NP treatments, showed thatthe absorbed NO₃^--N were mainly distributed in stem. However, 15N abundance is higherin leaves than in stem and root under 15AN and 15ANP treatments, evidenced that theabsorbed NH₄⁺-N were mainly distributed in leaves.Under water stress, NH₄⁺-N nutrition increased the tolerance of water stress of riceseedlings. NH₄⁺-N increased root activity and futher ensured the water requdment fromtranspiration, the chlorophyll content was higher in NH₄⁺-N nutrition and futher provide theenergy and carbon assimilates.