The Effects Of Long-Term Different Ffertilization Regimes On Soil Organic Carbon And Active Organic Carbon Of Lou Soil

The soil organic carbon has significant effects on soil fertility and crop production, as well as the global carbon cycle. In this study, the dynamic changes of soil total organic carbon (SOC), active organic carbon (AOC) and soil organic carbon storages were investigated under two long-term experiments of different fertilization regimes and management on Lou soil. One long-term experiment included 11 treatments under irrigated winter wheat rotated with summer maize two crops per year and another one included 9 treatments under rainfed winter wheat rotated with summer fallow. The fertilization regimes involved were no any fertilizers input (CK), application of chemical fertilizers (N, NK, PK, NP and NPK), organic manure (M1, M2) and crop residue (S) combined with chemical fertilizers (M1NPK, M2NPK and SNPK), and soil management was setalide (no any fertilizers and no tillage) and fallow (no crop, no fertilizers, weed control and ploghed as crop plots). The main results are as follows:1. Different fertilization regimes increased both SOC and AOC contents in varying degrees relative to the control treatment under winter wheat-summer maize rotation system. The overall trend was?manure combined with chemical fertilizers > straw combined with chemical fertilizers > Setaside > balanced application of chemical fertilizers > inbalanced application of chemical fertilizers > CK > Fallow. Long-Term application of chemical fertilizer (NPK) significantly increased the total C content relative to CK in the top 10cm depth, but markedly reduced the total C content in the depth of 30-60cm. The treatment of SNPK significantly increased the total C content in plough layer (0-20cm), and the effect of M2NPK on the Total C content had reached further deeper layer (0-30cm). Different from the total C contents affected by treatments, the AOC was significantly influenced by different fertilizer management regimes in the whole profile tested (0- 60cm).2. Long-term different fertilization regimes did not significantly change distribution of dry-sieving aggregates, only had the tendency to increase percentage of dry-sieving aggregates bigger than 2 mm. The soil organic carbon content was higher in the smaller size of dry-sieving aggregates. There were significant differences of soil organic carbon contents at the same size of dry-sieving aggregates between treatments at 0-10 cm soil depth, no ?differences were observed at 10-20 cm soil depth. The partition of TOC in aggregate sizes of >7 mm and 1-3 mm under treatments of orgabic materials combined with NPK, and in aggregate size bigger than 10 mm under NPK were significantly enhanced on over CK at 0-10 cm soil depth, and no differences were detected for partition of TOC between treatments at 10-20 cm soil depth.3. In the rainfed condition, both SOC and AOC changed in varying degrees under fertilization treatments relative to CK. The mean TOC was in order as MNPK (11.55g·kg-1)> NPK (8.67g.kg-1)> Setaside( 8.60g.kg-1)> N( 7.74g.kg-1)> CK( 7.39g.kg-1)> Fallow( 6.96g.kg-1) and the mean AOC was MNPK( 4.15g.kg-1)> Setaside( 3.50g.kg-1)> NPK( 2.75g.kg-1)> N( 2.20g.kg-1)> CK( 2.11g.kg-1)> Fallow( 1.93g.kg-1). Long-Term application of NPK and MNPK significantly increased the total C content relative to CK in the top 20cm depth, no differences were observed at 20-100 cm soil depth.4. The amounts of soil organic carbon storage decreased with the increase of soil depth for both irrigated and rainfed conditions. The SOC storage under irrigated was greater than those under rainfed for the same treatment. In the 0-20 cm soil depth, SOC storage increased at 0.954t ha-1, 0.499t ha-1, 0.433t ha-1 and 0.034t ha-1 per year under treatments of MNPK, SNPK, NPK and CK, respectively, for irrigated condition, and at 0.683 t ha-1, -0.046 t ha-1, -0.243 t ha-1 per year under treatments of MNPK, NPK and CK, respectively, for rainfed condition. Under irrigation organic materials combined with NPK could significantly influence SOC storage in the tested 60 cm depth compared with CK, and NPK considerably affacted the top 30 cm soil depth. While under rainfed MNPK and NPK significantly influenced the SOC storage at the top 20cm soil depth only. The significant positive correlations were detected between yields of winter wheat and soil organic carbon storages at 0-10cm depth under irrigation and 0-20 cm depth under rainfed.All in all, balanced application NP or NPK and NPK combined with organic materials could significantly increased SOC contents over CK under both irrigated and rainfed cropping systems on Lou soil. The increased SOC contents were due to the increase of SOC in various sizes of aggregates under above treatments over CK. In addition, SOC levels at 0-20 cm soil depth were similar under NP or NPK or SNPK and under setalide during 19 years. In the irrigated condition, the SOC storage was markedly increased under NPK combined with organic materials compared with CK, furthermore SOC storage under CK showed the positive trend after 19 years. However, the SOC storage under NPK and CK showed negative trends in the rainfed condition.