Effects of Long-Term Winter Planted Green Manure on Distribution and Storage of Organic Carbon and Nitrogen in Water-Stable Aggregates of Reddish Paddy Soil Under a Double-Rice Cropping System

In agricultural systems, maintenance of soil organic matter has long been recognized as a strategy to reduce soil degradation. Manure amendments and green manures are management practices that can increase some nutrient contents and improve soil aggregation. We investigated the effects of 28 yr of winter planted green manure on soil aggregate-size distribution and aggregateassociated carbon（C） and nitrogen（N）. The study was a randomized completed block design with three replicates. The treatments included rice-rice-fallow, rice-rice-rape, rice-rice-Chinese milk vetch and rice-rice-ryegrass. The experiment was established in 1982 on a silty light clayey paddy soil derived from Quaternary red clay（classified as Fe-Accumuli-Stagnic Anthrosols） with continuous early and late rice. In 2009, soil samples were collected（0-15 cm depth） from the field treatment plots and separated into water-stable aggregates of different sizes（i.e., 〉5, 2-5, 1-2, 0.5-1, 0.25-0.5 and 〈0.25 mm） by wet sieving. The long-term winter planted green manure significantly increased total C and N, and the formation of the 2-5-mm water-stable aggregate fraction. Compared with rice-rice-rape, rice-rice-Chinese milk vetch and rice-rice-ryegrass, the rice-rice-fallow significantly reduced 2-5-mm water-stable aggregates, with a significant redistribution of aggregates into micro-aggregates. Long-term winter planted green manure obviously improved C/N ratio and macro-aggregate-associated C and N. The highest contribution to soil fertility was from macro-aggregates of 2-5 mm in most cases.

Soil water content and nitrogen differentially correlate with multidimensional leaf traits of two temperate broadleaf species

The variation and correlation of leaf economics and vein traits are crucial for predicting plant ecological strategies under different environmental changes.However,correlations between these two suites of traits and abiotic factors such as soil water and nitrogen content remain ambiguous.We measured leaf economics and vein traits as well as soil water and nitrogen content for two different shade-tolerant species(Betula platyphylla and Acer mono)in four mixed broadleaved-Korean pine(Pinus koraiensis)forests along a latitudinal gradient in Northeast China.We found that leaf economics traits and vein traits were decoupled in shade-intolerant species,Betula platphylla,but significantly coupled in a shadetolerant species,A.mono.We found stronger correlations among leaf traits in the shade tolerant species than in the shade intolerant species.Furthermore,leaf economic traits were positively correlated with the soil water gradient for both species,whereas vein traits were positively correlated with soil water gradient for the shade intolerant species but negatively correlated in the shade tolerant species.Although economic traits were positively correlated with soil nitrogen gradient in shade intolerant species but not correlated in shade tolerant species,vein traits were negatively correlated with soil nitrogen gradient in shade tolerant species but not correlated in shade intolerant species.Our study provides evidence for distinct correlations between leaf economics and vein traits and local abiotic factors of species differing in light demands.We recommend that the ecological significance of shade tolerance be considered for species when evaluating ecosystem functions and predicting plant responses to environmental changes.

Effects of degradation succession of alpine wetland on soil organic carbon and total nitrogen in the Yellow River source zone,west China

Wetland is an important carbon pool,and the degradation of wetlands causes the loss of organic carbon and total nitrogen.This study aims to explore how wetland degradation succession affects soil organic carbon(SOC)and total nitrogen(TN)contents in alpine wetland.A field survey of 180 soilsampling profiles was conducted in an alpine wetland that has been classified into three degradation succession stages.The SOC and TN contents of soil layers from 0 to 200 cm depth were studied,including their distribution characteristics and the relationship between microtopography.The results showed that SOC and TN of different degradation succession gradients followed the ranked order of Non Degradation(ND)>Light Degradation(LD)>Heavy Degradation(HD).SWC was positively correlated with SOC and TN(p<0.05).As the degree of degradation succession worsened,SOC and TN became more sensitive to the SWC.Microtopography was closely related to the degree of wetland degradation succession,SWC,SOC and TN,especially in the topsoil(0-30 cm).This result showed that SWC was an important indicator of SOC/TN in alpine wetland.It is highly recommended to strengthen water injection into the wetland as a means of effective restoration to reverse alpine meadow back to marsh alpine wetland.

Contents of soil organic carbon and nitrogen in water-stable aggregates in abandoned agricultural lands in an arid ecosystem of Northwest China

Soil organic matter content in water-stable aggregates（WSA） in the arid ecosystems（abandoned agricultural lands especially） of China is poorly understood. In this study, we examined the WSA sizes and stability, and soil organic carbon（OC） and nitrogen（N） contents in agricultural lands with abandonment ages of 0, 3, 12, 20, 30 and 40 years, respectively, in the Minqin Oasis of Northwest China. The total soil OC and N contents at depths of 0–20, 20–40 and 40–60 cm in abandoned agricultural lands were compared to those in cultivated land（the control）. Agricultural land abandonment significantly（P0.25 mm） as the age of agricultural land abandonment increased. The effect of abandonment ages of agricultural lands on MWD was determined by the changes of OC and N accumulation in WSA sizes ＆gt;2 mm. The total OC and N contents presented a stratification phenomenon across soil depths in this arid ecosystem. That is, both of them decreased significantly at depths of 0–20 and 40–60 cm while increased at the depth of 20–40 cm. The WSA sizes ＆lt;0.053 mm had the highest soil OC and N contents（accounting for 51.41%–55.59% and 42.61%–48.94% of their total, respectively）. Soil OC and N contents in microaggregates（sizes 0.053–0.25 mm） were the dominant factors that influenced the variations of total OC and N contents in abandoned agricultural lands. The results of this study suggested that agricultural land abandonment may result in the recovery of WSA stability and the shifting of soil organic matter from the silt＋clay（＆lt;0.053 mm） and microaggregate fractions to the macroaggregate fractions. However, agricultural land abandonment did not increase total soil OC and N contents in the short-term.

The effects of water and nitrogen on the roots and yield of upland and paddy rice

It is of great significance to study the root characteristics of rice to improve water and nitrogen(N) use efficiency and reduce environmental pollution. This study investigated whether root traits and architecture of rice influence grain yield, as well as water and N utilization efficiency. An experiment was conducted using the upland rice cultivar Zhonghan 3(a japonica cultivar) and paddy rice cultivar Huaidao 5(also a japonica cultivar) using three N levels, namely, 2 g urea/pot(low amount, LN), 3 g urea/pot(normal amount, NN), and 4 g urea/pot(high amount, HN), and three soil water potentials(SWPs, namely, well-watered(0 kPa), mildly dried(–20 kPa) and severely dried(–40 kPa). The results showed that with decreasing SWP, the percentage of upland rice roots increased in the 0–5 cm tillage layer, and decreased in the 5–10 and 10–20 cm tillage layers, whereas paddy rice roots showed the opposite trend. With increasing amounts of N, the yield of upland and paddy rice increased, and the percentage of root volume ratios of the two rice cultivars in the 0–5 and 5–10 cm tillage layers increased, whereas that in the 10–20 cm tillage layer decreased. The roots of upland rice are mainly distributed in the 10–20 cm tillage layer, whereas most paddy rice roots are in the 0–5 cm tillage layer. These results indicate that the combination of-20 kPa SWP and NN in upland rice and 0 kPa SWP and LN in paddy rice promotes the growth of the root system during the middle and late stages, which in turn may decrease the requirements for water and N fertilizer and increase rice yield.

Effects of biological soil crusts on profile distribution of soil water,organic carbon and total nitrogen in Mu Us Sandland,China

Aims Biological soil crusts(BSCs)can affect soil properties including water dynamics and cycling of soil carbon and nitrogen in dryland ecosystems.Previous research has mostly focused on effects of BSCs on soil water distribution or carbon and nitrogen fixation in the surface soil layer.Thus,little is known about effects of BSCs on properties throughout the soil profile.In the current study,we assessed the effects of BSCs on the distribution of soil water content(SW),soil organic carbon content(SOC)and soil total nitrogen content(STN)throughout the soil profile as well as the influence of water conditions on the effects of BSCs.Methods In a field investigation in Mu Us Sandland,North China,soil samples were taken from plots with and without BSCs on 13 and 28 September 2006,respectively.On the two sampling dates,average soil gravimetric water content was 3.83%(61.29%)and 5.08%(60.89%),respectively,which were regarded as low and high water conditions.Soil samples were collected every 5 cm to a depth of 60 cm,and SW,SOC and STN were measured in the laboratory.Important Findings(i)BSCs affected profile distribution of SW,SOC and STN.In addition,water conditions within the plots significantly modified BSCs’effects on the profile distribution of SW,but marginally affected the effects on SOC and STN.(ii)Under high water conditions,SW in the surface soil layer(0–10 cm)was higher in soils with BSCs compared to those without BSCs,while the opposite was true in the deep soil layer(30–55 cm).(iii)Under low water conditions,SW was lower with BSCs compared with no BSCs in near-surface(5–20 cm)and deep(25–40 cm)soil layers.(iv)BSCs affected SOC and STN only in the surface soil layer(0–5 cm)and were modified by plot water conditions.

等氮量有机替代对水稻田面水氮素动态变化特征研究

为了防控高原湖泊流域稻田氮素径流流失,保护受纳水体生态环境。在洱海流域水旱轮作种植模式下,设置不施肥(CK)、单施化肥(NPK)、有机无机配施(NPKS)、有机肥全量替代(SS)4个等氮量有机替代处理,研究水稻田面水氮素浓度的动态变化特征,探讨有机肥替代化肥施用对田面水氮素流失的影响。试验结果表明:基肥施用后田面水NH_(4)^(+)-N、NO_(3)^(-)-N、Org-N和TN浓度迅速升高,在3~7 d内达到峰值,施肥后7 d是防止田面水氮素大量流失的关键风险期。等氮量有机替代种植,田面水中NH_(4)^(+)-N/TN浓度占比为39.01%~54.01%,NO_(3)^(-)-N/TN浓度占比为11.33%~21.62%,Org-N/TN浓度占比为33.85%~41.94%。化肥氮施用增加田面水NH_(4)^(+)-N/TN浓度占比,有机肥施用增加田面水NO_(3)^(-)-N/TN和Org-N/TN浓度占比。等氮量有机替代对田面水氮素浓度的响应随施肥天数的增加而减弱,田面水NH_(4)^(+)-N、NO_(3)^(-)-N、Org-N、TN的浓度变化呈一元二次多项式下降,基肥施氮后35~40 d田面水氮素浓度趋于稳定低水平。在3种有机替代种植方式中,NPKS处理可降低田面水氮素浓度,降低稻田氮素流失风险。

施氮量对川东南冬水田稻鱼共作系统下杂交稻产量和土壤养分的影响

【目的】利用川东南冬水田区连续多年稻鱼共作系统,研究施氮(N)量对免耕栽培杂交稻产量形成和土壤养分的影响,为制定稻鱼共作系统下免耕栽培杂交稻长期、合理的氮肥管理策略提供理论依据。【方法】于2018—2022年在川东南冬水田区开展了5年大田定位试验,供试杂交稻品种为蓉优1015和内6优103,耕作方式为免耕。设置N 0、45、90、135 kg/hm^(2)4个施氮水平,分别记作N_(0)、N_(45)、N_(90)、N_(135)。在水稻收获期,调查杂交稻产量及产量构成因素,分析0—20 cm土层土壤全量和速效氮、磷、钾含量,以及有机质含量和pH,通过回归分析,研究施氮量与水稻产量和土壤养分因子含量变化之间的关系。【结果】稻鱼共作系统下,年份、施氮量对杂交稻产量及产量构成的影响达极显著水平。5年间,杂交稻产量与施氮量均呈极显著正相关(r=0.9070^(**)~0.9720^(**)),与低氮量处理N_(45)相比,N_(90)和N_(135)处理杂交稻产量分别增加了6.37%~26.53%、9.11%~25.11%,单位面积有效穗数和每穗粒数也显著增加。而N_(90)处理杂交稻产量与N_(135)处理相当或更高。逐步回归分析结果表明,杂交稻产量构成(单位面积有效穗数、每穗粒数、结实率和千粒重)与产量的偏相关系数达显著或极显著水平(t=2.20*~9.17^(**))。通径分析结果表明,杂交稻单位面积有效穗数和每穗粒数对产量的直接贡献(分别为0.8754和0.4987)和总贡献(分别为0.6364和0.3598)较大,表明单位面积有效穗数和每穗粒数是影响产量的主要因素。在N_(0)、N_(45)处理下,土壤全氮、碱解氮含量随稻鱼共作年限的增加而下降,而在N_(90)、N_(135)处理下随稻鱼共作年限的增加而增加。土壤全氮、碱解氮含量随施氮量增加而提高,而全磷、全钾、速效磷、速效钾含量则随施氮量增加而下降。杂交稻产量与土壤养分含量呈极显著正相关,可见提高磷素、钾素供给能力是稻鱼共作系统杂交稻高产的重要基础。【结论】川东南冬水田区稻鱼共作系统下,年施氮90 kg/hm^(2)可以提高杂交水稻的单位面积有效穗数和每穗粒数,进而维持甚至提高水稻产量。连续施用中、高量氮肥还可以提升土壤有机质、全氮、全磷、全钾、碱解氮、速效磷和速效钾含量,且随稻鱼共作年限延长呈增加趋势;土壤pH值则随稻鱼共作年限延长呈下降趋势。

水稻秸秆炭施用对水稻土团聚体稳定性及其碳氮分布的影响

[目的]水稻长期种植过程中大量化肥施用导致土壤结构变差,研究不同用量水稻秸秆生物炭和化肥配施对水稻土结构和碳、氮分布的影响,探索稻田优化施肥管理方式。[方法]水稻田间试验在浙江衢州进行,试验设不施肥对照(CK)、常规施肥处理(NPK)以及常规施肥基础上添加22.5 t/hm^(2)(NPK+1%B)、45 t/hm(NPK+2%B)和90 t/hm^(2)(NPK+4%B)水稻秸秆炭处理,共5个处理。水稻收获后采集0-20 cm土层样品,测定土壤及不同粒级团聚体(>2、0.25~2、0.053~0.25和<0.053 mm)的有机碳和全氮含量,评价团聚体的稳定性。[结果]与NPK处理相比,施用水稻秸秆炭4年后,土壤>0.25 mm粒级团聚体含量提高了2.43%~7.99%,<0.25 mm粒级团聚体含量降低了2.93%~9.63%,土壤有机碳和全氮含量分别提高了16.40%~45.16%和14.67%~36.69%,各指标的变幅均以NPK+4%B处理最大。与NPK处理相比,秸秆炭处理土壤中>2 mm粒级团聚体中的有机碳和全氮含量分别提高了23.96%~70.87%和19.44%~47.56%,0.25~2 mm粒级团聚体中分别提高了21.87%~49.27%和17.18%~37.47%,增幅均以NPK+4%B处理最高,而0.053~0.25和<0.053 mm粒级团聚体中的有机碳和全氮含量无显著差异(P>0.05),说明施用水稻秸秆炭4年后,增加的土壤有机碳和全氮主要积累在>0.25 mm粒级团聚体中。与NPK处理相比,秸秆炭处理水稻土C/N值提高了2.40%~5.69%,但各处理间差异不显著,而4个粒级团聚体的土壤C/N值均显著提升,且均以NPK+4%B处理提高效果最好。此外,施用水稻秸秆炭提高了>2和0.25~2 mm粒级团聚体的碳、氮贡献率6.54%~17.43%、3.67%~7.28%和5.16%~11.55%、0.57%~1.83%,降低了0.053~0.25和<0.053 mm粒级团聚体的碳、氮贡献率7.25%~29.27%、15.93%~33.68%和10.26%~26.80%、12.61%~30.78%(P<0.05)。[结论]施用水稻秸秆炭能够迅速显著提高水稻土有机碳和全氮含量,增加>0.25 mm粒级团聚体质量占比,提高>2 mm粒级团聚体中有机碳的贡献率,降低<0.25 mm粒级团聚体中有机碳和全氮贡献率,且其影响幅度与水稻秸秆炭施用量呈正比。由此可见,施用水稻秸秆炭能在一定程度上改善水稻土结构,提高水稻土碳、氮固持潜力,对保证水稻土结构稳定性和维持水稻持续高产具有重要意义。

地表水氮磷采测分离监测与研究

在“十四五”国家地表水环境质量监测网采测分离项目中,选择总磷和总氮两个指标作为研究对象。从总磷和总氮含量的分析方法、采样规范性和准确度、分析人员能力等多方面探讨研究单项测定结果对平均值的偏离程度。研究结果表明总磷浓度≤0.04 mg/L时,相对偏差范围应在±35%为宜;总磷浓度在0.04 mg/L~0.1 mg/L时,相对偏差范围应在±20%为宜;总磷浓度>0.1 mg/L时,相对偏差范围应在±15%为宜;总氮浓度≤1 mg/L时,相对偏差范围应在±20%为宜,总氮浓度在>1 mg/L时,相对偏差范围应在±10%为宜。

废弃矿区氨氮污染及其空间分布情况研究

为了对废弃矿区的氨氮污染及其空间分布进行分析,研究选取了江西省一座废弃的稀土矿作为研究区域,并进行土壤和水采样点的设置。研究对样品中的氨氮含量进行了测量,采用单因子指数法对氨氮污染进行评价,并对该污染的空间分布进行分析。结果显示,土壤样品氨氮含量最大值为492.8134 mg·kg^(-1),最小值为0.9595 mg·kg^(-1)。水样品氨氮含量的最大值71.54 mg·L^(-1),最小值为0.32 mg·L^(-1)。研究区域积液地及其附近地区地表水氨氮污染和土壤氨氮污染更加严重。

全自动凯氏定氮仪测定水系沉积物、土壤、岩石全氮含量方法的优化探索

本文通过改变硫酸钾(K_(2)SO_(4))和五水硫酸铜(CuSO4·5H2O)两个联合消化催化剂比例,以及消化催化剂加入量、辛醇滴入量和浓硫酸加入量等条件,探究KII60型全自动凯氏定氮仪在测定水系沉积物与土壤中全氮含量方法的优化以及对比。该方法得出在加入硫酸钾(K_(2)SO_(4))与五水硫酸铜(CuSO4·5H2O)质量比为9:1,加入浓硫酸量为6mL,辛醇最佳滴入量2滴为最佳条件。方法检出限低至25μg/g,相对标准偏差小于2.2%,相对误差小于0.65%,测定结果与传统方法无显著性差异。该方法简便、快捷、准确度高、精密度好,环境友好型,适用于水系沉积物、土壤和岩石中全氮含量的批量测定。

连续流动分析法同时测定地表水中的总氮和氨氮

结合地表水特性,为充分了解连续流动分析法在其总氮和氨氮测定中的实用价值。本研究通过采集地表水样本,运用连续流动分析法和手工法进行测定,统计两种方法的检测结果。连续流动分析法检测总氮、氨氮的线性范围内的相关系数(r)分别为0.9998、0.9997,检出限均为0.04 mg/L。检出精密度总氮、氨氮相对标准偏差分别在1.11%~2.38%、0.76%~1.28%范围内。以手工方法为对照,连续流动分析法的中总氮、氨氮样品检出准确度误差更低,且准确度与要求相符合。证实在地表水检测中,连续流动分析法不仅操作更加简单方便快捷,且有着更高的精密度和更好的准确度,可以更好满足实验室质量控制要求,可应用于地表水大批量样品的测定。

河北省入海河流总氮溯源经验及控制技术分析

本研究通过采用无人机飞行检查、人工加密监测、污染源沿河徒步排查等多种技术手段融合的总氮溯源方法,在河北省秦皇岛市重要河流入海口的上游流域,围绕氮素相关水质指标进行污染源排查和现场监测,对河流总氮的来源进行了分类统计与分析。结果表明,导致该地区河流总氮浓度升高的关键因子是硝酸盐氮,总氮污染的来源主要为工厂尾水排放、废水直排等工业源、城乡居民生活污水和垃圾等生活源以及农林种植、养殖等农业源,研究人员根据总氮溯源分析的实践经验,针对不同来源的总氮污染提出了控制削减技术与管理建议。

红壤性水稻土有机无机复合体中碳氮特征对长期施肥的响应

【目的】研究长期施肥对红壤性水稻土有机无机复合体中有机碳(OC)、全氮(TNOIC)特征的影响,为红壤性水稻土管理和培育土壤肥力提供依据。【方法】以长期定位施肥试验的红壤性水稻土为研究对象(始于1984年),选取CK(不施肥)、PK(施磷钾肥)、NPK(施氮磷钾肥)、NPKM(施70%氮磷钾肥+30%有机肥)4个处理。采集0—20 cm土层土样,分析各粒级(<2、2—10、10—20、20—50和50—250μm)有机无机复合体的分布,并探讨施肥对复合体中有机碳(OC)和全氮(TNOIC)含量、储量和碳氮比(C/N)的影响,以及有机无机复合体中OC和TNOIC对红壤性水稻土有机碳(SOC)、全氮(TN)贡献率的影响。【结果】与不施肥CK相比,施肥处理显著提高了20—50μm粒级复合体的比例,降低了<10μm粒级复合体比例,而NPKM处理与其他施肥处理相比,50—250μm粒级复合体的比例增加更显著;不同施肥对各粒级复合体中OC和TNOIC含量影响不同,与PK相比,NPK处理的50—250μm粒级复合体中OC和TNOIC分别增加了36.3%、80.6%;与NPK相比,NPKM处理的50—250μm粒级复合体中OC和TNOIC含量分别增加了35.4%、19.5%,OC和TNOIC主要分布在10—20μm粒级复合体中,施肥显著降低了<2μm粒级复合体OC和TNOIC储量,同时增加了20—50μm粒级复合体OC和TNOIC储量,与PK相比,NPK处理对<2和50—250μm粒级复合体OC储量分别增加了18.5%和31.2%,TNOIC储量分别增加了18.8%和73.7%,与NPK相比,NPKM处理对<2μm粒级复合体中OC和TNOIC储量分别降低了25.6%和27.4%,而50—250μm粒级复合体则分别提高了56.3%和38.6%;不同施肥处理显著影响50—250μm粒级复合体的C/N,与PK相比,NPK处理的50—250μm粒级复合体的C/N比降低了24.6%,与NPK相比,NPKM处理的50—250μm粒级复合体C/N比提高了13.4%;长期不同施肥显著影响各粒级有机无机复合体对土壤SOC、TN的贡献率,与PK相比,NPK处理50—250μm粒级复合体对SOC、TN贡献率分别提高了17.4%和47.4%。与NPK相比,NPKM处理50—250μm粒级复合体对SOC、TN贡献率分别提高了39.5%和32.8%。【结论】在红壤性水稻土中,长期施肥促使大粒级有机无机复合体形成;化肥中的氮投入显著提高50—250μm粒级复合体中OC、TNOIC含量和储量;有机无机肥配施有利于提高土壤有机碳含量,提高大粒级有机无机复合体比例,有助于保存施入的无机氮肥,是红壤性水稻土长期培肥管理的有效措施。

不同水氮管理模式下黑土稻田碳固定与碳减排效应分析

为探寻不同水氮管理模式对黑土稻田碳固定与碳减排效应的影响,进行了田间试验研究。设置常规淹灌(F)与控制灌溉(C)两种灌溉模式,选用110 kg/hm^(2)(N)、99 kg/hm^(2)(N1,减氮10%)、88 kg/hm^(2)(N2,减氮20%)3种施氮量,测定了6种水氮管理模式下的水稻土壤呼吸CO_(2)排放强度和CH4排放强度,水稻收获后各器官干物质量、碳含量及固碳量,并计算了净土壤碳收支情况。结果表明,不同水氮管理模式下,各处理土壤呼吸CO_(2)排放量呈现单峰值变化,并在分蘖期达到峰值;各处理甲烷排放量呈现双峰值变化且在分蘖期与穗肥施入后达到峰值。相同灌溉方式下,随着施氮量的减少,土壤呼吸CO_(2)排放强度与甲烷排放强度也显著减少(P<0.05)。相同施氮量下,控制灌溉相比常规淹灌有效地降低了甲烷排放强度,但提高了土壤呼吸CO_(2)排放强度。不同水氮管理模式下,水稻收获后总固碳量为319.37~489.00 g/m^(2),水稻收获后各器官固碳量由小到大依次为叶、根、茎、穗,分别为植株总固碳量的5.16%~6.72%、5.71%~10.78%、28.62%~36.66%、49.53%~58.70%。控制灌溉相较常规淹灌有效提高了植株固碳能力。在不同水氮管理模式下,水稻的净初级生产力(NPP)与总初级生产力(GPP)均在减氮量10%处理达到最高,相同灌溉方式下,随着施氮量的增大均呈现先增大后减小的变化趋势;相同施氮量下,控制灌溉下NPP、GPP均高于常规淹灌。控制灌溉相比常规淹灌具有更高的生产潜力。除CN处理净土壤碳收支数值呈负值外其余处理均为正值,即除CN处理外其余处理均为土壤净碳增益效果,相同施氮量常规淹灌下土壤净碳增益高于控制灌溉,但差异不显著(P>0.05);随着施氮量的减少相同灌溉制度下各处理土壤碳收支呈先增大后减小的变化趋势。综合考虑,CN1处理可以在保证较高生产能力下提高土壤固碳能力,减少土壤碳损失与稻田温室气体排放。

水氮耦合下黑土区稻田生态系统碳源汇效应分析

为探寻不同水氮耦合方式对黑土区稻田生态系统碳平衡的影响,于2022年开展田间试验,试验设置常规淹灌(F)和稻作控制灌溉(C)两种灌溉模式,同时设置常规施氮水平(N,110 kg/hm~2)、减氮10%水平(N1,99 kg/hm~2)、减氮20%水平(N2,88 kg/hm~2)3种施氮水平,分析不同水氮耦合方式对水稻各器官干物质量、碳含量、稻田土壤呼吸CO_(2)排放通量和CH_(4)排放通量及两者排放总量的影响,并采用净生态系统碳收支(NECB)评价体系对黑土区稻田生态系统碳源汇效应进行分析。结果表明:不同水氮耦合方式下,各处理水稻穗固碳量与根固碳量分别占其总固碳量的26.61%~40.92%、24.63%~31.95%。相同施氮量下,稻作控制灌溉相较于常规灌溉能提高水稻各器官碳含量、干物质量。在水稻全生育期内,各处理CH_(4)排放通量呈现先增加后减小再增加的变化趋势,均在分蘖期与拔节孕穗期出现峰值;各处理土壤呼吸CO_(2)排放通量呈现单峰变化,在分蘖期出现峰值。相同灌溉模式下,除返青期外,各处理CH_(4)排放通量与土壤呼吸CO_(2)排放通量均随施氮量的减少而降低。相同施氮量下,稻作控制灌溉与常规灌溉相比降低了土壤呼吸CO_(2)排放通量及排放总量,但提高了CH_(4)排放通量及排放总量。不同水氮耦合方式下,水稻净初级生产力为4245.82~6958.19 kg/hm~2,穗净初级生产力最高、凋落物净初级生产力最低,分别占其水稻净初级生产力的42.88%~51.82%、3.19%~3.90%。相同施氮量下,稻作控制灌溉模式各处理水稻净初级生产力均大于常规灌溉模式,其中CN、CN1、CN2各处理净初级生产力较FN、FN1、FN2各处理分别增加11.17%、31.92%、2.98%。此外,不同水氮耦合方式下NECB均为正值,表示该黑土区稻田生态系统为净碳“汇”,其中CN1处理净碳收支(1082.87 kg/hm~2)显著高于其他各处理(P<0.05),这说明稻作控制灌溉模式下减氮10%处理的稻田生态系统碳“汇”强度最大。

大亚湾深水网箱养殖海域表层沉积物碳、氮、磷分布特征及污染评估

为系统研究大亚湾深水网箱养殖海域表层沉积物碳、氮、磷分布特征并对其进行污染评估,分别于2021年10月和2022年5月、6月、8月在大亚湾大鹏澳海域采集表层沉积物样品,2021年11月和2022年5月、6月、8月在大亚湾圣告岛-小星山海域采集表层沉积物样品。基于所得表层沉积物中的总有机碳、总氮、总磷等检测结果,通过单因子污染指数(P_(i))法和内梅罗综合污染指数(P_(N))法进行污染状况评估。结果表明,圣告岛-小星山海域2021年11月平均综合污染指数显示处于中度污染状态(2<P_(N)≤3),2022年5月、6月、8月平均综合污染指数显示处于轻度污染状态(1<P_(N)≤2)。大鹏澳海域2021年10月、2022年6月、2022年8月平均综合污染指数显示处于中度污染状态(2<P_(N)≤3),而2022年5月处于轻度污染状态(1<P_(N)≤2)。研究海域表层沉积物总有机碳、总氮、总磷含量分布特征相似,总体上表现为大鹏澳海域略高于圣告岛-小星山海域,养殖区表层沉积物总氮和总磷含量总体上高于非养殖区;与国内其他海域相比,大亚湾表层沉积物总有机碳、总氮、总磷含量处于较低水平;深水网箱养殖对于表层沉积物总有机碳、总氮、总磷含量无明显影响。

水耕历史对稻田-田埂过渡区土壤物理性质与水-氮分布的影响

选取水耕年限分别为2年、19年和>100年稻田,通过野外样品采集与室内分析相结合的方法,对比了稻田田内和田埂土壤物理性质与水-氮分布差异,揭示了水耕历史对稻田-田埂过渡区土壤物理性质与水-氮流失过程的影响机制。结果表明,耕作活动影响了稻田-田埂过渡区土壤容重、孔隙、土壤水分特征曲线和饱和导水率(Ks)等物理性质。随着水耕年限的增加,田内耕作层与田埂表土层、田内犁底层与田埂硬质层的容重差异增大;耕作层的中小孔隙(直径<0.03 mm)含量增加,其他土层的总孔隙和大孔隙(直径>0.3 mm和>0.03 mm)含量降低;田内土壤的Ks下降速度较田埂更快。在测定的吸力范围内(0~100 kPa),2年和19年的耕作层与表土层持水能力相近,而100年耕作层持水能力高于表土层;2年和100年的硬质层与犁底层持水能力相近,而19年硬质层持水能力更强;19年和100年田埂底土层持水能力较田内强。随着水耕年限增加,耕作层与表土层Ks差异减小,硬质层与犁底层Ks差异增加,2年、19年和100年硬质层的Ks分别是对应犁底层的1.10倍、6.90倍和6.32倍,100年田埂底土层的Ks明显高于田内。土壤物理性质的变化影响稻田-田埂过渡区的水-氮分布特征,主要表现为2年稻田的水-氮含量明显低于19年和100年稻田,且19年和100年稻田的水-氮在耕作层聚集。当水耕年限较短时,水-氮同时通过田内和田埂区域快速流失;随着水耕年限的增加,水-氮更易通过田埂发生渗漏。老稻田新修田埂的硬质层土壤会发生退化,再次成为水-氮快速流失位点。因此,对于耕作年限长的稻田,其田埂区域的水-氮渗漏更应引起重视。

长期秸秆还田对潮土土壤团聚体碳氮和作物产量的影响

为探究潮土区长期秸秆还田对土壤团聚体碳、氮含量和作物产量的影响,以河北省低平原潮土区小麦-玉米轮作系统为研究对象,利用38年化肥与秸秆配施长期定位试验,研究了不施肥(CK)和等量氮、磷肥用量下0 kg/hm^(2)(S0)、2250 kg/hm^(2)(S2250)、4500 kg/hm^(2)(S4500)和9000 kg/hm^(2)(S9000)秸秆还田量下,土壤团聚体碳、氮含量和作物产量。结果表明:与不施肥CK相比,长期施肥与秸秆还田可以增加各粒径团聚体中有机碳和全氮含量,其中,秸秆还田对提高0~10 cm表层土壤水稳性团聚体有机碳含量效果较好,且随秸秆还田量的增加,水稳性团聚体有机碳提升效果越明显。长期秸秆还田对各粒径团聚体中碳氮比无较大影响。>0.25 mm团聚体中有机碳和全氮富集系数较高,且0~10 cm土层,S2250、S4500和S9000处理均表现为随着团聚体粒径减小团聚体中有机碳富集系数逐渐降低。长期秸秆还田可以提高作物产量,且高秸秆还田量对小麦产量的提高效果更明显。>0.25 mm团聚体中有机碳含量与小麦产量之间的关系最密切,当该粒径团聚体中有机碳含量增加1 g/kg时,小麦产量可以增加329.62 kg/hm^(2);而0.25~0.053和<0.053 mm团聚体中有机碳含量与小麦产量相关性较差。综上,秸秆还田可以增加土壤团聚体中有机碳含量,提升土壤肥力,促进作物增产。