2种保水剂对旱作土壤物理性状及马铃薯产量的影响比较

为促进宁夏干旱半干旱区马铃薯支柱产业的发展,解决马铃薯生产,特别是苗期干旱缺水等问题,以2种土壤保水剂(沃特保水剂和微生物保水剂)为对象,研究了不同保水剂施用量对旱作土壤物理性状及马铃薯产量的影响。结果表明,相对于不施保水剂处理(对照),2种保水剂均可有效降低土壤容重,改善土壤孔隙结构,穴施沃特保水剂90 kg·hm-2的0~30 cm土层土壤容重显著降低9.0%,穴施微生物保水剂90 kg·hm-2的30~60 cm土层土壤孔隙度显著增加8.9%。施用微生物保水剂各处理使0~30 cm土层0.25 mm机械稳定性团聚体数量均较对照显著提高,施沃特保水剂各处理使30~60cm土层0.25 mm团聚体数量较对照显著提高。在马铃薯关键生育期,施用微生物保水剂可改善马铃薯生育前期0~100 cm土层土壤贮水量,而施用沃特保水剂可提高马铃薯生育中后期土壤水分状况。2种保水剂处理下,马铃薯产量均显著高于对照,其中穴施沃特保水剂60~90 kg·hm-2的增产效果最佳(41.4%),商品薯率最高(21.1%)。该研究可为宁夏旱作区马铃薯合理施用保水剂提供参考。     

减氮条件下生物质炭施用对珠三角地区生菜产量、品质及土壤性质的影响

生物质炭(biochar,BC)施用具有改良土壤、提高作物产量等效应。本文探究了生菜产量、品质和土壤性质等对化肥氮(N)减施和生物质炭施用1年后的响应，以期为珠三角地区露地蔬菜生产中化肥合理减量和生物质炭科学施用提供依据。通过在佛山市三水区开展田间小区试验，观测了常规施氮(N100%)、减氮20%(N80%)、减氮40%(N60%)、减氮40%+生物质炭10 t/hm²(N60%+BC10)和减氮40%+生物质炭20 t/hm²(N60%+BC20)处理下生菜产量、品质、叶片SPAD值及土壤养分等指标的变化。结果表明：(1)较N100%处理，N60%处理生菜产量显著降低13.5%。减氮40%条件下，配施10～20 t/hm²生物质炭可提高生菜产量9.5%～22.7%，与N100%处理产量相当，说明生物质炭施用对生菜产量具有显著提升效果。(2)氮肥减量和生物质炭施用对生菜单株鲜重、直径和水分含量等均无显著影响，而对叶片SPAD值在不同生育期有不同影响。减氮条件下施用生物质炭处理生菜的氮和磷吸收量提高，是其增产机理之一。(3...     

不同水分条件下保水剂对黄瓜根系和叶片生理特征的影响

[目的]研究不同土壤干旱生境中保水剂对黄瓜根系和叶片生理特征的影响,探讨其生长效应与土壤水分的内在联系,为保水剂的合理施用和农田科学灌溉等提供一定的技术参考。[方法]利用盆栽模拟试验,通过定量灌水,系统研究在3种不同的土壤水分条件下,保水剂对黄瓜根际水分、根系形态特征、叶绿素荧光参数和叶片气孔性状等生理特性的影响。[结果](1)不同水分条件下,保水剂处理的黄瓜根系生长受到明显抑制。与对照相比,保水剂处理组在土壤含水量为田间持水量70%(FC₂)和55%(FC₃)时的总根长、平均根系直径、总根体积、根表面积和根干重均显著降低,分别降低了3.4%,24.2%,62.1%,41.0%和51.6%以上。(2)随着干旱胁迫的加剧,保水剂处理叶片的有效光合效率(F_v′/F_m′)和实际量子产量[Y(Ⅱ)]较对照出现先升后降的变化趋势,非光化学淬灭(NPQ)则呈相反的变化;尤其在FC₂和FC₃处理时,保水剂处理促使黄瓜叶片的光化学淬灭(q_P)较对照分...     

保水剂施用量对旱作土壤理化性质及马铃薯生长的影响

针对宁夏中部半干旱偏旱区土壤贫瘠,降水较少,土壤蒸发强烈、马铃薯低产等突出问题,采用以2种土壤保水剂为对象,研究了保水剂不同施用量对旱作土壤性状及马铃薯生长的影响。结果表明,穴施沃特保水剂90kg/hm2的耕层(0—30cm)土壤容重比不施保水剂处理显著降低5.2%。施用保水剂各处理耕层粒径0.25mm机械稳定性团聚体数量均较不施保水剂处理(对照)有所提高,而粒径0.1mm团聚体数量较对照明显降低;在马铃薯关键生育期(块茎形成至膨大期),与不施保水剂处理相比,施用保水剂各处理能明显提高0—100cm土层土壤贮水量,以穴施沃特保水剂处理的保水效果最佳。沃特保水剂改善了土壤结构和水分状况,加速土壤有机质的分解与矿化,促进土壤养分的转化供应,保蓄土壤的有效养分。施微生物保水剂能促进马铃薯初花期生长,进入块茎膨大期施用沃特保水剂效果显著。不同保水剂施用量植株养分含量和积累量显著提高,有利于提高肥料的利用率,且随保水剂施用量的增加,其养分利用率越高。不同保水剂施用量各处理的马铃薯产量均显著高于不施保水剂处理,其中穴施沃特保水剂90kg/hm2的增产效果最佳(44.1%),穴施沃特保水剂60kg/hm2的商品薯率最高(20.9%)。     

施硅对夜间增温条件下水稻叶片生理特性的影响

通过大田试验,研究施硅对夜间增温条件下水稻分蘖期、拔节期、灌浆期、成熟期叶片净光合速率(P_n)、蒸腾速率(T_r)、气孔导度(G_s)及胞间CO_2浓度(C_i)的影响。夜间增温设常温对照(CK)和夜间增温(NW)2个水平;施硅量设Si0(不施硅)和Si1(钢渣硅肥,200kg SiO_2·hm~(-2))2个水平。结果表明:(1)夜间增温可使水稻冠层和5cm土层温度升高,水稻冠层和5cm土层全生育期夜间平均温度分别提高1.21℃和0.41℃;(2)夜间增温处理可使生育期内水稻叶片P_n、T_r、G_s比对照分别下降11.0%、9.0%和20.2%,C_i比对照增加1.2%;施加钢渣硅肥处理可使叶片P_n、G_s比对照分别增加16.1%和25.8%,T_r、C_i比对照分别降低11.0%和2.0%;夜间增温条件下施硅比不施硅水稻叶片P_n、G_s分别增加22.0%和33.6%,T_r、C_i分别降低7.7%和2.3%。研究认为夜间增温降低了水稻叶片P_n、T_r、G_s,增加了C_i。施硅通过显著提高水稻叶片P_n、G_s,降低T_r、C_i,缓解了夜间增温引起的抑制效应。(3)夜间增温和施硅两种处理对水稻叶片叶绿素含量(SPAD值)影响不显著。夜间增温使叶片SPAD值平均下降3.0%;施硅使叶片SPAD值增加4.7%;夜间增温下施硅比不施硅叶片SPAD值增加5.7%。     

减氮量施用缓释氮肥对春玉米产量及土壤硝/铵态氮含量剖面分布的影响

通过田间试验的方法,研究了缓释氮肥与尿素等氮量配比、减少总氮用量对春玉米产量及土壤硝态氮、铵态氮含量剖面分布的影响。结果表明,(1)与尿素全部基施处理(CK)比较,减氮、施用缓释肥料可以保证春玉米稳产,其产量及构成因素整体表现优于对照;其中减少20%氮肥用量的处理增产率最高,产量比对照提高了10.8%;(2)减氮、施用缓释肥料对春玉米的株高、叶面积、地上部生物量及棒三叶的SPAD值等主要农艺性状没有显著影响;(3)施用等氮量缓释肥料的处理0～120 cm土层土壤硝态氮含量低于对照,降低了硝态氮向更深土层淋溶的风险。总之,春玉米栽培减量施用缓释氮肥具有可获得较高产量、减少环境污染风险等优点,值得推广应用。     

保水剂对旱作马铃薯产量及水分利用效率的影响

为探究宁南地区保水剂对马铃薯关键生育期水分利用及作物产量的影响,本研究采用沃特和微生物保水剂,以不施保水剂处理为对照,研究2种保水剂不同用量(30、60、90 kg·hm~(-2))对土壤水分、马铃薯产量及水分利用效率的影响并对经济效益进行分析。结果表明,在作物主要生育期,微生物保水剂可改善马铃薯生育前期耕层土壤水分含量,促进马铃薯的生长,而沃特保水剂的施用可提高马铃薯中后期深层土壤水分含量,其作物地上部生物量显著高于不施保水剂处理。与对照相比,沃特保水剂施用90 kg·hm~(-2)时马铃薯增产效果最佳,其水分利用效率最高,分别较对照提高44.1%和75.8%,微生物保水剂60 kg·hm~(-2)次之;施用沃特保水剂60 kg·hm~(-2)的商品薯率最高(87.3%),微生物保水剂60 kg·hm~(-2)次之。结合经济效益分析发现,在宁南旱地马铃薯生产中,推荐施用沃特保水剂30~60 kg·hm~(-2)能显著提高马铃薯的经济效益。本研究为保水剂在旱作区的应用提供了理论依据。     

保水剂施用方式对花岗岩红壤坡面水土保持的影响

为了获得保水剂对花岗岩红壤坡面水土保持效果最佳的施用方式,通过人工模拟降雨试验和室内分析相结合方法,开展保水剂混施、层施和沟施等施用方式对红壤坡面侵蚀的产流产沙过程影响研究。结果表明:(1)花岗岩红壤坡面施加保水剂后可降低坡面产流、产沙量,延缓产流时间。当雨强为1.0mm/min时,保水剂与土壤混合施用对降低坡面径流及产沙量的影响更为显著。与对照坡面相比,混合施用坡面累积径流降低34%,累积产沙量减少48%;雨强为1.5mm/min时层施保水剂对降低坡面径流及产沙量作用更显著。与对照相比,层施保水剂坡面累积径流降低46%,累积产沙量减少67%。(2)红壤坡面中混合施加保水剂能够增加坡面入渗率,减少坡面径流,增加土壤含水量,发挥了良好的蓄水保土效益。(3)相关性分析表明,保水剂不同施用方式下花岗岩红壤坡面累积产流、产沙量呈现显著相关(P0.05),坡面累积径流量和累积泥沙量间构成幂函数模型。研究结果为花岗岩红壤坡面应用保水剂控制水土流失和揭示相关机理提供参考。     

不同施肥下冬小麦生长过程中土壤矿质氮变化及其与冬小麦叶片SPAD值的关系

通过调查分析,研究了土长期施肥条件下土壤中矿质氮含量变化及其与地上冬小麦叶片SPAD值。结果表明:(1)整个冬小麦生长期不同土层硝态氮和铵态氮的变化趋势不一致,硝态氮含量是先下降后上升的变化,而铵态氮含量呈一直上升的变化趋势。在没有施过氮肥的处理中,0—20cm,20—40cm土层中土壤硝态氮、铵态氮含量显著低于施用氮肥的处理;(2)冬小麦生长时期,各个处理叶片SPAD值各异,但都是先升高后下降的变化,无氮肥施用的叶片SPAD值低于施氮肥的处理;(3)冬小麦各个生长时期叶片SPAD值与土壤不同层次(0—20cm,20—40cm)硝态氮含量呈正相关关系,而与铵态氮含量相关性不显著,这表明小麦是对硝态氮较为敏感的作物。本试验结果可以为进一步合理调控氮肥施用、明确施氮对小麦产量和品质的影响提供一定的基础依据。     

生物炭、EM菌有机肥和化肥混施对桃园土壤肥力、树体生长及果实品质的影响

为改善桃树经济性状,选取9年生湖景蜜露桃园为研究对象,以常规施肥为对照,选用不同配比生物炭、EM菌有机肥与化肥混施,研究了其对桃园土壤肥力、树体生长及果实品质的影响。结果表明：生物炭、EM菌有机肥和化肥混施后：(1)土壤pH值提高,土壤肥力指标也明显提高,在施用量小于对照的情况下有效养分值仍不低于或大于对照;(2)树体有效结果枝数量显著增加,旺长枝数量显著下降,根系活力增强;(3)桃果实品质指标显著提高。综合试验研究结果和投入产出比,以株混施生物炭∶EM菌有机肥∶化肥（高钾型三元复合肥）=3.750∶6.250∶0.375的复混肥10.375 kg为最优。     

低氮和干旱胁迫对富士和秦冠生长及氮素利用的影响

【目的】以富士（Fuji）、 秦冠（Qinguan）嫁接在平邑甜茶（Malus hupehensis Rehd.）上的当年生盆栽苗为试验材料,采用砂培方法,研究了缺氮胁迫和干旱对富士和秦冠生长情况、 光合参数、 植株各部位氮磷钾含量及氮素利用效率的影响,分析比较了低氮干旱条件下富士和秦冠生长及氮素利用的差异,以期为果树生产高效肥水利用提供理论指导。【方法】试验共设四个处理: 正常氮正常水（ZZ）、 低氮正常水（DZ）、 正常氮干旱（ZG）、 低氮干旱（DG）。氮素和水分均设置两个水平,分别为正常氮（6 mmol/L NO-3-N）、 低氮（0.3 mmol/LNO-3-N）、 正常供水（保持盆中砂子相对含水量为饱和含水量的80%~85%）、 干旱处理（保持盆中砂子相对含水量为饱和含水量的60%~65%）。【结果】富士和秦冠的生物量（茎和叶）、 株高茎粗等生长指标以及光合速率、 气孔导度、 蒸腾速率均为正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）,并且相对应处理下秦冠的以上指标均高于富士;正常供水下,缺氮处理使富士、 秦冠的根冠比比正常氮处理均有所增加,富士提高了2.05%,秦冠提高了22.40%。富士和秦冠的氮、 磷、 钾含量均表现出正常氮正常水（ZZ）＞低氮正常水（DZ）＞正常氮干旱（ZG）＞低氮干旱（DG）; 氮、 钾元素含量在植株各部位的分布顺序依次是叶＞根＞茎,磷元素则是根＞叶＞茎;光合氮素利用效率（PNUE）和氮素利用效率表现为秦冠处理之间差异极显著,富士处理之间差异不显著;秦冠的PNUE和NUE明显高于富士,在低氮正常水（DZ）处理下,秦冠氮肥利用率比富士高42.07%,在低氮干旱（DG）处理下高64.14%;低氮胁迫下富士和秦冠的NUE显著提高,并且秦冠提高的幅度高于富士。【结论】施用氮肥能够显著提高富士与秦冠的干物质量,同等水肥条件下,秦冠生长优于富士;水分亏缺会减少叶片对氮的吸收,干旱条件下适度增施氮肥,可提高果树的抗旱能力;低氮干旱胁迫下秦冠的生长指标、 光合指标及氮素利用效率指标均优于富士,表现出较强的抗低氮干旱胁迫的能力。     

Pasture Vegetation Elemental Analysis by Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy (LIBS) is a new technique for the analysis of plant material. This study investigates the application of LIBS to pasture-based plant samples. The LIBS measurements were obtained from pelletized pasture samples (100 samples) that had been also analyzed by inductively coupled plasma–optical emission spectroscopy (ICP-OES) following microwave digestion for calibration and comparison purposes. Comparisons for elements sodium (Na), potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), iron (Fe), copper (Cu), zinc (Zn), boron (B), phosphorus (P), and sulfur (S) showed that LIBS could be used for almost all the standard profile total elements with concentrations down to low mg/kg levels (observed error of Na: 0.024 percent, K: 0.18 percent, Mg: 0.016 percent, Ca: 0.073 percent, P: 0.017 percent, Mn: 31 mg/kg, Fe: 150 mg/kg, Zn: 6.6 mg/kg, and B: 1.1 mg/kg). Elemental analysis at less than mg/kg levels was not possible using LIBS. The elements S and Cu were particularly difficult to analyze with reliability using LIBS at the concentration levels found in the plant samples. Replacing microwave digestion and subsequent ICP analysis with a direct analysis of dried plant samples using LIBS has the potential to improve the productivity and reduce the cost of testing.     

Faculty positions:Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Biodiversity and ecogeography of wild Lactuca spp. in some European countries

Staff members of the Department of Botany of Palacký University in Olomouc and Gene Bank Department – Workplace Olomouc, Research Institute of Crop Production in Prague, Czech Republic, conducted an expedition in seven European countries (Austria, Czech Republic, France, Germany, Italy, the Netherlands, Switzerland) in August/September 1999 to collect wild Lactuca spp. germplasm and study its geographic distribution, ecology and biodiversity. During the mission, more than 600 locations were visited resulting in the collection of 602 seed samples (accessions) of wild Lactuca species and 13 seed samples of related genera (Chondrilla and Mycelis). Lactuca serriola f. serriola, L. serriola f. integrifolia, L. saligna and L. viminea subsp. chondrilliflora were prevalent in southern Europe (Italy, France), however, only L. serriola was common in central and western Europe (Austria, Czech Republic, Germany, Netherlands, Switzerland). The greatest diversity of Lactuca species was found in France, where also the most seed samples (165) were collected. The most characteristic habitats with a high density of Lactuca spp. populations were observed along roads and highways, grassy ditches, ruderal communities, and dust-heaps. Natural infections by powdery mildew (Erysiphe cichoracearum) and downy mildew (Bremia lactucae) on some wild Lactuca spp. were observed. Recent observations concerning the geographic distribution, population structure, habitats, and natural occurrence of diseases of Lactuca spp. are discussed. This assemblage of genetic resources of Lactuca spp. can serve as the basis of future studies of species diversification, spatial population structure, plant microevolution, domestication processes, and genetic variability of host-parasite interactions.     

Macroinvertebrates in North American tallgrass prairie soils: effects of fire, mowing, and fertilization on density and biomass

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils.     

Properties of anaerobically digested and composted municipal solid waste assessed by linking soil mesofauna dynamics and nitrogen modelling

We have studied the effect of anaerobically digested (ADMSW) and composted municipal solid waste (CMSW) on mineralization and foodweb dynamics to verify the hypothesis that ADMSW would immobilize N right after addition to soil in contrast to addition with CMSW. Another hypothesis was that the mesofauna (enchytraeids and microarthropods) would stimulate N release from the decomposer community. We measured excretion of -N and urea-N from the mesofauna and hypothesized that enchytraeids would release urea. ADMSW and CMSW were amended to pots with sandy loam and barley. The pots were divided into treatments with or without mesofauna. Mesofauna, plant N and biomass, soil N and ergosterol (fungal biomass) were measured over a 113-day period of four equidistant samplings. Soil respiration, N mineralization and N release by the mesofauna were modelled from concurrent studies. ADMSW- and CMSW-treated soils initially (<20 days) immobilized N. The amendments did not increase plant growth substantially, and this was probably due to N-limitation in the early stages of plant growth. Enchytraeid abundance was about three times higher in ADMSW- than CMSW-treated soils, indicating that ADMSW contained more labile compounds, bacteria, and microfauna. The mesofauna did not affect N-content, but the cumulated -N excreted by the mesofauna was estimated to be substantial and about one-fifth of total plant N in ADMSW. An explanation for this discrepancy might be that in the absence of the mesofauna, other members of the detrivore and microbivore community performed the mesofauna’s function. Neither enchytraeids nor microarthropods excreted urea.     

Faculty positions: Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Faculty positions: Center for Agricultural Resources Research,Chinese Academy of Sciences

正The Center for Agricultural Resources Research(CARR),the Institute of Genetics and Developmental Biology(IGDB),Chinese Academy of Sciences,invites applicants for several research group leader positions.CARR is one of the research organizations in Chinese Academy of Sciences(CAS).We seek nominations and applications from individuals who have expertise and a record of accomplishment in research areas related to ecology,agro-hydrology,     

Variation in quality parameters between and within 14 Nordic tree fruit and berry species

Abstract

A 3-year study was carried out to investigate quality parameters in 14 tree fruit and berry species grown in southern Norway. The species were blueberry, apple, aronia, sour cherry, sweet cherry, red raspberry, strawberry, blackcurrant, gooseberry, red currant and elderberry, harvested along with wild bilberry, cloudberry and lingonberry. Significant differences between species were identified for all quality parameters. The coefficient of variation between species was lowest for pH (12.5%), dry matter (18.9%) and soluble solids (25.3%), followed by titratable acids (59.3%), total phenolics (83.8%), antioxidant capacity FRAP (85.7%) and antiradical power by the DPPH-assay (97.8%), total monomeric anthocyanins (132%) and ascorbic acid (137%). Average coefficient of variation within species were lower and ranged from 4 (pH) to 62% (ascorbic acid). Only the FRAP values were significantly affected by harvesting year with lower levels in 2004 than in 2005 and 2006. There were significant interactions between species and harvesting year for dry matter, soluble solids, pH, ascorbic acid and FRAP. The results indicate generic ranges in composition within species independent upon growing location and climate, and the composition of the tree fruits and berries is not likely to deviate from these ranges. It is concluded that desirable composition of tree fruits and berries and their products should primarily be achieved by selection among species rather than searching fors broadened variation within individual species.     

Potassium Fixation and Release Characteristics in Rhizosphere and Nonrhizosphere Soils for a Rapeseed–Rice Cropping Sequence

Potassium (K) fixation and release in soil are important factors in the long-term sustainability of a cropping system. Changes in K concentration and characteristics of K fixation and release in rhizosphere and nonrhizosphere soils in the rapeseed (Brassica napus L.)–rice (Oryza sativa L.) rotation were investigated using a rhizobox system. The concentrations of different forms of K in both rhizosphere and nonrhizosphere soils decreased with plants compared to without plants, regardless of K fertilizer application. Potassium uptake by crops mainly came from the rhizosphere soil. In the treatment without K fertilizer (–K), the main form of K supplied by the soil to the crops was 1.0 mol L^?1 nitric acid (HNO₃) nonextractable K, followed by nonexchangeable K, and then exchangeable K. In the treatment with K fertilizer (+K), the main K forms supplied by the soil to the crops were exchangeable K and nonexchangeable K. The amount and rate of K fixation after one cycle of the rapeseed–rice rotation was greater in rhizosphere soil than in nonrhizosphere soil. The amount and rate of K fixation of soil in the +K treatment were significantly less than in the –K treatment. The cumulative amounts of K released with 1.0 mol L^?1 ammonium acetate (NH₄OAc) and 1.0 mol L^?1 HNO₃ extraction increased with the increasing numbers of extractions, but the K-releasing power of soil by successive extraction decreased gradually and finally became almost constant. The release of K was less in rhizosphere soil than in nonrhizosphere soil. The release of K in the +K treatment was similar to that in the –K treatment in rhizosphere soil, but the K release in nonrhizosphere soil was greater with the +K than the –K treatment. Overall, the information obtained in this study will be helpful in formulating more precise K fertilizer recommendations for certain soils.