Soil Phosphorus Release to the Water Bodies in the Upland Fields of Yellow Soil Areas and Impacting Factor

Soil phosphorus release to the water bodies in the upland fields of yellow soil areas and impacting factor was studied in Guizhou province. The results showed that the content of dissolved active P of surface runoff from various upland fields of yellow-soil were significantly different, which the concentrations of dissolved active P of runoff correlated with the contents of available-P, amorphous oxides of A1, and organic matter in the soils. The amount of soil phosphorus release to the water bodies affected by the level of applying P fertilizer and the process of corn growth, which with fertilizing from 150 to 900 kg P205 ha^-1 in the soil with high P level, the average contents of dissolved active P in the permeability-water of the soil increased from 0.020 mg L^-1 to 0.137 mg L^-1. The amount of soil phosphorus release to the water bodies also affected by environmental factor, which the amount of soil phosphorus release significantly increased under the conditions that temperature is 30℃-35℃, water/soil ratios is 15：1-25：1, submergence-time by water is 12-18 h and pH value of acid rains is 3.82-3.73.

Effects of land use change on hydrological cycle from forest to upland field in a catchment,Japan

Understanding the effects of land use change on the hydrological cycle is very important for development of sustainable water resource in an upland field catchment.In this study,soil and hydrological properties in an upland field catchment,which was reclaimed partially from a forest catchment,were compared with another forest catchment.The soil properties of surface and subsurface layers were investigated in the two catchments.The soil was compacted and waterholding capacity of soil in the upland field catchment became smaller after the reclamation from forest to upland field,which decreased infiltration rate and water storage in the soil layers.We found that peak discharge and direct runoff in the upland field catchment increased compared with the forest catchment.Annual evapotranspiration from the upland field catchment tended to be lower due to the change in vegetation type and soil properties.Furthermore,a semi-distributed hydrological model was applied in the upland field catchment to understand the integrated effects of reclamation on the hydrological cycle.The model parameters,which were determined using a nonlinear optimization technique—the Shuffled Complex Evolution method(SCE),were compared between the two catchments.The Nash and Sutcliffe coefficient was used to evaluate the model performance.The simulated results indicated that evapotranspiration was decreased and change in discharge was more obvious in the surface layer.We considered that declined infiltration and water storage and increased peak discharge and direct runoff have a negative impact on water resources in the upland field catchment.This study will provide information for forest managers in planning and making decisions for land and water resource management.

Effects of Long-term Fertilization on Soil M icrobial Com m unity Structure,Labile Organic Carbon and Nitrogen and Enzym e Activity in Paddy Field and Upland

To investigate the effects of long-term fertilization systems on soil microbial community structure,labile organic carbon and nitrogen and enzyme activity in yellow sand paddy field and upland,a field experiment was conducted at the experimental station of Dongyang Institute of Maize Research in Zhejiang Province,China in 2009.The experiment consisted of six treatments with three replicates,and they were arranged in a completely randomized design,including no fertilization in paddy field (PCK),conventional fertilization in paddy field (PCF),formulated fertilization by soil testing in paddy field (PSTF),formulated fertilization by soil testing with organic manure in paddy field (PSTF+OF),conventional fertilization on upland (DCF),and formulated fertilization by soil testing with organic manure on upland (DSTF+OF).Soil nutrients,enzyme activity,microbial biomass and community structure were determined in 2015.The results showed that compared with no fertilization in paddy field (PCK),fertilization increased soil phosphorus and potassium content,and decreased pH value.No fertilization in paddy field (PCK) had no significant effect on soil culturable microorganisms in paddy field and upland,but formulated fertilization by soil testing with organic manure on upland (DSTF+OF) significantly increased the number of fungi.Formula fertilization by soil testing with organic manure (PSTF+OF) also significantly increased soil microbial biomass carbon and nitrogen in paddy field and upland.Moreover,fertilization had no significant effect on soil cellulase activity,but formula fertilization by soil testing with organic manure (PSTF+OF) significantly increased soil dehydrogenase and catalase activity.Therefore,long-term application of chemical fertilizer with organic fertilizer can effectively improve soil fertility.

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。

坡耕地红壤剖面磷的储存容量及其流失风险研究

基于土壤磷储存容量的变化差异,准确评估与判断坡耕旱地与稻田红壤磷的剖面流失风险。以江西鹰潭孙家典型红壤小流域内位于坡上(T)、坡中(M)及坡下(B)的花生旱地(PU)及稻田(PF)各发生层土壤为对象,分析了各发生层土壤全磷(TP)、有效磷(Olsen-P)、磷饱和率(PSR)、磷吸持指数(phosphorussorptionindex,PSI)及磷储存容量(Soil phosphorus storage capacity,SPSC)随剖面的变化特征及差异,估测了坡耕地红壤磷的剖面流失风险,探讨了土壤pH、Eh及容重(BD)等因子对坡耕地红壤发生层SPSC的影响差异。结果表明,不同坡位花生旱地与稻田红壤表层TP、Olsen-P含量均显著高于底层土壤,且稻田红壤TP与Olsen-P的剖面变异显著高于花生旱地剖面。与耕作层(Ap1)相比,花生旱地底层土壤PSI显著增加了33.1%~146%,且随剖面深度增加而缓慢降低;而稻田红壤PSI则随着剖面深度增加而增大。花生旱地与稻田红壤(PF-M除外)PSR均随着剖面深度的增加而逐渐降低,SPSC变化范围分别为–89.2~298.3 mg·kg^(-1)与^(-1)38.1~101.1mg·kg^(-1)。PU-T与PU-M剖面SPSC均为正值,且随剖面深度增加呈降低趋势;而PU-B(耕作亚层Ap2除外)剖面的SPSC均为负值。PF-T(氧化还原层Br2除外)、PF-M(Ap1除外)及PF-B剖面各发生层的SPSC均为负值,且随剖面深度增加变化显著。基于SPSC理论对坡耕红壤剖面土壤磷储量及其环境流失风险的评估,花生旱地土壤磷沿剖面及坡位的迁移与运移迹象明显,当土壤Olsen-P>27.6mg·kg^(-1)时,花生旱地剖面土壤磷的流失风险将急剧增加,应及时采取管控措施。稻田红壤剖面各发生层均存在不同程度的磷流失风险,需立即停止施磷并及时采取有效措施。

湘南丘陵区水田改旱地后土壤磷的有效性及淋失风险

【目的】研究不同母质发育的水稻土改旱地后土壤有效磷变化特征及主要影响因素,为红壤区磷素高效利用提供依据。【方法】采集3种母质(石灰岩、第四纪红色黏土和砂页岩)发育的水稻土及相邻的水田改旱地土壤样品,分析了土壤全磷、有效磷、水溶性磷和无机磷组分(Al-P、Fe-P、Ca-P和O-P)的变化特征,通过主成分分析(PCA)和随机森林分析,探究水田改旱地后土壤磷素有效性变化的主要驱动因子。【结果】水田改为旱地后,石灰岩、砂页岩发育的土壤有效磷含量分别增加了20.48和17.60 mg/kg (P<0.05),但水溶性磷含量均低于磷素环境阈值;土壤磷活化系数分别提高了2.67和2.22个百分点;Al-P含量分别增加了46.07和51.28mg/kg;石灰岩发育的土壤Fe-P含量增加了62.11 mg/kg。相关分析表明,水田改旱地后,Fe-P、Al-P与磷活化系数呈显著或极显著正相关,PCA和随机森林分析结果表明Fe-P、Al-P是土壤磷素有效性变化的主要驱动因子。【结论】湘南红壤丘陵区水田改为旱地后,第四纪红色黏土发育的红壤磷素有效性未发生显著变化,石灰岩和砂页岩发育的土壤磷素有效性由于铁磷和铝磷在全磷中比例的增加而显著提升。3种母质发育的水田改旱地后,其水溶性磷含量均低于环境磷阈值,引发磷淋失的风险较低。

Assessing Silicon Availability in Soils of Rice-Growing Lowlands and Neighboring Uplands in Benin and Nigeria

Silicon(Si) is known as a beneficial nutrient in the cultivation of rice, playing a key role in photosynthesis enhancement, lodging resistance and tolerance to various environmental stress. The present study aimed to examine available Si content in both lowland soils(n = 29) and neighboring upland soils(n = 21) collected from Benin and Nigeria and to evaluate the validity of the assessment results through a pot experiment. Our results revealed that the acetate-buffer method predicted Si concentration in rice straw at the harvest stage(R^2 = 0.68, P < 0.01) better than the anaerobic-incubation method(R2 = 0.31, P > 0.05), and 76% of the uplands and 38% of the lowlands were deficient(< 50 mg/kg) in acetate-buffer soluble Si. These findings suggest that the Si-deficiency soils prevail across the study area, making rice plants starved for Si and prone to environmental stress.

长期不同施肥水田和旱地铁氧化物对红壤团聚体有机碳固持特性的影响

红壤中铁氧化物是影响有机碳固持的主要因素之一。探究红壤旱地和水田土壤有机碳与不同形态铁氧化物的关系,有助于理解土壤有机碳的稳定机制,为农田合理管理提供科学依据。本文依托我国南方红壤旱地和水田长期施肥定位试验(均超35年),分别采集长期不施肥(CK)、单施氮肥(N)、氮磷钾配施(NPK)和NPK与有机肥配施(NPKM)等4种施肥处理的土壤样品,采用沙维诺夫干筛法获得土壤大团聚体(>2 mm)、小团聚体(0.25~2 mm)和微团聚体(<0.25 mm),测定土壤团聚体有机碳含量及络合态、游离态和无定形等形态铁氧化物的含量。水田土壤大、小和微团聚体的平均有机碳含量分别为8.21 g∙kg^(-1)、7.65g∙kg^(-1)和2.08 g∙kg^(-1),而旱地分别为2.93 g∙kg^(-1)、6.68-1 g∙kg和1.33 g·kg^(-1);水田土壤大、小和微团聚体中的平均可溶性有机碳含量分别为70.72 mg∙kg^(-1)、79.83 mg∙kg和30.29 mg·kg^(-1),而旱地分别为7.27 mg∙kg^(-1)、21.49-1 mg∙kg和5.88 mg·kg^(-1)。无论是旱地还是水田,土壤小团聚体和微团聚体无定形铁氧化物含量与土壤有机碳含量均呈显著正相关关系,土壤各粒级团聚体无定形铁氧化物含量与可溶性有机碳含量均呈显著正相关关系。水田土壤各粒级游离态铁氧化物含量与土壤有机碳含量均呈显著正相关关系,尤以微团聚体贡献率较高。水田条件下,土壤微团聚体中的游离态铁氧化物含量与可溶性有机碳含量呈显著正相关关系。随着土壤团聚体粒级的增加,铁氧化物含量表现为先增加后降低的趋势。无定形铁氧化物对旱地和水田土壤有机碳均具有固持作用,游离态铁氧化物仅对水田土壤有机碳具有固持作用。

长江中游典型稻田种植模式的经济效益及土壤固氮能力比较

为研究比较长江中游地区稻田不同种植模式的经济效益和土壤氮素固持能力,设置紫云英-早稻-晚稻(CRR,CK)、紫云英-早稻-甘薯||晚大豆(CRI)、油菜-早稻-晚稻(RRR)、油菜-早稻-甘薯||晚大豆(RRI)、马铃薯-早稻-晚稻(PRR)5种稻田典型种植模式进行田间定位试验。结果表明,与CK相比,两年内,RRI、PRR、RRR、CRI模式均能增加作物产量,增幅为16.40%—32.85%和21.04%—49.60%(P<0.05),且均是RRI、PRR模式的作物产量较高。RRI和PRR模式的经济效益较好,分别显著高出对照30.27%、44.15%和65.13%、51.38%(P<0.05)。CRI、RRI模式显著提高了土壤微生物量氮的含量,增幅为53.57%—58.85%(P<0.05),降低了微生物量C/N。此外,与CK相比,CRI、RRI模式显著降低了土壤硝态氮的残留,降幅为48.35%—69.23%(P<0.05)。综上所述,RRI模式和马铃薯模式(PRR)能提高作物产量,增加氮素有效输出,提高经济效益,CRI、RRI模式更能增强土壤微生物氮素固持能力,降低土壤氮素流失风险。可见油菜-早稻-甘薯||晚大豆和马铃薯-早稻-晚稻模式的增产、增收、固氮等综合效果较好,可以在长江中游地区推广应用。

不同类型黄壤旱地的磷素流失及其影响因素分析

在贵州中部黄壤旱地上 ,通过模拟降雨试验方法 ,对不同类型黄壤旱地磷素流失及其影响的主要因素进行研究。结果表明 ,黄壤旱地磷素流失以颗粒态形式流失为主 ,其占地表径流总磷含量的 86 .4%～ 99.9% ;不同类型黄壤旱地随地表径流流失的颗粒态磷 (泥沙结合态磷 )量和磷酸根态磷 (水溶态磷 )量存在较大差异 ,高肥力旱地磷的流失量明显高于低肥力旱地。影响黄壤旱地颗粒态磷和磷酸根态磷流失量的首要土壤因子都是有效磷含量 ;在土壤磷素水平一致下 ,黄壤旱地颗粒态磷流失量与 <0 .0 0 1mm粘粒含量呈显著正相关 ,而磷酸根态磷流失量与土壤交换性钾含量呈显著负相关。此外 ,降雨强度对旱地磷素流失产生明显影响 ,高降雨强度将加速颗粒态磷的流失 ,从而明显地提高旱地磷素流失量 ;

中国主要旱地农田N_2O背景排放量及排放系数特点

【目的】收集中国已发表的旱地农田N_2O排放田间监测文献并建立数据库,以此为基础解析中国主要旱地农田(小麦地、玉米地、蔬菜地)的N_2O背景排放值(不施肥情况下土壤的N_2O排放量)和排放系数(EF)及影响因子,为估算区域温室气体清单和提出相应的减排策略提供数据支持。【方法】利用亚组归类和回归分析等方法对主要类型旱地农田N_2O背景排放量的影响因子(如土壤全氮含量和土壤碳氮比)及影响EF的因子(如氮肥用量及肥料类型——硝化抑制剂和缓控释肥)进行分析。【结果】(1)中国旱地农田N_2O背景排放量为0.70—3.14 kg N_2O-N·hm^(-2);小麦地和夏玉米地的N_2O背景排放量和蔬菜地的N_2O日背景排放量均随土壤全氮含量增加而增加,并随土壤碳氮比的增加而降低,灌溉促进小麦地N_2O背景排放量增加;(2)EF随着无机氮肥用量的增加而增加,不同作物种植类型农田的EF大小依次为蔬菜地(0.61%—1.13%)>夏玉米地(0.50%—0.68%)>春玉米地(0.35%—0.40%)>小麦地(0.22%—0.36%);夏玉米地的EF是小麦地的2倍左右;(3)使用不同种类硝化抑制剂后氮肥的EF均有不同程度的降低,EF降低了34%—60%,EF降低程度依次为:DCD+HQ(58.9%)>NBPT+DCD(52.9%)>DMPP(51.1%)>NBPT(44.1%)>吡啶(39.5%)>DCD(38.9%);硝化抑制剂降低EF的效果在不同旱地农田的表现为:小麦地(60.0%)>蔬菜地(50.6%)>春玉米地(39.6%)>夏玉米地(34.7%);(4)与常规尿素相比,不同类型缓控释肥使得EF降低了15.9%—78.9%,降低次序依次为:长效碳酸氢铵(78.9%)>聚合物包膜尿素(59.8%)>脲甲醛(53.4%)>树脂包膜尿素(44.9%)>硫磺包膜尿素(30.6%)>钙镁磷肥包膜尿素(15.9%);缓控释肥降低EF的效果在不同农田表现为:蔬菜地(78.4%)>春玉米地(58.2%)>小麦地(49.2%)>夏玉米地,控释肥在降低夏玉米地EF的作用较小。【结论】旱地农田N_2O排放主要受土壤养分状况(全氮含量和碳氮比)和管理措施(灌溉和施肥)及其他因素的共同影响,应依据不同气候生态区的气候和土壤特点以及作物类型并考虑氮肥用量和类型采取针对性的减排措施,以有效降低农田N_2O排放。

黄壤旱地-水系统中磷释放及影响因素的研究

目的探讨降雨-径流过程中土壤溶解态磷向水体迁移的规律及其影响因素。方法采用无界径流小区法以及盆栽试验和模拟试验研究贵州中部黄壤旱地磷释放及影响因素。结果旱地向水体释放的磷量受施磷水平以及玉米生长过程的影响;在高磷黄粘泥土上施磷肥(P2O5)150～900kg·ha-1,其渗透水中活性磷的平均含量达0.020～0.137mg·L-1。旱地向水体释放的磷量还受环境因子的影响,在温度为30～35℃、水土比为15﹕1～25﹕1、淹水时间为12～18h、酸雨pH值为3.82～3.43的条件下,土壤磷的释放量显著地增加。结论不同类型黄壤旱地地表径流中活性磷(磷酸根态磷)含量存在明显的差异,活性磷含量与土壤有效磷存在显著的正相关,与土壤无定型铝和有机质含量存在密切的负相关。

不同利用方式的苏打盐渍土剖面盐分组成及分布特征

通过野外调查、采样和室内分析,研究了松嫩平原不同利用方式的苏打盐渍土剖面形态特征及可溶盐含量与组成在土壤剖面中的变化。结果表明,土壤的利用方式不同,土壤剖面腐殖质层厚度、耕层和腐殖质层的有机质含量等有明显差异。在围栏草原、旱田、新水田及老水田4个剖面中,土壤可溶盐总量、pH与ESP均是在剖面中部最高,上部和下部较低;可溶盐组成均以K++Na+和HCO 3-、CO23-为主。表明草原围栏、旱田及水田利用均有抑制苏打盐分表聚的作用。放牧草原剖面的可溶盐含量自下向上逐渐增多,盐分表聚非常显著。开垦20余年的水田剖面中,表层土壤的可溶盐总量、pH和ESP值分别降至0.21%、7.56和9.1%,表明苏打盐碱地种稻较草原和旱田利用更有利于土壤脱盐脱碱。

中国农田氮淋失相关因素分析及总氮淋失量估算

通过对我国近10年382组农田N素淋失数据进行统计分析,发现水田的NO3--N淋失量与土壤体积质量、有机质、全N(TN)、黏粒含量百分比显著负相关,与施N量、灌水量显著正相关;旱地中NO3--N淋失量与全P(TP)、粉粒含量百分比、土层深度显著负相关,与土壤中TN含量、砂粒百分比含量、施N量、降雨量、灌溉水量显著正相关。水田中总N表观淋失率平均值为2.19%,95%的置信区间为1.56%～2.82%;旱地中总N表观淋失率平均值为4.35%,95%的置信区间2.88%～5.82%。根据2008年中国统计年鉴计算出2007年我国总N淋失量达到0.644 Tg,约占我国总施N量的2.80%。

旱塬麦田渗灌补水技术及经济效益

旱地干旱年型下，在关键时期采用地下渗灌补水技术，通过对不同时期渗灌、不同渗水量及埋管深度与土壤水分运行状况和经济效益的研究分析表明，小麦孕穗期，冬渗土壤水分经下渗后积聚在１００ｃｍ～１５０ｃｍ土层，比对照高３．４１个百分点；而春渗多积聚在２０ｃｍ～５０ｃｍ土层，比对照高２．２５个百分点。由于根系密集层与水分积聚层基本吻合，因此有利于小麦抽穗时期的生长发育，提高了水分利用率，春渗小麦比对照增产３３．７％。不同渗水量试验，以每公顷渗水３００ｍ３的土壤水分变化较为明显，比对照增产２７．３％；渗灌埋管深度由浅到深，水分下渗规律也呈同样趋势，根据小麦发育需水规律，以埋深２０ｃｍ较为理想。

湖南省旱地土壤硫素状况及作物施硫效应

对湖南省127个旱地表土(0～20 cm)和56个旱地底土(20～40 cm)进行了有效S含量分析及花生和油菜施S效应的田间试验.结果表明:湖南省旱地土壤有效S含量表土低于底土;表土有效S含量低于30mg/kg的土样所占的比例为49%,低于16mg/kg的土样所占的比例为21%;旱地土壤有效S含量和缺S频率因成土母质而异,河流冲积物发育的土壤有效S含量最低(16.4±4.80 mg/kg),S含量低于16mg/kg的频率最高(64%),其次为紫色砂叶岩发育的土壤(有效S含量为28.3±3.21mg/kg,S含量低于16mg/kg的频率为37%).花生、油菜施S效应因S肥类型和S肥用量而异,单作时S的增产量和经济效益均以SSP为好,S肥用量为30kg/hm2的经济效益较高;轮作时连续施S,S的经济效益以SSP最好,S95和ES次之,最差的数石膏,花生施S效益为油菜的1.8～11.4倍;S肥类型和S肥用量不同,S残效不同.此外,施用S肥还能够增加花生、油菜的吸N量和粗脂肪量,提高N肥利用率,但S对花生吸N量和粗脂肪的累积效果好于油菜.

蔬菜温室土壤某些化学性质的演变特征

To explore the changes of soil chemical properties in vegetable greenhouse,a comparative study was carried out with the samples gathered from vegetable greenhouse fields and their adjacent upland fields in Damintun Town,Xinming County,Liaoning Province.The results showed that compared with upland fields,the contents of soil organic carbon and total nitrogen in greenhouse fields increased significantly.At the depth of 0～30 cm,soil organic carbon in greenhouses of 1-,4-and 10-year increased by 31.09%,35.44%,and 66.80%,respectively,compared with the upland soil.Soil nitrate content at the depth of 0～30 cm in greenhouse fields was 5.05～12.49 times as much as that in upland fields.The nitrate content in different soil layers increased with the increasing age of greenhouse field.,e.g.,at the depth of 20～30 cm,soil nitrate content was significantly higher in 10-year than in 1-and 4-year greenhouse field,with an increase of 65.73% and 50.89%,respectively,and 6.55 times as much as that in upland field,which indicated that soil nitrate transported downwards,and obviously enriched in deeper soil layers under heavy application of fertilizer.Also with the increasing age of greenhouse field,soil pH decreased,while soil soluble salts accumulated.

深松对苏打盐碱化旱田改良与利用的影响

通过对不同深度深松对经过微咸水淋洗改良的中度和轻度苏打盐碱化旱田的土壤体积质量(容重)、含盐量和pH等理化性状及作物产量等相关性状的影响研究,结果表明:深松措施能够有效地降低经过淋洗改良的中度和轻度苏打盐碱化旱田的土壤体积质量、含盐量和pH,明显改善其土壤理化形状,有效地促进作物根系发育,显著提高作物产量。深松措施可作为苏打盐碱土改良与持续利用的有效耕作方式加以实施;深松方法以效果极为显著且具有可操作性的原垄垄沟深松40cm,中耕时垄沟深松30cm为佳。

江苏省主要农田杂草种子库物种组成和多样性及其与环境因子的相关性分析

采用水洗镜检法对江苏省31个农田样点(包括旱田和水田)0～15 cm土层土壤杂草种子库的种类组成和物种多样性进行了调查研究;采用典范对应法分析了杂草种子库种类与环境因子(包括淹水天数、土壤有机质含量、土壤pH、年降水量、年均温、样点经度和样点纬度)的相关性并绘制了样点和种类与环境因子的二维排序散点图。调查结果表明:在31个样点的土壤杂草种子库中共检测到杂草种子15科54种,旱田和水田各有41和45种,二者共有种类占多数但优势种有差异,通泉草〔Mazus japonicus(Thunb.)Kuntze〕、异型莎草(Cyperus difformis L.)、水苋菜(Ammannia baccifera L.)、千金子〔Leptochloa chinensis(L.)Nees〕、棒头草(Polypogon fugax Nees ex Steud.)和牛繁缕〔Malachium aquaticum(L.)Fries〕等种类为二者的共有优势种;杂草种类最多的为禾本科(Gramineae)和莎草科(Cyperaceae),分别占种类总数的22.6%和20.8%。旱田不同样点杂草种子库的优势种类变化较大,而水田杂草种子库优势种较稳定;二者优势种频度差异较大,旱田中频度高于0.30的杂草有19种,水田中频度高于0.50的杂草有20种;旱田和水田中平均重要值大于0.03的杂草各有11和9种,这些频度高的种类重要值也较大。旱田和水田土壤种子库种子密度分别为21 015和37 847 m-2,平均为31 008 m-2;旱田3层土壤中种子密度差异不显著,而水田上、中层土壤的种子密度显著高于下层。旱田以夏熟和秋熟杂草为主,而水田则以水田和夏熟杂草为主。按形态类型划分,水田及旱田中杂草种类数和密度从大到小均依次排序为阔叶草类、禾草类、莎草类,且水田中这3类杂草的种类数和种子密度均高于旱田。与旱田相比,水田杂草种子库的物种丰富度指数(S)、Shannon-Wiener指数(H')和Simpson指数(D)较高,但Pielou均匀度指数(E)较低;旱田杂草种子库的S、H'和D指数随土层深度增加而降低、E指数逐渐升高,水田各土层的物种多样性指数则无明显变化趋势。第1种类排序轴与淹水天数负相关性最高(R=-0.814 3),第2种类排序轴与年降水量和经度也有较高的负相关性;相关性分析和CCA分析结果均表明淹水天数是影响杂草种子库群落构成的最大因素。通过二维排序可将31个样点分为旱田和水田2大类,旱田可划分为长期旱连作和水旱轮作2个亚类;水田可划分为淮河以北地区和淮河以南长江流域地区2个亚类。研究结果说明:杂草种子库潜群落优势种与地上部农田杂草显群落优势种具有一致性,通过土壤杂草种子库的研究可以预测地上杂草的发生和危害情况。

喀斯特地区不同土地利用方式对土壤有机碳、全氮以及微生物生物量碳和氮的影响

以广西环江大才为代表,选择亚热带典型喀斯特峰林谷地样区,通过对样区土壤进行密集采样和测定分析,研究了土地利用方式对土壤有机碳(OC)和全氮(TN)含量及土壤微生物生物量碳(BC)和氮(BN)含量的影响.结果表明,3种土地利用方式下,土壤有机碳含量在稻田和林地中基本相同,而旱地显著低于稻田和林地.土壤全氮含量为稻田显著高于林地,而林地显著高于旱地.土壤微生物生物量碳含量为稻田显著高于林地,林地显著高于旱地.土壤微生物生物量氮含量在稻田和林地中基本相同,而旱地显著低于稻田和林地.旱地土壤pH值显著低于稻田和林地土壤.3种土地利用方式下,土壤微生物生物量碳与土壤有机碳、土壤微生物生物量氮与全氮含量之间均呈显著的正相关关系.土壤微生物生物量碳和氮含量可以作为评价喀斯特地区土壤质量和肥力的指标之一,对土地利用方式响应较为敏感.