Effects Of Organic Materials Addition On Soil Fertility Of Newly-Built Terraces On The Loess Plateau

Loess plateau area is a traditional dry farming area and a key area in the construction of "the second granary".Sloping farmland accounts for 83.38% of the total cultivated land area in the Loess Plateau region.As the main form of basic farmland in the hilly and gully region of the Loess Plateau,terraced farmland is a land consolidation method to control soil and water loss in sloping farmland and to achieve high and stable agricultural yield in dryland areas.However,due to the mechanical disturbance in it’s construction process,the raw soil is exposed and the soil structure is destroyed,which leads to the low content of organic matter,lack of nitrogen,phosphorus,poor permeability,water and fertilizer retention performance,low yield and instability.Depending on the traditional fertilizer cultivation method,crop yield can be low or can increase slowly from year to year.This has become a bottleneck for the future development of dryland agriculture.The primary task of the improved terrace is to quickly restore it’s soil fertility within a short time by adding organic materials,improve it’s productivity level,and achieve stable and increased yield of the newly repaired terrace in the loess plateau area.Different organic materials can cause changes in soil physical properties,chemical properties and biological properties,and significantly affect soil fertility,and then affect crop yield and water use efficiency.However,the mechanism of this process and the responses of microbial diversity have not been systematically analyzed.In order to analyze the effect of organic material addition on soil physical and chemical properties and biological properties of newly built terraced soil,this experiment was carried out at Dingxi Experimental Station of Gansu Academy of Agricultural Sciences in Tuanjie Town,Anding District,Dingxi City in the hilly region of the Loess Plateau in central Gansu Province.Principal component analysis and redundancy analysis were used to screen the soil fertility evaluation factors of these newly modified terraced fields,and the response of soil microbial and nematode community structure and diversity during soil fertility change was studied using Illumina Mi Seq high-throughput sequencing technology.Aim at systematically studing the soil fertility change rule of these newly modified terraced fields with the addition of organic materials.This paper reveals the mechanism of soil fertility change of newly built terraces,and provides theoretical support for soil fertility improvement and directional cultivation of newly built terraces in the study region.The main results of this study are as follows:1.The addition of organic materials significantly improved the soil physical properties of the newly modified terrace,and the bulk density of MSAWF(organic fertilizer + straw +curing agent + water retaining agent + fertilizer)and MSAF(organic fertilizer + straw +curing agent + fertilizer)treatments showed an interannual decreasing trend.Soil capillary porosity and field water capacity showed an increasing trend.The MWD(mean weight diameter)and the composition of water stable aggregates ≥0.25 mm in the treatment of organic material addition were significantly higher than those in the treatment of fertilizer F alone.Straw and fertilizer treatments significantly increased soil nutrient content,and MSAWF treatment had the highest increment of organic matter,available phosphorus and available potassium contents.The addition of organic materials significantly increased soil enzyme activity,microbial biomass carbon,nitrogen content and easily oxidized organic carbon content,and improved soil biological properties.Among them,the soil urease activity increased by 9.09% and 11.69% under MSAWF and MSAF treatment.The soil sucrase activity increased by 21.83% and 9.00%,with the highest increment recorded under MF treatment.Alkaline phosphatase activity increased the most with SF.Compared with F treatment.MSAWF and MSAF treatment increased soil microbial biomass carbon content by 98.05% and 78.84% respectively.2.The dominant phyla of the soil bacterial community in the newly repaired terraced fields were Actinomycetes(43.61%),Proteobacteria(18.45%),Flexuria green(12.29%)and Acidobacteria(7.78%),and the dominant genus was Arthrobacter(8.80%).MSAWF treatment significantly changed the relative abundance of Proteobacteria and Bacteroidetes.The fungal ascomycetes showed the dominant phylum(85.46% ～ 89.69%),and the dominant genus of soil fungi treated by MSAWF and MSAF was Chaetomium.Soil nematodes were dominant(52.46%～90.16%),and fertilization could improve the relative abundance of bacteria-eating nematodes.Redundancy analysis showed that soil microbial biomass nitrogen content and urease activity were the main environmental factors affecting soil bacterial community structure.Soil microbial biomass nitrogen(P=0.002)and organic matter(P=0.012)contents were the main environmental factors affecting soil fungal community composition,while soil available phosphorus content and urease activity were the main factors affecting soil nematode community.3.The results of comprehensive soil fertility evaluation showed that the weight of microbial entropy and alkaline phosphatase activity in 0-10 cm soil layer was high(0.636),while the weight of physical properties(0.306),chemical properties(0.316)and biological properties(0.378)in 10-20 cm soil layer were basically the same,indicating that the surface soil fertility was dominated by biological properties.The fertility of 10-20 cm soil layer was synergistically affected by physical,chemical and biological characteristics.Redundancy analysis showed that soil urease activity(P<0.01),microbial biomass carbon content(P<0.01)and fungi(P<0.01)were the main environmental factors affecting soil fertility index in the newly built terraced fields in the Loess Plateau,followed by water stable aggregates ≥ 0.25mm(P<0.05),available phosphorus content(P<0.05)and total nitrogen content(P<0.05).4.With the application of multiple materials,the soil fertility index(SFI)increased significantly year after year.The SFI of MSAFF,MSAWF and AF treatments in 0-10 cm soil layer was significantly higher than that of the other two materials,the SFI index of MSAWF treatment was 3.59% higher than that of MSAF treatment,and the SFI index of AF treatment was significantly higher than that of SF and MF;The SFI index of the 10-20 cm soil layer treated with MSAWF was significantly higher than that of the other two materials.In 0-20 cm soil layer,the SFI index of MSAWF and MSAF treatment increased significantly.The soil fertility index of MSAWF,MSAF,WF and AF treatments increased year by year,and the increase range of MSAWF,MSAF and AF treatments was higher;The SFI index of soil layers treated with F at 0-10 cm and 10-20 cm showed a downward trend;MF and SF treatment showed a decreasing trend in 10-20 cm soil layer,while WF treatment showed a decreasing trend in 0-10 cm soil layer.MSAWF,MSAF,AF treatment showed an increasing trend in the soil layer between years.There was no significant difference in the increase range between 0-10 cm and 10-20 cm soil layers.In 0-10 cm soil layer,the SFI treated by MSAWF,MSAF and AF increased by 30.40%,21.72% and 30.72% respectively year after year;In 10-20 cm soil layer,the SFI treated by MSAWF,MSAF and AF increased by 16.20%,13.83%and 9.66% respectively.5.The addition of organic materials can increase the SFI index,and then increase the crop yield.Among them,the multi material combined application treatment can significantly increase the yield of potatoes,wheat and corn,and the WF(water retaining agent+chemical fertilizer)treatment can significantly increase the yield of winged beans.Among them,the yield of potato in MSAF,MF(organic fertilizer+chemical fertilizer)and MSAWF treatment was 117.07%,116.77% and 95.69% higher than that in F treatment respectively;The yield of winged bean in WF,MF,MSAF,MSAF treatment was 2.92-15.68% higher than that in F treatment;The wheat yield of MSAWF,MF,MSAF treatment was significantly higher than that of other treatment MSAWF,MF,MSAF,AF(ripening agent+chemical fertilizer)treatment,and the corn yield of F treatment increased by 8.97%,7.66%,4.77%,4.16%.The wheat and corn yield of MSAWF treatment was the highest.In conclusion,the addition of organic materials significantly improved the soil physical properties of the newly built terraces.The addition of straw and chemical fertilizer increased the soil nutrient content,soil enzyme activity and soil microbial biomass carbon and nitrogen content,significantly changed the structure of soil bacterial and fungal communities,increased the relative abundance of bacterial nematodes,and significantly improved soil fertility.Considering the improvement of soil properties and crop yield by adding organic materials,MSAWF and MSAF treatments are more conducive to improving soil fertility and crop yield of newly built terraces.Therefore,organic materials formulated with soil ripening agent can be used as a technical model for rapid fertilization of newly built terraces in the Loess Plateau region,which is conducive for improving the productivity of newly built terraces and maintaining the sustainability of the agricultural ecosystem.