[Distribution characteristic of soil organic carbon pool in the plow layer of sloping farmland with different cultivation years in black soil region]. / ä¸åŒå¼€åž¦å¹´é™å¡åœ°é»‘åœŸè€•å±‚åœŸå£¤æœ‰æœºç¢³åº“åˆ†é ç‰¹å¾.

Tillage and erosion simultaneously cause soil movement from the top-slope position to the foot-slope position in a sloping farmland, with consequences on variation of soil organic carbon (SOC) content as well as its stability mechanism. To identify the accumulation-loss characteristics of organic carbon pool (OCP) of black soil under long-term cultivation, the distribution characteristics of different OCPs (free unprotected, physical protection, chemical protection, biochemical protection) of sloping farmland with different years of cultivation were quantified by Stewart physical-chemical fractionation method. The results showed that long-term cultivation and associated erosion resulted in significant accumulation of SOC in the foot-slope deposition area. The contents of four OCPs in the foot deposition area were significantly higher than those in top-slope eroded areas. SOC of sloping farmland was dominated by chemically protected carbon and biochemically protected carbon (＞90%). Furthermore, the top-slope erosion areas and foot-slope deposition areas mainly accumulated chemically protected organic carbon (84.6%) and biochemically protected organic carbon (51.4%), respectively. With the increases of cultivation years, the accumulation rate of four OCPs increased with the stability degree of SOC, that is, biochemical protection carbon pool (48%) ＞ chemical protection carbon pool (42.2%) ＞ physical protection carbon pool (6.4%) ＞ free unprotected carbon pool (3.4%). The proportion and accumulation rate of the free unprotected organic carbon pool were the smallest, but they were most sensitive to external interference. Thus, more attention should be paid to free unprotected organic carbon during the management of black soil.

[Responses of accumulation-loss patterns for soil organic carbon and its fractions to tillage and water erosion in black soil area]. / é»‘åœŸå¡è€•åœ°æœ‰æœºç¢³åŠå ¶ç»„åˆ†ç´¯ç§¯-æŸè€—æ ¼å±€å¯¹è€•ä½œä¾µèš€ä¸Žæ°´èš€çš„å“åº”.

Tillage and water erosion have been recognized as the main factors causing degradation in soil organic carbon (SOC) pools of black soil. To further explore the response of SOC and its fractions to different driving forces of erosion (tillage and water), geostatistical methods were used to analyze spatial patterns of SOC and its three fractions at a typical sloping farmland based on tillage and water erosion rates calculated by local models. The results showed that tillage erosion and deposition rates changed according to the slope positions, decreasing in the order: upper-slope > lower-slope > middle-slope > toe-slope and toe-slope > lower-slope > middle-slope > upper-slope, respectively; while the order of water erosion rates decreased in the order: lower-slope > toe-slope > middle-slope > upper-slope. Tillage and water erosion cooperatively triggered intense soil loss in the lower-slope areas with steep slope gradient. Tillage erosion could affect C cycling through the whole slope at different levels, although the rate of tillage erosion (0.02-7.02 t·hm-2·a-1) was far less than that of water erosion (5.96-101.17 t·hm-2·a-1) in black soil area. However, water erosion only played a major role in controlling C dynamics in the runoff-concentrated lower slope area. Affected by water erosion and tillage erosion-deposition disturbance, the concentrations of SOC, particulate organic carbon and dissolved organic carbon in depositional areas were higher than in erosional areas, however, microbial biomass carbon showed an opposite trend. Tillage erosion dominated SOC dynamic by depleting particulate organic carbon.

[Topsoil phosphorus forms and availability of different soil and water conservation plantations in typical black soil region, northeast China].

Aiming to understand soil phosphorus status of plantations in typical black soil region of Northeast China, the topsoil (0-10 cm) phosphorus fractionations and its availability were examined in four soil and water conservation plantations dominantly composed of Larix gmelini, Fraxinus mandshurica, Pinus sylvestris var. mongolica and Populus nigra var. italica x P. cathayan, respectively. The results showed that total P, Olsen-P and the concentration of different P fractionations in F. mandshurica and P. nigra var. italica x P. cathayan plantations were significantly higher than that of the other two coniferous plantations. Organic P was the major fractionation in the four plantations' topsoil, and sodium hydroxide extractable organic P (NaOH-Po ) representing moderately labile organic phosphorus was predominant, which accounted for 58.9% of total P. The contents of H2O-Pi and NaHCO3-P which were more labile to plant were lower, only accounting for 1.2% and 6.6% of total P, respectively. Except for NaHCO3-Po, all the other P fractions of four plantations correlated with each other, and they also had significant correlations with soil organic matter, total P, Olsen-P. Compared with the coniferous plantations, the broadleaf plantations presented higher availability of phosphorus.

[Responses of soil structure to seasonal freezing-thawing in a typical black soil cultivated region].

Taking the soil in a typical black soil cultivated region as test object, this paper analyzed its aggregate size distribution, wedge resistance, bulk density, porosity, saturation degree, and generalized structure index after a seasonal freezing-thawing cycle, and evaluated the effects of the freezing-thawing cycle on the soil structural characters. The seasonal freezing-thawing cycle aggravated the disruption of air-dried aggregates, but strengthened the aggregation of water-stable aggregates and lowered their destruction rate. After the freezing-thawing cycle, soil wedge resistance decreased by 15.45%, and soil bulk density remained relatively constant from 1.10 to 1.11 g x cm(-3). The volume percent of soil solid phase increased, and soil total porosity and capillary porosity decreased to different degree. Soil saturation degree was improved by 13.06%, which in turn decreased the soil potential storage capacity. Seasonal freezing-thawing cycle improved the soil structure and soil arability and increased the erosion resistance of soil aggregates, but decreased the soil erosion resistance and increased the risk of the water erosion of black soil.

[Surrounding characteristics of preferential flow in cultivated typical black soils of northeast China].

Taking the cultivated soils in typical black soil region of Northeast China as test objects, and by using dye tracer and double-ring infiltrometer techniques and photograph interpretation method, this paper measured and analyzed the dye-stained width and dye-stained coverage of soil transverse and longitudinal sections as well as the field maximum dye-stained depth, aimed to approach the water flow movement pattern and distribution characteristics in test soils. At soil depth 0-15 cm, matrix flow was the main soil water flow movement pattern; at depth 15-20 cm, lateral flow was observed, and the average dye-stained width and dye-stained coverage reached their maximum, being 23 cm and 20.73%, respectively. At depth 20-67 cm, the main soil water flow movement pattern was macro-pore flow, with cracks and macro-pores as the main preferential routes. The cracks at depth 20-35 cm made the preferential flow have distinct surrounding characteristics, and the macro-pores at depth 40-67 cm were the main preferential routes. Due to the existence of the preferential routes of cracks and macro-pores, the migration velocity of water in soil increased by 4.5 times, which could not only cause water loss, but also accelerate the migration of pesticides to ground water. It was suggested that these preferential routes should be decreased or eliminated during the cultivation and management on cultivated typical black soils.

[Effects of human disturbance on coarse woody debris of Larix gmelinii forest on northern slope of Greater Hinggan Mountains].

An investigation was conducted on the living tree volume, coarse woody debris (CWD) loading, and composition of Larix gmelinii forest along a human disturbance gradient, i.e., no disturbance (natural larch forest), one-time disturbance (natural forest was disturbed once only), and two-time disturbance (natural forest was disturbed two times consecutively), on the northern slope of Greater Hinggan Mountains. The results showed that under no disturbance, one-time disturbance, and two-time disturbance, the average living tree volume of L. gmelinii forest was 161.6, 138.3, and 114. 8 m3 x hm(-2), and the average CWD loading was 69.77, 36.64 and 32.61 m3 x hm(-2), respectively. In natural L. gmelinii forest, most of CWD was of 20-40 cm diameter class, among which, fallen logs occupied 72%, and snags and stumps occupied 28% ; while in one-time and two-time disturbance L. gmelinii forests, most CWD was of 10-30 cm diameter class, with the fallen logs, snags, and stumps occupied 70%, 14% and 16%, and 57%, 15% and 28%, respectively. Human disturbance reduced the CWD loading of L. gmelinii forest and altered the composition of the CWD.

[Splash erosion of black soil with different reclamation years and its relations to soil aggregates selective characteristics].

Taking the typical black soil with a reclamation history of 8, 30, and 50 years and the un-reclaimed secondary forest land as test objects, a simulation study was made on the process of splash erosion and the selective characteristics of soil aggregates under artificial rainfall condition, with the effects of reclamation on the splash erosion in black soil region analyzed. The splash amount of reclaimed black soil was evidently higher than that of un-reclaimed secondary forest land, and increased with increasing reclamation years, with a variation range of 0.95-7.06 g x cm(-1). There was a significant exponential correlation between splash amount and splash distance, and the percentages of small size water-stable aggregates increased with increasing splash distance. The critical particle size of soil aggregates for the enrichment and depletion of splash erosion was 1.0 mm. Soil water-stable aggregates larger than 2 mm and smaller than 0.25 mm in size and soil organic matter content were the main factors affecting the splash erosion characteristics of typical black soil.

[Effects of heavy machinery operation on the structural characters of cultivated soils in black soil region of Northeast China].

With the cultivated soils in black soil region of Northeast China as test objects, this paper measured their structural characters such as soil strength, bulk density, and non-capillary porosity/capillary porosity (NCP/CP) ratio before and after heavy and medium-sized machinery operation, aimed to study the effects of machinery operation on the physical properties of test soils. The results showed that after machinery operation, there existed three distinct layers from top to bottom in the soil profiles, i.e., plowed layer, cumulative compacted layer, and non-affected layer, according to the changes of soil strength. Under medium-sized machinery operation, these three layers were shallower, and there was a new plow pan at the depth between 17.5 and 30 cm. Heavy machinery operation had significant positive effects on the improvement of topsoil structure (P < 0.05). After subsoiling and harvesting with heavy machinery, the bulk density of topsoil decreased by 7.2% and 3.5%, respectively, and NCP/CP increased by 556.6% after subsoiling, which would benefit water infiltration, reinforce water storage, and weaken the threat of soil erosion. The main action of heavy machinery operation was soil loosening, while that of medium-sized machinery operation was soil compacting.