Effects Of Long-term Applications Of Organic Materials On Soil Structural Characteristics And Organic Carbon In Dryland Of The Loess Plateau

The Loess Plateau is located from 100°54'to 114°33'E and 33°43'to 41°16'N and accounted for one-third of the arable land of China,which plays a vital role in agricultural production.In last decades,the serious soil degradation and water losses was caused by unreasonable agricultural managements especially under semi-arid temperate continental climate like Loess Plateau.Therefore,it is urgent to explore appropriate measurements to maintain ecologically sustainable development on these Loess Plateau.The organic materials such as maize straw and organic manure are extensively applied weather individually or combined together to improve the soil structure and soil organic carbon(SOC).However,the knowledge about comparison effect and it is mechanisms of long-term application of these organic materials on the physical properties and SOC of arid and semi-arid soils are still unclear and lack.The overall objective of this thesis was to evaluate long-term impacts of organic material that was applied for 26 years ago on soil physical properties and SOC content.For this purpose,field experiment was conducted at Dryland Agriculture Demonstration Zone in Zongai Village,Shouyang County,Shanxi Province,China.Two types of organic materials(maize straw and organic manure)were applied individually or combined with balanced mineral N and P fertilizers which included(1)unfertilized control(CK),(2)maize straw at 3000 kg ha^-1(S),(3)cattle manure at a low rate of 1500 kg ha^-1(LM),(4)maize straw residue at the rate of 3000 kg ha^-1,cattle manure at the medium rate of 4500 kg ha^-1(S-MM)and(5)maize straw residue at the rate of 3000 kg ha^-1,cattle manure at the high rate of 6000 kg ha^-1(S-HM).To each treatment,a constant dose of nitrogen(N)and phosphorus(P)(ratio N:P₂O₅=1:1)at the rate of105 kg ha^-1was added to compensate the depletion as a result of intensive cultivation and also to make a balanced fertilization in the macro nutrients of the plants under study.These treatments were arranged in randomized design with two replicates with a plot area is 36 m²(6 x 6 m²).Soil layers were measured during the maize growth stages in 2018.Soil pore structure was measured by X-ray Microtomography in the soil column scale.SOC characteristics were evaluated using Fourier transform infrared spectrometry(FTIR).The coal-C content of soil samples was analyzed using a Chemi-thermal method.The regression analysis was used to assess the relationship between the soil physical properties,SOC,and TOC as well as their respective contributions to the improvement of these soil properties.The main results of the current study were as follows:(1)Effects on soil physical properties changes during maize growth period.The saturated hydraulic conductivity(Ks)values in S-HM,S-MM,LM,and S treatments increased significantly(P<0.05)by 115.50,61.00,51.32,and 15.25%respectively,compared to the CK treatment at 0-10 cm soil layer.During June to September period,a significant increase was observed in the Ks and total soil porosity due to S-MM and S-HM treatments from at surface(0-10 cm)and subsurface(10-20 cm)soil layers.The application of organic materials had a significant(P<0.05)effect on penetration resistance.In 0-10 cm soil layer,the penetration resistance showed low values with S-HM(2.07 MPa)and S-MM(2.1 MPa)treatments,while it showed high values with LM(3.12 MPa)compared to CK(2.96 MPa)treatment.Greatest soil bulk density was obtained in May and September for all organic materials additives and in July for CK treatment at both soil layers.(2)Effects on particle stability of aggregates in surface(0?10 cm)and subsurface(10?20 cm)soil layers.The soil aggregate-size distribution in 0-10 cm and 10-20 cm soil layers significantly(P<0.05)varied depending on the organic material additions and CK treatment.Microaggregates accounted for the majority of the aggregates(60%–68%)for all treatments in both the soil layers,followed by the silt+clay fraction(11%–25%).Compared with CK,the mass proportions of the microaggregate were higher in other treatments at both the soil layers.Long-term application of organic materials had significant(P<0.05)effects on the mean weight diameter(MWD).The highest MWD values of 0–10 cm layer was observed with S-HM,S-MM,LM,and S treatments(0.44,0.42,0.37,and 0.36 mm)compared to CK treatments,respectively.At both soil layers,it was at the highest values in July and September for all the treatments during the maize growth stages.The combined application of straw with different manure rates treatments had a significant effect on MWD than the S alone and CK treatments in 0-10 cm and 10-20 cm soil layer(P<0.05)and the MWD values in the subsurface layer were less than those in the surface layer with significant effects(P<0.05)among treatments.(3)Effects on soil organic carbon(SOC)content and reserves of soil aggregates during the maize growth stages.The SOC content significantly diverged among the application of organic materials and CK treatments with the range of 15.2 to 16.9 g C kg^-1soil at surface layer(0-10 cm)and between12.9 to 15.41 g C kg^-1 soil at subsurface layer(10-20 cm),respectively.Additionally,S and LM treatments slightly increased SOC content compared with CK treatment.The SOC contents in the different aggregate sizes of S-HM,S-MM,LM,and S treatments were higher than CK at both soil layers,except for the silt+clay fraction.Among the size of the different aggregates,the highest SOC contents were found in the microaggregates in both soil layers,with a range of 10–14 g C kg^-1 soil,which was significantly higher than that of the large macroaggregates,small macroaggregates,and the silt+clay fraction.The Fourier Transform Infrared Spectrometer(FTIR)data in bulk soil explained that Hydrophobic CH(A),and Hydrophilic C=O(B)functional groups,were higher in S-MM and S-HM treatments than that in CK treatments.Soil hydrophobicity(A:B ratio)was significantly increased by 10.85,13.57,and 23.28%for S,S-MM,and S-HM over the CK treatment.(4)Effects on soil pore structure in surface(0?10 cm)soil layer.The results showed that undisturbed topsoil from the application of organic materials had higher visible total porosity than the CK treatment.In the current study,results from X-ray CT proved that the combined application of organic materials led to a significant change in macroporosity(MP)and pore size distribution compared with the application of straw alone and CK treatment.The 575–100?m pores was dominated in all treatments.The effect of different organic material applications was primarily resulted in the increase in micropores<575?m,followed by pores ranging in size between 575–1125?m,and the macropores>1125?m.The Euler number(Ev),the mean diameter of macropores(MD),surface area(SA),and Fractal Dimension(FD)were significantly higher in the application of organic materials than the CK treatment.While the hydraulic radius(HR)was significantly lower in the application of organic materials than the CK treatment.These results indicate that the effectiveness of organic material applications for soil pore system development.(5)The results showed that soil bulk density,MWD,soil total porosity,soil penetration resistance,Ks,and soil infiltration rate were strongly influenced by SOC.A stronger linear relationship was observed between the SOC and the MWD,(R²=0.93,P<0.05)compared to that between total organic carbon and MWD which indicates the importance role of the SOC in improving soil aggregation relative to the effect of total organic carbon content.According to the principle component analysis,the application of organic materials had strong effects on soil carbon contents and soil physical properties.There was a significant positive correlation between SOC,Hydrophobic CH,Hydrophobic C=O functional group and porosity,pores in a range of 100–575?m,and 575–1125?m.While the hydrophobicity significantly correlated with the porosity and pore in the range 575–1125?m and>1125?m which related to soil water movement.The FD and MD were positively significant correlated with SOC,Hydrophobic CH and C=O functional group.While the HR was a significant negative correlation with SOC and(A:B ratio).Overall,the results from the long-term field experiment showed that the combined effect of straw with cattle manure at different rates can improve soil structure and SOC than individual addition of straw,manure and the Ck treatments.These findings advance our understanding of mechanisms of the impacts of application of organic material on soil physical properties and SOC in semi-arid soils to promote the developments of sustainable agriculture of the Loess Plateau of China.