Effects Of Biochar Combined With Nitrogen Fertilizer On Yield And Quality Of Rice And Its Mechanism

Rapid and continuous increase in the global population is demanding more food,thus nitrogen（N）fertilization can’t be ignored,which can directly influence crop yield and quality.However,the excessive use of synthetic nitrogen（N）fertilizers in rice（Oryza sativa L.）has resulted in high N loss and soil degradation.Increasing cereal grain production and quality on sustainable basis is the challenging issue to overcome the demand of food for increasing population.The addition of biochar（B）is believed to deliver multiple eco-friendly benefits to both soil and crops under increasing nitrogen with substantial reduction in nutrients losses.Therefore,the advantages of sole biochar application are recognized,however the information about optimal biochar with inorganic nitrogen fertilizer for higher rice grain yield and quality are scanty.Therefore,this thesis explored the effects of different biochar and nitrogen fertilizer application rates on soil quality,rice growth,and rice yield and quality,and proposes a reasonable ratio of biochar and nitrogen fertilizer,and clarifies the rational application of biochar the mechanism of nitrogen fertilizer to increase rice yield.The two consecutive pot and field experiments were carried out at the farm of Guangxi University in the early and late seasons of 2018 and 2019.The growing time of early rice and late rice is from March to July and July to November,respectively.The pot experiment consisted of eight treatments i.e.,（1）N1B0(0 t B ha^-1+270 kg N ha^-1),（2）N2B0(0 t ha^-1+360 kg N ha^-1),（3）N1B1(20 t B ha^-1+270 kg N ha^-1),（4）N1B2(40 t B ha^-1+270 kg N ha^-1),（5）N1B3(60 t B ha^-1+270 kg N ha^-1),（6）N2B1(B20 t ha^-1+360 kg N ha^-1),（7）N2B2(40 t B ha^-1+360 kg N ha^-1),and（8）N2B3(60 t B ha^-1+360 kg N ha^-1)for pot experiment.Whereas,the field experiment used the same eight treatments,but the amount of nitrogen fertilizer applied per unit area was halved on the basis of the pot experiment.The combined application of biochar and nitrogen fertilizer in different ratios significantly affects the soil physiochemical properties.The addition of biochar in combination with nitrogen fertilizer at the rate of 60 t ha^-1 along with270 kg N ha^-1 significantly increased paddy soil properties.i.e.soil porosity,moisture content,p H,organic carbon,total nitrogen,available phosphorus,and available potassium by 63.24%,63.66%,14.85%,58.0%,59.0%,22.39%,and2.9%respectively,under pot condition.Similarly,under field experiment,30 t B ha^-1 along with 180 kg N ha^-1resulted in higher p H,TN,AP,AK and SOC by16.43%39.14%,26.10%,14.40%and 25.25%,respectively whereas BD was decreased by 8%over non-biochar treatment under 135kg N ha^-1across the seasons.The soil microbial biomass carbon and nitrogen were significantly increased by 88%and 87%respectively in the combine treatment of 30 B ha^-1along with 135 kg N^-1 as compared to sole N applied treatment.The combined application of biochar and nitrogen fertilizer in different ratios significantly affects the yield and quality of rice.Biochar amendment at the rate of 60 t ha^-1combined with 270 kg N ha^-1 significantly increased plant height（PH）14.58%,filled grains percentage 17.97%,panicle length（PL）23.41%,thousand grains weight（TGW）23.78%,grain yield 60%and biological yield 52%during pot experiment.Whereas,during field experiment B integration at the rate of 30 t ha^-1 along with 180kg N ha^-1 significantly increased tillers hill^-1,PH,TGW,PL and grain yield by average 62%,4%,19%,23%and 30%over non-biochar treatment,respectively.The rice grain qualitative traits including AC,PC,GC and GT were increased by 21%,17%,30%and 35%,respectively in the combine treatment of biochar at 60 t ha^-1along with 27 kg N ha^-1.The combined application of biochar and nitrogen fertilizer in different ratios significantly enhanced root morphological traits i.e.TRL,TRSA,TRV and TARD were increased by 26%,12%,14%and 20%at 40 t B ha^-1 combined with 270 kg N ha^-1as compared to sole N application during pot experiment.Whereas under filed condition the roots traits,i.e.TRL,TRV,TRSA and TARD were increased at 30 t B ha^-1 under low N by 20%,13%,13%and 25%,respectively,over non-biochar treatment.The combined application of biochar and nitrogen fertilizer at the rate of40 t B^-1and 270 kg N ha^-1 significantly enhanced leaf photosynthetic attributes i.e.,Pn,Tr,WUE and gs by 52%,34%,27%and 28%respectively,under pot experiment.Whereas under field condition the leaf physiological traits i.e.Pn,chlorophyll a and chlorophyll b were improved significantly by 64%,111%and98%,respectively in the combine treatment of biochar at the rate 30 t ha^-1 with135 kg N ha^-1.The combined application of biochar at 30 t ha^-1 with 135 kg N ha^-1significantly increased starch metabolizing enzymes including SS,AGPase,SBE,DBE,SSS and GBSSS by 46%,45%,47%,41%,56%and 26%,respectively compared to non-biochar treatments.The gene expression related to starch metabolism in rice grains.Changes in starch metabolizing enzymes were resulted due to the up regulated gene expressions of isofrom genes i.e.SUS4,AGPS2b,SSS1,GBSS1,GBSEIIb,and ISA1 at 30 t B ha^-1 combined with135 kg N ha^-1during grain milking stageCorrelation analysis showed that the rice root diameter（0.76**）,total root length（0.89**）,total root surface area（0.73**）,TRV,total root volume（0.67**）and rice yield after heading were significantly positive correlated.Pn also played a very important role in the increase of rice yield.The initial photosynthetic rate（Pn）of leaves at the tillering stage,heading stage and mature stage was significantly positive correlated with rice yield.Rice yield and soil microbial carbon biomass（MBN）and microbial nitrogen biomass（MBC）,as well as soil physical and chemical properties,activities of rice nitrogen metabolism-related enzymes,and rice dry matter accumulation also showed significant differences.We concluded that the combined application of biochar and nitrogen fertilizer in different rates affected significantly on soil properties,rice growth and its yield and quality.Therefore,it is concluded that biochar application at60 t ha^-1+270 kg N ha^-1 in the pot experiment,and 30 t B ha^-1+135 kg N ha^-1in the field experiment is the promising combination for increasing rice yield.This work provides a sustainable fertilizer plan to enhance rice grain yield and soil health with low synthetic N fertilizer by using in combination with biochar amendment.