Effect Of Organic Materials Returning Depth On Organic Carbon Conversion In Fluvo-Aquic Soil In Northern Henan Province

Soil organic matter(carbon,SOC)is the important index for soil fertility.Tillage and organic material input are directly affected the SOC conversion.Henan province is the main area for grain production,the mono-rotation tillage is the main tillage mode while straw and manure are applied to the surface layer in this area.Which lead to the negative effect on SOC and soil quality.Therefore,the in-suit field cultivation experiment was carried out to explore the effects of tillage mode combined with organic material applied depth on the characteristics of the SOC components and contents,soil enzyme activity,the soil aggregate distribution and the spectrum of SOC.The results would suggest the reasonable tillage pattern and suitable organic material and soil depth in the northern of Henan province.Based on the results of the experiment from year 2016 to 2019,three typical tillage patterns as rotary tillage-rotary tillage-rotary tillage(RT-RT-RT),deep tillage-rotary tillage-rotary tillage(DT-RT-RT)and deep tillage-shallow rotary tillage-shallow rotary tillage(DT-SRT-SRT)were chosen.Three fertilizer treatments of fertilizer only(NPK),NPK combined with straw(NPKS),and NPKS combined with manure(NPKMS)were applied with three soil depth(0-10,10-20 and 20-30 cm)were set.Destructive sampling was done to collect the detailed data on 90,180 and 360 d.The soil physical,chemical and biological properties were measured and analyzed.The main results as follows:1)Compared with RT-RT-RT,the content and proportion of different organic carbon,the carbon pool management index(CPMI)and soil enzyme activity at 0-30 cm soil depths were changed under DT-RT-RT and DT-SRT-SRT.Compared with NPK treatment,the content of SOC,readily oxidized carbon(ROC)and the ROC proportion in SOC were increased under different soil depths.The content of SOC and ROC were increased by 51.8% and 34.6% in the NPKMS treatment at 0-10 cm soil layer,respectively.The labile SOC component and content and the percentage of non-labile organic carbon were decreased under NPKS and NPKMS treatment.The CPMI was increased at 0-20 cm soil depth,the increment was between 1.92% and137.37% under NPKS and NPKMS treatment.The maximum CPMI was up to 237.37 in the NPKMS treatment which returned to 10-20 cm soil layer under RT-RT-RT.The activity of soil sucrose(SC),cellobiase(CB)and β-D-Glucosidase(β-BG)were improved under NPKS and NPKMS treatment.2)Compared with RT-RT-RT,under DT-RT-RT and DT-SRT-SRT treatment,the percentage of < 0.053 mm aggregate and the value of fractal dimension(D)of soil aggregate was increased,while the SOC content of aggregate,the value of mean weight diameter(MWD),geometric mean diameter(GMD)and the proportion of those more than 0.25 mm aggregate(R0.25)were decreased.Which meant that the stability of aggregate structure was decreased.Compared with NPK treatment,the percentage of micro-aggregate,silt and clay aggregate were increased under NPKS and NPKMS treatment with the highest increment as 13.2% and 17.0%,respectively.The SOC content in < 0.053 mm aggregate was increased under NPKS and NPKMS treatment with the increment as 0.26-9.65 g·kg-1.The value of MWD,GMD,and R0.25 were increased while the D of soil aggregate were decreased under NPKS and NPKMS treatment.3)Compared with RT-RT-RT,the humification degree and the molecular weight and polymerization degree of dissolved organic carbon(DOC)under DT-RT-RT and DT-SRT-SRT were decreased.Compared to NPK treatment,the structure of SOC trended more stable under NPKS and NPKMS treatment.The humification degree and the molecular weight and polymerization degree of DOC were increased by1.3%-3.8% and 2.0%-22.2% under NPKS and NPKMS treatment,respectively.Meanwhile,the C-O chemical bond structure which belongs to polysaccharide of SOC were increased under these two treatments.In conclusion,the content of SOC and labile organic carbon,the CPMI and soil enzyme activities at 0-10 cm soil layer under NPKS and NPKMS treatments were increased.Furthermore,the distribution and stability of soil aggregate were improved under these two treatments.The NPKMS with DT-SRT-SRT rotation tillage pattern was beneficial to improve soil physical properties,SOC turnover and accumulation.Therefore,it was suggested as the optimum management in this area.