| In this research, taking eroded red soil of Xianning City, Hubei Province as experimental material, six treatments control (CK), PAM (C1), straw mulch (C2), contour hedgerow (C3), PAM+contour hedgerow (C4) and straw mulch+contour hedgerow (C5) were set in field test, and samples of topsoil were collected before planting peanut (A) and after harvesting of peanut (B) and wheat (C) respectively. Combining with soil incubation experiment, the changes of soil fertility, aggregates distribution and stability of different restoration measures were studied, as well as the distribution of organic matter (OM) in water stable aggregates of various sizes, aggregate interiors and exteriors. It was expected to study the effects of different measures on improving red soil fertility and soil structure in order to provide theoretical basis for the reconstruction of eroded red with degradated structure. The results showed that:1. In field test, both pH and cation exchange capacity (CEC) in all treatments (except C2) were higher than those of CK in B period, indicating that soil buffer capacity was strengthened and soil pH of all treatments decreased slowly relative to CK. Compared with A period, the content of total nitrogen and total phosphorus in B period were increased by 50%,56% respectively.The order of soil OM content in different periods of field test was B>C>A, and OM content of C2 treatment increased significantly by 20.63% in contrast to CK during C period, but there was no significant difference between other treatments. In soil incubation experiment, OM content of the treatment with 3.2 g kg-1 straw mulch (D1) significantly grew up to 8.13 g kg-1 compared with control (CK), while no significant differences were observed between other treatments.The content of soil available nitrogen in field test increased gradually from A period to C period, while the order of available phosphorus and available potassium were B>C>A. C4 treatment had the highest percentage of soil available nitrogen in either B period or C period. Besides, available potassium content of C2 and C5 treatment in C stage were significantly higher than that of CK, and its increasing extent reached 152.67%, 59.25% respectively. In soil incubation experiment, it was found that PAM enabled to improve soil available nitrogen content, while rice straw was beneficial to increasing the content of available phosphorus and available potassium, especially available potassium rose significantly with the increasing of rice straw amount.With restoration time prolonged, free iron-aluminum oxides content was gradually decreased, but the amorphous showed opposite trend, it reflected that iron-aluminum oxides gradually transformed from crystalline to amorphous with the improvement of activation grade.2. In both field test and soil incubation experiment, not only dry aggregates in all treatments were mainly distributed in>4 mm,4-2 mm, but also rice straw and PAM could significantly increase the content of>4 mm dry aggregate. After wet sieving, from high to low, the content of water stable aggregates percentage of field test were<0.25 mm,1-0.5 mm,0.5-0.25 mm,2-1 mm,4-2 mm,>4 mm. Micro-aggregates (<0.25 mm) were agglomerated to 2-1 mm and 0.5-0.25 mm, and the content of water stable aggregates (>0.25 mm) in all treatments were higher than that of CK in C period, with the increasing extent from 23.57% to 40.23%. Meanwhile, the percentage of>4 mm water stable aggregates were greatly improved with the increasing quantity of PAM.Aggregate stability were studied through three aspects which were>0.25 mm water stable aggregates (WSA),>0.25 mm percentage of aggregate disruption (PAD) and mean weigh diameter (MWD), the aggregate of C2 and C4 treatments were more stable in field test, while PAM2 g kg-1 (P1), straw mulch 1.6 g kg-1+PAM1 g kg-1 (D2P2), straw mulch 3.2 g kg-1+PAM1 g kg-1 (D1P2) were relatively stable in soil incubation experiment.3. In field test, the order of organic matter content of water stable aggregates in different periods was B>C>A, and the content were reduced with the diminishing of aggregate diameter. Water stable aggregates of C4 and C5 hit the highest organic matter percentage in B and C stage. Moreover, there was a linear positive correlation happened to organic matter between soil and water stable aggregates, and the correlation coefficients (r) of small aggregates (2-1 mm,1-0.5 mm,0.5-0.25 mm) ranged from 0.7792 to 0.8286, with a very significant level. The correlation coefficients of C2 treatment (0.9338-0.9962) were obviously higher than that of other treatments.4. Both in 4-5 mm dry aggregate and in water stable aggregate of field test, organic matter in aggregate exteriors was lower than that in interiors. Organic matter content of aggregate interiors in B period was over that in C period. Compared with soil organic matter, organic matter content of dry aggregate exteriors was lower, but slight difference for interiors. However, soil organic matter was much lower than that of water stable aggregate interiors and exteriors.5. With respect to improving fertility and aggregate stability of eroded red soil, C2 and C4 treatments had better restoration effect in field test. |
