Interplay of omnivory, energy channels and C availability in a microbial-based soil food web

 To study the effects of omnivory on the structure and function of soil food webs and on the control of trophic-level biomasses in soil, two food webs were established in microcosms. The first one contained fungi, bacteria, a fungivorous nematode (Aphelenchoides saprophilus) and a bacterivorous nematode (Caenorhabditis elegans), and the second one fungi, bacteria, the fungivore and an omnivorous nematode (Mesodiplogaster sp.) feeding on both bacteria and the fungivore. Half of the replicates of each food web received additional glucose. The microcosms were sampled destructively at 5, 9, 13 and 19 weeks to estimate the biomass of microbes and nematodes and the soil NH₄ ⁺-N concentration. The evolution of CO₂ was measured to assess microbial respiration. Microbial respiration was increased and soil NH₄ ⁺-N concentration decreased by the addition of glucose, whereas neither was affected by the food-web structure. Supplementary energy increased the biomass of fungi and the fungivore, but decreased the biomass of bacteria, the bacterivore and the omnivore. The omnivore achieved greater biomass than the bacterivore and reduced the bacterial biomass less than the bacterivore. The biomass of the fungivore was smaller in the presence of the omnivore than in the presence of the bacterivore at three sampling occasions. Fungal biomass was not affected by food-web structure. The results show that the effects of the omnivore were restricted to its resources, whereas more remote organisms and soil processes were not substantially influenced. The results also indicate that the presence of an omnivore does not necessarily alter the control of populations as compared with a food web containing distinct trophic levels, and that the fungal and bacterial channels may respond differently to changes in energy supply. Received: 15 December 1997     

Continuous manuring combined with chemical fertilizer affects soil microbial residues in a Mollisol

In this study, the influence of 10 years’ continuous application of organic manure at various rates combined with chemical fertilizer on microbial residues was evaluated in a highly fertile temperate soil. The presence and origin of microbial residues were indicated by amino sugar analysis. The treatments were: (1) CK, unfertilized control; (2) OM₀, only chemical fertilizer, no manure added; (3) OM₁, organic manure added at 7.5 Mg?ha^?1?year^?1 plus chemical fertilizer; (4) OM₂, organic manure added at 15 Mg?ha^?1?year^?1 plus chemical fertilizer; and (5) OM₃, organic manure added at 22.5 Mg?ha^?1?year^?1 plus chemical fertilizer. Fertilization significantly increased the total amino sugar concentrations, especially in the plots with higher manure addition rates (OM₂ and OM₃ plots, P?<?0.05). This suggests a positive effect of organic manure combined with chemical fertilizer on the accumulation of microbial residues in soil. However, the highest manure rate (OM₃) did not lead to further increase in the total amino sugar pool as compared with the moderate manure rate (OM₂). This suggests manure addition “saturates” in its effect on microbial residue build-up. The different patterns of individual amino sugars suggest a change in the quality of microbial-derived soil organic matter after 10 years.     

设施蔬菜有机肥/秸秆替代化肥模式对土壤线虫群落的影响

  【目的】  利用天津市西青区基地日光温室蔬菜不同施肥模式定位试验,研究有机肥/秸秆替代化肥模式对设施蔬菜土壤线虫总数、群落结构和生态指数的影响,为构建健康的土壤动物区系提供科学依据。  【方法】  定位试验共设6个处理,分别为:1) 全部施用化肥氮 (4/4CN);2) 3/4化肥氮 + 1/4猪粪氮 (3/4CN + 1/4MN);3) 2/4化肥氮 + 2/4猪粪氮 (2/4CN + 2/4MN);4) 1/4化肥氮 + 3/4猪粪氮 (1/4CN + 3/4MN);5) 2/4化肥氮 + 1/4猪粪氮 + 1/4秸秆氮 (2/4CN + 1/4MN + 1/4SN);6) 2/4化肥氮 + 2/4秸秆氮 (2/4CN + 2/4SN),各处理为等氮磷钾设计。第16茬 (土壤消毒后) 和第18茬 (土壤消毒1年后) 蔬菜 (春茬番茄) 拉秧后,分别采集0—5、5—10和10—20 cm土层土壤样品,测定土壤线虫相关指标。  【结果】  1) 有机肥/秸秆替代化肥模式0—5、5—10和10—20 cm土层土壤线虫总数均高于单施化肥模式,平均分别增加16.8%、31.8%和11.2%;配施高量有机肥模式 (1/4CN + 3/4MN) 和配施秸秆模式 (2/4CN + 1/4MN + 1/4SN、2/4CN + 2/4SN) 各土层线虫总数相对较高,较单施化肥模式分别提高12.1%～26.4%、34.3%～42.8%、13.2%～18.3%。2) 与单施化肥模式相比,有机肥/秸秆替代化肥模式,尤其是配施高量有机肥模式和配施秸秆模式可提高0—5和5—10 cm土层土壤有益线虫 (食细菌、食真菌和捕食/杂食性线虫) 营养类群个体数量,其中0—5 cm土层上述线虫营养类群个体数量平均分别增加13.0%、7.4%和26.7%,5—10 cm土层平均分别增加35.5%、20.2%和56.5%。有机肥/秸秆替代化肥模式0—5和5—10 cm土层土壤有害植食性线虫数量虽均高于单施化肥模式,但其相对丰度均低于单施化肥模式,平均分别降低6.3%和13.1%。3) 有机肥/秸秆替代化肥模式,尤其是配施高量有机肥模式和配施秸秆模式,MI值、WI值、EI值和SI值均高于单施化肥模式,0—5 cm土层平均分别增加3.9%、11.5%、6.2%和130.4%,5—10 cm土层平均分别增加1.8%、19.1%、2.4%和138.7%。  【结论】  在N、P₂O₅和K₂O投入量不变的情况下,有机肥/秸秆替代化肥模式可促进土壤有益线虫 (食细菌线虫、食真菌线虫和捕食/杂食性线虫) 生长繁殖,还可降低土壤有害植食性线虫相对丰度,对土壤有害植食性线虫起到一定的抑制作用。综合来看,有机肥/秸秆替代化肥模式,尤其是配施高量有机肥模式和配施秸秆模式,可优化土壤线虫群落结构,降低土壤环境的受干扰程度,改善土壤的质量,使设施蔬菜土壤生态系统向稳定健康的方向发展。结合本试验9年产量数据 (2/4CN + 1/4MN + 1/4SN模式产量最高)、土壤线虫群落相关研究结果以及实际可操作性,化肥与有机肥、秸秆配施模式(2/4CN + 1/4MN + 1/4SN)可实现设施蔬菜持续高产。     

Chemical and microbiological soil quality indicators and their potential to differentiate fertilization regimes in temperate agroecosystems

The study examined the interrelationships between chemical and microbiological quality indicators of soil and their ability to differentiate plots under contrasting fertilization regimes. The study was based on a long-term field experiment established on an Udic Ustocrepts in 1966. The soil was cropped with maize (Zea mays L.) and winter wheat (Triticum aestivum L.) and received no organic fertilization (control), wheat straw and maize stalk (crop residue) or cattle manure (manure) in combination with increasing levels of mineral N (N₀ and N₂₀₀). To asses whether seasonal fluctuations of measured properties might mask the effects of fertilization, soil samples were collected four times within a growing season. Manure amendment increased soil TOC and TN, while crop residue amendment had no significant effects. Mineral N increased TN only in April, while in September it decreased water extractable organic C (WEOC). Data of diffuse reflectance Fourier transform mid-infrared spectroscopy (DRIFTS) gave evidence for a higher relative contribution of the aliphatic peak at 2930 cm⁻¹ and a lower relative contribution of the aromatic peaks at 1620 cm⁻¹ and 1520 cm⁻¹ under manure. Manure amendment stimulated enzymatic activities, increased microbial biomass carbon (C_mic) and total phospholipids (PLFAs), and reduced the metabolic quotient (qCO₂). Patterns of PLFAs indicated that manure amendment increased the ratio of Gram-positive to Gram-negative bacteria. Crop residue amendment had no significant effects, while in September mineral N inhibited protease activity and reduced the Gram-positive to Gram-negative ratio. Microbial-related parameters fluctuated over time but their seasonality did not hamper the identification of fertilization-induced effects. The selected properties proved to be valuable indicators of long-term changes of soil quality and were strongly interrelated: changes in soil organic matter content and composition induced by manure amendment were accompanied by changes in abundance and function of the soil microbial community. Partial least square analysis obtained relating DRIFTS spectra to measured soil properties produced accurate predictive models for TOC and PLFAs, and moderately accurate models for C_mic, showing the potential of DRIFTS to be used as a rapid soil testing technique for soil quality monitoring.     

长期施用有机肥对红壤旱地土壤线虫群落的影响

基于红壤旱地(玉米)的长期施肥试验,研究长期施用有机肥对土壤线虫分布特征及群落结构的影响。田间试验处理包括:CK(对照)、ON1(低量有机肥)、ON2(高量有机肥)和ON2L(高量改良有机肥)。结果表明,施肥8a后,红壤旱地中共鉴定出15科、29属土壤线虫,包括8属植物寄生线虫、9属食细菌线虫、3属食真菌性线虫和9属捕食杂食性线虫,短体属(Pratylenchus)、小杆属(Rhabditis)和原杆属(Pro-torhabditis)为优势属。不同施肥处理中,土壤线虫总数的大小顺序为ON2>ON1>ON2L>CK。线虫群落生态指数对于施用有机肥有不同的响应:除SI外,其他虫群落生态指数均有显著差异,通过线虫群落结构的变化很好地反映了土壤的肥力变化状况,土壤线虫可以作为施有机肥过程中指示土壤健康质量的一个重要的生物学指标。     

Influence of organic Crotalaria juncea hay and ammonium nitrate fertilizers on soil nematode communities

Comparisons of organic and inorganic fertilizer effects on nematode communities depend on the specific organic fertilizer used. Field experiments were conducted during 2001 and 2002 in a squash (Cucurbita pepo) agroecosystem to determine if applying sunn hemp (Crotalaria juncea) hay as an organic fertilizer improved nematode communities involved in soil nutrient cycling compared to an equivalent N rate (100 kg N/ha) of ammonium nitrate. Fertilizer source had minimal effect on nematode communities in 2001 when treatments were applied after a winter cover crop of oats (Avena sativa), but differences (P ≤ 0.05) between the fertilizer sources occurred in 2002 when no winter cover cropping preceded squash. Fertilization with sunn hemp hay increased abundance of the bacterivore guilds Ba₁ and Ba₂, and increased fungivores at the end of the experiment. Compared to ammonium nitrate, fertilization with sunn hemp hay resulted in a community with lower maturity index, higher enrichment index, and lower channel index, consistent with a disturbed and nutrient-enriched soil food web undergoing bacterial decomposition. Sunn hemp hay occasionally stimulated omnivorous nematodes, but suppressed plant-parasitic nematodes relative to ammonium nitrate fertilizer. Increasing the sunn hemp hay rate to 200 kg N/ha increased the abundance of bacterivores, fungivores, and predatory nematodes, and total nematode abundance compared to hay at 100 kg N/ha. Fertilization with ammonium nitrate increased the percentage of herbivores, but reduced percentage and abundance of omnivores. In conclusion, sunn hemp fertilizer maintained greater numbers of nematodes involved in nutrient cycling as compared to ammonium nitrate.     

Soil ameliorants alter physicochemical properties and fungal communities in saline-sodic soils of Northeast China

To understand the mechanisms of soil ameliorants affecting microbial communities is important for saline-sodic soils reclamation. High-throughput sequencing was used to characterize the fungal community in soils amended with four types of ameliorants over an 8-year period. Besides a control without any additional ameliorant (CK), other four treatments including 1) amendment with sandy soil (SS), 2) amendment with desulfurization gypsum (DG), 3) amendment with farm manure (FM), and 4) amendment with a mixture of SS, DG, and FM (M) were analyzed. Soil pH and electrical conductivity significantly decreased with the addition of soil ameliorants, whereas the soil organic carbon (SOC), total nitrogen (TN), and SOC/TN ratio (C/N) significantly increased in the FM and M treatments compared with the CK treatment. Fungal richness increased significantly with the mixed ameliorants addition (M). Distinct fungal community structures were observed in the treatments with soil ameliorants. The fungal community composition was significantly associated with the SOC, C/N, aggregate content with a diameter > 0.25 mm and geometric mean diameter. The changes in these soil characteristics were highly correlated with the ameliorants additions, suggesting that the impacts of ameliorants on the soil fungal community occurred indirectly as a result of alterations to soil physiochemical properties.     

Soil nematode community,organic matter,microbial biomass and nitrogen dynamics in field plots transitioning from conventional to organic management

Dynamics of soil bulk density, organic matter, microbial biomass, nitrogen, and nematode communities were assessed for a period of 4 years in field plots transitioning from conventional to organic farming practices. A rotation of soybeans, corn, oats and hay was used as an organic transitioning strategy and the conventional farming system had a corn and soybean rotation for comparison. Organic corn received raw straw pack beef manure and poultry compost at the rate of 27 and 28 Mg/h, respectively, and organic oats received raw straw pack beef manure and poultry compost at the rate of 18 and 1.8 Mg/h, respectively, while conventional plots received synthetic fertilizers. All crops in the organic system received primary tillage (chisel plow, disked and tined) whereas only corn received primary tillage in the conventional system but soybeans were no-till. Weed control was mechanical (twice diskings, rotary hoeings and row cultivation) in the organic system whereas herbicides were used in the conventional system. Soil bulk density did not differ in the two systems over a 4-year period but organic farming had slightly higher organic matter, mineral associated organic matter and particulate organic matter. Conventional system had more N in the mineral pools as indicated by higher NO₃⁻-N whereas organic system had higher N in the microbial biomass indicating shifts in nitrogen pools between the two systems. Bacterivore nematodes were more abundant in the organic than the conventional system for most of the study period. In contrast, the conventional system had significantly higher populations of the root lesion nematode, Pratylenchus crenatus, than the organic system after completion of the rotation cycle (transition period) in spring 2004. The organic hay plots had the lowest populations of P. crenatus compared to corn, soybeans and oats. Nematode faunal profile estimates showed that the food webs were highly enriched and moderately to highly structured and the decomposition channels were bacterial in both systems. The lack of differences in structure index between the organic and conventional systems is probably due to the excessive tillage in the organic farming system, which may have prevented the build up of tillage-sensitive omnivorous and predatory nematodes that contribute to the structure index. We conclude that transition from conventional to organic farming can increase soil microbial biomass-N and populations of beneficial bacterivore nematodes while simultaneously reducing the populations of predominant plant-parasitic nematode, P. crenatus. Our findings also underscore the potential benefits of reducing tillage for the development of a more mature soil food web.     

Distribution of carbon and nitrogen in water-stable aggregates and soil stability under long-term manure application in solonetzic soils of the Songnen plain,northeast China

Purpose

Excessive exchangeable sodium and high pH significantly decrease soil structural stability and permeability. Long-term application of cattle manure is an important management practice that can affect water-stable aggregates (WSAs), as well as aggregate stability and distribution of soil organic carbon (SOC) and total nitrogen (TN) in solonetzic soils.

Material and methods

Experiments were carried out in a randomized complete block design comprising five treatments according to the cattle manure application history: corn (Zea mays) with manure applied for 1, 5, 12, and 17 years were used as the experimental treatments and corn without manure application was used as a control. Soil properties, including WSAs, mean weight diameter (MWD), and SOC and TN concentrations in bulk soils and WSAs, were measured across all treatments. The relationships among the measured soil attributes were determined using stepwise regression analysis.

Results and discussion

Results indicated that micro-aggregates mainly accumulated in soils without manure application, while manure application significantly increased macro-aggregates formation. MWD was highest when manure was applied to the soil for 1 year, decreased after 5 years, and increased again after 12 years. SOC and TN concentrations in bulk soils and WSAs increased with the number of years of manure application, with the highest concentrations observed for 17 years in bulk soils. Stepwise regression analysis showed that WSAs 2–5 mm, SOC in WSAs 0.25–0.5 mm, and TN in WSAs 0.1–0.25 mm were dominant independent variables affecting aggregate stability, and that SOC in WSAs 0.25–0.5 mm and TN in WSAs <0.1 mm were dominant independent variables affecting SOC and TN concentrations in bulk soils, respectively.

Conclusions

Long-term application of manure to a solonetz significantly increased macro-aggregates and aggregate stability as well as SOC and TN in bulk soils and all aggregate sizes. These results are likely related to binding agent production as well as C and N accumulation from manure application.     

长期施肥对栗褐土有机碳含量及其组分的影响

【目的】作为土壤质量的重要指标,土壤有机碳及其组分在耕地生产力和作物产量方面发挥着重要作用。本文以25年长期定位施肥试验为依托,分析了不同施肥处理对栗褐土有机碳含量及其组分的影响,为调控农田土壤肥力及栗褐土有机碳库的管理提供科学依据。【方法】田间试验开始于1988年,设置8个施肥处理为不施肥(CK);单施氮肥(N);氮磷肥合施(NP);单施低量有机肥(M1);低量有机肥与氮肥合施(M1N);低量有机肥与氮磷肥合施(M1NP);高量有机肥与氮肥合施(M2N);高量有机肥与氮磷肥合施(M2NP)。于第25年玉米播种前,采集以上处理的耕层(0—20 cm)土壤样品。借助有机碳物理分组方法和化学分析方法,测定了土壤总有机碳和有机碳各组分的含量。【结果】长期施用不同肥料不同程度地提高了栗褐土总有机碳、游离态颗粒有机碳以及闭蓄态颗粒有机碳含量,其中有机肥与化肥配施尤其是高量有机肥与化肥配施的作用更加明显。与不施肥相比,高量有机肥与无机肥配施(M2N、M2NP)总有机碳含量增加了121.1%、166.8%,游离态颗粒有机碳增加了239.2%、359.2%,闭蓄态颗粒有机碳增加了288.4%、289.9%。单施氮肥(N)及有机肥与氮磷肥配施(M1NP、M2NP)可显著提高矿物结合态有机碳含量,增幅分别为27.8%、34.8%、33.3%。不施肥条件下,栗褐土有机碳中颗粒有机碳与矿物结合态有机碳所占的比例相当,长期施肥提高了颗粒有机碳特别是闭蓄态颗粒有机碳的比例,降低矿物结合态有机碳所占的比例,闭蓄态颗粒有机碳成为栗褐土有机碳的主要贮存库。相关分析表明,长期施肥条件下栗褐土游离态、闭蓄态颗粒有机碳含量之间及其与总有机碳含量之间均呈极显著正相关,矿物结合态有机碳含量与总有机碳及其他组分的有机碳之间均无明显相关。【结论】化肥、有机肥以及有机肥与化肥配施能够提高栗褐土游离态颗粒有机碳、闭蓄态颗粒有机碳以及总有机碳含量。高量有机肥与化肥配施更有助于栗褐土游离态、闭蓄态颗粒有机碳的积累,有利于土壤养分有效性的提高和有机碳品质的改善。氮肥单施、有机肥与氮磷肥配施则是提高矿物结合态有机碳含量的有效措施。     

旱地红壤线虫群落对不同耕作年限的响应及指示意义

我国热带和亚热带地区的红壤农田肥力水平低,严重制约着农业生产力的提升。不同农业管理措施会对土壤理化性质和生物群落产生不同的影响。本文研究了不同耕作年限条件下的旱地土壤,选取耕作10 a、20 a、50 a的花生地和菜地,并以未开垦的原始荒地作为对照。结果显示,与荒地相比,各年限花生地的土壤肥力等指标表现出下降的趋势,菜地土壤的各项性质则呈现提升的趋势。耕作20 a的花生地土壤有机碳、全氮、微生物生物量碳、有效磷等指标均最低,同时耕作50 a的菜地各项性质相对于10 a有显著的提升(p0.05)。花生地中植食性线虫比例伴随耕作年限延长而下降,而菜地中食细菌线虫比例伴随耕作年限延长而逐渐上升。从线虫生态指标数据显示,花生地相对于频繁施肥和耕作的菜地表现出更为稳定的土壤食物网。因此,线虫群落对不同耕作年限下旱地红壤生态系统的变化表现出一定的指示潜力。     

Soil carbon and nitrogen response to 25 annual cattle manure applications

Improving manure management to benefit both agricultural production and the environment requires a thorough understanding of the long‐term effects of applied manure on soil properties. This paper examines the effect of 25 annual solid cattle manure applications on soil organic carbon (OC), total N (TN), and KCl‐extractable NO₃‐N and NH₄‐N under both non‐irrigated and irrigated conditions. After 25 annual manure applications, OC and TN contents increased significantly with the rate of manure application at the top two sampling depths (0–15 cm and 15–30 cm), and the increases were not affected by the irrigation treatment. The NO₃ content increased at all sampling depths with greater increases observed under non‐irrigated conditions, while NH₄ content was not affected by manure application rates or the irrigation treatment. The changes in OC and TN at the surface (0–15 cm) and 15–30 cm depth were dependent on the cumulative weight of manure added over the years. The relationships between cumulative manure OC added and soil OC content and between cumulative manure TN added and soil TN content were linear and not affected by the irrigation treatment. For every ton of manure OC added, soil OC increased by 0.181 g kg^–1 in the topsoil (0–15 cm). Similarly, for every ton of manure TN added, surface soil TN increased by 0.192 g kg^–1. The linear relationship between manure C added and soil C content suggests that the soil had a high capacity for short‐term C sequestration. However, the total amount of NO₃‐N in the soil profile (0–150 cm) was affected by both the manure application rates and the irrigation treatment. A large amount of NO₃ accumulated in the soil, especially under non‐irrigated conditions. The extremely high level of NO₃ in the soil increases the potential risk of surface and groundwater pollution and losses to atmosphere as N₂O.     

间伐对杉木人工林土壤碳氮及其组分特征的影响

为探究不同间伐强度对杉木人工林土壤碳氮及其组分特征的影响,以福建省三明市官庄国有林场11年生杉木(Cunninghamia lanceolata)人工林为研究对象,采用弱度间伐(LIT)、中度间伐(MIT)、强度间伐(HIT)等3种间伐强度,研究不同间伐强度林分0—10,10—20,20—40,40—60,60—80,80—100 cm土层总有机碳(SOC)、全氮(TN)及易氧化有机碳(ROC)、硝态氮(NO_3~--N)、铵态氮(NH_4~+-N)、微生物量碳(MBC)、微生物量氮(MBN)、微生物熵碳(qMBC)、微生物熵氮(qMBN)的变化特征,以探讨不同间伐强度对杉木人工林土壤碳氮及其组分特征的影响。结果表明:间伐降低了土壤SOC和TN的含量,降低幅度分别为1.4%～36.9%,3.1%～45.7%。间伐增加了土壤MBC、NO_3~--N的含量,而对ROC、NH_4~+-N和MBN的程度在不同土层有差异,qMBC和qMBN随着间伐强度的增加而增大。相关性分析表明,土壤SOC分别与TN、qMBC、ROC、NH_4~+-N、MBC、MBN呈极显著正相关(P0.01);TN与qMBN、ROC、NH_4~+-N、MBC、MBN呈极显著正相关(P0.01)。杉木人工林间伐处理降低了土壤表层SOC和TN含量,增加了土壤SMBC和qMBC、qMBN,同时也增加了土壤表层(0—10 cm)SMBN。抚育间伐导致土壤SOC和TN含量降低主要是由于活性碳、氮含量的增加,提高土壤中有机质分解速率,最终导致土壤SOC和TN含量降低。     

Changes in soil microbial community composition in response to fertilization of paddy soils in subtropical China

Repeated fertilizer applications to cultivated soils may alter the composition and activities of microbial communities in terrestrial agro-ecosystems. In this study, we investigated the effects of different long term fertilization practices (control (CK), three levels of mineral fertilizer (N₁P₁K₁, N₂P₂K₂, and N₃P₃K₃), and organic manure (OM)) on soil environmental variables and microbial communities by using phospholipid fatty acid (PLFA) biomarkers analysis in subtropical China. Study showed that OM treatment led to increases in soil organic carbon (SOC), total nitrogen (TN) and total phosphorus (TP) contents, while the mineral fertilizer treatment led to increases in dissolved organic carbon (DOC) content. Changes in soil microbial communities (eg. bacteria, actinomycetes) were more noticeable in soils subjected to organic manure applications than in the control soils or those treated with mineral fertilizer applications. Fungal PLFA biomarkers responded differently from the other PLFA groups, the numerical values of fungal PLFA biomarkers were similar for all the OM and mineral fertilizer treatments. PCA analysis showed that the relative abundance of most PLFA biomarkers increased in response to OM treatment, and that increased application rates of the mineral fertilizer changed the composition of one small fungal PLFA biomarker group (namely 18:3ω6c and 16:1ω5c). Further, from the range of soil environmental factors that we examined, SOC, TN and TP were the key determinants affecting soil microbial community. Our results suggest that organic manure should be recommended to improve soil microbial activity in subtropical agricultural ecosystems, while increasing mineral fertilizer applications alone will not increase microbial growth in paddy soils.     

Carbon and nitrogen pools in different aggregates of a Chinese Mollisol as influenced by long-term fertilization

Purpose  

It is known that soil organic matter (SOM) dynamics are sensitive to fertilizations, but it is different from soil to soil. It is unclear how the long-term applications of organic manure and mineral fertilizers impact the accumulation and distribution of soil organic carbon (SOC) and total nitrogen (TN) especially in soil aggregate fractions of Chinese Mollisols, which have been intensively cultivated for decades under maize monocropping and conventional tillage ways. Thereby, the research of this kind is very important for the sustainable use of agricultural land in China, where land resources are extremely limited for its huge population. The objectives of this study were to identify how the long-term fertilization treatments would affect the aggregate, SOC and TN distribution pattern in the Chinese Mollisol, and how soil aggregation contribute to the storage and stabilization process of SOC and TN.     

Arginine ammonification and L‐glutaminase assays as rapid indices of corn nitrogen availability

Increasing use of N fertilizer for crop production necessitates more rapid estimates on N provided by the soil in order to prevent under‐ or overfertilization and their adverse effect on plant nutrition and environmental quality. A study was conducted to investigate the responses of arginine ammonification (AA), L‐glutaminase activity (LG), soil N–mineralization indices, corn (Zea mays L.) crop–yield estimation, and corn N uptake to application of organic amendments. The relationships between corn N uptake and the microbial and enzymatic processes which are basically related to N mineralization in soil were also studied. The soil samples were collected from 0–15 cm depth of a calcareous soil that was annually treated with 0, 25, or 100 Mg ha^–1 (dry‐weight basis) of sewage sludge and cow manure for 7 consecutive years. Soil total N (TN), potentially mineralizable N (N₀), and initial potential rates of N mineralization (kN₀) were significantly greater in sewage sludge–treated than in cow manure–treated soils. However, the amendment type did not influence soil organic C (SOC), AA, LG, and anaerobic index of N mineralization (N_ana). The application rates proportionally increased N‐availability indices in soil. Corn N concentration and uptake were correlated with indices of mineralizable N. A multiple stepwise model using AA and N_ana as parameters provided the best predictor of corn N concentration (R = 0.86, p < 0.001). Another model using only LG provided the best predictor of corn N uptake (R = 0.78, p < 0.001). This results showed that sewage‐sludge and cow‐manure application is readily reflected in certain soil biological properties and that the biological tests may be useful in predicting N mineralization and availability in soil.     

Impact of organic amendments on the dynamics of soil microbial biomass and bacterial communities in cultivated land

In the course of a 1 year study on agricultural plots (mustard-beet) the impact of organic materials and soil management on soil microbial communities was assessed after amendment with three types of organic materials (sewage sludge, turkey manure and compost made of turkey manure and ligneous waste) and a mineral fertilizer. Transient impacts on potential metabolic activity, on genetic structure and on quantities of soil microorganisms, measured with three different methods (C_mic, total DNA content and CFU enumeration), were observed. The extent of these impacts depended on the composition of the amendment. The proportions of mineralisable carbon and lignin in organic materials seemed to influence the behaviour of the bacterial communities during the first 3 months after amendment. After a period of 6 months, no effect specific to the type of organic materials was detected. The dynamics of microbial biomass was assessed by both microbial carbon and by total DNA, but no correlation was found between the results; DNA seemed to be more sensitive to time-related variations in microbial biomass. Finally, although the bacterial functional and genetic structures were strongly modified between 3 and 6 months, this modification was not related to the type of amendment. This result suggests that organic amendments have less effect than seasonal variations or others anthropic factors such as the mechanical management of the soil.     

不同有机物料对苏打碱化土有机碳库和化学性质的影响

以内蒙古河套灌区苏打碱化土为研究对象开展田间试验,设置常规施肥(CK)、生物炭+常规施肥(BC)、牛粪+常规施肥(CD)、玉米秸秆+常规施肥(SW)和羊粪+常规施肥(GM)5个处理,研究不同有机物料添加对碱化土壤有机碳(SOC)库和化学性质的影响。分别于2019年和2020年收获季采集0—30 cm耕层土壤,分析不同有机物料添加下SOC及其活性碳组分和主要盐碱指标的变化特征及其相关关系。结果表明:与CK相比,2019年和2020年各有机物料添加处理下SOC平均增幅分别为22.7%和17.2%,土壤有机碳储量(SOCs)平均增幅分别为22.9%和18.2%;4种有机物料均提高了碱化土壤活性有机碳组分含量,其中,CD和GM处理下各活性碳组分含量增幅较其他处理更高;2019年各有机物料添加处理下碳库管理指数(CPMI)较CK提高53.8%~108.3%,2020年提高71.3%~144.1%(P＜0.05),CD和GM对CPMI的提升作用更明显。土壤化学性质方面,2020年各有机物添加处理下pH均显著下降,BC和CD处理下碱化度(ESP)分别显著下降36.9%和29.3%,CD处理下蔗糖酶活性提高36.7%(P＜0.05)。主成分分析(PCA)表明,影响苏打碱化土SOC含量变化的主要因素为活性有机碳组分和ESP。牛粪和羊粪施用对苏打碱化土有机碳库质量提升作用较好,生物炭施用对盐碱化指标改良效果最明显。     

Rate of soil‐aggregate formation under different organic matter amendments—a short‐term incubation experiment

To improve soil structure and take advantage of several accompanying ecological benefits, it is necessary to understand the underlying processes of aggregate dynamics in soils. Our objective was to quantify macroaggregate (> 250 μm) rebuilding in soils from loess (Haplic Luvisol) with different initial soil organic C (SOC) contents and different amendments of organic matter (OM) in a short term incubation experiment. Two soils differing in C content and sampled at 0–5 and 5–25 cm soil depths were incubated after macroaggregate destruction. The following treatments were applied: (1) control (without any addition), (2) OM₁ (addition of OM: preincubated wheat straw [< 10 mm, C : N 40.6] at a rate of 4.1 g C [kg soil]^–1), and (3) OM₂ (same as (2) at a rate of 8.2 g C [kg soil]^–1). Evolution of CO₂ released from the treatments was measured continuously, and contents of different water‐stable aggregate‐size classes (> 250 μm, 250–53 μm, < 53 μm), microbial biomass, and ergosterol were determined after 7 and 28 d of incubation. Highest microbial activity was observed in the first 3 d after the OM application. With one exception, > 50% of the rebuilt macroaggregates were formed within the first 7 d after rewetting and addition of OM. However, the amount of organic C within the new macroaggregates was ≈ 2‐ to 3‐fold higher than in the original soil. The process of aggregate formation was still proceeding after 7 d of incubation, however at a lower rate. Contents of organic C within macroaggregates were decreased markedly after 28 d of incubation in the OM₁ and OM₂ treatments, suggesting that the microbial biomass (bacteria and fungi) used organic C within the newly built macroaggregates. Overall, the results confirmed for all treatments that macroaggregate formation is a rapid process and highly connected with the amount of OM added and microbial activity. However, the time of maximum aggregation after C addition depends on the soil and substrate investigated. Moreover, the results suggest that the primary macroaggregates, formed within the first 7 d, are still unstable and oversaturated with OM and therefore act as C source for microbial decomposition processes.     

The impact of exogenous organic matter on SOM contents and microbial soil quality

Eight fertilization strategies were compared in a field trial on Alfisol in Belgium (humid temperate climate): cattle slurry (CSL); farmyard manure (FYM); vegetable, fruit and garden waste compost (VFG); high C/N farm compost (FCP1); low C/N farm compost (FCP2); exclusively mineral fertilizer (MIN N); no fertilization (NF+), no fertilization and no crop (NF?). After five growing seasons, VFG resulted in the highest soil organic C (1.46% SOC) and total N contents (0.117%TN). SOC and TN contents of the MIN N plots, on the other hand, remained unchanged and were even similar to those of NF+ plots, despite greater biomass production on the MIN N plots than on the NF+ plots. Application of organic matter mostly increased dehydrogenase, β-glucosidase and β-glucosaminidase activity, but only FYM raised the activity of all three enzymes significantly compared to MIN N. Of the five organic amendments tested, only VFG suppressed Rhizoctonia solani (65% suppressiveness). Plots treated with FCP1, on the other hand, were highly conducive to R. solani (28.3% suppressiveness). Suppressiveness against R. solani probably depended on the maturity and cellulose content of the organic amendments. Highest microbial biomass C contents were found in the VFG plots. PLFA 16:1ω5c contents sensitively reacted to the different treatments and were significantly higher in VFG than in MIN N plots (3.84 and 2.20 nmol g^?1 dry soil, respectively). Finally, a soil quality index was developed using stepwise canonical discriminant analysis. β-glucosaminidase and β-glucosidase activity, and TN content were the most important parameters of the index. According to this index, FYM resulted in a significantly higher soil quality than the other treatments. We conclude that farmyard manure seems to be the preferred organic amendment for maintaining soil quality in arable fields under temperate climatic conditions.