The Effect Of Nitrogen Reduction Combined With Organic Fertilizer On Rape Yield And Nitrogen Absorption And Utilization Under Different Water Conditions

In agricultural production,nitrogen plays a very important role.In order to increase the output,more and more nitrogen is applied in agriculture,which not only makes the utilization ratio of nitrogen lower and lower,but also makes the negative effects such as the decline of soil fertility,the eutrophication of water body,the aggravation of air pollution,the damage of agricultural product quality and the serious environmental pollution appear.In order to improve the utilization rate of chemical fertilizer,guarantee the yield of crops and improve the quality of soil,organic fertilizer is paid more and more attention in China.Combined application of organic fertilizer can improve soil fertility,improve soil structure,ensure crop yield and improve nitrogen utilization rate.It is an ecological and efficient way of fertilization.The rape（Brassica campestris L）planting area in Southwest China is wide,but the frequent seasonal drought often results in serious yield reduction.Therefore,in this paper,through the pot experiment,the blank treatment（no nitrogen under normal water,W1CK;no nitrogen under drought stress,W2CK）and conventional nitrogen application（conventional nitrogen under normal water,W1CF;conventional nitrogen under drought stress,W2CF）were used as the control,and the three factors of water treatment,nitrogen reduction level and organic fertilizer application were set up.The main factor is water treatment（keep 80%field water capacity）,W1 in the whole growth period;control water for 25 days from the beginning of bolting period,water gradient is 50%field water capacity,80%field water capacity in the rest period,W2),the side factor is nitrogen fertilizer dosage（reduce nitrogen 15%,F1;reduce nitrogen 30%,F2）,and the side factor is the proportion of organic fertilizer under equal nitrogen condition（with organic fertilizer 0%,O1;with organic fertilizer 15%,O2;with 30%organic fertilizer,O3）,16 treatments in total.The effects of nitrogen reduction combined with organic fertilizer on rape yield and nitrogen use efficiency under different water conditions were studied in order to provide scientific basis for establishing the fertilization mode of nitrogen reduction,yield and drought resistance in agricultural production.The main results are as follows:1.The effect of nitrogen reduction combined with organic fertilizer on agronomic traits of rape under different water conditions:under normal water conditions,the stem diameter,leaf area per plant and root system index of 30%nitrogen reduction and no fertilization control（CK）decreased significantly,and the plant height is the largest under the no fertilization control（CK）;the application of organic fertilizer increases the plant height,stem diameter,leaf area and total root length,root surface area and root volume of rapeseed,thereby improving plant agronomy characters,the treatment of F1O3 with organic fertilizer had better agronomic characters.Under drought stress,the plant height,leaf area and root growth of rape were significantly inhibited.The leaf area and root index of rape decreased gradually with the decrease of nitrogen application,the plant height and leaf area of single plant increased with the application of organic fertilizer at the flowering and maturity stages.2.The effect of nitrogen reduction combined with organic fertilizer on physiological indexes of rape under different water conditions:under normal water conditions,the chlorophyll content,net photosynthetic rate and antioxidant enzyme activity of rape leaves under 30%nitrogen reduction and CK were significantly reduced,but the photosynthetic capacity and antioxidant enzyme activity of rape leaves were increased by organic fertilizer,but there was no significant effect on chlorophyll content.Drought stress significantly reduced the net photosynthetic rate,stomatal conductance,intercellular CO₂ concentration and transpiration rate of rape,significantly reduced the activities of superoxide dismutase and catalase in rape leaves,but significantly increased the activities of peroxidase in rape leaves;with the decrease of nitrogen application,the chlorophyll content,net photosynthetic rate,intercellular CO₂ concentration and antioxidant enzyme activity in rape leaves gradually decreased The activity of antioxidant enzymes in leaves increased and the resistance of rape increased with organic fertilizer,and the activity of antioxidant enzymes in leaves was higher with organic fertilizer F1O2.3.The effect of nitrogen reduction combined with organic fertilizer on soil enzyme activity and soil nutrient under different water conditions:under normal water conditions,with the decrease of nitrogen application,the content of soil nutrient and enzyme activity gradually decreased,and the activity of total nitrogen,total potassium,organic matter,available phosphorus,invertase and urease in 30%nitrogen reduction and CK decreased significantly;30%organic fertilizer treatment can significantly increase soil enzyme activity soil total nutrients,organic matter content,alkali hydrolyzed nitrogen content,invertase activity and protease activity.The activities of soil organic matter,catalase,sucrase and protease were significantly decreased under drought stress;with the decrease of nitrogen application,the activities of soil nutrients and soil enzymes were gradually reduced,which were significantly lower than that of conventional nitrogen application（CF）at 30%nitrogen reduction and no fertilization;the content of total nitrogen,alkali hydrolyzed nitrogen,total phosphorus,available phosphorus and organic matter were increased by organic fertilizer,so the content of soil nutrients was increased.Also the activities of invertase,protease and urease were increased,and the soil fertility was improved.4.The effect of nitrogen reduction combined with organic fertilizer on rape yield and nitrogen use efficiency under different water conditions:under normal water conditions,with the decrease of nitrogen application,the agronomic nitrogen use efficiency,nitrogen contribution rate,number of pods per plant,number of pods per pod,1000 grain weight,yield per plant and protein content of rape gradually decrease;when reducing nitrogen by 30%,the contribution rate of nitrogen,the number of pods per plant and the yield per plant decreased significantly;but when 15%of nitrogen was reduced and 30%of organic fertilizer was applied,the nitrogen utilization rate,yield components and yield per plant increased.Under drought stress,the number of pod and the number of seeds per pod were decreased,so the yield of rape was decreased.The number of pod and the number of seeds per pod were increased by applying organic fertilizer.Under drought stress,the yield of rape was increased by applying organic fertilizer,and the effect of F1O2 was the best,which was 132.63%higher than CK.Drought stress also reduced the nitrogen partial productivity and the nitrogen agronomic utilization rate of rape.Through the application of organic fertilizer,the nitrogen partial productivity,the nitrogen agronomic utilization rate and the nitrogen contribution rate can be increased.The nitrogen partial productivity,the nitrogen agronomic utilization rate and the nitrogen contribution rate of rape with 15%organic fertilizer under the level of 15%nitrogen reduction are larger.Compared with the conventional fertilization control（CF）,the nitrogen partial productivity and nitrogen agronomic utilization rate of F1O2 treatment increased by 28.3%and 36.25%,respectively.In conclusion,under normal water condition,15%nitrogen reduction and 30%organic fertilizer can improve the agronomic characters,photosynthetic capacity and stress resistance,increase the content of soil nutrients and enzyme activity,and increase the yield and nitrogen utilization rate of rape.Under drought stress,15%nitrogen reduction combined with 30%organic fertilizer can increase soil enzyme activity and promote root growth;15%nitrogen reduction combined with 15%organic fertilizer can improve rape agronomic characters,enhance rape resistance,ensure stable yield and improve nitrogen utilization rate.