| In southern of Jiangsu province,Rice-wheat rotation is the dominant practice,rice and wheat production play a unique position in national food security.However,excessive application of nitrogen fertilizer very common in this region.Long term of excessive use nitrogen fertilizer has limited ability to improve production,but has led to severe environmental problems,for instance,eutrophication,greenhouse gas and acidification.Field experiments were conducted from 2013 to 2015 with the continuous two cycles of rice-wheat rotation in the Danyang test base of Nanjing Agricultural University.Three treatments were designed at local farmers nitrogen fertilizer rate,80%of local farmers nitrogen fertilizer rate,60%of local farmers nitrogen fertilizer rate for rice and wheat season,respectively.In the rice season local farmers nitrogen fertilizer rate 300 kg/ha for rice and 225 kg/ha for wheat.A blank control(CK)in which nitrogen fertilizer was not applied was also included.The reduction fertilizer rate effect on yield,nitrogen use efficiency and soil available nitrogen in rice and wheat season.The main results obtained were as follows:1.In the rice season reduction 20%and 40%of conventional rate(300 kg/ha)both have not significantly decrease yield,but effect on yield components such as total number of spikelets and gain weight.The interaction of R×W for yield components of among all treatments showed no significant difference except grain weight.Reduction fertilizer effect on tillers number among all treatments showed no significant difference during key growth stage of rice season except for maturity stage.The dry matter accumulation among all treatments have similar trends:among all treatments showed no significant difference in rice season except for heading stage in 2015.As to wheat season:Current season reduction fertilizer effect on yield have difference between years.In the wheat season of 2013-2014 among all treatments showed no significant difference,however,in the season of 2014-2015 nitrogen rate have significant effect on yield,and the former rice nitrogen rate also effect on succeeding wheat yield.The dry matter accumulation among all treatments showed no significant difference during 2013-2014 season,but in the 2014-2015 wheat season the dry matter accumulation reduction with nitrogen reduction.2.The nitrogen accumulation all showed similar tends was positive correlated with nitrogen application rate,and fertilizer rate have significant effect.The interaction of R×W have no significant difference among all treatments.The nitrogen use efficiency indices all showed similar tends was negatively correlated with nitrogen application rate,reduction fertilizer has significant improve NAE,NPF and NRE.In the rice season,compared with conventional fertilizer rate,nitrogen fertilizer reduction 20%,40%,NAE increased by 19.5-51.0%,NPF increased by 23.2-61.6%and NRE increased by 4.3-32.0%.In the wheat season compared with conventional fertilizer rate,nitrogen fertilizer reduction 20%,40%,NAE increased by 18.9-50.4%,NPF increased by 21.6-57.6%and NRE increased by 16.3-38.9%.Postponing nitrogen application help to improve nitrogen use efficiency.3.From panicle initiation stage to maturity stage the soil available nitrogen gradually decreased.In the wheat season the soil available nitrogen concentration were significant higher than rice season,and the concentration rapidly decreased compared with rice season.This suggests that the soil available nitrogen concentration effect by the plant nutrient demand and environment conditions.The results suggest that reduction fertilizer have no effect on soil available nitrogenCollectively,in the rice season,reduction 20%,40%fertilizer rate have no significant effect on yield and dry matter accumulation in rice season,and increased the nitrogen use efficiency,reduced the loss of nitrogen,more important,have no effect on soil available nitrogen.However,in the wheat season reduction fertilizer effect on yield inconsistent,increase the nitrogen use efficiency also fund in wheat season,as well as have no effect on soil available nitrogen. |
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