Experimental Study On Water And Nitrogen Utilization Effects Of Controlled Irrigation And Nitrogen Fertilizer Reduction In Black Soil Rice

The black soil area of Northeast China has fertile soil,loose soil and high organic matter content.It is an important commercial grain base in my country.In rice production,there is a common problem of excessive use of nitrogen fertilizers in order to blindly pursue yield.Fertilizer nitrogen cannot be completely absorbed and utilized by plants after being applied to the soil,and its utilization degree and loss depend on the characteristics of soil nitrogen transformation and its maintenance and supply process.Even if nitrogen fertilizer is applied,soil nitrogen is still an important source of nitrogen for crop growth.More than half of the nitrogen accumulated in crops comes from soil.Excessive nitrogen fertilizer not only limits the performance of nitrogen fertilizers,but also inhibits the nitrogen supply capacity of black soil,resulting in a decline in nitrogen fertilizer utilization.When the amount of fertilizer application is insuff icient,rice mainly obtains nutrients for growth by absorbing soil fertility and photosynthesis,and the yield decreases.Therefore,in order to meet the needs of crop growth under the condition of reducing nitrogen and ensure stable or even increased rice yield,more reasonable field management measures are required.In this paper,the conventional nitrogen application rate of traditional flooding irrigation was used as a control,and different gradient nitrogen reduction treatments under controlled irriga tion were set up.In order to provide data support and theoretical basis for the sustainable utilization of water and fertilizer in the cold black soil region,a more suitable water and fertilizer management model was selected to maintain soil fertility an d reduce nitrogen loss.The results of the experimental study are as follows:（1）Compared with the conventional nitrogen application rate of conventional flooding irrigation,moderately reducing nitrogen fertilizer application under controlled irrigation is beneficial to the accumulation of nitrogen and dry matter in various organs of rice.Excessive nitrogen reduction will result in a decrease in dry matter and nitrogen accumulation.Under the control irrigation mode,the nitrogen accumulation in the shoots of each organ gradually decreased with the decrease of nitrogen application rate.N1 treatment had the largest leaf nitrogen transport,but there was no significant difference with N2 treatment（P>0.05）.Under the control irrigation mode,leaf nitrogen transport and stem-sheath transport rate gradually decreased with the decrease of nitrogen application rate.The leaf nitrogen transport rate under the model zero nitrogen treatment was higher than other treatments,and the leaf nitrogen transport rate of N5 treatment was the highest.,the nitrogen transport contribution rate increase d in all treatments,and there was no significant difference between N1 and N2 treatments（P>0.05）.（2）The accumulation of soil NH₄⁺-N gradually decreased with the decrease of nitrogen application rate under controlled irrigation.Compared with the CK tre atment,the accumulation of NH₄⁺-N in the soil layer of 0～20cm in the N1 and N2 treatments increased by 28.18%and 21.71%,respectively,while that in the N3,N4,N5,and CK2 treatments decreased by 8.40%～36.65%.It shows that the control of irrigation and the appropriate reduction of nitrogen fertilizer significantly increase the accumulation of NH₄⁺-N in the soil layer of 0～20cm,but the excess will lead to the decrease of the accumulation of NH₄⁺-N.The accumulation of NH₄⁺-N in 20～60cm soil layers decreased.The accumulation of NH₄⁺-N in the two irrigation modes gradually decreased with the increase of soil depth,and the accumulation of NO₃^--N in the controlled irrigation was mainly concentrated in the surface layer,and there was a certain risk of leac hing after rice harvest,while the conventional nitrogen flooding The accumulation of NO₃^--N in irrigation is mainly concentrated in 20～60cm,which means that NO₃^--N has been leached into the lower soil along with the water,which is easy to threaten the groundwater safety.Compared with the CK treatment,the controlled irrigation and reasonable reduction of nitrogen fertilizer will increase the SON accumulation in the 0～20cm soil layer,decrease the SON accumulation in the 20～40cm and40～60cm soil layers,and the SON accumulation will gradually decrease with the decrease of nitrogen application..With the increase of soil depth,the accumulated amount of SON in conventional flooding first increased and then decreased.Controlling irrigation and reducing nitrogen fertilizer application increased the accumulation of MBN in the 0～20 cm soil layer and decreased the MBN accumulation in the 20～60 cm soil layer.Both irrigation methods gradually decreased with the increase of soil depth.（3）The water use efficiency of rice under the conventional flood irrigation mode was significantly lower than that of the control irrigation mode.Moderate reduction of nitrogen fertilizer application increased the economic yield,N_PFP,N_AE,and N_RE of rice.Excessive reduction of nitrogen fertilizers（N3,N4）cannot meet the normal growth needs of crops,resulting in a decrease in yield.With the decrease of nitrogen application rate,the partial productivity of nitrogen fertilizer gradually increased,the agronomic efficiency of nitrogen fertilizer,and the apparent nitrogen utilization efficiency showed a trend of first increasing and then decreasing.（4）The study found that under the two irrigation modes,conventional nitrogen application soil nitrogen was in surplus.Compared with CK treatment,N1 treatment increased soil nitrogen surplus,but there was no significant difference（P>0.05）.The N2 treatment was in the state of soil nitrogen surplus,and was close to the critical point of soil nitrogen gain and loss.However,N3,N4,N5,and CK2 treatments were all in deficit.Under the control irrigation mode,the soil nitrogen surplus decreased gradually with the reduction of nitrogen application rate.Under the controlled irrigation mode,when the nitrogen application rate was 8 8～99 kg·hm^-2,the soil nitrogen was at the critical point,which was beneficial to the sustainable development of the paddy system.To sum up,the controlled nitrogen application rate of 99 kg·hm^-2 is beneficial to the sustainable development of paddy fields.