Effects Of Tillage Practices And Straw Returned To The Field On Labile Organic Carbon Fractions

This study was carried out at the Junchuan and Huaqiao town in Hubei Province of China from2011to2012, take rice-wheat rotation system as the object, the experiment is a split-plot design and randomized complete block, the main plot is tillage practices (plough tillage (PT) and no-tillage (NT)) and straw returning level (5250kg/hm2(SR3),3500kg/hm2(SR2),1750kg/hm2(SR1) and0kg/hm2(SRo) as the sub-plot treatment, conducted to study the effects of tillage practices and wheat-straw returned to the field on soil liable organic carbon (LOC), microbial diversity and rice grain yield. The main results are summarized follows:1. The amount of aggregates2-1mm and1-0.25mm was the largest in clay loam soil and sandy loam soil. The NT increased the content of0.25-0.053mm aggregate14%-23%but reduced the content of2-1mm aggregate7%-11%i n the0-5cm layer for clay loam soil. For sandy loam soil, NT increased the content of1-0.25mm aggregate2%-13%but reduced the amount of0.25-0.053mm aggregate25%-48%in the5-10cm layer. That indicated NT benefit the formation of macro-aggregates for clay loam soil, but promoted the accumulation of big aggregates for sandy loam soil.2.Compared with PT, the NT decreased TOC content in2-1mm aggregate8%-14%and increased TOC content in<0.053mm aggregate6%-18%for clay loam soil, straw returned increased TOC content in2-lmm aggregate0.2%-16%in the0-5cm for clay loam soil. The tillage practices and straw returned had no significant effects on TOC distribution of soil aggregates. For the clay loam soil, TOC is enrichment in0.25-0.053mm and1-0.25mm aggregates mainly. In the sandy loam soil, TOC is enrichment in0.25-0.053mm and2-1mm aggregates mainly.3. Compared with PT, the NT treatment decreased the TOC, EOC, MBC content5%-21%,7%-43%and10%-46%respectively in the10-20cm layer and DOC content23%-36%in the5-10cm of sandy loam soil, increased the MBC content2%-37%in the0-5cm layer and TOC content11%-32%in the5-10cm, but decreased DOC content33%-67%in the5-20cm layer of clay loam soil. The SR had no significant effects on EOC and MBC content of two soil types, but increased DOC content in the5-20cm layer of clay loam soil and5-10cm layer of sandy loam soil17%-59%,29%-42%respectively. For clay loam soil, the contents of the fractions of EOC is fraction Ⅱ> fractionⅢ> fraction Ⅰ.The amount of5250kg/hm2straw returned treatment increased fraction I content14%-18%in0-5cm layer, NT treatment reduced fraction I content15%-19%in5-10cm layer. For sandy loam soil, the contents of the fractions of EOC is fractionⅢ> fraction II> fraction I.The NT treatment reduced fraction Ⅱcontent23%-43%in10-20cm layer. Soil TOC significantly positive correlated with MBC, indicating that MBC can be used as an ideal indicator to assess the soil carbon balance and soil fertility.4. The NT treatment reduced6%-44%of CPMI in the10-20cm of sandy loam soil and0.7%-22%of AI in the5-10cm layer of clay loam soil, increased5%-9%of AI in the5-10cm layer of sandy loam soil. For the0-5cm layer, the CPMI is higher significantly in clay loam soil compared with sandy loam soil. But in the10-20cm layer, the result is opposite.5. The SR treatment increased the microbial diversity significantly in the surface layer (0-5cm) for clay loam soil, the main two principal components explained55.95%of the total variance. The NT treatment increased the microbial diversity in the surface layer (0-5cm) for sandy loam soil, the main two principal components explained64.23%of the total variance. All the microbial indexes were highly expressed in the first principal component, the soil quality expressed in the second principal component. Under NT treatment, soil microbial diversity of straw returned was significantly difference compared with no straw returned for clay loam soil, soil microbial diversity of the amount of5250kg/hm2straw returned was significantly difference compared with no straw returned.6. The amount of3500kg/hm2and1750kg/hm2straw returned increased rice grain yield15%-35%,2%-28%respectively for the sandy soil and clay loam soil. The tillage had no significant effects on rice grain yield. Correlation analysis showed that rice grain yield had a significantly positive correlation with EOC, significantly negative correlation with DOC, revealed that EOC and DOC is active organic carbon that more sensitive to the changes of tillage practices and straw returned, closely associated with crop growth.