Effect of humic acids from Leonardite on the stability of soil aggregates and melon roots under greenhouse conditions

Leonardite is an oxidized form of lignite carbon, which is obtained from fossilized organic materials. Such materials are used for the extraction of humic acids (HA). The result of the addition of HA of organic origin on soil structure is known; however, the effects of adding HA of Leonardite on soil structure have been scarcely investigated. The objectives of this research were (1) to determine the influence of humic acids derived from Leonardite in increasing the aggregate stability of an Aridisol under greenhouse conditions, and (2) evaluate the morphology of the root xylem during the phenological development of melon plants (Cucumis melo L.). Three treatments of HA solution application to the soil were used: soil without solution application (HA0), and application of HA solution to the soil with pH 6 (HA6) or (HA7). Aggregate stability (As) and bulk density (Da) were evaluated as soil variables. Development and quantification of xylem area were studied on plants. There were significant differences in aggregate stability. Also, there was an increase in the root xylem area, and the best treatment was when AH7 solution was applied. Humic acids derived from Leonardite increased the stability of soil aggregates when plants grew under greenhouse conditions, and fostered the development of xylem conduits during the fruiting stage.     

Biochemical origin and refractory properties of humic acid extracted from maize plants: the contribution of lignin

The soil organic carbon (SOC) pool is the largest terrestrial reservoir of carbon and plant residues play an important role in its maintenance. Up to 70–80% of SOC in arable soil is composed of humic substances (HS). In these soils post-harvested residues, left in arable soil after harvesting the crops, are the basic source of humus. Previous research indicated that maize plants residue contain a humic acid (HA) fraction possessing recalcitrant compounds that contributed to soil-HA fraction. This study presents updated results obtained using Pyrolysis-Gas Chromatography/Mass Spectrometry (Py-GC/MS) to provide an indication of the contribution of the lignin to the soil HA. Results obtained indicated that the HAs from maize plants were mainly composed of lignin-derived moieties that were likely derived from the partial hydrolysis of p-coumaric and ferulic acid that are linked to lignin, polysaccharides or other biopolymers of the cell wall. Lignin composing the HAs derived from plants and incubated in soil was substantially preserved. Nevertheless the modification of the syringyl/guaiacyl ratio and the oxidation of the side-chains of lignin, suggested a turnover of lignin-derived molecules in soil-HA fraction. This fact indicated an involvement of the alkali insoluble fraction of maize plant residue (humin) in the soil-HA formation, up-dating our previous knowledge.     

不同用量腐植酸复合肥在辣椒上的施用效应及其防衰增产机理研究

以辣椒为供试作物进行盆栽试验,对不同用量腐植酸复合肥在辣椒上的施用效应及其防衰增产机理进行研究。结果表明,不同肥料用量对辣椒体内各种生理活动均有明显影响,并最终影响产量,且与无机复合肥相比,腐植酸复合肥表现了明显的优势。NRA随施肥量的增加而提高,但变化速率逐渐下降;SOD活性在施肥量低于0．2g·kg^-1时,随施肥量的增加显著提高,但当施肥量超过0．2g·kg^-1后,SOD活性开始显著降低;对POD活性的影响与对NR活性的影响趋势基本一致,但当施肥量超过0．3g·kg^-1时,无机肥处理的POD活性显著提高,而HA复合肥处理的POD活性变化则始终较平缓;对辣椒叶片蒸腾速率的影响与对SOD活性的影响趋势是一致的。施肥量与辣椒产量之间呈显著二次曲线相关,HA复合肥最高产量施肥量(纯养分量)为0．27g·kg^-1,每盆最高产量为165．22g。     

Spectroscopic properties of sedimentary humic acids from a salt marsh (Ria de Aveiro, Portugal): comparison of sediments colonized by Halimione portulacoides (L.) Aellen and non-vegetated sediments

The influence of the colonization of salt marsh sediments with Halimione portulacoides, on the composition of the sedimentary humic acids was evaluated. For this purpose, cores of colonized and non-colonized sediments from a salt marsh in Ria de Aveiro (Portugal) were collected, and the humic acids of different layers were extracted and characterized by Fourier transform infrared, synchronous molecular fluorescence ( = 60 nm) and UV-visible spectroscopies and also by elemental analysis. The infrared spectra suggest the presence of more peptide residues and carbohydrates in the sedimentary humic acids from surface and around the plant roots at the site colonized by H. portulacoides, when compared with the humic acids from the depth-equivalent sediment layers at the non-colonized site. The higher content of protein-type materials is confirmed by the lowest values of C/N ratios and the highest relative intensities of a band at _exc = 280 nm in the fluorescence spectra. The lowest ₂₈₀ values obtained in the UV-visible spectra, and the infrared spectra suggest a lower aromatic content of the humic acids from the colonized site.     

Contrasting effects of rabbit exclusion on nutrient availability and primary production in grasslands at different time scales

Herbivores influence nutrient cycling and primary production in terrestrial plant communities. However, both empirical and theoretical studies have indicated that the mechanisms by which herbivores influence nutrient availability, and thus their net effects on primary production, might differ between time scales. For a grassland in southeast England, we show that the effects of rabbits on primary production change over time in a set of grazed plots paired with exclosures ranging from 0 to 14 years in age. Herbivore exclusion decreased net aboveground primary production (APP) in the short term, but increased APP in the long term. APP was closely correlated with N mineralization rates in both grazed and ungrazed treatments, and accumulation of litter within the grazing exclosures led to higher N mineralization rates in exclosures in the long run. Rabbit grazing did not influence litter quality. The low contrast in palatability between species and the presence of grazing-tolerant plants might prevent rabbits from favoring unpalatable plant species that decompose slowly, in contrast to results from other ecosystems. Our results indicate that it is essential to understand the effects on N cycling in order to predict the effect of rabbit grazing on APP. Rabbits might decrease N mineralization and APP in the long term by increasing losses of N from grasslands.     

Effect of different levels of humic acids on nutrient content and growth of corn (Zea mays L.)

Summary The effect of humic acids on nutrient uptake and growth of corn plants (Zea mays L.) was investigated by growing corn in plastic growth pouches containing a Hoagland nutrient solution to which were added 0, 320, 640, 1,600 or 3,200 ppm HA, pH 7.0. The experiments were carried out in three replicates for a growing period of 16 days after germination. Humic acid was in general beneficial to shoot and root growth of corn plants. Dry matter yield in corn shoots was stimulated by HA, especially by treatments with 640 ppm HA. Nutrient uptake showed a number of differences as a result of treatments with HA. Moderate applications with HA resulted in a significant increase in N content of corn shoots, while large amounts of HA had a tendency to reduce the N concentration in corn shoots. As a result of the HA treatments, P concentrations in corn shoots were decreased, but differences in K contents were statistically nonsignificant and Mn contents in shoots were also nonsignificantly different among the treatments. However, Zn content showed a tendency to increase with increasing applications of HA.Contribution of the University of Georgia, College Agri. Exp. Stn., College Stn., Athens, GA 30602. Current address of junior author: c/o Soil and Fertilizer Section, Field Crop Division, Department of Agriculture, Bangkok, Thailand.     

The effect of pH on the lability of lead and cadmium sorbed on humic acid particles

Abstract

Sorption of lead(II) or cadmium(II) ions on humic acid particles (at pH 3.5) yields surface complexes which are sparingly soluble in the pH 3.55 region. Interaction of these species with acetic acid or dilute nitric acid released ASV labile metal species (mainly hydrated metal ion). When the pH was adjusted between 4 and 7, increasing amounts of the metal humate species (and humic acid substrate) dissolved and low levels of ASV labile species were detected. Overnight interaction with an excess of acetate ions (0.01 M) led to higher lability values (attributed to acetate/humate ligand exchange). The percentage of labile metal ion detected in acetate solutions varied with the amount of metal ion initially sorbed (range 100 to 500 mmol g^?1). With the lower loadings, the ASV labile levels peaked in the pH 6–7 region (at around 12% of total sorbed cadmium, and 4% of total lead). In alkaline solutions, the percentage of labile Cd fell to about half of the peak value, but with Pb, lability values increased at pH > 8, due possibly to the formation of hydroxy complex species. The ASV lability of the Cd and Pb humates, and their 24 hour lability values (determined using a transfer to cation exchanger technique) has been compared with the behaviour of Cu and Zn humates (using similar conditions).     

Soil resource availability and its effect on the ecophysiology and establishment of Stipa pulchra

Aims The objectives of this study were to (i) determine the importance of soil moisture and soil nitrogen availability as resource requirements for the establishment ofStipa pulchra, (ii) to examine how changes in slope within a local habitat can affect the accumulation of soil moisture and soil nitrogen and (iii) to measure the physiological responses ofS. pulchraamong such slope locations.     

Influence of paddy and corn in different rotations on wheat yield,nutrient removal and soil properties

Summary In a 3 year field study, the effect of two rotations, paddy (Oryza sativa L.), wheat (Triticum aestivum L.), mung (Phaseolus aureus L.) and corn (Zea mays L.), wheat (Triticum aestivum L.), mung (Phaseolus aureus L.) on wheat yield and chemical, physical and biological properties of soil was evaluated. Grain yield of the wheat sown after paddy during 1972–73, 1973–74 and 1974–75 was lesser by 0,300 and 390 kg/ha respectively than that of the wheat following corn. The reduction in the yield of wheat was attributed to relatively higher NPK removal by paddy, greater immobilization of N applied to wheat and deterioration of soil physical conditions in the paddy field. Total NPK removal by paddy average 131 kg/ha more than that by corn. Sharp increase in bacterial population of soil during early growth of wheat that followed paddy and the concurrent less available N in soil and low N content in wheat plants suggested that the N applied to wheat was immobilised to organic form. The increase in soil bulk density and particle dispersion ratio and decrease in water storage in deeper soil layers in the paddy field probably restricted the root proliferation and growth of wheat.     

红壤坡地不同土地利用方式土壤侵蚀的时空分布规律研究

应用定位土芯Eu(Europium)示踪新方法 ,研究红壤坡地不同土地利用方式下土壤侵蚀的时空分布规律 .结果表明 ,新方法对以片蚀和细沟侵蚀为主的红壤坡地是适用的 ;土壤侵蚀的时间分布与降雨量的年时间分布相一致 ,过程性暴雨期表现为全年土壤侵蚀的高峰期 ;在复合坡面 ,随坡面的陡、缓、凹 ,土壤侵蚀表现强、弱、沉积 ;相同坡度和坡长条件下 ,幼龄板栗园的土壤侵蚀速率 >雷竹园 >稀疏马尾松林地 >茶园 .     

不同质地土壤的水热状况及其对冬小麦产量形成的影响

对豫东平原３种质地土壤的水热状况和冬小麦籽粒生长特征进行了研究．结果表明,冬小麦籽粒生长阶段,粘壤土５ｃｍ处的日平均温度最低,为１８．３℃,砂壤土最高,为１９．５℃,中壤居中,为１９．１℃．３种土壤的含水量大小顺序为粘壤＞中壤＞砂壤,粘壤土上小麦籽粒灌浆时间最长,千粒重最高,分别为３８ｄ和４５．５ｇ,砂壤土小麦籽粒灌浆时间最短,千粒重最低,分别为３３ｄ和４２．４ｇ,中壤土小麦２项指标居中,分别为３６ｄ和４３．１ｇ．高产栽培条件下,粘壤土冬小麦产量最高,为８２５３ｋｇ·ｈｍ－２,中壤次之,为７９８０ｋｇ·ｈｍ－２,砂壤最低,为７６１７ｋｇ·ｈｍ－２     

Effects of different molecular weight fractions of dissolved organic matter on the growth of bacteria,algae and protozoa from a highly humic lake

Effects of different molecular size fractions (< 1000 MW, < 10 000 MW, < 100 000 MW and <0.1 μm) of dissolved organic matter (DOM) on the growth of bacteria, algae and protozoa from a highly humic lake were investigated. DOM from catchment drainage water as well as from the lake consisted mostly (59–63%) of high molecular weight (HMW) compounds (> 10 000 MW). With excess inorganic nutrients, the growth rate and yield of bacteria were almost identical in all size fractions. However, in < 1000 MW fractions and with glucose added, a longer lag phase occurred. Without added nutrients both the growth rates and biomasses of bacteria decreased towards the smaller size fractions and the percentage of dissolved organic carbon (DOC) used during the experiment and the growth efficiency of bacteria were lower than with excess nutrients. The growth efficiency of bacteria was estimated to vary between 3–66% in different MW fractions, largely depending on the nutrient concentrations, but the highest growth efficiencies were observed in HMW fractions and with glucose. The growth of algae was clearly lowest in the < 1000 MW fraction. In dim light no net growth of algae could be found. In contrast, added nutrients substantially enhanced algal growth and in deionized water with glucose, algae achieved almost the same growth rate and biomass as in higher MW fractions of DOM. The results suggested that bacteria and some algae were favoured by DOM, but protozoans seemed to benefit only indirectly, through bacterial grazing. The utilization of DOM by bacteria and algae was strongly affected by the availability of phosphorus and nitrogen.     

不同来源生物炭对砷在土壤中吸附与解吸的影响

采用OECD Guideline 106批平衡方法研究了由凋落松针、玉米秸秆、牛粪制备的3种生物炭对As(Ⅴ)在棕壤中的吸附和解吸特性的影响.结果表明：3种生物炭的添加量为0.5%时,对As(Ⅴ)在土壤中的吸附量大小顺序为牛粪炭处理＞松针炭处理＞玉米秸秆炭处理,这与生物炭的基本性质密切相关;等温吸附曲线能用Langmuir方程进行很好的拟合(R² =0.997);与对照相比,生物炭处理对砷的吸附容量(lgK_f 为1.99～2.10)和吸附强度(1/N 为0413～0.449)降低,生物炭对As(Ⅴ)的主要吸附机制为物理吸附;生物炭处理对As(Ⅴ)解吸率大小顺序为：玉米秸秆炭处理＞松针炭处理＞牛粪炭处理,解吸率在14.5%～18.7%.添加3种来源生物炭降低了棕壤对As(Ⅴ)的吸附,这可能会导致砷的有效性增强,更易被生物吸收,进而增强土壤中砷的毒性.     

不同腐解期玉米秸秆对塿土胡敏酸基本性质及级分变异的影响

采用田间腐解试验,在研究不同腐解期玉米秸秆对土壤胡敏酸性质影响的基础上,利用酒精分级沉淀法对土壤胡敏酸进行分级,研究了不同腐解期土壤胡敏酸级分组成及性质变化.结果表明,在整个腐解过程中土壤胡敏酸由A型转化为P型又转化为A型,呈现由复杂到简单又到复杂的变化趋势.不同腐解期土壤胡敏酸的级分组成不同.玉米秸秆更新土壤胡敏酸过程是一个双向过程,一方面使胡敏酸中结构复杂成分(级分1、2、3)向简单化发展,另一方面一些小分子胡敏酸(级分6、7)随时间推移按Rp→P→A途径逐渐缩合.     

微立地土壤水分—物理性质差异及对水曲柳幼林生长的影响

采用较小立地尺度对土壤水分物理性质的变化及与水曲柳生长的关系进行研究。结果表明,除传统尺度立地上土壤水分－物理性质存在较大差异外,该尺度立地内部微立地间亦存在较大的变化,一些指标如非毛管孔隙度、土壤通气度和土壤渗透系数等在微立地间的变化甚至超出立地间的变化,土壤水分－物理性质的差异,使得不同微立地间水曲柳生长存在较大差异,同一立地内不同微立地间林木生长差异明显高于不同立地间的差异,土壤水分－物理性质及林木生长受到局部地段微立地的影响,微立地的研究对进一步实现适地适树具有重要意义。     

Impact of tree species on nutrient and light availability: evidence from a permanent plot study of old-field succession

This paper compares vegetation composition, light availability, carbon and nutrient pools and Ellenberg indicator values among four old-field successional permanent plots that have received an initial treatment (ploughing, herbicide or sterilisation) prior to being left undisturbed in 1969, a second set of six plots received additional treatments (continued ploughing or mulching until 1982). On all plots species rich pioneer forests developed. Vegetation still varies among plots with different initial treatments: Sterilised plots can be distinguished from the others by dominance of Betula pendula, ploughed plots by Fraxinus excelsior, whereas herbicide-treated plots are intermediate with proportions of both species. By affecting light availability at the ground, tree species in turn influences ground vegetation and soil properties. Light availability turned out to be the dominant factor determining the composition of the vegetation in old-field succession.     

宁南山区植被恢复对土壤团聚体养分特征及微生物特性的影响

测定了宁夏黄土丘陵区植被恢复近30年的天然草地和农地不同粒径团聚体的土壤养分含量、微生物生物量、呼吸特性和生态化学计量比等指标,探索黄土丘陵区植被恢复对不同粒径土壤团聚体的养分特性和微生物学性质的影响.结果表明: 微团聚体(粒径<0.25 mm)质量百分比、各粒径土壤团聚体养分(有机碳、全氮、速效钾)含量、C/N均表现为天然草地大于农地,其中1～2 mm粒径团聚体有机碳、全氮含量在天然草地和农地中均最高,C/N也较高,说明植被恢复能有效促进土壤团粒的形成,适宜养分积累和有机碳的汇集,且在1～2 mm粒径团聚体上表现最为突出;天然草地各粒径土壤团聚体微生物生物量(碳、氮)、基础呼吸强度均高于农地,而呼吸熵低于农地,可见植被恢复措施可有效提高各粒径土壤微生物生物量与活性,并使土壤生境趋于稳定;但由于养分特性的差异,不同粒径团聚体微生物特性对植被修复的响应存在差异,其中天然草地土壤1～2 mm粒径团聚体微生物生物量碳,<0.25、0.25～1、1～2 mm粒径团聚体微生物生物量氮,以及1～2、>5 mm粒径团聚体基础呼吸强度显著高于其他粒径,即上述粒径团聚体的微生物生物量和微生物活性在植被恢复过程中逐渐被改善.表明宁南山区植被恢复有效改善了土壤团聚体的肥力状况与结构特征,且1～2 mm粒径团聚体的改良效果最为突出.     

微立地土壤水分-物理性质差异及对水曲柳幼林生长的影响

采用较小立地尺度对土壤水分物理性质的变化及与水曲柳生长的关系进行研究.结果表明,除传统尺度立地上土壤水分-物理性质存在较大差异外,该尺度立地内部微立地间亦存在较大的变化,一些指标如非毛管孔隙度、土壤通气度和土壤渗透系数等在微立地间的变化甚至超出立地间的变化.土壤水分-物理性质的差异,使得不同微立地间水曲柳生长存在较大差异,同一立地内不同微立地间林木生长差异明显高于不同立地间的差异.土壤水分-物理性质及林木生长受到局部地段微立地的影响.微立地的研究对进一步实现适地适树具有重要意义.     

不同耕作和覆盖方式对紫色丘陵区坡耕地水土及养分流失的影响

采用随机区组试验,研究了四川紫色丘陵区坡耕地不同耕作和覆盖方式对玉米生育期中水土及养分流失的影响。结果表明:秸秆覆盖对减少水土流失和增加玉米产量的效果均优于地膜覆盖。秸秆覆盖能显著减少地表径流(73.9%—86.2%),但增加了壤中流(15.4%—156.4%);使径流总量降低32.5%—66.6%,并极显著降低土壤侵蚀总量达96.4%—98.1%。地膜覆盖虽能在一定程度上减少壤中流和径流总深,但差异未达到显著水平。土壤N平均损失量达37.4kg/hm2,其中70.1%经由壤中流流失。秸秆覆盖虽然增加了一定的壤中流N损失,但能减少N流失总量达12.8%—65.1%。土壤P素损失量相对较小,仅为9.32kg/hm2,并主要随侵蚀泥沙迁移,占流失总量的92.1%。土壤K损失量达183.3kg/hm2,其流失载体也主要是侵蚀泥沙,占96.5%。因此,两种覆盖方式均能显著控制土壤P和K的损失。无论是秸秆还是地膜覆盖,与顺坡垄作相比,横坡垄作均能减少地表径流、地下径流、土壤侵蚀量及氮、磷、钾素总流失量,同时还能提高玉米产量。从简便、增产和防治面源污染的角度考虑,紫色土区坡耕地最适宜的种植方式为平作+秸秆覆盖。