Effects of Nitrogen Application Rate on Photosynthetic Characteristics, Yield, and Nitrogen Utilization in Rainfed Winter Wheat in Southern Shanxi

Abstract

The objective of this study was to optimize the application rate of nitrogen(N) fertilizer in winter wheat production in the rainfed area of southern Shanxi Province,China.In a two-year field experiment from October 2008 to June 2010,we tested the effects of N application rate on photosynthetic characteristics,grain yield and its components,and N use efficiency of wheat cultivar "Linhan 6" and the soil residual nitrate-nitrogen(NO 3-N) in 0-200 cm soil profile after harvest under four treatments of N application(N rates of 0,90,180,and 270 kg ha-1).In the N application range tested,the chlorophyll content,net photosynthetic rate(Pn),stomatal conductance(Gs),and transpiration rate(Tr) of flag leaf were enhanced,and intercellular CO 2 concentration(Ci) was declined with increasing N mount.When N application level was higher than 180 kg ha-1,no significant changes in these photosynthetic indices,except for Tr,were observed.The values of N absorption in grain,seasonal N recovery efficiency,and N agronomic efficiency in N180 treatment were the highest,which were significantly higher than those in N90 treatment.The biomass of N270 was the highest among the treatments,which was significantly different from that of other treatments;however,the treatments with N rate higher than 180 kg ha-1 had no significant contributions to grain yield.In local wheat production,spike number and grain number per spike are the major restraints of wheat yield.Nitrogen application rates from 90 to 270 kg ha-1 resulted in NO 3-N residues in 0-200 cm soil layers,with the residue rate as high as 35% of the total Napplication amounts,particularly in 20-40 and 40-60 cm soil layers,which caused a risk of increasing N leaching and the insensitive response of yield to N application.Therefore,in a comprehensive consideration of grain yield,N use efficiency,and NO 3-N residue in soil,we propose the optimal N application rate of 180 kg ha-1 in rainfed winter wheat growing in southern Shanxi Province or dryland areas with similar ecological condition to that of the experiment.