Delaying application time of slow-release fertilizer increases soil rhizosphere nitrogen content,root activity,and grain yield of spring maize

Gungho Li,Pengxio Fu,Guigen Cheng,Weiping Lu,b,Dlei Lu,b,*

a Jiangsu Key Laboratory of Crop Genetics and Physiology/Jiangsu Key Laboratory of Crop Cultivation and Physiology/Jiangsu Co-Innovation Center for Modern Production Technology of Grain Crops,Yangzhou University,Yangzhou 225009,Jiangsu,China

b Joint International Research Laboratory of Agriculture and Agri-Product Safety,the Ministry of Education of China,Yangzhou University,Yangzhou 225009,Jiangsu,China

Keywords:Spring maize Slow-release fertilizer Fertilization stage Root activity Grain yield

ABSTRACT Application of slow-release fertilizer(SF)is a nutrient-management measure aimed at improving maize nutrient use and yield and saving labor cost.One-time application of SF at sowing usually results in nutrient deficiency during the post-silking stage,owing to the long growth period of spring maize.This study was conducted to investigate the effects on spring maize of SF application stage(zero,three-,and six-leaf stages,designated as SF0,SF3,and SF6,respectively)on grain yield,total soil rhizosphere nitrogen(N)content,and root activity,in comparison with the conventional fertilization mode(CF,application of compound fertilizer at sowing time,and topdressing urea at six-leaf and tasseling stages)at the same fertilization level as the control.Compared with no fertilization(F0)and CF,SF increased grain number and weight.The maize cultivars Suyu 30(SY30)and Jiangyu 877(JY877)produced the highest grain yield and net return under SF6 treatment over the three years.SF6 increased enzymatic activities including oxidoreductase,hydrolase,transferase,and lyase in rhizosphere soil at silking(R1)and milking stages(R3).SF6 increased the total N contents of rhizosphere soil by 7.1% at R1 and 9.2% R3 stages compared with SF0.The activities of antioxidant enzymes in roots were increased under SF6 treatments at R1 and R3.The mean root activities of SF0,SF3,and SF6 increased by 7.1%,12.8%,and 20.5%compared with CF at R1 and by 8.8%,13.0%,and 23.5%at R3.Delaying the application time of SF could increase grain yield by increasing total N content of rhizosphere soil,delaying root senescence,and increasing root activity at the late reproductive stage.Applying SF at the six-leaf stage is recommended as an effective fertilization strategy for the sustainable production of spring maize in southern China.

1.Introduction

Maize(Zea mays L.)is a high-yielding C4grain-producing cereal and the second largest area crop in the world,representing a primary target for increasing total crop production capacity[1,2].Maize yield increased rapidly in the USA(5.0-10.6 Mg ha-1),Brazil(1.6-5.5 Mg ha-1),and China(1.7-6.3 Mg ha-1)from 1965 to 2019,leaving a large gap between China and the US[2].With the world facing the challenge of providing food security for a growing population[3]increasing maize yield is essential[4].

Increasing applications of fertilizer increase maize yields[5].However,linear increases in fertilizer application have not produced substantial increases in maize yield,but have reduced fertilizer use efficiency[6]and increased environmental pollution[7,8].The growth period of spring-sown maize is longer than that of summer maize.Thus,fertilizer management to meet nutrient demand during the post-silking stage of spring maize is challenging because the soil N supply normally cannot satisfy it[9].Increasing the frequency of topdressing applications incurs greater production costs.Identifying fertilization strategies that can increase food production while reducing labor costs is urgent.

In the last decade,application of slow-release fertilizer(SF)as an alternative to multiple fertilizer application timings has been extensively used in maize production worldwide[10,11].The N release rate of SF is synchronized with plant N requirements for physiological function,increasing maize yield[12,13].Maize yield under slow-release urea was increased by 10% over that with normal urea[14].SF promoted biomass and N accumulation and produced higher grain yield than CF[15,16].Studies[17,18]of maize yield response to fertilizer have shown that optimized fertilization strategy maximized crop aboveground production,soil carbon,and soil health.Soil properties such as texture[19],fertility[20],and fertilizer management[21],influence maize root traits.SF increased maize yield on light-textured soils with low organic matter content[13].In rice[22]and wheat[23],application of SF increased soil nutrient content,soil N availability,and root development.A combination of SF and CF application increased maize yield by improving soil structure and nutrient content[4,24].Optimum levels of SF improved morphological and physiological characteristics of roots,facilitating the absorption of water and nutrients and thereby increasing maize yield[25,26].These studies focused on one-time application of SF or blended SF with CF at sowing stage,influencing soil environment and root development and thereby yield.However,the effects of one-time SF application at the three-or six-leaf stage on soil nutrient supply and root absorptive capacity as well as grain yield in spring maize have not been reported.

Sufficient N supply in the later growth stage of maize could increase the enzymatic activities involved in carbon-N metabolism,increase net photosynthesis and post-silking biomass accumulation,and result in high grain yield[27].Ensuring the N supply for maize in the later growth stage is essential for high yield[28].Spring maize in southern China has a long growth period,with low temperature in the early stage and high temperature and rainfall in the later stage.These special climatic conditions are likely to cause loss of fertilizer,so that ensuring the supply of nutrients during the grain-filling stage of maize is difficult[29].Our group has recommended[16,30]that the N rate of conventional fertilizers is approximately 405 kg ha-1for achieving high grain yield,but conventional fertilizers have low effective assimilation and readily migrate.CF is readily lost because of N transformation into nitrate(which is leached)or ammonium(which is volatilized).Studies of the effects on spring maize yield of delaying SF application time are limited,especially those describing effects on enzyme activities in soil and root,soil nutrient content,and root activity during the post-silking stage.

The present study aimed to investigate the influence of SF application stage on(i)dynamic changes of soil rhizosphere enzymatic activities and N content during the post-silking stage;(ii)activities of antioxidant enzymes in roots and root activity;(iii)grain yield and its relationship with these indicators in field experiments.

2.Materials and methods

2.1.Experimental site

A field experiment was conducted from 2018 to 2020 at Jiangxinsha farm(31°48′N,121°05′E)in Nantong city,Jiangsu province,China.The effective cumulative temperature,total precipitation,and sunlight during maize growth were 2817 °C,290 mm,and 671 h,in 2018,respectively;2926 °C,370 mm,and 858 h in 2019;and 2790 °C,873 mm,and 664 h in 2020(Fig.S1).The soil type was sandy loam.The soil fertility in the top 0-20 cm of soil prior to sowing is described in Table 1.

2.2.Experimental materials and design

The field experiment was laid out in a two-factor completely randomized design with three replicates for each treatment.Two hybrids:Suyu 30(SY30)and Jiangyu 877(JY877)widely cultivated in Jiangsu province were used.Five fertilization modes were investigated.F0:no fertilizer(F0).CF:N,P2O5,and K2O(405/135/135 kg ha-1)were applied at 135 kg ha-1(conventional compound fertilizer,N/P2O5/K2O=15%/15%/15%)at sowing time,225 kg ha-1N(urea,46%)at six-leaf stage,and 45 kg ha-1N(urea,46%)at tasseling stage.SF0,SF3,and SF6:slow-release fertilizer(N/P2O5/K2O=27%/9%/9%)was applied once at sowing,three-,and sixleaf stages,respectively,with the same N/P2O5/K2O rates(405/135/135 kg ha-1)as those in the CF mode.An amino acid polymer biological preparation having a negative charge with strong adsorption was added to this slow-release fertilizer and metabolizes into amino acids,which act as biostimulants.All fertilizers were provided by Jiangsu Zhongdong Fertilizer Co.,Ltd.(Changzhou,Jiangsu,China).Each plot was 45 m long and 3.6 m wide with double row planting(wide and narrow row spacing’s were 0.8 and 0.4 m,respectively).The plant density was 75,000 plant ha-1.Maize was sown on April 1 for three years and harvested at maturity on August 3,2018,August 5,2019,and August 4,2020.

2.3.Sampling and measurement

2.3.1.Soil enzymes and N content

Surface soil samples(0-20 cm)used to measure basal fertility were collected in each year from five locations in each plot using a soil auger with a diameter of 5 cm.At the V6(six-leaf),R1(silking),R3(milking),and R6(physiological maturity)stages,the soil adhering to the roots,designated as rhizosphere soil,was shaken off vigorously and brushed into a paper bag.Any visible fine roots were picked out.The total N content in rhizosphere soil of the subsample was measured after air drying.The second subsample was stored at-80°C for determination of enzyme activity.Total N was measured by Kjeldahl digestion[31].The activities of rhizosphere oxidoreductases including nitrate reductase(NR),dehydrogenase(DHO),peroxidase(POD),and catalase(CAT);soil hydrolases including phosphatase(Pho),urease(Ure),invertase(Inv),and protease(Pro);soil transferases including transaminase(Tsa),levansucrase(LS),and transglycosidase(TGS);and soil lyases including aspartate decarboxylase(ASPD),glutamate decarboxylase(GAD),and tryptophan decarboxylase(TDC)were measured using an MLBIO Plant Sucrose Synthase ELISA Kit(catalog numbers correspond to ml39040,ml30644,ml39061,ml307342,ml30621,ml304067, ml307124, ml307129, ml305877, ml305845,ml308048,ml307043,ml307079,and ml307056),following the manufacturer’s instructions(Shanghai Enzyme-linked Biotechnology Co.,Ltd.,Shanghai,China)and a previously described method[32,33].

2.3.2.Root antioxidant enzymes and root activity

The underground roots of three representative plants were collected from each plot at the R1,R3,and R6 stages in the field experiment.For each plant sample,a block of soil(40 cm length×40 cm width×20 depth)was extracted from the center region surrounding the plant.The top 20-cm soil layer was placed into nylon netting bags,and roots were washed and collected after the soil was passed through a 0.5 mm sieve using a hose and nozzle attachment.Each root sample was mixed thoroughly and a subsample taken for root reducing activity(0.5 g fresh weight)and enzymatic activity measurement.Root activity was measured by the triphenyltetrazolium chloride method[34].Malondialdehyde(MDA)content and enzymatic activities including superoxide dismutase(SOD),POD,and CAT were measured with the MLBIO Plant Sucrose Synthase ELISA Kit(catalog number ml0566148,ml01376,ml01691,and ml02278),following de Azevedo Neto et al.[35].

Table 1The soil properties of experimental field prior to sowing at 0-20 cm soil depth in three years.

2.3.3.Grain yield and economic analysis

Thirty ears were sampled from the two middle rows of each plot to measure 1000-kernel weight and kernel number.In all cases,the moisture content was standardized to 14%.

Cost-profit analysis was performed following Guo et al.[9]:

Where cost(other)includes the costs of plowing,harrowing,seed,sowing,herbicide,insecticide,and harvesting.

The grain price was 1.8 CNY kg-1in 2018 and 2019,and 1.9 CNY kg-1in 2020.The SF,common compound fertilizer and urea price is 2.3,2.0 and 2.0 CNY kg-1.The costs of plowing,harrowing,seed,sowing,herbicide,insecticide,and harvesting were 675,300,225,750,195,225,and 750 CNY kg-1,respectively.

2.4.Statistical analysis

Treatments were compared using Duncan’s test at P≤0.05.Analysis of variance was performed with SPSS 17.0(SPSS Institute Inc.,Chicago,IL,USA).Spearman correlations were calculated to determine the relationships between maize growth indexes and yields using the cor function of the base R package‘‘stats,”and the correlation results were visualized with the corrplot mixed function of the R package‘‘corrplot.”.

3.Results

3.1.Grain yield and economic analysis

Year and fertilization mode affected kernel number per ear,1000-kernel weight,and yield(Table 2).Compared with CF,SF significantly increased kernel number per ear,1000-kernel weight,and yield of spring maize.The mean grain yields of SF0,SF3,and SF6 treatments were increased by 8.1%,11.6%,and 17.2%(SY30),respectively,and 6.2%,6.5%,and 16.0%(JY877)compared with CF.Both varieties produced the highest grain yield at SF6 in 2018,2019,and 2020,and the mean yield of JY877 was 6.0%higher than that of SY30.The mean kernel number per ear,1000-kernel weight,and yield followed the trend 2019＞2018＞2020 owing to the differences in climatic conditions(Fig.S1)over the three years.Rainfall varied widely during the 3-year experiment.In 2020,excessive precipitation in the later stage of maize growth caused mild waterlogging stress,leading eventually yields lower than those in 2018 and 2019.The interaction year×fertilization also affected grain yield.

Table 3 shows the gross returns,costs and net returns of treatments.Year,fertilizer,and variety had significant effects on gross and net returns.Because of the different climate conditions and maize prices in three years,the year×fertilization interaction also had affected gross and net returns.The cost difference was mainly fertilizer price and fertilization costs.SF6 showed the greatest economic benefit among all the treatments in the three years,and the mean net return of SF0,SF3 and SF6 increased by 23.3%,27.9%and 42.2% relative to CF.The mean net returns for JY877 were 7.5%higher than those for SY30.

Table 2Effects of slow-release fertilizer application stage on yield and its components in spring maize.

Table 3Economic analysis(CNY ha-1)of SF rates in 2018,2019,and 2020.

3.2.Dynamic changes of enzyme activities and N content in rhizosphere soil

The dynamic changes of enzyme activities in rhizosphere soil from 2018 to 2020 are presented in Figs.S2-S5,and the total N content of rhizosphere soil is shown in Fig.S6.Table 4 presents the analysis of variance associating SF application stage with enzyme activities and total N content in rhizosphere soil.The effects of year,variety,and fertilization mode on rhizosphere soil enzyme activities and total N contents were significant,and those of fertilization mode highly significant(P＜0.01).The trend from 2018 to 2020 was consistent with only minor variation among the years,and the overall performance of mean activities showed the following trend:2019＞2018＞2020(Table 4).

The oxidoreductase activities of rhizosphere soil(Fig.S2),hydrolases(Fig.S3),and transferases(Fig.S4)initially increased and then decreased,and all treatments reached their maximum values in R3.The lyase activities of rhizosphere soil including ASPD and TDC also increased initially and then decreased,but the activity of GAD decreased gradually from R1 to R6(Fig.S5).The mean activities of JY877 were higher than those of SY30.At R1,R3,and R6,fertilization significantly increased the activity of enzymes in rhizospheric soil,and the increases in SF treatments were greater than those of CF.Delaying the application time of SF increased the enzyme activities of rhizosphere soil and showed SF6＞SF3＞SF0＞CF overall.However,the NR and POD activities of rhizospheric soil behaved differently,such that SF0 showed the maximum value at R1 in JY877,2019(Fig.S2).

The total N content of rhizosphere soil initially increased and then decreased from V6 to R6,and reached maximum at R1(Fig.S6).Fertilization significantly increased the content of total N at R1,R3,and R6,and the increases in SF treatments were greater than those of CF.At the same fertilization rate,the mean total N content showed the following trend:SF6＞SF3＞SF0＞CF.The mean total N content of SF0,SF3,and SF6 treatments increased by 14.2%,17.6%,and 22.1%(R1);10.6%,12.7%,and 16.0%(R3);22.2%,27.6%,and 31.9%(R6)compared with CF.SY30 had a total N content similar to that of JY877.

3.3.Root activity and antioxidant enzyme activity

The dynamic changes in root activities and MDA content in 2018,2019,and 2020 are presented in Fig.1,and the activities of antioxidant enzymes including SOD,CAT,and POD in the root are shown in Fig.2.The analysis of variance presented in Table S1 shows that the effects of year and fertilization mode on root activities,MDA contents,and the activities of antioxidant enzymes were highly significant(P＜0.01).

Table 4Analysis of variance for slow-release fertilizer application stage on enzyme activities and total N content in rhizosphere soil of spring maize.

Fig.1.Effects of slow-release fertilizer application stage on root activity and MDA content in 2018,2019 and 2020.Vertical bars indicate means±standard deviation(n=9,from 3 independent plots).R1,R3 and R6 represent silking,milking,and physiological maturity stages,respectively.R-MDA,malondialdehyde in root.

Root activity decreased gradually from R1 to R6,whereas MDA content increased gradually from R1 to R6 in the root(Fig.1).Fertilization significantly increased root activities at R1,R3,and R6,and the increases in SF treatments were greater than those of CF.Under the same fertilization rate condition,the mean root activities showed the following trend SF6＞SF3＞SF0＞CF.The root activities of SF0,SF3,and SF6 treatments increased by 7.1%,12.9%,and 20.5%(R1)and 9.0%,13.1%,and 23.7%(R3)compared with CF.The trend of the MDA content under different treatments was opposite to that of root activity and showed CF＞SF0＞SF3＞SF6.The MDA contents of SF0,SF3,and SF6 treatments in SY30 were decreased by 6.8%,11.6% and 12.1%(R1),and 10.5%,14.3% and 19.3%(R3)compared with CF.The activities of SOD,CAT,and POD increased and then decreased from R1 to R6 in root and showed SF6＞SF3＞SF0＞CF under the same fertilization rate overall(Fig.2).The trend from 2018 to 2020 was consistent with only minor variation among years,and the performance of the root activities and enzymatic activities showed the following trend:2019＞2018＞2020;the trend of the MDA content was 2020＞2018＞2019.

Fig.2.Effects of slow-release fertilizer application stage on activities of root antioxidant enzymes in 2018,2019 and 2020.Vertical bars show means±standard deviation(n=9,from 3 independent plots).R1,R3 and R6 represent silking,milking,and physiological maturity stages,respectively.R-SOD,superoxide dismutase;R-CAT,catalase;RPOD,peroxidase in root.

3.4.Spearman correlation

The activities of oxidoreductases,hydrolases,transferases,and lyases in rhizosphere soil,as well as the total N content of rhizosphere soil,were significantly positively correlated with kernel number,kernel weight,and yield under these experimental conditions.Root activities and root antioxidant enzymes were also significantly positively correlated with yield and yield components,whereas the content of MDA in root was negatively correlated with grain yield(Fig.3).

4.Discussion

4.1.Grain yield response to fertilization

Efficient and sustainable N management must be adopted to obtain higher maize grain production to satisfy the demands of the increasing human population worldwide[36,37].Maize yield is determined by kernel number per unit area and kernel weight[38].Delaying application time of SF to V6 increased maize yield(by 16.6%)and net return(by 42.2%)relative to CF(Tables 2 and 3).The economic analysis reflected the differences of economic benefits among fertilization treatments under pot experimental conditions.At the farm scale,the costs of plowing,harrowing,sowing,herbicide,insecticide and harvesting should be reduced by mechanization.Given that seed fertilizer co-sowing technology is widely used on Chinese farms,the fertilization costs of SF0 and CF should be reduced.In view of these factors,the mean net return of SF6 still showed the greatest economic benefit among all the treatments in three years.The increase in yield was due mainly to the increase in kernel number per ear and kernel weight.Fertilization increases maize yield[28],and Zhao et al.[39]found that controlled-release fertilizers increased the grain yield of summer maize in comparison with common compound fertilizer.Azeem et al.[12]and Zhang et al.[13]also reported that the N release rate of SF was synchronized with plant N requirements for physiological functions and increased maize yield.Some studies on the onetime application of mixture of SF and CF at the sowing date have been conducted.Guo et al.[9]showed that blending SF and urea in a one-time application could potentially improve grain yield and create a simpler,more efficient,and business-friendly system of high-yielding maize production.Gao et al.[24]and Guo et al.[8]also discussed the optimum ratio of SF and CF in maximizing maize yield.Our findings were consistent with those of these studies.We also solved the problem of nutrient deficiency during the postsilking stage of spring maize and demonstrated that delaying the application time of SF could increase grain yield by increasing enzyme activities and nutrient content in rhizosphere soil,delaying root senescence,and increasing root activity during the grain-filling period.

Fig.3.Spearman correlations among rhizosphere soil characteristics,maize growth indexes,and yields based on three years of spring maize.Blue represents positive correlation and red represents negative correlation.The narrower the ellipse of the graph,the stronger the correlation.The darker the color,the stronger the correlation,and vice versa.Numbers in cells are correlation coefficients.R-MDA,malondialdehyde content in root.

4.2.Soil characteristic response to fertilization

Good soil structure is expected to regulate the soil rhizosphere environment and promote root activity.A continuous supply of nitrate increases maize lateral root elongation,induces morphological changes,and promotes crop nutrient uptake[40,41].Surveys[42,43]have provided evidence of a strong association between total N content and plant productivity in maize fields.Chikowo et al.[44]and Zhao et al.[45]showed that integrated fertilization generally results in higher soil nutrient contents,soil fertility,and maize yield.Our findings were consistent with these,with fertilization treatments resulting in higher total N content of rhizosphere soil from V6 to R6 stages than F0.Soils assayed for total N content and enzyme activity were sampled from the soil adhering to the roots,which was regarded as rhizosphere soil.Fertilizer types and fertilization methods influence nutrient especially N,content in rhizosphere soil by affecting root metabolism[46,47].Fertilization increased the activities of rhizosphere soil metabolic enzymes,as found in previous studies on soil oxidoreductases[48]and hydrolases[33].SF,as a high-efficiency fertilizer,is designed to release nutrient based on crop demand,reduce excess inorganic N accumulation and N loss from the soil profile[12],and increase soil fertility[14].These critical measures achieve high crop yields and save labor while maintaining eco friendliness[27,49].In recent years,researchers have investigated the mechanisms by which SF affects the soil environment to increase crop yield.Gao et al.[24]found that SF increased soil nutrient supply by increasing soil humus and water-stable aggregate content,resulting in increased maize yield.Li et al.[23]showed that SF increased the abundance of soil bacteria involved in cellulose lignin degradation,accelerating soil mineralization and humification during the filling stage and ultimately increasing soil N availability and crop yield.The results of the present study also indicated that SF gave the advantage of increasing activities of rhizosphere soil metabolic enzymes during post-silking stage compared with CF.Delaying the application time of SF increased the activities mainly of NR and POD in rhizosphere soil oxidoreductases at R1 and R3.In rhizosphere soil hydrolases,SF3 and SF6 increased the activities mainly of Pho and Urea at R3.Delaying the application time of SF also increased the activities of LS at R3 in soil transferases and ASPD and TDC at R1 and R3 in soil lyases.The increase in SF6 was significantly higher than those in SF0 and SF3.In spring maize production,delaying SF application time to V6 could increase activities of rhizosphere soil metabolic enzymes,thereby accelerating soil mineralization and promoting N accumulation during the filling stage.Thus,soil fertility is improved and maize grain yield is increased.

4.3.Root physiological characteristic response to fertilization

Root activity and physiological characteristics are associated with nutrient and water capture in soil and contribute to crop yield[50,51].Soil nutrient level influences root development in maize,and aboveground plant growth and biomass depend heavily on root systems[34,52].Strong relationships have been observed[53]between root activity and fertilizer level for maize.Our results also showed that fertilization increased the activities of SOD,CAT,and POD during post-silking stage and delayed root senescence,promoting root activities.To efficiently absorb N from the soil,plants promote lateral root growth on nitrate-rich flanks while inhibiting lateral root growth on nitrate-poor flanks[54].Li et al.[23]found that the slow release of nutrients from SF increased levels of ammonium and nitrate N in the soil,promoted root elongation,and increased root surface area and root volume compared with CF.These results are consistent with our findings that SF increased root activity and delayed root senescence process by increasing the activities of SOD,CAT,and POD and reducing MDA accumulation in roots at critical growth stages compared with CF.Delaying the application time of SF resulted in better root activities and root antioxidant enzymes,and the increase in SF6 was significantly higher than that in SF0 and SF3.Our results suggest positive correlations among root activity,root antioxidant enzyme activities,and grain yield(Fig.3).

5.Conclusions

Delaying the application time of slow-release fertilizer resulted in clear effects on rhizosphere soil fertility and root growth in spring maize production.SF6 promoted activities of rhizosphere soil metabolic enzymes,increased soil nutrient content,delayed root senescence,and increased root activity during the postsilking stage.These effects increased soil nutrient supply and root absorptive capacity,and ultimately led to high yield and economic benefit.Considering the results of our three-year field experiments,we recommend one-time application of SF at the six-leaf stage as a fertilization strategy for high-yield production of spring maize in southern China.

CRediT authorship contribution statement

Guanghao Li:Writing-original draft.Pengxiao Fu:Software.Guigen Cheng:Methodology.Weiping Lu:Project administration,Resources.Dalei Lu:Project administration,Data curation,Writing-review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

We would like to acknowledge the financial support of the National Key Research and Development Program of China(2016YFD0300109),National Natural Science Foundation of China(32101828,32071958),Natural Science Foundation of Jiangsu Province(BK20200952),the Open Project Program of Joint International Research Laboratory of Agriculture and Agri-Product Safety(JILAR-KF202010),the Jiangsu Agricultural Industry Technology System of China(JATS[2020]444),and the Priority Academic Program Development of Jiangsu Higher Education Institutions.

Appendix A.Supplementary data

Supplementary data for this article can be found online at https://doi.org/10.1016/j.cj.2022.04.014.