Effect Of Long-term Fertilization On Soil Aggregation And Aggregate Associated Carbon And Nitrogen On Lou Soil

Soil aggregates play an important role in soil structure. It also had great influence in the protection of soil organic carbon and sustaining and supplying of nutrient elements. This study investigated the effects of soil different fertilization on the distribution of aggregate associated carbon and nitrogen based on the 21-year long-term experiment on Lou soil in Guanzhong Plain, Shaanxi province, China. The wheat-maize cropping system was combined with the following nutrient management treatments: control(CK, no nutrient input), nitrogen only(N), nitrogen and potassium(NK), phosphorus and potassium(PK), NP, NPK, straw plus NPK(SNPK) and two levels of manure plus NPK(M1NPK and M2NPK). The main results obtained are as follows:1. Long-term fertilization had significantly affected the distribution of dry aggregates at the surface(0-10 cm) and water stable aggregates at 0-30 cm soil layers. Generally, various fertilization regimes increased the proportion of >2 mm dry aggregates and decreased the proportion of < 2 mm dry aggregates compared with the control. The various fertilization regimes decreased the proportion of > 1 mm water stable aggregates and increased the proportion of 0.25-1 mm water stable aggregates compared with the control. Long-term fertilization affect the aggregate stability on Lou soil. Application of high rate of organic manure significantly increased soil aggregate stability on Lou soil.2. Long-term fertilization had significantly affected the distribution of organic carbon and nitrogen in dry aggregates in all soil layers. Generally, The SOC contents in dry aggregates were higher in the NK,NP, NPK, SNPK, M1 NPK and M2 NPK treatments than in the CK at all soil layers. The nitrogen contents in dry aggregates were higher in the NP, NPK, SNPK, M1 NPK and M2 NPK treatments than in the CK at surface and subsurface soil layers, the nitrogen contents in aggregates of the 20-30 cm soil layer had no an obvious trend over the control. The various fertilization regimes increased the allocation proportions of SOC and nitrogen in >2 mm aggregates and decreased the allocation proportions of SOC and nitrogen in < 2 mm aggregates compared with the control. There were no significant effects on the allocation proportions of SOC and nitrogen in the long-term fertilization treatments compared with the control treatment in the 10~30 cm soil depth.3. Long-term fertilization had significantly affected the distribution of organic carbon and nitrogen in water stable aggregates in the all soil layers. Generally, compared with the control, the SOC and nitrogen contents in all aggregates, especially in marcoaggregates, in the NP, NPK, SNPK, M1 NPK and M2 NPK treatments were increased. The allocation proportions of SOC and nitrogen in >1 mm aggregates were decreased, but the allocation proportions of SOC and nitrogen in 0.25-1 mm aggregates were increased in the long-term balanced fertilizer treatments than in the control. The allocation proportions of SOC and nitrogen in other aggregate had similar number between treatments.In conclusions, long-term fertilization significantly influenced the distribution of aggregates as well as aggregate stability, increased the content of SOC and nitrogen in all aggregates, and promoted the accumulation of SOC and nitrogen in 0.25-1 mm aggregates on Lou soil under wheat-miaze cropping system.