| In order to explore the effect of different improved materials under different application methods and application amounts on soil improvement and growth effect of Amorpha fruticosa in 35° steep slope area of the Loess Area in West Shanxi,to screen out the best improvement effect of the mixed application of biochar and water retention agent.In this study,Amorpha fruticosa was used as the test plant,using three kinds of single application treatment(water retention agent,coconut shell biochar,bamboo biochar single application treatment)and two kinds of mixed application treatment(coconut shell biochar + water retention agent,bamboo biochar + water retention agent mixed application)Treatment),studied the effects of single or mixed application of different modified materials on the growth physiological indexes of Amorpha fruticosa and soil physical and chemical properties indexes,analyzed the relationship between the soil physical and chemical properties indexes and plant growth indexes,and principal component analysis was used to comprehensively evaluate the effects of single or mixed application of different improved materials on plant growth and soil improvemen.The main conclusions were as follows:(1)The effects of water-retaining agent and coconut shell biochar application on plant growth and soil improvement showed a trend of increasing first and then decreasing with the increase of application amount,while the single application of bamboo biochar showed a gradual increasing trend;the effect of mixed application of coconut shell biochar and water retention agent on plant growth and soil improvement showed a trend of increasing first and then decreasing with the increase of biochar application,and the mixed application of bamboo biochar and water retention agent showed a gradual increasing trend;the water-retaining agent,bamboo biochar,coconut shell biochar + water-retaining agent,bamboo biochar + water-retaining agent had the best plant growth promotion effect and soil improvement effect at S1T3(water retention agent 45g/plant),S3T4(bamboo biochar 45g/plant),M1T2(water retention agent 30g/plant + coconut shell biochar 300g/plant),M2T4(water retention agent 30g/plant + bamboo biochar 600g/plant)respectively;S2T3(coconut shell biochar 450g/plant)had the best effect on plant growth in the single application of coconut shell biochar,and S2T2(coconut shell biochar 300g/plant)had the best effect on soil improvement;M1T2 had the best plant growth promotion effect in all treatments,M2T4 has the best soil improvement effect in all treatments.(2)For the single application of biochar at the same application rate,in terms of plant growth,bamboo biochar and coconut shell biochar had no significant difference in the promotion of plant height,leaf and stem organic carbon content.Compared with bamboo biochar,coconut shell biochar was beneficial to increase plant water content,root organic carbon content,plant dry weight,and ground diameter.In terms of soil improvement,the effect of coconut shell biochar on soil improvement was better than bamboo biochar at lower application rates,but the opposite was true at higher application rates,mainly reflected in the changes of soil moisture content,capillary porosity,saturated water content and capillary moisture capacity(3)For the mixed application treatment with the same biochar application amount,the coconut shell biochar + water retention agent had better effect on promoting plant moisture content,plant height,root organic carbon content and plant dry weight than bamboo biochar + water retention agent at lower application amount,bamboo biochar + water retention agent is superior to coconut shell biochar + water retention agent in promoting the ground diameter,SPAD value,leaf and root organic carbon content,and plant dry weight at higher application rates.In terms of soil improvement,the effect of coconut shell biochar + water retention agent on soil improvement was better than bamboo biochar + water retention agent at lower application rates,but the opposite was true at higher application rates,mainly reflected in the changes of capillary porosity,saturated water content and capillary moisture capacity.(4)Adding water retention agent to biochar was beneficial to increase plant height,ground diameter,plant dry weight,plant moisture content,and leaf organic carbon content,but had little effect on SPAD value and root organic carbon content,and it would even decrease at higher biochar application rates;adding water retention agent to coconut shell biochar and bamboo biochar would have different effects on stem organic carbon content,the former was a promoting effect,and the latter was an inhibitory effect.(5)Adding water retention agent to biochar was beneficial to improve the soil water-holding capacity,especially at higher biochar application rate;adding water retention agent to coconut shell biochar had no significant effect on soil bulk density,while adding water retention agent to bamboo biochar with higher application amount had a significant effect on reducing soil bulk density;adding water-retaining agent to biochar was beneficial to increase the organic carbon content,especially the promotion effect of the surface soil organic carbon content was more significant.(6)Redundancy analysis showed that the total explanation degree of soil physical and chemical properties for plant growth was 50.6%,and the soil saturated water content of 20-40 cm soil layer had the largest explanation degree for the growth physiological index of Amorpha fruticosa,which is 26.71%;compared with the soil physical and chemical properties of the 0?20cm soil layer,the 20-40 cm soil layer had a greater impact on plant growth.Therefore,we should pay attention to the improvement of deep soil in afforestation on steep slopes.In summary,choosing M1T2 or M2T4 can have a better effect on plant growth and soil improvement in the process of afforestation on steep slopes. |
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