Coupling of reduced inorganic fertilizer with plant-based organic fertilizer as a promising fertilizer management strategy for colored rice in tropical regions

Colored rice is a type of high-quality,high-added-value rice that has attracted increasing attention in recent years.The use of large amounts of inorganic nitrogen fertilizer in rice fields results in low fertilizer use efficiency and high environmental pollution.Organic fertilizer is a promising way to improve soil quality and sustain high yields.However,most studies focus on the effect of animal-based organic fertilizers.The effects of different ratios of plantbased organic fertilizer and inorganic fertilizer on the grain yield and quality of colored rice have rarely been reported.Therefore,a two-year field experiment was conducted in 2020 and 2021 to study the effects of replacing inorganic N fertilizers with plant-based organic fertilizers on the yield,nitrogen use efficiency(NUE),and anthocyanin content of two colored rice varieties in a tropical region in China.The experimental treatments included no nitrogen fertilization(T1),100% inorganic nitrogen fertilizer(T2),30%inorganic nitrogen fertilizer substitution with plant-based organic fertilizer(T3),60%inorganic nitrogen fertilizer substitution with plant-based organic fertilizer(T4),and 100% plantbased organic fertilizer(T5).The total nitrogen provided to all the treatments except T1 was the same at 120 kg ha-1.Our results showed that the T3 treatment enhanced the grain yield and anthocyanin content of colored rice by increasing nitrogen use efficiency compared with T2.On average,grain yields were increased by 9 and 8%,while the anthocyanin content increased by 16 and 10% in the two colored rice varieties under T3 across the two years,respectively,as compared with T2.Further study of the residual effect of partial substitution of inorganic fertilizers showed that the substitution of inorganic fertilizer with plant-based organic fertilizer improved the soil physiochemical properties,and thus increased the rice grain yield,in the subsequent seasons.The highest grain yield of the subsequent rice crop was observed under the T5 treatment.Our results suggested that the application of plantbased organic fertilizers can sustain the production of colored rice with high anthocyanin content in tropical regions,which is beneficial in reconciling the relationship between rice production and environmental protection.

A comparative study on the role of conventional,chemical,and nanopriming for better salt tolerance during seed germination of direct seeding rice

Salinity is one of the most significant risks to crop production and food security as it harms plant physiology and biochemistry.The salt stress during the rice emergence stages severely hampers the seed germination and seedling growth of direct-seeded rice.Recently,nanoparticles(NPs)have been reported to be effectively involved in many plant physiological processes,particularly under abiotic stresses.To our knowledge,no comparative studies have been performed to study the efficiency of conventional,chemical,and seed nanopriming for better plant stress tolerance.Therefore,we conducted growth chamber and field experiments with different salinity levels(0,1.5,and 3‰),two rice varieties(CY1000 and LLY506),and different priming techniques such as hydropriming,chemical priming(ascorbic acid,salicylic acid,and γ-aminobutyric acid),and nanopriming(zinc oxide nanoparticles).Salt stress inhibited rice seed germination,germination index,vigor index,and seedling growth.Also,salt stress increased the over accumulation of reactive oxygen species(H_(2)O_(2) and O_(2)^(-)·)and malondialdehyde(MDA)contents.Furthermore,salt-stressed seedlings accumulated higher sodium(Na^(+))ions and significantly lower potassium(K^(+))ions.Moreover,the findings of our study demonstrated that,among the different priming techniques,seed nanopriming with zinc oxide nanoparticles(NanoZnO)significantly contributed to rice salt tolerance.ZnO nanopriming improved rice seed germination and seedling growth in the pot and field experiments under salt stress.The possible mechanism behind ZnO nanopriming improved rice salt tolerance included higher contents of α-amylase,soluble sugar,and soluble protein and higher activities of antioxidant enzymes to sustain better seed germination and seedling growth.Moreover,another mechanism of ZnO nanopriming induced rice salt tolerance was associated with better maintenance of(K^(+))ions content.Our research concluded that NanoZnO could promote plant salt tolerance and be adopted as a practical nanopriming technique,promoting global crop production in saltaffected agricultural lands.

Nanopriming with selenium doped carbon dots improved rapeseed germination and seedling salt tolerance

Soil salinity is a big environmental issue affecting crop production.Although seed nanopriming has been widely used to improve seed germination and seedling growth under salinity,our knowledge about the underlying mechanisms is still insufficient.Herein,we newly synthesized selenium-doped carbon dots nanoparticles coated with poly acrylic acid(poly acrylic acid coated selenium doped carbon dots,PAA@Se-CDs)and used it to prime seeds of rapeseeds.The TEM(transmission electron microscope)size and zeta potential of PAA@Se-CDs are 3.8±0.2 nm and-30 mV,respectively.After 8 h priming,the PAA@Se-CDs nanoparticles were detected in the seed compartments(seed coat,cotyledon,and radicle),while no such signals were detected in the NNP(no nanoparticle control)group(SeO_2 was used as the NNP).Nanopriming with PAA@Se-CDs nanoparticles increased rapeseeds germination(20%)and seedling fresh weight(161%)under saline conditions compared to NNP control.PAA@Se-CDs nanopriming significantly enhanced endo-β-mannanase activities(255%increase,21.55μmol h^(-1)g^(-1)vs.6.06μmol h^(-1)g^(-1),at DAS 1(DAS,days after sowing)),total soluble sugar(33.63 mg g^(-1)FW(fresh weight)vs.20.23 mg g^(-1)FW)and protein contents(1.96μg g^(-1)FW vs.1.0μg g^(-1)FW)to support the growth of germinating seedlings of rapeseeds under salt stress,in comparison with NNP co ntrol.The respiration rate and ATP content were increased by 76%and 607%,respectively.The oxidative damage of salinity due to the overaccumulation of reactive oxygen species(ROS)was alleviated by PAA@Se-CDs nanopriming by increasing the antioxidant enzyme activities(SOD(superoxide dismutase),POD(peroxidase),and CAT(catalase)).Another mechanism behind PAA@Se-CDs nanopriming improving rapeseeds salt tolerance at seedling stage was reducing sodium(Na^(+))accumulation and improving potassium(K^(+))retention,hence increasing the K^(+)/Na^(+)ratio under saline conditions.Overall,our results not only showed that seed nanopriming with PAA@Se-CDs could be a good approach to improve salt tolerance,but also add more knowledge to the mechanism behind nanopriming-improved plant salt tolerance at germination and early seedling growth stage.

Engineered biochar improves nitrogen use efficiency via stabilizing soil water-stable macroaggregates and enhancing nitrogen transformation

The use of inorganic nitrogen(N)fertilizers has increased drastically to meet the food requirements of the world’s growing population.However,the excessive use of chemical nitrogen fertilizer has caused a series of soil and environmental problems,such as soil hardening,lower nitrogen use efficiency(NUE),nitrate pollution of water sources,nitrous oxide emissions,etc.In this review,we aimed to elaborate and discuss the role of engineered biochar in inducing the stability of water-stable macroaggregates,improving inorganic N transformation,and utilization efficiency to address the current uncertainties of nitrogen loss and maintaining soil and water quality.Firstly,we elucidated the characteristics of engineered biochar in improving biochar quality to work as a multifunctional player in the ecosystem and promote resource utilization,soil conservation,and ecosystem preservation.Secondly,we discussed how the engineered biochar modulates the stability of water-stable macroaggregates and soil inorganic nitrogen transformation to enhance plant response under various toxic or deficient nitrogen conditions in the soil.Thirdly,the role of engineered biochar in biological nitrogen fixation,mediating nirK,nirS,and nosZ genes to promote the conversion of N_(2)O to N_(2),and decreasing denitrification and N_(2)O emission was reviewed.Altogether,we suggest that engineered biochar amendment to soil can regulate soil water-stable macroaggregates,reduce N input,improve nitrogen metabolism,and finally,NUE and crop growth.To the best of our knowledge,this is the first time to evaluate the combined interactions of"engineered biochar×soil×NUE×crop growth,"providing advantages over the increasing N and water utilization and crop productivity separately with the aim of enhancing the stability of water-stable macroaggregates and NUE together on a sustainable basis.