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1.
长期轮作施肥棕壤磷素对磷盈亏的响应 总被引：4，自引：1，他引：3
2.
【目的】土壤微团聚体是磷素储存与周转的重要载体,明确长期施肥下旱地红壤微团聚体中赋存磷素的形态及其生物有效性,为磷肥的高效合理施用提供理论依据。【方法】以位于鹰潭农田生态系统国家野外科学观测研究站院内的长期肥料定位试验(1988～2014)为依托,分别以有机无机配施区的1/2 NPK(CK)、低量NPK+稻秆(RS)与低量NPK+猪厩肥(PM)处理及无机肥区的NK与NPK处理的旱地红壤为研究材料,采用水分散-吸管法逐级提取了土壤中0.25～0.05 mm、0.05～0.01 mm、0.01～0.005 mm与<0.005 mm粒级微团聚体,对比分析了各粒级微团聚体中全磷、有效磷及磷活化系数的变化差异。基于土壤磷素分级结果,分析了旱地红壤中大小粒级微团聚体中极有效磷、中等有效磷及非有效磷对长期施肥的响应。借助于结构方程模型探讨了微团聚体中各形态磷、磷活化系数、颗粒组成、有机质、铁铝氧化物等因子与有效磷的互应关系。【结果】长期配施猪粪可以显著增加旱地红壤各粒级微团聚体中全磷、有效磷、磷活化系数及极有效磷、中等有效磷及非有效磷的含量,且<0.005 mm粒级微团聚体中的各组分磷增... 相似文献
3.
典型农耕区棕壤水稳性团聚体及其有机碳特征 总被引：1，自引：0，他引：1
对山东半岛棕壤区耕地和荒地土壤水稳性团聚体及其有机碳进行解析.结果表明:各级土壤团聚体质量比总体呈“两头低中间高”的不规则“W”形分布,耕地和荒地土壤微团聚体(＜250μm)平均含量分别为51.74％和51.61％,耕种的扰动增加了土壤颗粒分散度,水流对大团聚体的破坏作用更大.有机碳分布受团聚体分配的制约,其含量随团聚体粒径减小而增加.耕地和荒地有机碳在大团聚体中平均含量分别为5.98,3.48 g/kg,而在微团聚体中含量分别为8.05,9.11 g/kg,有机碳含量比例分别高达55.36％和68.58％,其中＜20 μm粉黏团聚体中有机碳含量最高(耕地为10.97 g/kg;荒地为11.63 g/kg),可作为研究区土壤固碳潜力评价指标.傅立叶变换红外光谱(FTIR)解析发现,棕壤微团聚体有机碳以芳香碳和多糖碳为主. 相似文献
4.
福州市郊菜地土壤磷素特征及流失潜能分析 总被引：9，自引：0，他引：9
对福州市郊11片蔬菜基地土样的磷素含量、等温吸附特征及流失潜能进行分析.结果表明:与林坡地自然土壤相比.菜地土壤全磷(2.043 g/kg)、速效磷(Oslen-P.182.893 mg/kg)和CaCl2-P(1.018 mg/kg)平均含量都呈现出明显的累积特征;菜地土壤可用Langmuir等温方程很好拟合(R2=0.991**～0.998**),其等温吸附特征值,如易解吸磷(RDP)、磷吸持饱和度(DPS)和磷零吸持平衡浓度(EPC0)均出现大幅度提高.而最大缓冲能力(MBC)和吸附常数K则明显降低;据Langmuir方程求得菜地土壤指导施磷量范围为11.62～67.37(P)kg/hm2,平均为27.18(P)kg/hm2;菜地土壤的速效磷和全磷含量均显著高于由回归方程求得的土壤发生磷素淋失的速效磷临界值(56.96 mg/kg)和全磷的临界值(1.146 g/kg);菜地土壤的DPS平均为23.12%,已经接近容易流失的阈值(25%),其中4片菜地土样的DPS已经超过容易流失的阈值.因此,福州市郊菜地土壤磷素具有很高的流失潜能,应作为农业面源磷污染控制的关键源区. 相似文献
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通过8年定位试验,研究了不同施肥制度下褐土及其微团聚体磷素肥力变化规律,从各级微团聚体全磷和有效磷储量角度探讨了不同施肥制度下土壤磷素肥力的变化实质。结果表明,不施肥处理主要是由于10～50μm粒级全磷储量和<10μm粒级有效磷储量减少而造成土壤磷素肥力下降;单施常量NPK化肥和增量NPK化肥处理主要通过提高<10μm粒级全磷和有效磷储量增加土壤磷素含量;有机肥(物)料配施常量NPK化肥处理则在提高小粒级微团聚体磷素贮备和供应能力的同时,增强了大粒级特别是10～50μm粒级全磷和有效磷储量,进而使土壤磷素肥力得到提高。采用有机肥(物)料配施常量NPK化肥是改善土壤磷素肥力的有效措施。 相似文献
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为明确侵蚀环境中长期施用化肥条件下农田土壤养分积累特征及其对流域面源污染的潜在威胁。在高塬沟壑区,分别采集塬面—坡地—沟道和川地—河漫滩—河道中土壤及泥沙样品,分析不同侵蚀地貌单元中团聚体粒级分布特征和不同团聚体中C、N、P含量变化及其潜在环境风险。结果表明:(1)沟道和河道等低洼地带＜63 μm粒级团聚体占比最高,川地—河漫滩—河道系统中＜63 μm粒径含量显著高于塬面—坡地—沟道系统;(2)塬面有机碳(SOC)、全氮(TN)、全磷(TP)、有效磷(Olsen—P)含量分别为8.49,1.19,1.23 g/kg和51.80 mg/kg,是80年代初的1.39,1.49,1.76,16.27倍;川地分别为6.80,1.00,1.07 g/kg和27.40 mg/kg,是80年代初的1.12,1.25,1.52,8.13倍,磷素积累最为明显。各粒级团聚体中SOC、TN、TP、Olsen—P含量由高到低依次为＞250 μm粒级,63~250 μm粒级,＜63 μm粒级;(3)无论是从塬面到沟道,还是从川地到河道,不同粒级团聚体中SOC、TN、TP、Olsen—P都呈现了显著降低趋势,但沟道和河道＜63 μm粒级团聚体中有效磷素含量已升高到塬面上世纪80年代初水平。易侵蚀迁移的团聚体(＜250 μm)分布特征和CaCl2—P的突变点问题突出,成为塬面和川地农田土壤养分积累影响水体环境的潜在风险源。因此,防治水土流失和改善施肥措施是确保黄河流域高质量发展的基础。 相似文献
7.
植茶年限对土壤团聚体氮、磷、钾含量变化的影响 总被引：3，自引：1，他引：2
采用野外调查和室内分析相结合的方法,研究了植茶年限对土壤团聚体氮、 磷、 钾含量变化的影响。结果表明, 1）土壤团聚体速效钾含量随粒径的减小先升高后降低,在0.5~0.25 mm粒径中较高,为38.52~70.32 mg/kg; 全磷、 全钾和碱解氮含量在各粒径中分布较均匀,其变异系数分别为2.77%~11.58%、 0.82%~3.72%和5.98%~10.62%;而全氮和有效磷含量则集中在 0.25 mm 粒径的团聚体中,分别为0.40~0.98 g/kg和8.53~29.32 mg/kg。2）随着植茶年限的增加,各粒径团聚体全氮、 碱解氮、 全磷和有效磷含量逐渐升高,而速效钾含量则有所降低,全钾含量变化不明显。3）不同粒径土壤团聚体对土壤氮、 磷、 钾含量的贡献率有45%~72% 来自5 mm 的团聚体,随着植茶年限的增加,5 mm 的团聚体对土壤养分的贡献率先升高后降低,在植茶23年和31年时较高,为60%~72%。不同粒径团聚体对土壤氮、 磷、 钾的保持和供应能力存在明显差异,长期植茶有利于土壤团聚体全氮、 碱解氮、 全磷和有效磷的积累,但速效钾含量却逐年降低,故在茶园的生产管理中,需平衡施用氮、 钾肥,植茶23年后应增施有机肥料,以促进土壤大团聚体含量的增加,提高茶园土壤的保肥和供肥能力。 相似文献
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田间陈化生物质炭提高稻田土壤团聚体稳定性和磷素利用率 总被引：3，自引：2，他引：1
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磷硅肥配施对盐渍土壤水稻生长及养分吸收的影响 总被引：1，自引：0，他引：1
针对滨海盐渍化稻田土壤根系易受盐碱胁迫、磷素养分含量及有效性低的问题,采用田间微区试验研究磷肥与硅肥配施对滨海盐渍化稻田土壤水稻根系生长、土壤磷素含量、水稻磷营养、产量及经济效益的作用。试验采用双因素设计,磷肥设2个水平:P1,P_2O_5 64 kg/hm~2;P2,P_2O_5 128 kg/hm~2;硅肥分土施和喷施,土施设3个水平:Si1,SiO_2 0 kg/hm~2;Si2,SiO_2 60 kg/hm~2;Si3,SiO_2 120 kg/hm~2;Si4为叶面喷施SiO_215 kg/hm~2。结果表明,喷施硅肥与低量磷肥配施的P1Si4处理在各生育时期的水稻总根长、总表面积和总根体积均为最高,与P2Si4处理无显著性差异。同时,磷肥配施硅肥可有效提高滨海盐渍化水稻土壤磷素有效性,其中P2Si4处理速效磷含量显著高于P1Si3、P2Si1,分别高出35.16%,27.47%;高磷处理的土壤全磷含量高于低磷处理。且施用硅肥的P1Si3、P1Si4处理的水稻产量显著高于不施硅肥和少量施硅的P1Si1、P1Si2处理,其中P2Si3水稻产量达9 547.5 kg/hm~2;各处理的有效穗数无显著性差异,每穗实粒数P2Si3处理最高,达162.47个/穗。P2Si3处理水稻籽粒中磷积累量最高,且显著高于其他处理,比P1Si3、P2Si1处理分别高出8.46%,9.68%。在低磷或高磷施用条件下,叶面喷施硅肥(P1Si4、P2Si4)处理收入分别达到14 953.6,14 323.2元/hm~2。综上所述,与不施硅肥的处理相比,磷肥配施硅肥可显著促进滨海盐渍化土壤水稻根系生长,提高磷素有效性、水稻产量及经济效益,其中以P1Si4处理(叶面喷硅,P_2O_5 64 kg/hm~2)处理最佳。 相似文献
10.
长期不同施肥下潮土磷素的演变特征 总被引：6，自引：5，他引：1
【目的】研究在施磷量相等的条件下长期施用有机肥和化肥对潮土全磷、有效磷的演变的影响,为潮土地区农业生产和地力培育提供理论依据。【方法】以河南封丘的肥料长期定位试验(开始于1989年)为平台试验设置7个处理,即有机肥(OM)、1/2有机肥+1/2化肥(1/20M)、氮磷钾(NPK)、氮磷(NP)、磷钾(PK)、氮钾(NK)和不施肥处理(CK)分析比较了不同处理土壤的全磷、有效磷含量及两者比值的演变规律。【结果】所有施磷处理土壤全磷均与试验年份呈显著线性相关,1/2有机肥+1/2化肥、有机肥和氮磷钾处理土壤全磷年均增加量为0.0083、0.0081和0.011 g/kg;各处理2008~2010年3年平均土壤有效磷含量大小顺序为PKOM1/20MNPKNPCKNK施磷处理下试验进行的前11年土壤有效磷快速增加,以后达到稳定状态;有机肥处理和1/2有机肥+1/2化肥处理土壤有效磷与全磷的比值显著高于氮磷钾处理,试验20年后有机肥处理和1/2有机肥+1/2化肥处理有效磷/全磷是氮磷钾处理的1.9和1.4倍。磷素平衡与全磷及有效磷含量均达到了极显著相关相关系数分别为0.981和0.886。磷素盈亏每增加100 kg/hm2土壤全磷含量增加0.04 g/kg土壤有效磷含量增加约为2 mg/kg。试验20年后其他理化性质与土壤全磷、有效磷含量之间的相关关系均未达到显著水平。但土壤有机质和土壤全氮与有效磷/全磷的相关系数达到了显著水平,说明土壤有机质和全氮含量提高有利于土壤磷素的活化。【结论】土壤全磷和有效磷的演变都显著受磷素盈亏的影响。在每年P_2O_5投入量相当于135 kg/hm~2时施用化肥更加有利于潮土全磷含量的提高;经过21年的不同施肥处理,平衡施用化肥处理有效磷含量只能维持在7 mg/kg左右这一水平处于中低水平,依旧需要磷的投入才能维持作物的高产。施用有机肥可以在不增加施磷量的条件下增加作物可吸收利用的磷。因此减少施磷量增施有机肥可能成为潮土地区减肥增效的重要手段。 相似文献
11.
以棕壤为例研究了15对不同肥力水平的典型棕壤、棕壤型水稻土的特征微团聚体（＜10m和＞10m）的组成比例，结果表明该比例即微团聚体（＜10m）／微团聚体（＞10m）可成为土壤肥力水平的一个综合指标。以该指标为标准的典型棕壤和棕壤型水稻土肥、瘦地区分界数分别为0.25和0.35，小于此二值分别为各自肥地，反之亦反。土壤培肥措施可使肥、瘦地特征微团聚体的比例降低并提高土壤肥力水平或根本改变瘦地肥力实质。 相似文献
12.
《Communications in Soil Science and Plant Analysis》2012,43(3-4):607-620
Abstract The effect of placement (broadcast versus banded) and level of phosphorus (P) applied as superphosphate at 0 to 450 kg P/ha was measured using the yields of cauliflower (Brassica oleracea var botrytis) on newly cleared Karrakatta sands of low natural P fertility. While there was a significant (P<0.01) yield response to level of P, there was no significant response to fertilizer placement. Phosphorus recovery efficiency by curds (P uptake curds/P applied both in kg/ha) decreased from 0.35 at 20 to 0.09 at 320 kg applied P/ha. Phosphorus recovery efficiency by whole plants decreased from 0.58 at 20 kg P/ha to 0.18 at the highest level. Bicarbonate‐soluble P extracted from the top 15 cm of soil was determined on residual P sites from experiments over two years where P was applied from 0 to 450 kg P/ha. These soil test values were related to yield. The critical soil test values required for 95 and 99% of maximum yield were 40 and 55 (μg/g, respectively. The level of freshly‐applied P required for either 95 or 99% of maximum yield varied from 108 to 175 kg P/ha, respectively at <5 μg/g soil test P to 0 at the critical values. Phosphorus in the youngest expanded leaf at buttoning required for 95 and 99% of maximum yield was 0.46±0.02 and 0.47±0.02%, respectively. 相似文献
13.
Martin S. A. Blackwell Alison M. Carswell Roland Bol 《Biology and Fertility of Soils》2013,49(1):79-87
The rate at which dried soils are rewetted can affect the quantities and forms of nutrients in leachates. Both dried and moist replicated (n?=?3) samples of two contrasting grassland soil types (clayey vs brown earth) were irrigated during laboratory experiments with identical total amounts of water, but at different rates, ranging from 0 h, increasing by 30-min increments up to 4 h, and additionally a 24-h rewetting rate. Total P concentrations in leachates from dried samples of both soils generally decreased as rewetting rate increased, ranging from 2,923?±?589 μg P L?1 (0.5 h rewetting rate) to 731?±?46.0 μg P L?1 (24 h, clayey soil) and 1,588?±?45.1 μg P L?1 (0.5 h) to 439?±?25.5 μg P L?1 (24 h brown earth). Similar patterns in concentrations occurred for molybdate reactive P (MRP), although concentrations were generally an order of magnitude lower, indicating that the majority of the leached P was probably organic. The moist brown earth leached relatively high concentrations of MRP (maximum 232?±?10.6 μg P L?1, 0.5 h), unlike the moist clayey soil (maximum 20.4?±?10.0 μg P L?1, 0 h). The total oxidised N concentrations in leachates were less affected by rewetting rate, although longer rewetting rates resulted in decreased concentrations in leachates from the dried samples of both soils. The difference in responses to rewetting rates of the two soils is probably due to differences in the fate of the microbial biomass and adsorption properties in the soils. Results show that soil moisture could be an important factor in regulating nutrient losses and availability, especially under changing patterns of rainfall predicted by future climate change scenarios. 相似文献
14.
施肥条件下瘠薄红壤的物理肥力恢复特征 总被引：7，自引：1，他引：7
在中国科学院红壤生态开放实验站布置田间长期定位试验,研究施肥条件下瘠薄红壤的肥力恢复特征,本文报道土壤物理性状的变化。结果表明,施用有机肥处理的大团聚体含量比单施化肥处理高100~150g/kg。施用有机肥6年,旱作条件下大团聚体含量达到500~600g/kg,已接近丰产桔园红壤的含量水平,而单施化肥处理为400~450g/kg,比一般红壤条件还低。耕种6年后,红壤的容重降至0.9~1.1mg/cm3。施用有机肥还提高土壤的总孔隙度1%~8%;提高传导孔隙的比例3%~20%;使 >200 m孔隙的比例达到9.6%~.9%,平均14.6%,接近丰产桔园的水平;提高田间持水量0.7%~4.5%,显著增强土壤的持水能力。因此,有机肥施用是恢复和保持红壤物理肥力的重要而有效的措施。 相似文献
15.
M. M. Morales N. Comerford I. A. Guerrini N. P. S. Falcão J. B. Reeves 《Soil Use and Management》2013,29(3):306-314
The term biochar refers to materials with diverse chemical, physical and physicochemical characteristics that have potential as a soil amendment. The purpose of this study was to investigate the P sorption/desorption properties of various slow biochars and one fast pyrolysis biochar and to determine how a fast pyrolysis biochar influences these properties in a degraded tropical soil. The fast pyrolysis biochar was a mixture of three separate biochars: sawdust, elephant grass and sugar cane leaves. Three other biochars were made by slow pyrolysis from three Amazonian tree species (Lacre, Ingá and Embaúba) at three temperatures of formation (400 °C, 500 °C, 600 °C). Inorganic P was added to develop sorption curves and then desorbed to develop desorption curves for all biochar situations. For the slow pyrolysis, the 600 ºC biochar had a reduced capacity to sorb P (4–10 times less) relative to those biochars formed at 400 °C and 500 °C. Conversely, biochar from Ingá desorbed the most P. The fast pyrolysis biochar, when mixed with degraded tropical mineral soil, decreased the soil's P sorption capacity by 55% presumably because of the high soluble, inorganic P prevalent in this biochar (909 mg P/kg of biochar). Phosphorus desorption from the fast pyrolysis biochar/soil mixture not only exhibited a common desorption curve but also buffered the soil solution at a value of ca. 0.2 mg/L. This study shows the diversity in P chemistry that can be expected when biochar is a soil amendment and suggests the potential to develop biochars with properties to meet specific objectives. 相似文献
16.
Nitrogen (N) and phosphorus (P) deficiencies are key constraints in rainfed lowland rice (Oryza sativa L.) production systems of Cambodia. Only small amounts of mineral N and P or of organic amendment are annually applied to a single crop of rainfed lowland rice by smallholder farmers. The integration of leguminous crops in the pre‐rice cropping niche can contribute to diversify the production, supply of C and N, and contribute to soil fertility improvement for the subsequent crop of rice. However, the performance of leguminous crops is restricted even more than that of rice by low available soil P. An alternative strategy involves the application of mineral P that is destined to the rice crop already to the legume. This P supply is likely to stimulate legume growth and biological N2 fixation, thus enhancing C and N inputs and recycling N and P upon legume residue incorporation. Rotation experiments were conducted in farmers' fields in 2013–2014 to assess the effects of P management on biomass accumulation and N2 fixation (δ15N) by mungbean (Vigna radiata L.) and possible carry‐over effects on rice in two contrasting representative soils (highly infertile and moderately fertile sandy Fluvisol). In the traditional system (no legume), unamended lowland rice (no N, + 10 kg P ha?1) yielded 2.8 and 4.0 t ha?1, which increased to 3.5 and 4.7 t ha?1 with the application of 25 kg ha?1 of urea‐N in the infertile and the moderately fertile soil, respectively. The integration of mungbean as a green manure contributed up to 9 kg of biologically fixed N (17% Nfda), increasing rice yields only moderately to 3.5–4.6 t ha?1. However, applying P to mungbean stimulated legume growth and enhanced the BNF contribution up to 21 kg N ha?1 (36% Nfda). Rice yields resulting from legume residue incorporation (“green manure use”–all residues returned and “grain legume use”–only stover returned) increased to 4.2 and 4.9 t ha?1 in the infertile and moderately fertile soil, respectively. The “forage legume use” (all above‐ground residues removed) provided no yield effect. In general, legume residue incorporation was more beneficial in the infertile than in the moderately fertile soil. We conclude that the inclusion of mungbean into the prevailing low‐input rainfed production systems of Cambodia can increase rice yield, provided that small amounts of P are applied to the legume. Differences in the attributes of the two major soil types in the region require a site‐specific targeting of the suggested legume and P management strategies, with largest benefits likely to accrue on infertile soils. 相似文献
17.
The Soreq recharge basins, used for wastewater reclamation employing the Soil-Aquifer Treatment (SAT) system, have been recharged, on average, by about 1,800 m depth of secondary effluent during their operation period of ～25 years. An estimated amount of ～6 kg P m?2 was added to the soil/sediment column during this period. The objective of this study was to compare phosphorous sorption characteristics of representative pristine soils in the Soreq recharge site to those of the basin soils sampled after a long period of effluent recharge. Batch isotherm experiments were conducted: samples of one g of soil were equilibrated with 25 mL of 0.02 M NaCl solution containing 0–3.2 mM of phosphate for 7 days at 25± 1°C and P sorption was measured. Long-term effluent recharge significantly decreased the maximum P sorption capacity of the top sandy soil (0.15–0.3 m) and only very slightly decreased maximum P isotherm capacity of the deep clayey-sand soil (10–10.5 m). The retention of P in the basin sandy soil primarily involved sorption and surface precipitation reactions on soil carbonates. In the basin clayey-sand soil, P was retained by its sorption on surfaces of Fe, Al, Mn oxide/hydroxides and clay minerals. Long-term effluent recharge increased EPC0, (the equilibrium P concentration in solution at which there is no sorption or desorption to or from the soil under the given conditions), of the basin soils compared to the pristine soils. Due to loading of the top horizons with P by prolonged recharge and reduced P concentration in the effluent, EPC0 of the basin sandy soil is now equal to the average P concentration of the recharged effluents. If effluent P concentration will decrease further, the top sandy soil will become a source of P to the reclaimed water, rather than a sink. The clayey-sand layers and lenses in the vadose zone of the SAT system of the Soreq site offer a large capacity for P adsorption. With gradual leaching of carbonate minerals and synthesis of secondary clay minerals, driven by long-term effluent recharge, P retention mechanisms in the basin soil may be changed, but this process would be extremely slow. 相似文献
18.
This study set out to determine the effects of cattle manure and inorganic N‐fertilizer application on the hydraulic properties and maize yield of a clay and sandy soil in a smallholder farming area of Zimbabwe. Four fields classified as homefields (HF: more fertile and closer to homesteads) and outfields (OF: less fertile and further from the homesteads) were selected on clay and sandy soil. They were subjected to four treatments, control (no fertility amendment), 5, 15 and 25 t/ha cattle manure + 100 kg/ha N (as ammonium nitrate) for 7 years. A two‐way randomized complete block design was used with fertility and field type as the two factors. Clay soil hydraulic properties, which included density of macropores with a diameter >300 μm, unsaturated hydraulic conductivity, steady‐state infiltration rate, moisture retention under low suction and maize grain yield, were significantly improved (P < 0.05) by fertility management compared with the control and were generally comparable between the HF and OF. Fertility management significantly improved maize grain yield on sandy soils but did not enhance hydraulic parameters, thereby indicating poor responsiveness in structural build‐up. On the other hand, significantly different hydraulic parameters between the sandy soil HF and OF suggested effects of other factors not related to soil fertility and field type treatments. We therefore concluded that application of a high rate (25 t/ha) of cattle manure and inorganic N‐fertilizer is beneficial for fertility restoration to the degraded OFs with associated comparable hydraulic properties on HFs and OFs on clay soil, unlike on sandy soil. 相似文献
19.
Storage and dynamics of carbon and nitrogen in soil physical fractions following woody plant invasion of grassland 总被引：1，自引：0，他引：1
Woody plant invasion of grasslands is prevalent worldwide. In the Rio Grande Plains of Texas, subtropical thorn woodlands dominated by C3 trees/shrubs have been replacing C4 grasslands over the past 150 yr, resulting in increased soil organic carbon (SOC) storage and concomitant increases in soil total nitrogen (STN). To elucidate mechanisms of change in SOC and STN, we separated soil organic matter into specific size/density fractions and determined the concentration of C and N in these fractions. Soils were collected from remnant grasslands (Time 0) and woody plant stands (ages 10-130 yr). Rates of whole-soil C and N accrual in the upper 15 cm of the soil profile averaged 10-30 g C m−2 yr−1 and 1-3 g N m−2 yr−1, respectively, over the past 130 yr of woodland development. These rates of accumulation have increased soil C and N stocks in older wooded areas by 100-500% relative to remnant grasslands. Probable causes of these increased pool sizes include higher rates of organic matter production in wooded areas, greater inherent biochemical resistance of woody litter to decomposition, and protection of organic matter by stabilization within soil macro- and microaggregates. The mass proportions of the free light fraction (<1.0 g cm−3) and macroaggregate fraction (>250 μm) increased linearly with time following woody plant invasion of grassland. Conversely, the mass proportions of free microaggregate (53-250 μm) and free silt+clay (<53 μm) fractions decreased linearly with time after woody invasion, likely reflecting stabilization of these fractions within macroaggregate structures. Carbon and N concentrations increased in all soil fractions with time following woody invasion. Approximately half of the C and N accumulated in free particulate organic matter (POM) fractions, while the remainder accrued in stable macro- and microaggregate structures. Soil C/N ratios indicated that the organic C associated with POM and macroaggregates was of more recent origin (less decomposed) than C associated with the microaggregate and silt+clay fractions. Because grassland-to-woodland conversion has been geographically extensive in grassland ecosystems worldwide during the past century, changes in soil C and N storage and dynamics documented here could have significance for global cycles of those elements. 相似文献
20.
P. F. NORTH 《European Journal of Soil Science》1976,27(4):451-459
Calibrations enabled controlled application of a range of known dispersive energies to a selected soil sample. The corresponding levels of dispersion were measured in terms of the weight fraction of particles <2 μm equivalent spherical diameter produced, and are used to define a dispersion characteristic for the test soil. Interpretation of this characteristic in terms of a microaggregate theory provides the energy value associated with complete ‘primary dispersion’ of microaggregates, which under normal field conditions is a direct practical measure of soil stability. This leads to a definition of the specific stability index (σ) of a soil which for the gleyed brown earth used in this work has the value (25±3) J g?1. 相似文献