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1.
《Soil & Tillage Research》2007,92(1-2):48-56
Degradation of soil structure can lead to increased risk of run-off and soil erosion, and therefore, it is necessary to implement management practices that are more sustainable and will enhance and rehabilitate soils while increasing food production. The impact of small-grain rotations grown with legumes, fallow and continuously on total C (CT), labile C (CL), non-labile C (CNL), total N (NT), aggregation expressed as mean weight diameter (MWD) and infiltration determined as unsaturated hydraulic conductivity (Kunsat) were examined in a long-term rotation trial established in 1966 on a Black Earth (Pellic Vertisol) and a Red Clay (Chromic Vertisol) soil near Tamworth, in New South Wales, Australia. The results were compared with an adjacent uncropped pasture on each soil type. Cropping reduced all C fractions, NT, MWD and Kunsat on both soils, which were further degraded when long fallowing was included in the rotation. CL decreased by 70% with long fallow in the Red Clay and by 78% in the Black Earth compared with the adjacent pasture, while MWD decreased by 61% in the Red Clay and 91% in the Black Earth. Rotation of cereals with legumes resulted in smaller decreases in C fractions, NT, MWD and Kunsat when compared with pasture. Rotation with lucerne (Medicago sativa) resulted in 41% higher CL, 45% higher MWD and 87% higher Kunsat (10 mm tension) than long fallow on the Red Clay soil and 65, 126 and 43% higher on the Black Earth soil. There were strong positive correlations of soil C fractions and NT with MWD for both soil types. Similar significant relationships were found for all C fractions and NT with Kunsat (10 mm tension) for the Red Clay soil, but not for the Black Earth. Rotations with forage legumes can limit declines in C fractions, NT, MWD and Kunsat when cropping these soils and has potential to increase soil sustainability.  相似文献   

2.
We investigated C management index (CMI; an indicator of sustainability of a management system and is based on total and labile C) and soil aggregation in medium-textured soils (silt loam and silty clay loam) under different cropping systems as follows: maize-wheat (M-W), rice-wheat (R-W), soybean-wheat (S-W), Guinea grass, and Setaria grass. Field experiments were 6–32 years long and were located in the wet-temperate zone of northwest Himalayas. The plant nutrients were applied through chemical fertilizers (urea, superphosphate, and muriate of potash) with or without organic materials (FYM, wheat straw, and Lantana spp.). The content of total C (CT), labile C (CL), CMI, mean weight diameter (MWD), and aggregate porosity varied significantly under different cropping systems. The range was 1.59 (R-W)–4.29% (Setaria) for CT, 1.23 (R-W)–3.89 mg/kg (Guinea grass) for CL, 52.09 (R-W)–129.77 (Guinea grass) for CMI, 0.90 (R-W)–5.09 (Guinea grass) for MWD, and 41.5 (R-W)–56.8% (S-W) for aggregate porosity. Aggregate porosity was highest (56.8%) under S-W, followed by grasses (50.1–51.2%), and M/R-W (41.5–50.0%). As per these data, (a) continuous use of N alone as urea lowered soil sustainability over control (no fertilizers); (b) use of NPK at recommended rates improved soil productivity over control; (c) the NPK + organic amendments further improved soil sustainability; and (d) the sustainability under different cropping systems followed the order: perennial grasses > soybean-wheat > maize-wheat > rice-wheat.  相似文献   

3.
Changes in soil carbon (C) from forest to agriculture land in Mukah, Sarawak, and Simpang Renggam (SR) Johor were studied. The changes in labile C (CL) (Mukah, 0.7–43%; SR, 0.2–20%) were greater than changes in the total C (CT) (Mukah, 0.5–9%; SR, 0.3–7%) as compared to the forest. In Mukah, oil palm and pineapple ecosystems showed approximately 18% and 6% increases in CL at a soil depth of 0–15 cm, respectively, as compared to the forest, and thus had greater C management index (CMI) values. In the sago ecosystem, the decline in CL was approximately 26% at the soil depth of 0–15 cm as compared to the forest. In SR, oil palm and pineapple ecosystems showed approximately 0.2% and 19% decreases in CL, respectively, at soil depths of 0–15 cm, resulting in low CMI value. The CL and the CMI can be used to monitor the rate of changes in soil C for different land uses on peat.  相似文献   

4.
Changes in total organic C (C T), water-soluble organic C (C WS), microbial biomass C (C MB), C mineralization, particulate organic C (C P), labile organic C (C L), C management index (CMI), and C storage in surface Hapli-Ustic Cambisol (0–20 cm) under straw incorporation after both 2- and 10-year durations were investigated in a maize (Zea mays L.) field experiment in northeast China, in order to examine the effectiveness of these active C fractions and CMI as early indicators for total C change. The treatments included straw removal (0%S), 50% of straw incorporation (50%S), and 100% of straw incorporation (100%S). Under the straw incorporation, C T concentration and C storage did not significantly change under 2-year duration, while were significantly increased under 10-year duration. However, C MB, total C mineralization (C TM), C P, and C L, and CMI were significantly increased under the straw incorporation even after only 2-year duration, and the responses were more significant after 10-year duration. There were positive correlations between all these C indicators with each other. Our findings demonstrate that the measured active C fractions (except for C WS) and CMI can provide an early indication of change in total soil organic C induced by straw incorporation.  相似文献   

5.
Impacts of organic manure and inorganic fertilizer on total organic carbon (CT), water‐soluble organic C (CWS), microbial biomass C (CMB), particulate organic C (CP), labile organic C (CL), C storage and sequestration, and C management index (CMI) in surface soil (0–20 cm) were investigated in a 20‐yr field experiment under a greenhouse vegetable system in northeast China. The treatments included unfertilized control (CK), N fertilizer (N), balanced NPK fertilizer (NPK), organic manure alone (M) and the NPK fertilizer combined with the manure (MNPK). Under the treatments of N and NPK, CT content and C storage were not significantly changed over the experimental period, while CWS, CMB, CP, CL concentrations and CMI were significantly increased compared with the unfertilized control. In comparison with the control, the manure treatments, M and MNPK, significantly increased CT content and C storage, sequestrating organic C of 8.9 and 9.2 Mg/ha, respectively. The M and MNPK treatments showed higher CWS, CMB, CP and CL concentrations and CMI than the other three treatments. Pearson’s correlation coefficients were used to show that CWS, CMB, CP, CL and CMI could be useful indicators for assessing soil quality and total C changes. The M treatment is effective in sequestrating soil C, but resulted in lower crop yield compared with the NPK treatment. The MNPK treatment showed the greatest increases in crop yield and C sequestration in the greenhouse vegetable system.  相似文献   

6.
陈曦  王改玲  刘焕焕  殷海善  樊文华 《土壤》2021,53(2):375-382
为探究不同撂荒年限土壤结构及有机碳分布特征,试验选取黄土高原吕梁山自然撂荒1、2、3、5、10、15、20 a枣园土壤为研究对象,以清耕作业下的枣园土壤为对照(CK),利用干筛和湿筛法测定并分析各样地0～20 cm土层中土壤团聚体稳定性、团聚体有机碳与土壤总有机碳含量及其相关性。结果表明:撂荒初期,土壤团聚体含量呈波动变化趋势,撂荒3 a后土壤水稳性大团聚体含量(0.25 mm团聚体含量,R_(0.25))及团聚体平均重量直径(MWD)、几何平均直径(GMD)随撂荒年限的增加逐步提高。20 a撂荒地土壤水稳性大团聚体含量占团聚体总量的69.6%,较CK提高了55.2个百分点。土壤总有机碳、团聚体有机碳含量随撂荒年限的延长均呈先降低后增加的趋势,撂荒20 a土壤总有机碳含量达最大值7.88 g/kg;团聚体有机碳含量随团聚体粒径的减小呈先增加后降低的特点,主要集中于1～0.25 mm团聚体内。不同撂荒年限土壤中机械稳定性大团聚体有机碳对土壤总有机碳的贡献率为54.3%～82.2%,较CK(29.3%)提高25.0～52.9个百分点;水稳性大团聚体有机碳对土壤总有机碳的贡献率为17.7%～71.8%,除撂荒1 a和3 a土壤外,其他样地均高于CK (21.1%)。水稳性团聚体MWD、R_(0.25)与土壤总有机碳含量极显著相关(P0.01);水稳性团聚体GMD与土壤总有机碳含量显著相关(P0.05);水稳性团聚体R_(0.25)与2～1、1～0.25和0.25 mm水稳性团聚体有机碳含量极显著相关(P0.01),与5～2 mm团聚体有机碳含量显著相关(P0.05)。可见,撂荒恢复促进了土壤有机碳及水稳性团聚体有机碳含量的提高,从而提高了团聚体的稳定性。  相似文献   

7.
《Soil & Tillage Research》2007,92(1-2):39-47
Manure is a source of plant nutrients and can make a valuable contribution to soil organic matter (SOM). Two experimental sites were studied on a Halpic Phaeozem soil near Bad Lauchstadt in Germany. The first experiment, called the static experiment, commenced in 1902. The impact of fresh farmyard manure (FYM) (0, 20 and 30 t ha−1 2 year−1) combined with P, K and N fertiliser application on total organic C (CT), labile C (CL), non-labile C (CNL), total N (NT), mean weight diameter (MWD) and unsaturated hydraulic conductivity (Kunsat) was investigated. The second experiment commenced in 1984 and investigated the effect of extreme rates of fresh FYM applications (0, 50, 100 and 200 t ha−1 year−1) and cropping, or a continuous tilled fallow on the same soil properties. At both sites a nearby grassland site served as a reference. On the static experiment, FYM application increased all C fractions, particularly CL, where application of 30 t ha−1 2 year−1 increased CL by 70% compared with no FYM application. Fertiliser additions to the static experiment had a positive influence on C fractions while NT increased from both FYM and fertiliser application. MWD increased as a result of FYM application, but did not reach that of the grassland site. Both fertiliser and FYM application increased Kunsat (10 mm tension) on the static experiment. In the second experiment application of 200 t ha−1 year−1 of FYM increased concentrations of CL by 173% and of CNL by 80%, compared with no FYM application to make them equivalent to, or greater than the grassland site. A continuously tilled fallow resulted in significant decreases in all C fractions, NT and MWD compared with the cropped site, while Kunsat (10 mm tension) was increased on the 0 and 50 t ha−1 year−1 treatments as a result of a recent tillage. There was no difference in Kunsat between the cropped and the continuous tilled fallow at FYM applications of 100 and 200 t ha−1 year−1. There were similar significant positive correlations of all C fractions and NT with MWD on both experimental sites but the relationships were much stronger on the extreme FYM experiment. Weaker relationships of C fractions and NT with Kunsat (10 mm tension) occurred for the static experimental site but these were not significant for the extreme FYM experimental site. The strongest relationship between C fractions and Kunsat was with CL. This research has shown that applications of FYM can increase SOM and improve soil physical fertility. However, the potential risk of very high rates of FYM on the environment need to be taken into consideration, especially since the application of organic materials to soils is likely to increase in the future.  相似文献   

8.
Long-term effect of mungbean inclusion in lowland rice-wheat and upland maize-wheat systems on soil carbon (C) pools, particulate organic C (POC), and C-stabilization was envisaged in organic, inorganic and without nutrient management practices. In both lowland and upland systems, mungbean inclusion increased very-labile C (Cfrac1) and labile C (Cfrac2) in surface soil (0–0.2 m). Mungbean inclusion in cereal-cereal cropping systems improved POC, being higher in lowland (107.4%). Lowland rice-based system had higher passive C-pool (11.1 Mg C ha?1) over upland maize-based system (6.6 Mg C ha?1) indicating that rice ecology facilitates the stabilization of passive C-pool, which has longer persistence in soil. Organic nutrient management (farmyard manure + full crop residue + biofertilizers) increased Cfrac1 and carbon management index (CMI) over inorganic treatment. In surface soil, higher CMI values were evident in mungbean included cropping systems in both lowland and upland conditions. Mungbean inclusion increased grain yield of cereal crops, and yield improvement followed the order of maize (23.7–31.3%) > rice (16.9–27.0%) > wheat (lowland 7.0–10.7%; upland 5.4–16.6%). Thus, the inclusion of summer mungbean in cereal-cereal cropping systems could be a long-term strategy to enrich soil organic C and to ensure sustainability of cereal-cereal cropping systems.  相似文献   

9.
Abstract

Soil carbon (C) content in agro‐ecosystems is important in a global context because of the potential for soil to act as a sink for atmospheric CO2. However, soil C storage in agro‐ecosystems can be sensitive to land management practices. The objective of this study was to examine the impact of land management systems on C and nitrogen (N) cycling in an Ultisol in Alabama. Soil samples (0–10, 10–20, and 20–30 cm depths) were collected from a Marvyn sandy loam soil (fine‐loamy, siliceous, thermic Typic Hapludults) under five different farm scale management systems for at least 5 years. The five systems were cotton (Gossypium hirsutum L.) production managed with 1) conventional tillage only, 2) conventional tillage with a grazed winter cover crop (wheat, Triticum aestivum L.), 3) conservation tillage with a winter cover crop grown for cover only with strip tillage; or taken out of cotton production with either 4) long‐term fallow (mowed), or 5) Conservation Reserve Program with loblolly pine (Pinus taeda L.) (CRP‐pine). Total N, total organic C (TOC), total P, and soil C:N ratios were determined. Potential C mineralization, N mineralization, C turnover and C:N mineralization ratios were determined on samples during a 30‐day laboratory incubation study. The fallow system had significantly higher TOC concentration (7.7 g kg‐1 C) while the CRP‐pine system had lower TOC concentration (3.1 g kg‐1 C) compared with the farmed management systems (=4.7 g kg‐1 C). The fallow system had a significantly lower C turnover at all three soil depths compared with the other management systems. At the 0–10 cm depth, the highest C:N mineralization ratio levels were observed in management systems receiving the most tillage. Our results indicate that for Ultisols in the Southeast the use of surface tillage in land management systems is a controlling factor which may limit soil C sequestration.  相似文献   

10.
Information on the effects of soil physical properties on plantain yield is rare. A factorial trial was conducted in three southern Cameroonian villages comparing four cropping systems comprising: two planted legumes, (1) Flemingia macrophylla and (2) Pueraria phaseoloides; a crop, (3) hot pepper; and (4) natural regrowth, all planted to plantain established in old forest versus young bush fallow. Initially, bush fallow had significantly higher sand content, mean weight diameter (MWD) and proportion of macroaggregates, but lower clay content and lower proportions of mesoaggregates and microaggregates than forest soil. Between 2002 and 2006, clay and silt content, MWD, geometric mean diameter and the proportion of macroaggregates increased, whereas sand content, bulk density, and the proportions of mesoaggregates and microaggregates decreased in all villages, fallows and cropping systems. Changes in aggregate stability parameters were greater in forest than in bush fallow at Ngoumou and Mfou, and greater in the F. macrophylla and natural regrowth systems than in the pepper and Pueraria systems. In Ngoumou and Nkometou, available water capacity increased. Plantain fresh-bunch yield was unaffected by village, fallow and cropping systems, and was not correlated with soil physical properties or their changes.  相似文献   

11.
植物是影响土壤有机碳含量和土壤团聚体稳定性的重要因素。选取华南典型花岗岩侵蚀区荒草地、桉树林、湿地松林和木荷林4种植被类型径流小区的土壤为研究对象,分析测定不同坡位、不同土层深度的土壤有机碳特性和团聚体稳定性等指标,评价不同植被类型对土壤养分的分布特性以及团聚体稳定性差异,明确花岗岩侵蚀退化区较为理想的生态恢复措施,旨在为合理利用土壤、重建坡面植被和改善土壤结构提供科学依据。结果表明:土壤总有机碳(TOC)、全氮(TN)和溶解性有机碳(DOC)含量随土层加深逐渐降低,而林地小区土壤碳氮比(C/N)则相反,荒草地碳氮元素的坡面变异系数(CV)显著高于其他3种林地,其中桉树林地TOC、TN、DOC和C/N的坡面分布的变异系数较荒草地分别降低40%,56.18%,68.5%和25.81%;湿地松林地TOC、TN、DOC和C/N的坡面分布的变异系数较荒草地分别降低62.73%,33.71%,46.46%,58.06%;木荷林地TOC、TN、DOC和C/N的坡面分布的变异系数较荒草地分别降低41.82%,38.2%,51.18%,48.39%,表明林地较荒草地更有利于土壤碳氮在坡面的均质化和有机质的积累。荒草地和木荷林地0.25 mm粒径以上的团聚体在上、中坡位的质量分数显著高于其他植被类型,而林下植被生物量较高的木荷林地的平均质量直径(MWD)和几何平均直径(GMD)显著高于其他植被类型。其中木荷小区水稳性团聚体平均质量直径(MWD)较荒草地、桉树和湿地松分别高20.10%,19.58%,23.20%;几何平均直径(GMD)较荒草地、桉树和湿地松分别高20.00%,19.54%,22.23%,表明在花岗岩侵蚀区林地空间结构较好的林草模式有利于土壤有机碳的积累和土壤结构的稳定。  相似文献   

12.
Soil samples from the upper 10-cm-thick layer of the humus horizon (without forest litter) were taken in Podol’sk and Serpukhov districts (1130 and 1080 km2, respectively) of Moscow oblast. At each sampling site, ecosystem (forest, plowland, or fallow), soil (soddy-podzolic, soddy-gley, bog-podzolic, meadow alluvial, gray forest, and anthropogenically transformed soils of lawns and industrial zones), predominant vegetation, and topography (floodplain and low, medium, and upper parts of watersheds) were determined. The carbon content of the microbial biomass (Cmic) was determined by the method of substrate-induced respiration; we also determined the rate of basal (microbial) respiration (BR) and the organic carbon content, pH, and particle-size distribution. Overall, 237 samples from Serpukhov district and 45 samples from Podol’sk district were analyzed. The BR/Cmic ratios (respiration quotient qCO2) and Cmic/Corg ratios were calculated. The Cmic content in the soils ranged from 43 to 1394 μg C/kg; the BR varied from 0.06 to 25 μg CO2-C/g per h, qCO2, from 0.34 to 6.52 μg CO2-C/mg Cmic per h; and the Cmic/Corg ratio, from 0.19 to 10.65%. It was found that the most significant factors affecting the variability of the Cmic and BR are the parameters of ecosystem (50% and 80%, respectively) and soil (30% and 9%, respectively). The most significant variability of these indices was found in forest soils; it was mainly controlled by the soil texture (33 and 23%) and the Corg content (19 and 24%). The Cmic parameter made it possible to differentiate the soils of the territory for the purposes of their evaluation, monitoring, and biological assessment more clearly than the BR value and the soil chemical characteristics.  相似文献   

13.
[目的]研究民勤荒漠绿洲区免耕(Tn)、少耕(Tm)、深松(Ts)和秋翻(Tf)4种耕作方式下土壤呼吸速率的动态变化及其与土壤酶活性的关系,为制定科学有效的土壤碳调控管理措施提供依据。[方法]在2a的田间定位试验基础上,利用LI-8100土壤碳通量测量系统测定不同生育时期(苗期、抽穗期和成熟期)玉米田土壤呼吸速率动态变化,同时取0—20cm土样测定土壤酶活性和理化性质。[结果](1)民勤荒漠绿洲区土壤呼吸具有典型的日动态变化,4种耕作措施土壤呼吸速率日变化在玉米整个生育期呈单峰曲线变化,土壤呼吸速率依次为:TfTmTsTn,有机碳含量与土壤呼吸速率呈显著正相关(p0.05),说明在民勤荒漠绿洲区,传统耕作明显加快了玉米农田土壤碳的释放。(2)土壤脲酶、蔗糖酶、蛋白酶、过氧化氢酶和β-葡萄糖苷酶活性与土壤呼吸有较好相关性(p0.05),其中与过氧化氢酶、脲酶、蔗糖酶活性达到极显著水平(p0.01);pH值、速效钾、有机碳与脲酶、蔗糖酶、β-葡糖糖苷酶活性达到极显著水平(p0.01)。[结论]耕作方式可以通过改变荒漠绿洲区土壤理化性质、激发酶活性从而使土壤呼吸速率发生不同程度的改变,影响玉米田CO2的释放。  相似文献   

14.
The effect of tillage systems and crop rotation on microbial biomass phosphorus (MBP) and acid phosphatase (P‐ase) activity, and the amount of different phosphorus (P) forms measured by 31P‐NMR spectroscopy were studied on a field experiment carried out in a temperate Ultisol from southern Chile. Two tillage systems, no tillage (NT) and conventional tillage (CT) and two crop rotations, oat–wheat (OW) and lupine–wheat (LW) were evaluated 4 yr after the start of the experiment to determine the effects of such management on some soil biological parameters and P forms at three depths (0–5, 0–10 and 10–20 cm). Microbial biomass P ranged from 6.5 to 22.6 mg/kg, whereas the mean total P (PT) was 1995 mg/kg for all treatments (OW and LW). Microbial biomass carbon (MBC) and surface P accumulation (at 0–5 cm depth), including Olsen P, MBP, orthophosphate monoesters (monoester‐P), were larger under NT than CT. Tillage effects were greater than crop rotation effects in enhancing P availability. The LW rotation showed enhanced P‐ase activity and increased monoester‐P forms (57 vs. 30% of the total integral area of the spectra, in average) compared with OW. Nevertheless, OW rotation increased orthophosphate (ortho‐P), especially at 10–20 cm. Microbial biomass carbon ranged from 532 to 2351 mg/kg, which represented 1.2–4.5% of total organic C (Co). Furthermore, MBP correlated positively with MBC (r = 0.80), Olsen P (r = 0.77), Co (r = 0.77), pH (r = 0.65), PT (r = 0.65) and P‐ase activity (r = 0.57), suggesting the importance of the microbial biomass on soil P availability.  相似文献   

15.
Methane (CH4) oxidation potential of soils decreases with cultivation, but limited information is available regarding the restoration of that capacity with implementation of reduced tillage practices. A study was conducted to assess the impact of tillage intensity on CH4 oxidation and several C-cycling indices including total and active microbial biomass C (t-MBC, a-MBC), mineralizable C (Cmin) and N (Nmin), and aggregate-protected C. Intact cores and disturbed soil samples (0–5 and 5–15 cm) were collected from a corn (Zea mays L.)–soybean (Glycine max L. Merr.) rotation under moldboard-plow (MP), chisel-plow (CP) and no-till (NT) for 8 years. An adjacent pasture (<25 years) and secondary growth forest (>60 years) soils were also sampled as references. At all sites, soil was a Kokomo silty clay loam (mesic Typic Argiaquolls). Significant tillage effects on t-MBC and protected C were found in the 0–5 cm depth. Protected C, a measure of C retained within macro-aggregates and defined as the difference in Cmin (CO2 evolved in a 56 days incubation) between intact and sieved (<2 mm) soil samples, amounted to 516, 162 and 121 mg C kg−1 soil in the 0–5 cm layer of the forest, pasture and NT soils, respectively. Protected C was negligible in the CP and MP soils. Methane uptake rate (μg CH4-C kg−1 soil per day, under ambient CH4) was higher in forest (2.70) than in pasture (1.22) and cropland (0.61) soils. No significant tillage effect on CH4 oxidation rate was detected (MP: 0.82; CP: 0.41; NT: 0.61). These results underscore the slow recovery of the CH4 uptake capacity of soils and suggest that, to have an impact, tillage reduction may need to be implemented for several decades.  相似文献   

16.
A large area (180 Mha) of central Brazil is occupied by a savanna biome known as the Cerrado. Annual rainfall in this region varies from 1200 to 2000 mm, although there is a long (5 month) dry season with almost no rain. This region is regarded by Brazilians as their agricultural frontier and there is a steady growth in the area dedicated to permanent cropping in the region, which today is estimated to occupy 14 Mha. Owing to the dearth of long-term experiments, the impact of continuous cropping on soil carbon stocks remains unclear. The objective of this study was to evaluate the effects of different tillage systems (zero till (ZT) and conventional tillage (CT)) on the change in soil carbon stocks over a 20-year period of the same crop sequence compared to that under a neighbouring area of native vegetation (NV). Only approximately 10 Mg ha−1 of soil carbon in the 0–100 cm depth interval was lost under continuous ZT. However, under CT systems losses were greater (up to 30 Mg C ha−1) when the mouldboard plough was used and/or tillage was performed twice a year. We did not have access to instrumentation to accurately assess soil charcoal but the C/N data and peroxide and dichromate oxidative techniques suggested that 40% of soil C was in this form. The 13C natural abundance of soil profiles indicated that residues of crops (maize) and the spontaneous annual fallow of Brachiaria spp. resulted in integration of significant C4 residues to a depth of at least 40 cm. It would appear that zero tillage, which is already widely adopted in the Cerrado region of Brazil, will have only a small negative long-term impact on soil C stocks, but ploughing, especially more than once a year, will lead to considerably larger soil C losses.  相似文献   

17.
This study investigates if Araucaria forest (C3 metabolism) expansion on frequently burnt grassland (C4 metabolism) in the southern Brazilian highland is linked to the chemical composition of soil organic matter (SOM) in non‐allophanic Andosols. We used the 13C/12C isotopic signature to group heavy organo‐mineral fractions according to source vegetation and 13C NMR spectroscopy, lignin analyses (CuO oxidation) and measurement of soil colour lightness to characterize their chemical compositions. Large proportions of aromatic carbon (C) combined with small contents of lignin‐derived phenols in the heavy fractions of grassland soils and grass‐derived lower horizons of Araucaria forest soils indicate the presence of charred grass residues in SOM. The contribution of this material may have led to the unusual increase in C/N ratios with depth in burnt grassland soils and to the differentiation of C3‐ and C4‐derived SOM, because heavy fractions from unburnt Araucaria forest and shrubland soils have smaller proportions of aromatic C, smaller C/N ratios and are paler compared with those with C4 signatures. We found that lignins are not applicable as biomarkers for plant origin in these soils with small contents of strongly degraded and modified lignins as the plant‐specific lignin patterns are absent in heavy fractions. In contrast, the characteristic contents of alkyl C and O/N‐alkyl C of C3 trees or shrubs and C4 grasses are reflected in the heavy fractions. They show consistent changes of the (alkyl C)/(O/N‐alkyl C) ratio and the 13C/12C isotopic signature with soil depth, indicating their association with C4 and C3 vegetation origin. This study demonstrates that soils may preserve organic matter components from earlier vegetation and land‐use, indicating that the knowledge of past vegetation covers is necessary to interpret SOM composition.  相似文献   

18.
No-tillage systems affect soil properties depending on the soil, climate, and the time since its implementation. In heavy no-tilled soils a surface compacted layer is commonly found. Such layer can affect root growth and soil water infiltration. In several cases, surface organic carbon can buffer these problems. The aim of this study was to evaluate the effect of 4- and 7-year-old conventional (CT) and no-tillage (NT) treatments on soil physical properties, root growth, and wheat (Triticum turgidum L. var. durum) yield in an Entic Haploxeroll of Central Chile. In both tillage treatments we study soil water retention, bulk density (ρb), soil particle density (ρs), soil water infiltration, mean-weight diameter of soil aggregates (MWD), penetration resistance, grain yield, and root length density (Lv) up to a depth of 15 cm. The MWD and the penetration resistance were higher under NT as compared to CT. For the top 5 cm of soil, Lv was greater under NT as compared to CT. Differences of Lv between NT and CT were 2.09, 7.60, and 4.31 cm root cm−3 soil during the two leaves, flowering and grain filling phenological stages, respectively. Generally, the effect of NT on these properties was more evident near the soil surface. In contrast, fast drainage macropores, ρs, and soil water infiltration rates were higher under CT than under NT. Tillage treatments did not significantly affect ρb and yield. A longer time under no-tillage enhanced aggregate stability, however, other soil physical properties were negatively affected.  相似文献   

19.
土地利用方式对桂西北石漠化地区土壤理化性质的影响   总被引：1，自引：1，他引：0  
在广西壮族自治区凌云县典型石漠化地区对7种不同土地利用方式土壤理化性质进行了调查分析.结果表明,不同土地利用方式对土壤容重、含水量、总孔隙度、毛管孔隙度、非毛管孔隙度存在极显著差异(p＜0.01),有机质、全氮、全磷、全钾、速效氮、速效磷、速效钾及交换性Ca2+含量差异极显著(p＜0.01).相对阔叶林地土壤,灌木林、针叶林、退耕台地、草地、退耕坡地、农田土壤的退化程度依次增加.农田土壤质量最低,针叶林地、草地、退耕坡地、退耕台地土壤质量为中等,灌木林地与阔叶林地土壤质量较高.人为干扰是影响土壤理化性质的主导因素,干扰强度大,土壤理化性质退化严重.控制不合理的人为干扰及恢复结构良好的地上植被对改善土壤质量具有重要意义.  相似文献   

20.
Soil total organic carbon (TOC) is a composite indicator of soil quality with implications for crop production and the regulation of soil ecosystem services. Research reports on the dynamics of TOC as a consequence of soil management practices in subtropical climatic conditions, where microbial carbon(C) loss is high, are very limited. The objective of our study was to evaluate the impact of seven years of continuous tillage and residue management on soil TOC dynamics (quantitative and qualitati...  相似文献   

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