Impact Of In-situ-Recycled Chili Residue And Plant Growth-Promoting Rhizobacteria On Vegetable Crop Performance And Soil Quality In A Chinese Solar Greenhouse

China accounted for 83% of the world's greenhouse farming in 2019,the system which produces high quality horticultural crops year-round.Nonetheless,crop intensification in this production system,characterized by over-dependence and abuse of synthetic fertilizers,causes dwindling crop yields and overwhelming environmental pressure.Therefore,it becomes pertinent to develop alternative crop nutrition strategies which are not only affordable and profitable,but also guarantee high yield and nutritional quality for human consumption;conserve soil microbial diversity,and sustainability with minimum environmental footprint.However,there is a wide knowledge gap regarding how horticultural crop residues,many of which are still burnt in the open air,can be optimized to improve the performance of high-value crops and soil productivity in the greenhouse production system.The current study was conducted to investigate the impact of in-situ incorporation of chili residue and plant growth-promoting rhizobacteria(PGPR)application on the physiology,growth and yield of leaf and fruit vegetable crops,soil chemical and microbial properties in a solar greenhouse.The treatments imposed in the study were:Chili residue that was directly incorporated in soil with Bacillus subtilis(B1),B.laterosporus(B2),or B.amyloliquefaciens(B3);other treatments were residue alone without PGPR(NP)and conventional chemical fertilizer(CF)which served as the control,arranged in a randomized complete block design(RCBD).In the first study,the impacts of chili residue and PGPR nexus on the photosynthetic performance,growth,nutrient uptake,and yield,soil chemical properties,microbial biomass,and bacterial community diversity and composition of leaf mustard(Brassica juncea L.)in a Chinese solar greenhouse were investigated.Chili residue and PGPR nexus significantly enhanced the leaf mustard's productivity and soil quality than NP and CF.Specifically,B1,B2,and B3 improved the crop yield by51–63% than NP and CF.The inoculated treatments also increased net photosynthetic rate,leaf chlorophyll-a,total soluble solids,plant uptakes of N,P,K,Mg,Ca,Mn,Zn,and soil microbial quotient compared to NP and CF.Further,B.laterosporus and residue synergy markedly improved the soil organic carbon,total nitrogen,microbial carbon contents,and the microbial quotient.Moreover,16S rRNA high throughput sequencing revealed that inoculating soil containing chili residue with B.laterosporus more consistently enriched the rhizospheric bacterial community composition at the phylum and genus levels.Chili residue inoculation with B.laterosporus is a strategy with immense benefits as a bio-fertilizer for sustainable greenhouse vegetable production,which also renders soil ecological services within a short term.Following the leaf mustard crop,the second study was carried out to determine the effects of chili residue and PGPR on folate derivatives,mineral and nitrate contents,in addition to the leaf gas exchange,plant biomass and yield of a successive cropping of two long cayenne pepper cultivars(Capsicum annuum L.vars.‘Xin Xian La 8 F1'and‘La Gao F1')in the same Chinese solar greenhouse.This study excludes CF in the treatment structure.B1 elicited higher net photosynthesis and photosynthetic water use efficiency,while B2 and B3 had higher transpiration rates than B1 and NP.PGPR were re-inoculated but without residue being re-incorporated.B1 and B3 led to a 27–36%increase in pepper fruit yield than other treatments,whereas B3 elicited 24–27.5%and 21.9–27.2%higher 5–methyl tetrahydrofolate(5-MTHF)and total folate contents,respectively than B1 and NP.However,chili residue without PGPR inoculation improved fruit calcium,magnesium and potassium contents than the inoculated treatments.‘Xin Xian La 8 F1'cultivar had higher yield and plant biomass,fruit potassium,total soluble solids,and total folate contents,compared to‘La Gao F1'.Agronomic biofortification through the synergy of B.amyloliquefaciens and chili residue produced better yield and folate contents with a trade off in the mineral contents of long cayenne pepper.In the third study,the residual response of the soil chemical properties and bacterial microbiome to in-situ incorporation of chili residue and PGPR application under a Mustard-Pepper cropping system was assessed.After the second cropping,the soil p H,electrical conductivity,total carbon,organic carbon,total nitrogen,carbon to nitrogen ratio,and NO₃-N obtained from the inoculated treatments were similar to those from chemical fertilizer and only-residue treatments whereas,NH₄-N produced by NP was significantly higher(0.69mg kg^-1)in comparison with other treatments(0.22–0.45 mg kg^-1).Further,B1,B2,and B3 produced 34.3–47.9%,45.9–56.1%,and 46.6–56.6%higher available P,respectively,than those obtained from NP and CF.However,NP had a markedly higher available K than B3,B1,B2,while CF had the least.With respect to microbial biomass C,B3 elicited the highest,followed in order by B2>B1>NP>CF.Microbial biomass N produced by B1 and B2(8.31 and 8.34mg L^-1,respectively)were higher than those from B3(7.85 mg L^-1),CF(6.82 mg L^-1),and NP(5.38 mg L^-1).As regards heavy metals availability,the highest cadmium content was found in B2 treated plots,followed by B1>CF>B3>NP.The same B2 treatment had the highest Pb content,followed by the trio of B3,NP,and CF while B1 had the least,indicating the potentials of B1 to immobilize Pb in soil.Compared to other treatments,B1 had the highest Chao 1 index,number of bacterial species,Shannon index,and exhibited more phylogenetic diversity in the bacterial community,while CF had the least in all the bacterial community diversity parameters.Further,B1 consistently elicited the highest population of Actinobacteria,Firmicutes,and Bacteriodetes,which were among the dominant bacterial phyla in the pepper's rhizosphere.The notable increase in the soil available P(at least 36%)as a result of the augmentation of the chili residue regardless of PGPR specie,in addition to the soil Pb immobilization,the enrichment of soil bacterial diversity and the substantial shift in the composition of the pepper's rhizospheric bacterial community as a result of chili residue and B.subtilis reveal that their nexus has a positive impact on the greenhouse soil fertility and biological properties on a relatively long term.Conclusively,the results of this study demonstrate that chili residue and PGPR synergy exhibit great potentials as a biofertilizer for sustainable greenhouse vegetable production and a tool for nutrition-sensitive agriculture.Their interaction renders ecological services by utilizing vegetable crop residue in an environment-friendly manner.This study also provides a strong basis for a long-term experimentation.