| Soil aggregate is the material base of soil structure and the important carrier of soil fertility, whose composition and stability are affected by both biotic and abiotic factors. Long-term applications of organic manure and chemical fertilizers could influence the composition and distribution of soil aggregates in different extents, and also change the habitat for soil biota, then affect the distribution and availability of soil nutrients. This experiment was based on the long-term fertilizing experiment of brown earth in Shenyang Agricultural University (26 years). The treatments of CK, inorganic N fertilizer only (NF), manure fertilizer only (MF), and manure plus N inorganic fertilizer (MNF) were chosen. Bulk soils of each treatments were sampled at the beginning and the end of the growing season, and were separated into four different size aggregates (>2 mm,1～2 mm,0.25～1 mm and<0.25 mm) by dry sieving. The study was aimed to know the effects of different long-term fertilizing on the compositions of soil aggregates and on the distribution of SOC and total nutrients, available nutrients, soil pH and cation exchange capacity among the aggregates. Based on these results, we could also find the relationship among aggregates decompositions, the storages of soil nutrients in each aggregates, and the aggregate stability indexes. The results were as follows:(1) The aggregates under different treatments was all dominated by the size of 0.25～1 mm. The treatments of MF and MNF increased the ratio of macro-aggregate (>0.25 mm), thus improved aggregate stability (MWD and GMD) and soil structure, but the NF treatment increased the ratio of micro-aggregates (<0.25 mm), decreased soil aggregating degree.(2) The treatments with organic matter (MF and MNF) increased the contents of soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP) and total potassium (TK) in all sizes of aggregate, especially in macro-aggregate. In addition, the macro-aggregate had the highest storage of total carbon, nitrogen, phosphorus and potassium.(3) Compared with CK and NF treatments, the treatments of MF and MNF had higher available soil nutrients in each size of aggregate. The content of available nitrogen reduced with the increase of aggregate size, while available phosphorus kept the same, and the available potassium increased. Compared to the control treatment (CK), MF and MNF treatments increased soil cation exchange capacity (CEC) in all sizes of aggregate, while NF treatments decreased them. The results showed that there was no significant difference between different size of soil aggregates under a given treatment (P>0.05).(4) The proportion of>2 mm size aggregate showed significant positive correlations with the storage of SOC, TN, TP in soil aggregates (P<0.05), and the same relationship also happened between the proportion of>2 mm aggregate (P<0.05), as well as 1～2 mm aggregate (P<0.01), and the mean weight diameter (MWD), geometric mean diameter (GMD). As a result, the application of organic fertilizer in Brown earth plays an important role to improve soil structure and increase soil fertility. |
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