| The Huang-Huai-Hai area is an important commercial grain production base and pig breeding base in China,where anaerobic fermentation is one main way of livestock manure treatment,and the large amount of manure and urine resources produced great potential for organic fertilizers production.The integrated application of the biogas slurry in the crop-livestock system?ICLSs?plays an important role in improving soil fertility and structure as it can reduce the dependence on chemical fertilizers and risk from manure pollution.However,the effect of biogas slurry application on the chemical and physical properties of the salinized fluvo-aquic soil of this region is unclear.It is urgent to study the biogas slurry application and its improvement of soil fertility and soil structure in the saline-alkali land areas in the context of the regional salinization control,food security,and green agricultural development.In this study,the salinized fluvo-aquic soil in Shandong province was studied.The stability of soil aggregates was evaluated using wet sieve method.The soil pore structure was analyzed using X-ray scans combined with image analysis.Using the principal component analysis,the soil structure stability on different levels was evaluated.And key factors affecting the soil structure stability were screened using factor sensitivity analysis.This work tried to provide a theoretical reference to the physical and chemical improvement of the soil in the saline-alkali area,and the rational application of the biogas slurry technology system.The main results are as follows:?1?The 4-year biogas slurry application had significantly increased the content of large aggregates in the 0-40 cm soil layer and thus improved the aggregates stability.In terms of the size characteristics,the soil aggregates of CK,BS1,BS3,and BS4 were mainly 1-0.053 mm in diameter throughout the soil profile.The 4-year application significantly promoted the soil aggregate conversion of<0.053 mm and0.25-0.053 mm soil aggregates into>2 and 2-1 mm aggregates in the 0-40 cm soil layer.The soil aggregates stability evaluation showed that the 4-year biogas slurry application increased MWD value in the 0-40 cm layer,which improved the aggregates stability.?2?The results of CT scan revealed that the continuous biogas slurry application improved the anisotropy,the fractal dimension and the connectivity of soil pore.The results of visual analysis showed that regular pore like the round and oval pores increased significantly,the larger pore proportion increased dramatically,and the distribution of the pores tended to be even as the years of biogas slurry irrigation increased.The quantified analysis using image software of the soil pores in CK,BS1,BS3,and BS4 showed that BS4 significantly increased the DA,tDA,the connectivity and fractal dimension of pores compared with CK?P<0.05?.Especially,fractal dimension of pores increased significantly with the increase of the biogas slurry application years.Soil developed into a looser and more connected complex of porous structure,which is conducive to the conservation and supply of water and fertilizer,thereby improving soil fertility and quality.?3?Continuous biogas slurry application changed the characteristics of soil pores distribution,increasing the number of soil macro-pores,and improved the fractal dimension and anisotropy of pores.In terms of the size,soil pores of CK,BS1,BS3,and BS4 were mainly>2000 um in diameter,accounting for 4.0%,7.02%,9.07%,and 9.12%,respectively.What's more,compared with CK,BS4significantly increased the number of the macro-pores>2000 um.The morphology of pores was studied by image analysis technique and the results showed that the pore connectivity per unit volume of pore<1000 um in CK?BS1?BS3?BS4 were all negative,but it increased with the pore size.The continuous4-year biogas slurry application increased the fractal dimensions and anistropy,the connectivity of pores<1000 um compared with CK.This indicated that the pore system was getting more connected,good in nutrients and water conservation and supply,i.e.,hence improving soil fertility and quality.?4?The four principal components that affected soil structural stability and a comprehensive model for soil structure stability were determined.The principal component 1?PC1?represented soil mechanical and fertility characteristics,with a variance contribution of 49.2%.PC2 represented aggregate stability and soil pore,with a variance contribution of 19.3%.PC3 represented the basic physical properties of the soil,with a variance contribution of 11.5%.PC4 was pH,with a variance contribution of 9.2%.The comprehensive principle component PC0 was calculated as:PC0=0.552PC1+0.216PC2+0.129PC3+0.103PC4.The soil structural stability indexes of the four treatments were calculated based on PC0 to be within the range from-10.49 to 92.67.The soil structure stability of each soil layer of four treatments were classified using cluster analysis into 3 grades:class??58.28?96.27?,class???23.90?58.28?,class????-10.49?23.90?.?5?Based on the factors sensitivity analysis,15 factors that characterize soil structure stability were selected.They are indicators of soil fertility,?ammonium nitrogen,nitrate nitrogen,total nitrogen,total phosphorus,organic carbon,and cation exchange capacity?,indicators of aggregate stability(GMD,MWD,R0.25),indicators of soil mechanical characteristics?penetration resistance,shear strength,soil compactness?,and soil pore structure indicators?DA,CP,total soil porosity?.This study has important theoretical and practical value in clarifying how biogas slurry application affects the basic physical and chemical properties of the salinized fluvo-aquic soil,revealing the micro-physical mechanism of soil structure improvement by biogas slurry application,assessing the impact of biogas slurry application on soil structure stability,and promoting the sustainable development of ICLSs. |
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