不同介质条件对银杏淀粉糊流变特性的影响

淀粉糊流变特性是影响淀粉类食品加工品质的主要因素。该文采用布拉班德尔黏度计，考察不同介质条件如浓度、pH值、蔗糖和食盐对银杏淀粉糊黏度特性的影响。银杏淀粉糊的布拉班德尔黏度测定结果表明：随着银杏淀粉糊浓度增加,其起糊温度降低，峰值黏度增高，热稳定性、冷稳定性下降，凝沉性增强；60 g/kg银杏淀粉糊黏度性质受酸碱介质的影响较大，在pH值中性7左右，其淀粉糊黏度热稳定性最好，凝沉性最强，但冷稳定性最差；食品介质蔗糖对60 g/kg银杏淀粉糊黏度曲线影响较大，其淀粉起糊温度、峰值黏度随蔗糖浓度增加而增加，淀粉糊黏度的冷稳定性、热稳定性均降低，凝沉性增强；而食盐影响较小。该结果对银杏淀粉类食品深加工开发具有较大的指导意义。     

盐胁迫对枸杞叶片糖代谢及相关酶活性的影响研究

试验研究盐胁迫对枸杞叶片糖代谢及相关酶活性的影响结果表明,随NaCl浓度升高和处理时间的延长,枸杞叶片多糖和可溶性糖含量显著增加(P<0.05),蔗糖含量呈上升趋势,而淀粉含量显著下降(P<0.05),还原糖含量呈下降趋势。随NaCl浓度的增加,枸杞叶片中中性转化酶活性显著降低(P<0.05);3g/kg、6g/kg NaCl处理对酸性转化酶活性影响较小,3g/kg NaCl处理降低蔗糖合成酶而对蔗糖磷酸合成酶活性基本无影响;6g/kg NaCl处理蔗糖合成酶活性随时间先降后升,而对蔗糖磷酸合成酶活性影响较小;但9g/kg NaCl处理显著降低酸性转化酶、蔗糖磷酸合成酶活性(P<0.05)。     

超高压处理对太白葛根淀粉理化特性的影响

采用超高压技术对太白葛根淀粉进行处理，研究超高压处理对太白葛根淀粉理化特性的影响。试验结果表明，超高压处理对太白葛根淀粉的颗粒大小和形态没有明显影响。超高压处理可使太白葛根淀粉糊的透明度明显增大，淀粉糊的冻融稳定性降低，提高太白葛根淀粉糊黏度对pH值的稳定性，但对其糊化黏度特性的影响不明显。300 MPa高压处理可改善太白葛根淀粉的理化特性。     

几种淀粉的糊化特性及力学稳定性(简报)

为探索淀粉糊化的力学稳定性,以不同来源淀粉为原料,采用快速黏度分析仪于不同搅拌速度下,研究外力作用对淀粉糊化特性的影响,为淀粉质食品的品质控制提供依据。结果表明,不同来源淀粉的黏度曲线及其力学稳定性有差异。以小麦淀粉的糊化温度最低;马铃薯淀粉糊的黏度和温度稳定性最大;马铃薯和莲子淀粉的峰值黏度较高,冷糊稳定性好;莲子淀粉的热糊稳定性差;玉米淀粉糊易于老化。外力作用对淀粉糊的黏度曲线有影响。较强的外力作用后,会导致淀粉糊的强度、黏度和糊化温度降低,改善热糊稳定性和冷糊稳定性。淀粉糊化的力学稳定性与其颗粒强度有关,较大颗粒强度的淀粉的力学稳定性较好。     

栖热菌4-α-糖基转移酶对马铃薯淀粉的改性作用

该文将栖热菌4-α-糖基转移酶（TSαGT）作用于马铃薯淀粉,分别利用理化分析、质构TPA分析及酶解分析等方法研究该酶对淀粉糊化、凝胶特性和消化性的影响。结果表明,TSαGT可以显著降低马铃薯淀粉中直链淀粉质量分数,使从初始的21%降低至15%,从而使淀粉糊冻融稳定性得以提高、糊透明度得到改善;对酶处理马铃薯淀粉凝胶的研究结果显示,TSαGT对淀粉的改性存在最适作用条件,控制0.024～0.06?U/g的酶用量作用30?min可以明显改善淀粉凝胶质构特性,使凝胶硬度降低,而弹性、咀嚼性、黏结性和胶着性得到不同程度的提高;进一步的消化试验结果表明,使用0.024?U/g以下的酶用量作用30?min,马铃薯淀粉的抗消化性得到提高,继续加大酶量则使抗消化性下降。因此,应用TSαGT对马铃薯淀粉改性处理,控制合适的酶作用程度可以显著提高马铃薯淀粉糊及凝胶的应用特性,同时增加其抗消化性。     

藕淀粉的加工性能研究

该文从化学成分、淀粉颗粒大小、淀粉糊、热力学、淀粉颗粒形态和表面结构以及对酶水解耐受力等方面，对藕淀粉的加工性质进行了较为详尽的研究。结果表明，藕淀粉(重庆产)的水分含量为15.32%、蛋白质0.16%、脂肪0.07%、粗纤维0.02%、灰分0.54%、磷0.053%，其直链淀粉含量(30.61%)高于玉米淀粉的。藕淀粉的平均粒径为50.27 μm，而玉米淀粉的为38.97 μm。藕淀粉颗粒呈小圆形和椭圆形，但在某些淀粉颗粒一端有凹陷。淀粉的X-衍射图谱为B型，糊化温度为54.09℃，透明度为57.9%，淀粉糊达到最大黏度即呈现平缓的特征，黏度峰值远低于玉米淀粉糊的。该研究对实际生产中，提高藕淀粉得率和纯度以及应用具有指导意义。     

一定碳氮比条件下不同有机物对烤烟生长及烟叶品质的影响

通过选用蔗糖、淀粉、纤维素和腐殖酸等4种有机物质,调节土壤碳氮比为20的情况下,研究了不同有机物对烤烟生长、烟叶生理生化特性及烟叶化学成分的影响。结果表明,不同有机物均能有效地促进烟株生长,且不同程度地提高了烤烟叶绿素的含量,以蔗糖和腐殖酸处理表现较好;成熟期各处理可以降低烤烟中叶绿素含量、硝酸还原酶活性、转化酶活性;淀粉酶活性较旺长期大,利于淀粉的分解转化,提高烤烟单株叶重;有机物显著提高了烟叶氮、磷、钾含量和积累量,其中以蔗糖处理和腐殖酸处理效果最显著;同时,显著提高烟叶总糖、还原糖和烟碱含量,并能降低烟叶中淀粉含量,各项指标综合来看以蔗糖的显著最为显著。烤后烟叶香气成分总含量以蔗糖处理最高,趋势为蔗糖处理>腐殖酸处理>淀粉处理>对照>纤维素处理,且香气成分含量较高的种类以蔗糖处理最高,腐殖酸处理次之。     

甘薯淀粉糊与绿豆淀粉糊流变行为的共性与区别

淀粉糊在粉丝加工中作为黏结剂，它的流变特性是粉团搅拌、形成、漏粉和定型的关键因素。本研究通过对甘薯淀粉糊和绿豆淀粉糊在不同浓度、温度、剪切速率和升温扫描过程中的流变行为的考察和分析比较，表明两种淀粉糊有触变共性，在流变曲线图上都呈现出不同滞后面积大小的开口型滞后回路，用Cross方程拟合精度比幂律方程高；用Arrhenius方程描述两者都具有温度敏感性。两者的区别在于：甘薯淀粉糊在各条件下的滞后面积比绿豆淀粉糊小，说明在粉团形成中甘薯淀粉糊的持续增黏效果高于绿豆淀粉糊；虽然绿豆淀粉糊的零剪切黏度值比甘薯淀粉糊要低，但在浓度较低(≤8%)时，两者差别不大，因此用甘薯淀粉糊替代绿豆淀粉糊是可行的。     

60Co-γ射线辐照处理后马铃薯淀粉糊的流变特性

为深入了解辐照处理对淀粉糊流变特性的影响,采用60Co-γ射线对马铃薯淀粉进行0～400 kGy辐照处理后制成淀粉糊,使用流变仪研究了不同剂量处理辐照后马铃薯淀粉糊的流变特性。静态流变特性测定结果表明,不同辐照剂量处理后马铃薯淀粉糊均呈假塑性流体特征,符合幂定律;辐照剂量越大,马铃薯淀粉糊的表观黏度和剪切稀化程度越低,并逐渐偏近牛顿流体。动态流变特性测定结果表明,马铃薯淀粉糊的弹性模量峰值及其相应的峰值系统温度和20℃弹性模量均随辐照剂量的增加而降低。研究结果可为辐照处理后淀粉的应用提供基础数据。     

酸雨胁迫对大豆萌发种子糖代谢动态的影响

为了探索酸雨胁迫对大豆萌发种子糖代谢动态的影响,试验采用蒸馏水浸泡大豆种子,再以pH2.5、4.5模拟酸雨(AR)处理大豆种子,考察不同强度AR胁迫对大豆萌发种子可溶性糖、还原性糖、蔗糖、淀粉及α、β-淀粉酶含量的影响。结果表明,第1天AR组的可溶性糖含量上升,第2天明显降低,随后稳定降低;AR胁迫下的第1天-第4天,还原糖含量维持较高水平,第3天-第5天呈下降趋势;pH2.5组在第2天-第5天蔗糖含量减少;AR胁迫的第2天-第4天淀粉含量降低;总体上,AR组的α-淀粉酶活性CK,但从第5天起pH2.5组的α-淀粉酶活性CK;β-淀粉酶活性在第1天-第6天高于或接近CK,pH2.5组在第7天低于CK。糖代谢各项指标和淀粉酶活性之间的关系表明,可溶性糖、还原糖、蔗糖含量变化幅度随AR胁迫强度增大而增加,淀粉含量变化与之相反;AR组对淀粉酶活性影响是导致萌发改变的内在因素之一。     

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,     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

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.     

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.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

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.