Response Of Nitrogen Fertilizer Utilization,yield,and Quality Of Hybrid Indica Rice To Nitrogen Reduction With Organic Fertilizer Application In The Karst Region

To investigate the effect of nitrogen reduction and combined application of organic fertilizer on nitrogen utilization,yield,and quality of hybrid indica rice in the karst area,using rice(Yixiangyou 2115)as the material,a split-plot design experiment of two factors of organic fertilizer application rate as the main plots and nitrogen reduction rate as the subplots was carried out.The organic fertilizer application rate had three levels: M0(0 kg/ha),M1(low organic fertilizer,1673 kg/ha),and M2(high amount organic fertilizer,3346 kg/ha).The nitrogen reduction rate had four levels:R1(nitrogen reduction rate 0%),R2(nitrogen reduction rate 25%),R3(nitrogen reduction rate 50%),and R4(nitrogen reduction rate 100%).In this experiment,there were three modes of nitrogen reduction and organic fertilizer application,Mode 1 : nitrogen reduction under the same amount of organic fertilizer(M-R1、R2、R3、R4);Mode 2 : nitrogen reduction and organic fertilizer application under equal nitrogen conditions(R1M0 and R2M2;R2M0 and R3M2);and Mode 3 : nitrogen reduction and combined application of organic fertilizer under non-isonitrogen conditions(R1M0 and R2M1、R3M1、R3M2;R2M0 and R3M1).The main research results are as follows:(1)Rice yield was the highest under R3 in mode 1.In modes 2 and 3,compared with single nitrogen fertilizer(R1M0),the yield of 25% nitrogen reduction combined with a high amount of organic fertilizer(R2M2)increased significantly.In terms of yield components,under mode 1,with an increase in the nitrogen reduction rate,the effective panicle number showed a continuous decreasing trend,and the number of spiklets per panicle increased first and then decreased.The 1000-grain weight and spikelet filling had no obvious change trend,but both were highest under R4.In modes 2 and 3,spikelet filling under nitrogen reduction combined with organic fertilizer treatment was higher than that of the single fertilizer treatment.(2)In model 1,plant height,leaf area index(except heading stage),photosynthetic potential(except middle and early reproductive stage)and net assimilation rate at early growth stage were the highest in R2,while the number of tillers,leaf area index at heading stage and photosynthetic potential at middle growth stage were the highest in R1,but there was no significant difference between R1 and R2.Dry matter accumulation(jointing stage and maturity stage),dry matter accumulation(early growth stage and late growth stage),dry matter accumulation rate(early growth stage and late growth stage),total dry matter accumulation,dry matter assimilation and dry matter assimilation contribution rate were all highest under R2.Therefore,in general,R2 was the most suitable nitrogen reduction rate for each growth index.In mode 2 and 3,compared with chemical fertilizer alone,plant height,leaf area index,photosynthetic potential,net assimilation rate,dry matter accumulation,dry matter stage accumulation,dry matter stage rate,dry matter assimilation amount and dry matter assimilation contribution rate increased in nitrogen reduction combined with organic fertilizer treatment.(3)In terms of nitrogen accumulation and transport,in mode 1,nitrogen accumulation,nitrogen transfer volume,and nitrogen transport rate at jointing stage were all the highest in R3,indicating that nitrogen reduction mode 1 was beneficial to nitrogen transport,but could only improve nitrogen accumulation at the early stage.Under mode 2 and 3,compared with single fertilizer application,nitrogen accumulation,nitrogen transfer volume,nitrogen transport rate and nitrogen transport contribution rate increased under nitrogen reduction combined with organic fertilizer treatment.In terms of nitrogen efficiency,in mode 1,with the increase in the nitrogen reduction rate,nitrogen recovery efficiency(RE),agronomic efficiency(AE),and partial factor productivity(PFP)showed a continuous increase trend,all of which were highest under R4.In Mode 2,compared with R1M0,the RE of R2M2 significantly increased.In mode 3,compared with R1M0,the AE and PFP of 50% nitrogen reduction with low or high amounts of organic fertilizer were significantly increased.(4)In terms of rice processing quality,in mode 1,as the nitrogen reduction rate improved,the milled rice rate and head rice rate continued to decline,but in modes 2 and 3,compared with the treatment of chemical fertilizer alone,the brown rice rate,milled rice rate,and head rice rate of the treatment of nitrogen reduction combined with organic fertilizer improved.In terms of appearance quality and cooking nutritional quality of rice,under the same amount of organic fertilizer,compared with no nitrogen reduction,the chalky degree and chalky rice rate of nitrogen reduction decreased,but gum consistency increased,while under the condition of isonitrogen or non-nitrogen level,compared with single nitrogen fertilization,the consistency of gel of the treatment of nitrogen reduction combined with organic fertilizer increased.(5)In terms of soil microbial biomass,under mode 1,with the increase of nitrogen reduction rate,soil microbial biomass carbon and soil microbial biomass C/N ratio increased first and then decreased,while soil microbial biomass N showed the opposite trend.Under mode 3,the soil microbial biomass carbon and nitrogen in the treatment of reducing nitrogen and applying organic fertilizer increased to different degrees compared with that of applying chemical fertilizer alone.(6)In terms of soil enzyme activity,under mode 1,with the increase of nitrogen reduction rate,the soil sucrase activity first increased and then decreased;the activity of catalase increased continuously;there was no obvious change in urease activity.Under mode 2 and 3,compared with the single application of chemical fertilizer,the activity of three enzymes increased under the condition of reducing nitrogen and applying organic fertilizer.(7)The correlation analysis of soil indexes and yield showed that urease activity had a significant positive correlation with yield,indicating that urease releases available nitrogen in soil,making soil nitrogen supply sufficient,and then increasing rice yield.In conclusion,under the same amount of organic fertilizer,nitrogen reduction compared to no nitrogen reduction and under equal or non equal nitrogen conditions,nitrogen reduction combined with organic fertilizer application compared to single application of chemical fertilizers,which all have some significant effects on increasing yield,agronomic efficiency of nitrogen,recovery efficiency of nitrogen,partial factor productivity of nitrogen,upgrading chalkiness degree,chalkiness rate,gel consistency,protein content,increasing leaf area index during jointing and booting stages,dry matter accumulation during heading and maturity stages,dry matter assimilation amount,contribution rate of dry matter assimilation,soil microbial biomass carbon,soil urease,sucrase,catalase activity.