[Effects of grazing disturbance on soil active organic carbon in mountain forest-arid valley ecotone in the upper reaches of Minjiang River].

Effects of grazing disturbance on the soil carbon contents and active components in the four vegetations, i.e., artificial Robinia pseudoacacia plantation, artificial poplar plantation, Berberis aggregate shrubland and grassland, were studied in the mountain forest-arid valley ecotone in the upper Minjiang River. Soil organic carbon and active component contents in 0-10 cm soil layer were greater than in 10-20 cm soil layer at each level of grazing disturbance. With increasing the grazing intensity, the total organic carbon (TOC), light fraction organic carbon (LFOC), particulate organic carbon (POC) and easily oxidized carbon (LOC) contents in 0-10 cm soil layer decreased gradually in the artificial R. pseudoacacia plantation. The LFOC content decreased, the POC content increased, and the TOC and LOC contents decreased initially and then increased with increasing the grazing intensity in the artificial poplar plantation. The POC content decreased, and the TOC, LFOC and LOC contents decreased initially and then increased with increasing the grazing intensity in the B. aggregate shrubland. The POC and TOC contents decreased, and the LFOC and LOC contents decreased initially and then increased with increasing the grazing intensity in the grassland. The decreasing ranges of LOC, LFOC and POC contents were 0.1-7.9 times more than that of TOC content. There were significant positive relationships between TOC and LOC, LFOC and POC, suggesting that the active organic carbon components could reflect the change of soil total carbon content.

[Relationships between grazing-path and Berberis aggregate population characteristics in upper reaches of Minjiang River, Southwest China].

Taking the Berberis aggregate shrubs in the ecotone of dry valley and montane forests in upper reaches of Minjiang River as study objects, and by the methods of tracking grazing and field survey, this paper studied the characteristics of habitat utilization by livestock and the features of grazing-path. The major factors affecting the features of grazing-path were screened by redundancy analysis (RDA), and the relationships of the grazing-path features with the coverage, size class, and distribution pattern of the shrubs were analyzed. It was shown that the distribution pattern of the grazing-path could intuitively reflect the characteristics of the habitat utilization by livestock, being in accordance with the results of tracking grazing. The Morisita index at 5 m scale could objectively reflect the distribution type of the grazing-path. Sample plots 1, 2 and 6 presented a contagious distribution of grazing-path, while the other plots showed regular distribution. In slope scale, the coverage and height of the shrubs were the notable affecting factors, which had negative correlations with the grazing-path features. There was a significant negative correlation between the coverage of B. aggregate population and the area of grazing-path. The population structure of B. aggregate had a close correlation with the distribution of grazing-path. The ratio of the long axis to short axis of the shrubs was averagely 1.29, and the shape of the shrubs approached to round. It was considered that the grazing-path landscape and the livestock on the grazing-paths had the function of reconstructing the shape of the shrubs. The directionality of the population pattern of B. aggregate was generally in line with the distribution type of grazing-path, but actually, they were opposite in distribution. The patches of the shrubs were in aggregated or uniform distribution in the areas deviated from the grazing-path.

[Fractal features of soil aggregate structure in slope farmland with different de-farming patterns in South Sichuan Province of China].

By using fractal model, this paper studied the fractal dimension of soil aggregate structure (D) in the slope farmland (CK), its 5-year de-farmed Neosinocalamus affinis plantation (NAP), Bambusa pervariabilis x Dendrocalamopsis oldhami plantation (BDP), Alnus crenastogyne + Neosinocalamus affinis plantation (ANP), and abandoned farmland (AFL) in south Sichuan Province of China, and analyzed the relationships between the D and soil physical and chemical properties. In the de-farmed plantations and abandoned farmland, the contents of > 0.25 mm soil aggregates and water-stable aggregates were increased significantly, compared with those in the slope farmland. The D was 1.377-2.826, being in the order of NAP < BDP < ANP < AFL < CK, and decreased with the increasing contents of > 0.25 mm soil aggregates and water-stable aggregates. Comparing with CK, de-farming increased the soil natural water content, capillary porosity, and contents of soil organic matter, total N, alkali-hydrolysable N, total P, and total K, and decreased soil bulk density, non-capillary porosity, and aeration porosity. There were close relationships between the fractal dimension of soil aggregate structure and the soil physical and chemical properties. All the results suggested that the de-farming of slope farmland was beneficial to the increase of the contents of > 0.25 mm soil aggregates and water-stable aggregates, and the enhancement of soil structure stability. The D could be used as an ideal index to evaluate soil fertility, and planting Neosinocalamus affinis on the de-farming slope farmland was a good measure for the improvement of soil fertility in the research area.

[Effects of long-term fertilization on soil particulate organic carbon and nitrogen in a wheat-maize cropping system].

0-20 cm soil samples were collected from an 18-year wheat-maize rotation field on the North China Plain to study the effects of long-term fertilization on the contents and storages of soil particulate organic carbon (POC), particulate organic nitrogen (PON), incorporated organic carbon (IOC), and incorporated organic nitrogen (ION). The long-term fertilization experiment was designed to include 7 treatments, i.e., chemical NPK (NPK), organic manure (OM), 1/2 organic manure plus 1/2 chemical NPK (1/20 MN), chemical NP (NP), chemical PK (PK), chemical NK (NK), and control (CK). After 18 years experiment, all the fertilization treatments showed higher contents of soil POC, PON, IOC and ION, higher proportions of soil POC to soil total organic carbon (TOC) and of soil PON to soil total nitrogen (TON), and higher C/N ratio of soil particulate organic matter. The storages of soil POC and PON under fertilization treatments were increased by 11.7%-196.8% and 13.0%-152.2%, respectively, compared with the control. The contribution of soil POC to the increased storage of soil TOC ranged from 31.5% to 67.3%, and that of soil PON to the increased storage of soil TON ranged from 14.3% to 100.0%. The storages of soil IOC and ION under fertilization treatments increased by 2.0%-75.0% and 0.0%-69.8%, respectively, compared with the control. Among the fertilization treatments, treatment OM had the highest storages of soil POC, PON, IOC and ION, followed by treatment 1/20 MN, and the treatments of applying chemical fertilizers alone. Balanced application of chemical fertilizers (treatment NPK) showed higher storages of soil POC, PON, IOC and ION than imbalanced application (treatments NP, PK, and NK). It was suggested that applying organic manure or its combination with chemical NPK and the balanced application of chemical NPK could be the keys for the increase of soil POC, PON, IOC and ION contents and storages.