Effect Of Organic Materials Returning Depth On Soil Carbon And Nitrogen Conversion

Tillage and fertilization directly influence soil structure and fertility,further affecting the availability and efficient use of soil nutrient.The effect of tillage modes and fertilization on soil properties were explored on the Fluvo-aquic soil with wheat-maize rotation in Northern Henan province.The indoor incubation experiment was carried out based on two tillage modes:(1)continue rotary tillage(RT-RT-RT),(2)deep tillage-rotary tillage-rotary tillage(DT-RT-RT)with three years cycle.The soil was sampled with 10 cm interval in the 0-30 cm soil layers and mixed with five fertilizations:(1)no fertilizer(CK),(2)chemical fertilizer alone(NPK),(3)chemical fertilizer with straw(NPKS),(4)chemical fertilizer with organic fertilizer(NPKM),(5)chemical fertilizer with straw and organic fertilizer(NPKSM).Then,all the treatments were incubation in one year.The characteristics of changes in soil respiration,soil enzyme activity,soil nutrient content and soil aggregates distribution were measured and analyzed.The main results were as follows:(1)The soil CO2 emission rate showed a trend of increasing then decreasing and gradually stabilizing as the incubation progressed during the incubation period of 0-90 d.The cumulative CO2 emission gradually increased with the incubation time.The soil CO2 emission rate,cumulative emission and cumulative priming effect were significantly enhanced by incorporating straw and organic fertilizer.The cumulative CO2 emission and cumulative priming effects were the highest in both tillage RT-RT-RT and DT-RT-RT.The cumulative emission was 1548 mg·kg-1 and 1745 mg·kg-1,respectively,and the cumulative priming effects were 2471% and 3638%,respectively.The soil carbon potential mineralization amount and mineralization rate constants under NPKSM were increased compared with CK.Straw and manure input increased soil microbial biomass carbon and nitrogen,dissolved organic carbon and nitrogen content,and promoted β-1,4-glucosidase,β-1,4-N-acetylglucosaminidase and neutral phosphatase enzyme activities by 2.35%,9.36%,and 5.67%,respectively.Meanwhile,RT-RT-RT and DT-RT-RT improved soil multifunctionality indexes in 0-10 cm and 20-30 cm,respectively.(2)Soil nutrient content decreased with soil depth increasing at 90 d,180 d and 360 d.RT-RT-RT and DT-RT-RT increased soil nutrient content in 0-10 cm and 20-30 cm,respectively.Compared to CK,NPKM and NPKSM increased the organic matter content by on average 11.52% and 17.50%,respectively.Manure input increased the soil total nitrogen and phosphorus content with an average increase of 20.99% and 48.32%,respectively,compared with CK.The readily oxidizable organic carbon(ROC)increased by an average of 8.31% and 21.09% under NPKM and NPKSM.Soil alkaline nitrogen and available phosphorus contents were 55.70 mg·kg-1 and 64.26 mg·kg-1 under the treatments with manure,respectively.,Soil total phosphorus,alkaline nitrogen,and state nitrogen showed a gradual decrease during the incubation period,ranging from 11.08%-75.89%,31.75%-60.09%,and 51.76%-86.38%,respectively.Soil available phosphorous content at 360 d was on average 3.50% lower than at 90 d.The soil C : N ratio,C : P ratio,N : P ratio and ROC : SOC were 4.82-9.79,3.39-29.93,0.60-2.78 and 6.26%-48.78%,respectively.The C : N,N : P and ROC : SOC reduced under the treatments with straw or manure.,Soil C : N ratio and C : P ratio showed a decreasing trend followed by an increasing trend with incubation,and soil N : P ratio gradually increased with the incubation.(3)Soil aggregate percentages under RT-RT-RT and DT-RT-RT ordered as >0.25 mm,0.053-0.25 mm,and <0.053 mm with values of 60.33%,32.54% and 7.13%,respectively.Compared with RT-RT-RT,DT-RT-RT improved soil aggregate mean weight diameter(MWD)and geometric mean diameter(GMD)by 10.06% and 55.41%,with stronger aggregate stability.Soil aggregate organic carbon content ordered as: <0.053 mm,>0.25 mm,and 0.053-0.25 mm with values of 8.12 g·kg-1,7.63 g·kg-1 and 6.04 g·kg-1.RT-RT-RT and DT-RT-RT benefited soil aggregate organic carbon in the 0-10 cm and 20-30 cm,respectively,with an average increase of 40.23% and 32.28%,respectively.The soil aggregates organic carbon content was significantly positively correlated with the total soil organic carbon both in 0-10 cm and 20-30 cm,and manure input was beneficial to increase the soil aggregates organic carbon content.In conclusion,the soil CO2 cumulative emission was significantly increased with organic fertilizer application.DT-RT-RT showed a higher cumulative priming effect than RT-RT-RT.NPKSM significantly increased soil enzyme activity,and the content of carbon,nitrogen and phosphorus.In 0-10 cm and 20-30 cm,soil multifunctional index was increased by RT-RT-RT and DT-RT-RT,respectively.Soil aggregate stability was increased under DT-RT-RT than that under RT-RT-RT.Soil aggregate organic carbon and soil organic carbon were influenced significantly by organic materials.