Effects Of Nitrogen Amounts Under Tillages On The Physical And Chemical Properties Of Paddy Soil And The Nitrogen Use Efficiency

A field experiment was conducted and rice was planted as tested material.This experiment conducted different cultivation mode and combined with different fertilization measures,we aimed to investigate the effect of different agricultural management on soil fertility and on rice productivity,this research would be important for the maintain and improvement of the productivity of rice.The experimental site was located in the rice production base of Henan Agricultural University in Xin Yang city,Henan province,China.This study was conducted for two consecutive,years from 2015 to 2016.Two tillage mode was selected:conventional tillage(15 cm)and deep ploughing(30 cm);6 levels of nitrogen was added into the soil,include 0 kg/hm2,150 kg/hm2,210 kg/hm2,300 kg/hm2,390 kg/hm2,450 kg/hm2;and 5 rice cultivars(from the first stage to the fifth stage of super hybrid rice cultivars).The yield and their constituent factors,nitrogen accumulation,nitrogen use efficiency were studied;the change of pH and Eh in soil during the whole growth period was monitored,the soil bulk density and soil aggregates and the nutrient content in each fraction was also analyzed.This research would provide a basis for exploring suitable tillage measures and nitrogen fertilizer usage,and would be helpful to improve nitrogen use efficiency.The main results were as follows:1 The variance analysis showed that the yield and the components of the five super hybrid rice were both significantbetween the cultivars,nitrogen fertilizer levels and the interaction effect was observed between the cultivars and nitrogen fertilizers.The overall trend of the yield and its constituent factors are consistent with interannual and different tillages.With the increase of potential yield,both theoretical yield and actual yield were shown an increase trend firstly and then decrease.From the first stage to the fifth stage of the rice cultivars,the kernels per spike was gradually increased,and the number of effective panicles showed a decrease trend.The nitrogen accumulation trend was consistent between the two years,and the accumulation amount increases gradually with the growth period.Correlation analysis showed that the amount of nitrogen accumulation in the mature stage showed a second parabolic relationship with the rice yield.The partial nitrogen productivity was decreased with the increase of nitrogen application level,and the difference between cultivars was not significant.2 Soil bulk density and compaction were increased with the increase of soil depth,and the cultivation method mainly affected the density and compaction of 15-30cm soil layer,and no difference observed between nitrogen application levels.The change of soil pH and Eh showed the opposite trend before the full heading stage,and then changed consistently.3 The soil used in this experiment was dominated by the fraction of microaggregates of<0.25mm.Compared with conventional tillage,deep ploughing increased the content of<0.25mm aggregates.The application of nitrogen fertilizer significantly effected the formation of soilaggregates in rice paddy,but there was no difference between nitrogen fertilizer levels.Under different treatments,the organic carbon and total nitrogen of soil aggregates decreased with the increase of soil depth.With the decrease of particle size fractions,the organic carbon and total nitrogen content of aggregates gradually decreased.Soil aggregate organic carbon and total nitrogen was mainly stored in 0.5-0.25 mm soil aggregate,deep ploughing increased organic carbon and total nitrogen distribution in<0.25 mm aggregate Soil aggregate C/N was difference under different fertilizer levels,of which 15-30 cm soil aggregate C/N under deep ploughing was lower than the no fertilizer treatment.Conclusions:According to the measured yield results,increasing the depth of ploughing layer is beneficial to increase rice yield.Under different nitrogen fertilizer dosage,the absorption and utilization rate of nitrogen fertilizer increased and then decreased as a whole.It is suggested that the reasonable fertilizer amount should be 210-300kg/ha.Among the 5 varieties,Y2 shows better advantages and can be used as the main promotion variety.