| In the farmland ecosystem, management practices such as tillage and organic matter input directly affect the variation trend of soil physical and chemical properties and crop growth. The effects of management practices on global carbon balance, soil quality, crop yield, and water use efficiency became a global concern in recent years.This study included three different experiments: First part, a field experiment began in 2002, and the site is part of an irrigation area managed by Northwest A&F University in the southern part of the Loess Plateau. Six conservation tillage treatments were applied by different combinations of rotary tillage(RT), sub-soiling(SS), and no-till(NT), with or without finely-chopped straw retention. Conventional tillage(CT) acted as the control.Second part, we elucidated the short-term effects of wheat-burned biochar(BC) versus straw application on soil aggregation, organic carbon(C) sequestration, enzyme activity, organic carbon functional groups and wheat growth. In 2014, a 9-month pot experiment was established by growing winter wheat in silty clay loam soil. Two types of exogenous C were applied at equal rates: 1%, 3% and 10% in straw treatments(Str1.0, Str3.0 and Str10.0, respectively) and 0.8%, 2.4% and 8% in BC treatments(BC0.8, BC2.4 and BC8.0, respectively). No-C application treatment(CK) was used as the control.Third part, a 210 d laboratory culture experiment was conducted to study the influence of BC versus straw application on soil organic carbon mineralization. The treatments in this experiment part were similar to the pot experiment. In this study, the results showed as follows:(1) Effects of different conservation tillage practices on soil physical and chemical properties and crop growth in Lou soil in Guanzhong Plain. Sub-soiling plus straw retention effectively maintained or improved soil structural stability and soil productivity, and is recommended for tillage management in the study area.1 Soil bulk densities increased by 11.3% and 12.9% in 0-10 and 10-20 cm in NT plus straw applied treatment, and increased by 16.5% and 16.9% in NT without straw applied treatment compared with control. Soil bulk density in NT treatment was non-significant when compared with CK in 20-30 cm soil. Soil bulk density in SS and RT tillage practices was non-significant compared with CK in 0-10, 10-20, and 20-30 cm soil layers.2 Effects of different tillage practices on WSA distribution. The effects of tillage on WSA distribution mainly attributed to the pedoturbation of each tillage management. Effects of subsoiling on soil structure were mainly observed in 10-20 cm soil depth. SS increased the content of WSA 0.25-2 mm fraction compared with the control.Effects of RT on soil structure were mainly observed in 10 cm soil depth. The content of WSA 0.25-2 mm decreased by 6% in RT compared with the control, and the decrease was greater in the deeper soil depth. Effects of NT on soil structure were mainly observed in the 0-10 cm surface soil. The proportion of water-stable aggregates(WSA) < 0.05 mm was 18% less while that for WSA > 2 mm was 98% more under NT treatments compared with CT.3 Effects of different tillage practices on SOC stocks. The results indicated that SOC stocks increased under SS, RT, and NT(by 15% on average) relative to CT. Soil POC content was increased by 36.9% in SS+straw tillage practice, by 30% in RT+straw, and by 27% in NT+straw. The contents of POM-OOC and WSA-OOC were increased by 25%-36% in SS and RT tillage practices. The content of POM-OOC was not significant in RT compared with the control. The content of POM-AOC was decreased with the soil depth. In surface soil, POM-AOC contents were inceased by 30% in SS and RT on average. The POM-AOC content was determined by straw application in the NT treatment.4 Effects of different tillage practices on crop yield and water use efficiency. Grain yield(wheat + maize) showed similar increasing trends in all the tillage treatments compared with CT. Comparing with CT, all conservation tillage increased water use efficiency, especially in SS with straw return treatment which increased water use efficiency by 16.4%. Average water use efficiency increased by 10.5% and 7.9% in RT and NT treatments. Comparing with non-straw applied treatments, straw treatments had greater water use efficiency.(2) Effects of different exogenous carbon inputs on soil structure and organic carbon activity in Lou soil. Moderately soil BC amendment(2.4%) is beneficial to soil structure improvement and an effective way for the harmless disposal of excess plant residues in the Guanzhong Plain, Northwest China.1 Effects of different exogenous carbon inputs on WSA distribution. The proportion of macroaggregates(> 0.25 mm) was increased by 16.9% in BC2.4 and 45.8% in BC8.0. The effect of biochar application on soil macroaggregates(> 0.25 mm) was greater than on microaggregates. Straw application mainly increased the content of WSA > 2 mm fraction. Compared with the control, WSA > 2 mm fractions were increased by 65.1%, 136%, and 208% in Str1.0, Str3.0, and Str10.0 respectively.2 Effects of different exogenous carbon inputs on soil organic carbon. Soil organic C was increased by 13.2-155.1% on average in the BC treatments when compared with CK(BC0.8 < BC2.4 < BC8.0). A small quantity of BC(0.8% and 2.4%) increased microbial biomass C content but decreased dissolved organic C content, while a large quantity of BC(8%) had the reverse effects. In straw applied treatments, SOC contents were increased by 8.6%-68.6%(Str1.0 < Str3.0 < Str10.0). The content of DOC was increased with the amount of straw application. In different crop growth stages, DOC contents were increased by 21.7%-411% in straw applied treatments compared with CK.(3) Effects of different exogenous carbon inputs on soil enzymatic activity and enzyme dynamics in Lou soil.1 Soil urease activity was inhibited with crop growth in biochar treatments. In crop flowering stage, soil urease activity were decreased by 29.2%, 27.8% and 32.8% in BC0.8, BC2.4 and BC8.0 respectively, when compared with CK. In straw applied treatments, soil urease activities were increased by 26.0%-190.3% during different wheat growth stages.2 Soil invertase activity was increased by 6.9%-32.8% in biochar applied treatments. However, soil invertase activity was decreased by 6.7% in BC8.0 treatment. Soil invertase activity was determined by the degradation degree in straw treatments, and invertase activity was increased with straw degradation. In stem elongation stage, soil invertase activity was increased by 33.5% in Str3.0, while decreased by 21.8% and 25.9% in Str10.0 and Str1.0. In flowering stage, soil invertase activity increased by 10.0% in Str10.0, but decreased by 3.7% and 4.5% in Str1.0 and Str3.0.3 Soil catalase activity was inhibited with the amount of biochar application. In straw treatments, catalase activity was first increased then decreased with crop growth. Compared with CK, soil catalase activity was decreased by 4.0%-11.6% in biochar treatments. In straw treatments, catalase activity was increased by 5.6%, 7.3% and 8.9% in leaf development stage, but decreased by 5.5%, 3.8% and 3.1% in flowing stage.4 Biochar application increased the affinity between urease and the substrate. The potential capacity of urease was also increased in biochar treatment. The affinity between urease and substrate was biggest in Str3.0 among all treatments. Application of biochar or straw both increased the affinity between urease and the substrate.(4) Effects of different exogenous carbon inputs on soil organic carbon functional groups in Lou soil.Biochar or straw application both changed the chemical stability of soil organic carbon. Biochar was the source of aromatic C, aromatic amino, aromatic ketone and esters in soil. Straw was the main source of olefin C and polysaccharide-C in soil.(5) Effects of different exogenous carbon inputs on soil organic carbon mineralization in Lou soil.With the same carbon input amount condition, straw significantly increased the liberation accumulation amount of CO2 compared with biochar. Appropriate amount of biochar application(0.8% and 2.4%) decreased the liberation accumulation amount of CO2, but significantly increased of CO2 liberation was observed in the excess biochar application(8.0%) treatment. After 210 d soil culture, CO2 liberation were changed by-5.04%,-8.08% and 26.19% in BC0.8, BC2.4 and BC8.0, respectively.Compared with the control, the liberation accumulation amount of CO2 were increased by 139.50%, 378.22% and 631.03% in Str 1.0, Str3.0 and Str10.0, respectively.(6) Effects of different exogenous carbon inputs on crop growth in Lou soil.1 Effects of different exogenous carbon inputs on crop photosynthesis and transpiration. Crop photosynthesis and transpiration were increased with crop growth in BC applied treatments. Crop net photosynthetic rates were increased by 44.9%, 66.1%, and 53.9% in BC0.8, BC2.4, and BC8.0 respectively compared with CK. Excess BC application(8.0%) led to a waste of BC resources. Crop transpiration rates were increased by 9.6% and 21.3% in BC0.8 and BC2.4 treatments compared with CK in wheat flowering stage, while decreased by 27.3% in BC8.0. Straw applied at 1.0% and 3.0% rateas improved the photosynthesis of wheat, while restrained crop growth at the 10.0% application rate.2 Effects of different exogenous carbon inputs on crop yield. Biochar application increased the growth and yield of wheat, while restrained in the excess biochar application treatment. The transpiration rate was increased by 9.6% and 21.3% in BC0.8 and BC2.4, while decreased by 27.3% in BC8.0 treatment. Straw also restrained the crop growth when applied at 3% and 10% rate. Crop yield was significantly increased by 6.0% in Str1, while significantly decreased by 37.3% and 90.1% in Str3 and Str10.(7) Correlation analysis between soil structure, organic carbon, and biological indicators in tillage and exogenous carbon applied conditions.1 Correlation analysis results of different tillage practices showed that, the increase of POC improved the formation of soil macroaggregates. Compared with POC and OOC, POM-AOC was more sensitive when assessing the effects of tillage practices on soil physicochemical property.A significant correlation was found between the content of POC and the proportion of WSA 0.25-2 mm. The content of POM-AOC was significantly correlated with those of POC and WSA-AOC in the <0.05 mm fraction.2 Correlation analysis results of different exogenous carbon applied treatments showed that, in biochar applied treatments, the increases of soil macroaggregates formation and active organic carbon stock were attributed to the improvement of urease and catalase activity. The growth of crop was significantly affected by soil invertase activity. Soil urease and catalase activity were significantly correlated with macroaggregates fractions. The photosynthetic rate, chlorophyll and crop yield were negatively correlated with the urease and catalase activity.In straw applied treatments, the formation of WSA > 2mm fraction was improved, and active organic carbon was tightly wrapped in those sized aggregates. The competition of N between microorganism and crop growth impeded the biomass accumulation of wheat. In straw treatments, MBC and DOC content was only significantly correlated with the WSA > 2 mm fraction. The photosynthetic rate, chlorophyll and crop yield were negatively correlated with the urease. |
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