Pesticides and heterotrophic nitrogen fixation in paddy soils

The effect of three pesticides, benomyl, carbofuran and gamm-BHC at 5 parts 10⁶, rates equivalent to recommended field levels, on the heterotrophic N₂ fixation in five air-dried, cellulose-amended, submerged tropical soils was invevstigated employing ¹⁵N tracer technique under laboratory conditions. Addition of benomyl, a carbamate fungicide, to alluvial, laterite and two acid sulphate soils resulted in significant increases in N₂ fixation, while carbofuran, a methylcarbamate insecticide, exerted a stimulatory effect on N₂ fixation in alluvial, alterite and acid saline soils. Gamma-BHC, a chlorinated hydrocarbon insecticide, stimulated N₂ fixation in alluvial and acid sulphate pokkali solis, while considerable inhibition of N₂ fixation was evident inother soils. Results showed differential responses of specific groups of N₂-fixing organisms to the pesticides depending ont he soil type.     

Nitrogen-fixing microorganisms in paddy soils (Part 1) Characteristics of the nitrogen fixation in paddy soils

In most paddy soils, as is already well-known, the crop yield goes on decreasing just for the first few years and then stabilizes at a comparatively high level with no supply of fertilizer or manure.     

Nitrogen fixation in paddy soils

The 4 long-term experimental plots (Umbric haplaquept) with different fertilizer treatment at Cent. Agric. Exp. Sta. in Konosu City, Saitama Prefecture, were used for the sites of investigation. The 4 plots were NF (applied with no fertilizer), IF (applied with inorganic fertilizers), GM (applied with green manure and CaCO₂), and OM (applied with manure and inorganic fertilizers). Flooded water, floating weed, upper (0-2cm) and lower (2-10cm) parts of Apg horizon and rhizosphere were collected from each plot before flooding, during flooding, and after drainage. These samples were analyzed for N₂-fixing activity by acetylene reduction method, pH, Eh, and contents of Fe²⁺, NH₄ ⁺, chlorophyll-type compounds, and water-soluble carbohydrates.

The N₂-fixing activity of all samples showed almost the same pattern of change with time: very low before flooding, rapidly increased after flooding, the maximum value at the maximum tillering stage of rice plant, declined afterwards and reached a very low value after drainage.

Rough estimation of the “N₂-fixing capacity” of each part of the paddy field revealed that the most important site of the N₂ fixation was the reduced Apg horizon, that the importance of flooded water and/or the oxidized layer in the N₂ fixation was rather low except in infertile soil, and that the role of rhizosphere in the N₂ fixation could not be neglected also in Japan.

Reduced condition and content of easily decomposable organic substances were judged to be main factors which control the N₂-fixing activity in the flooded soil on the basis of correlations between the Nt-fixing activity and several analytical data of the paddy soils.     

Nitrogen fixation in paddy soils

Several important features of the N. fixation in paddy fields which were reported previously were confirmed and some new additional results regarding the evaluation of the N₂ fixation in the rhizosphere were obtained by reinvestigation in the fields. In addition, rice plants were cultivated in the submerged soil in pots and various parts of the soil were analyzed for the N₂-fixing activity as well as several other properties. The results of the pot experiments were found to be fairly similar to those observed in the field investigations, indicating the validity of the submerged soil in a pot as a rather simulated model for the actual paddy field. By using this model system, the following facts were ascertained: (1) Water-percolation had almost no effect on the N₂-fixing activities of both the rhizosphere and the non-rhizosphere soils. (2) Suppressing effect of washing the root of rice plant on the N₂-fixing activity was slight in the seedling stage and marked in the tillering and flowering stages. (3) The N₂-fixing activity of a single rice root varied from tip to base.     

Effect of carbon sources on asymbiotic nitrogen fixation in a paddy soil

The effect of various carbon sources on asymbiotic N₂ fixation in a paddy soil was studied by C₂H₂ reduction and ¹⁵N tracer techniques. N₂ fixation increased with increasing concentrations of cellulose and rice straw, but the former was more effective. N₂ fixation was considerably enhanced in soils amended with glucose, sucrose, succinate, acetate, butyrate, pyruvate or n-propanol, while n-butanol, ethanol, lignin or paraffin were ineffective. Succinate at low moisture content and butyrate under flooded conditions stimulated N₂ fixation during a 15-day incubation.     

pH change, carbon and nitrogen mineralization in paddy soils as affected by Chinese milk vetch addition and soil water regime

Purpose

The aim of the research was to explore the effect of Chinese milk vetch (CM vetch) addition and different water management practices on soil pH change, C and N mineralization in acid paddy soils.

Materials and methods

Psammaquent and Plinthudult paddy soils amended with Chinese milk vetch at a rate of 12 g?kg^?1 soil were incubated at 25 °C under three different water treatments (45 % field capacity, CW; alternating 1-week wetting and 2-week drying cycles, drying rewetting (DRW) and waterlogging (WL). Soil pH, dissolved organic carbon, dissolved organic nitrogen (DON), CO₂ escaped, microbial biomass carbon, ammonium (NH₄ ⁺) and nitrate (NO₃ ^?) during the incubation period were dynamically determined.

Results and discussion

The addition of CM vetch increased soil microbial biomass concentrations in all treatments. The CM vetch addition also enhanced dissolved organic N concentrations in all treatments. The NO₃–N concentrations were lower than NH₄–N concentrations in DRW and WL. The pH increase after CM vetch addition was 0.2 units greater during WL than DRW, and greater in the low pH Plinthudult (4.59) than higher pH Paleudalfs (6.11) soil. Nitrogen mineralization was higher in the DRW than WL treatment, and frequent DRW cycles favored N mineralization in the Plinthudult soil.

Conclusions

The addition of CM vetch increased soil pH, both under waterlogging and alternating wet–dry conditions. Waterlogging decreased C mineralization in both soils amended with CM vetch. Nitrogen mineralization increased in the soils subjected to DRW, which was associated with the higher DON concentrations in DRW than in WL in the acid soil. Frequent drying–wetting cycles increase N mineralization in acid paddy soils.     

不同水分条件下添加白云石对酸性水稻土有机碳矿化的影响

施用石灰改良酸性土壤是常用的农艺措施之一。施用石灰影响土壤理化性质,进而影响土壤有机碳（Soil Organic Carbon,SOC）矿化。而SOC矿化与土壤肥力保持和有机碳库的大小存在紧密联系。因此,明晰施用石灰对酸性土壤有机碳矿化的影响具有重要的理论和现实意义。该研究以2种母质的酸性水稻土为对象,在50%、90%和130%土壤最大田间持水量（Water Holding Capacity,WHC）条件下添加和不添加白云石,再进行为期45 d的室内培养试验,探讨白云石和水分对SOC矿化的影响。研究结果表明,添加白云石显著影响2种土壤有机碳矿化速率,但白云石添加和水分的交互作用不显著。土壤含水量较低时（50% WHC）,2种土壤有机碳矿化均受到抑制。在较高土壤含水量情况下（90%～130% WHC）,白云石添加和水分的共同作用对SOC矿化的影响因土壤质地不同而异,淹水条件下（130% WHC）棕红壤有机碳矿化量高于湿润条件（90% WHC）,而红壤中的情况正好相反。白云石添加和水分均显著影响SOC累计矿化量,但二者交互作用仅在棕红壤中显著。添加白云石后,2种土壤pH值随着水分含量的增加而提高;土壤含水量较低时（50% WHC）,土壤pH值即可达到或接近目标值（pH值6.5）。这些结果表明,在评估施用白云石对SOC矿化的影响时,需要考虑土壤含水量和土壤本身的性质,以便为农业生产实践中合理施用白云石提供指导和建议。     

Influence of redox conditions and rice straw incorporation on nitrogen availability in fertilized paddy soils

Biology and Fertility of Soils - Temporal nitrogen (N) availability in fertilized rice paddies is the result of a balance of processes, mainly the gross rates of N mineralization, microbial and...     

水稻土和菜田添加碳氮后的气态产物排放动态

【目的】动态连续监测添加碳氮底物后各气体产物—O2、 NO、 N2O、 CH4和N2的排放,对土壤碳氮转化过程和气体产生过程做更深入的理解,揭示不同土地利用方式典型红壤的温室气体产生机制。【方法】采集长江中游金井小流域不同土地利用方式稻田和菜地土壤为研究对象,利用全自动连续在线培养检测体系(Robot系统),通过两组试验分别研究土壤碳氮转化过程中各气体产物的动态变化。试验1采用菜地和稻田土壤进行好气培养,设置不施氮对照、 添加40 mg/kg铵态氮、 添加40 mg/kg铵态氮+1%硝化抑制剂、 添加40 mg/kg硝态氮、 添加40 mg/kg硝态氮+1%葡萄糖、 缺氧条件下添加40 mg/kg硝态氮+1%葡萄糖6个处理。试验2采用稻田土壤进行淹水培养,设不施氮对照、 添加40 mg/kg铵态氮、 添加40 mg/kg铵态氮+1%硝化抑制剂、 添加40 mg/kg铵态氮+1%秸秆、 缺氧条件下添加40 mg/kg铵态氮+1%的葡萄糖、 添加40 mg/kg硝态氮、 添加40 mg/kg硝态氮+1%葡萄糖、 缺氧条件下添加40 mg/kg硝态氮+1%葡萄糖8个处理。培养温度均为20℃,土壤水分含量为70% WFPS (土壤孔隙含水量),培养周期为15天。【结果】从菜地和稻田土壤不同碳氮添加处理气态产物及无机氮的动态变化可看出: 1)菜地土壤好气培养初期硝化作用产生了大量N2O; 受低碳和低含水量的限制,反硝化作用较弱。当提供充足碳源和厌氧条件,出现N2O和NO的大量排放。2)在好气稻田和淹水稻田培养过程中,反硝化作用是N2O产生的主要途径。3)稻田土壤中,提供充足碳源和厌氧条件,各气态产物出现的顺序依次是NO、 N2O和N2,与三种气体在反硝化链式反应过程中的生成顺序一致。淹水稻田加铵态氮和碳源处理N2为主要产物,添加硝态氮处理后,N2O成为主要气态产物。当土壤碳源充足时,反硝化过程进行彻底,反硝化产物以终产物(N2)为主。4)在稻田土壤出现厌氧或添加碳源条件下,均检测到大量CH4产生; 且在甲烷产生的同时,NO-3几乎消耗殆尽。【结论】金井小流域典型红壤菜地N2O主要来自于硝化作用,好气和淹水稻田N2O主要来源于反硝化作用; 当碳源充足和厌氧时,菜地及稻田反硝化作用增强; 反硝化产物组成、 产物累积量及出峰顺序与碳源和氧气浓度有关。     

Pesticides and nitrogen fixation in a paddy soil

The influence of six pesticides, applied singly or in combination, on ¹⁵N₂ incorporation and C₂H₂ reduction in a submerged paddy soil was studied under laboratory conditions. While the application of diazinon had no marked effect, benomyl, carbofuran, parathion, nitrofen and γ-HCH, at concentrations close to recommended field application rates (5μg ^?1) significantly stimulated N₂ fixation. Synergistic stimulatory effects of the pesticides on N₂ fixation were evident particularly in combinations of carbofuran with benomyl, nitrofen and γ-HCH. On the contrary, diazinon slightly retarded the stimulatory effect of benomyl and carbofuran. Results indicated that the differential effects of pesticides on N₂ fixation could be attributed partly to fluctuations in the population of certain groups of N₂ fixers in submerged soil.     

Influence of physical treatments on acetylene reduction (nitrogen fixation) in soils

Abstract

The effect of physical treatments such as drying, freezing, and heating on acetylene (C₂H₂) reduction (nitrogen fixation) in 3 types of soils was measured. Most treatments significantly affected ethylene (C₂H₄) production in the sandy loam. None of the treatments suppressed C₂H₄ formation in the sandy clay loam before 2 days. Muck soil with treatments of air‐drying, freeze‐drying, and freezing did not show different patterns in C₂H₄ production. However, auto claving and oven‐drying resulted in a pronounced increase in formation of C₂H₄. With exception of the heat treatments, no significant decreases in numbers of non‐symbiotic nitrogen‐fixers in soils were observed.     

Mechanisms of fixation and release of ammonium in paddy soils after flooding II. Effect of transformation of nitrogen forms on ammonium fixation

An incubation experiment under aseptic and septic conditions using ¹⁵N-labelled NH₄⁺-N and NO₃^–-N, was carried out to study the effect of N transformations after flooding on NH₄⁺ fixation in a paddy soil from China. After flooding ammonification was favoured, providing NH₄⁺ for fixation by clay minerals. NH₄⁺ fixation was more pronounced under low redox potential (E_h) conditions. Close correlations existed between exchangeable NH₄⁺, E_h, and non-exchangeable NH₄⁺. Therefore, two major conditions for NH₄⁺ fixation induced by flooding in paddy soil were found, namely flooding promoted net production of NH₄⁺ due to the deamination of organic N and, in addition, decreased the E_h of the soil. A lower E_h was caused by reduction and dissolution of Fe oxide coating on the clay minerals' surfaces, eliminating the obstacles for NH₄⁺ diffusing into or out of the interlayers of clay minerals. A higher concentration of exchangeable NH₄⁺ from deamination of organic N would drive NH₄⁺ diffusing from the soil solution into the interlayers of clay minerals. ¹⁵N-labelled NO₃^– incorporated into the flooded soil was not reduced to NH₃. The addition of NO₃^– retarded the decrease in the soil E_h and, therefore, NH₄⁺ fixation.     

Effect of moisture content,temperature and nitrogen fertilization on carbon dioxide evolution from field soils

The evolution of CO₂ from field plots was measured for 3 yr, on two soil types, with and without N fertilization and relationships with average air temperature, average soil water content and an interaction term were derived. Multiple correlation coefficients ranged between 0.64 and 0.85 and average air temperature accounted for most of the variance in the relationships. Negative correlation coefficients with average soil water content predominated particularly in the fall when rainfall was high and evaporation was low. Regression equations relating the three factors were homogeneous within but not between soils.N consistently reduced the CO₂ evolved from the soils despite the effect of the year, soil type or rate of application. The reduced microbial activity due to N fertilization observed in the field was confirmed with laboratory incubations using Warburg techniques. Laboratory experiments showed that the lowering of soil pH by N addition was largely, but not entirely responsible for the decreased activity.     

上海地区水稻土氮素矿化模拟

Six paddy soils of Shanghai, China, were studied after 120 days of anaerobic incubation at 25 ℃ and 35 ℃. Four models, the effective accumulated temperature model, the one-component first-order exponential model (the one-pool model), the two-component first-order exponential model (the two-pool model), and the two-component first-order plus zero-order exponential model including a constant term (the special model), were fitted to the data of observed mineral-N during incubation using non-linear regression procedures. The two-pool model and the special model gave the best fits amongst the four models, and parameters in the special model were more reasonable than those in the other three. Results showed that the special model gave a better prediction of nitrogen mineralization under flooded conditions than the other three models.     

Bacteriological studies on the mineralization of organic nitrogen in paddy soils

In this report we studied the effects of mechanical grinding of paddy soils on nitrogen mineralization and bacterial number when soils were incubated under a submerged condition after grinding.

Nitrogen mineralization was increased by grinding soil samples as compared with those without grinding. The value of (Nd-Nu)/Nu, where Nd is the amount of ammonia-nitrogen formed by incubation of disrupted samples and Nu those of the undisrupted soils, was in good correlation with clay/humus ratio.

Although significant difference was not observed between the number of aerobic bacteria with undisrupted and disrupted soil samples, higher anaerobic bacterial numbers were found with disrupted than with undisrupted ones.

A significant correlation was also obtained between the amounts of nitrogen mineralization increased by the grinding of soil and the numbers of anaerobic bacteria.     

水分状况对红壤水稻土中有机物料碳分解和分布的影响

以室内模拟的方法研究了好气、淹水和干湿交替3种水分条件下有机物料碳在红壤水稻土中分解和分布的差异。试验结果表明,干湿交替条件下有机物料的分解速率最高,好气条件下次之,淹水条件下较低。好气和淹水条件下添加物料促进土壤原有有机碳的矿化,产生正激发效应,而干湿交替条件显著抑制了土壤原有有机碳的矿化,呈负激发效应,随着培养时间的延长激发效应减弱。干湿交替条件下添加有机物料处理的土壤胡敏酸(Humic acid,HA)色调系数和E4/E6比值显著低于淹水和好气条件,淹水培养使土壤胡敏酸的结构简单化,干湿交替使胡敏酸芳构化和腐殖化程度增加,结构复杂化。有机物料碳在土壤腐殖质组分中的分配比例显示,干湿交替和好气条件促进了胡敏酸的形成,提高了土壤原有富里酸(Fulvic acid,FA)组分的转化和胡敏酸组分的分解;淹水条件下物料碳在富里酸组分中分布比例较高,且抑制了土壤原有胡敏酸组分的分解。有机物料碳在0.053 mm粒级团聚体中分布比例较大,干湿交替和淹水条件下更为明显。     

不同施肥措施对稻田土壤氮矿化的影响

采集田间通过不同施肥处理的水稻土为研究对象,在室内采用淹水培养方法,研究不同施肥措施对水稻土氮矿化的影响。结果表明:与不施肥处理相比,施加氮肥和饼肥能提高土壤的氮矿化能力;与常规施氮处理相比,采用新型施肥措施,氮肥+木质素、一次施用的水稻缓释肥、氮肥+有机碳源均降低土壤的氮矿化作用,其中氮肥+有机碳源处理与常规施氮处理相比,土壤全氮增加了16.7%,但淹水培养期间土壤的氮矿化量却减少了18.5%,这一结果说明,采用这些新型施肥措施有利于增加土壤对氮的固持,降低氮素向环境损失的风险。     

Bacteriological studies on the mineralization of soil organic nitrogen in paddy soils

Anaerobes were isolated from both disrupted and undisrupted soil samples incubated under submerged condition. All isolates were divided into 9 groups based on their gram stain and morphological characteristics. Correlation coefficients between the amount of nitrogen mineralized and the number of each group were calculated. A significant correlation was observed only between the amount of nitrogen mineralized and the number of gram positive-rod shaped anaerobic microorganisms (r=0.768 at P=0.05). This result indicates that in this study system, sorne particular anaerobes may play an important role in the mineralization of soil organic nitrogen.     

红壤双季稻田土壤活性碳、氮周年变化及影响因素

【目的】 研究红壤稻田土壤活性碳、氮含量及其周年变化和影响因素,为弄清红壤双季稻田土壤活性碳、氮季节变化规律,提高土壤养分利用效率提供理论依据。 【方法】 以红壤稻田长期定位试验 (1990年开始) 为对象,选择不施肥 (CK)、单施NPK化肥 (NPK) 和有机物 (紫云英、稻草) + NPK化肥 (NPKM) 三个施肥处理,在早稻、晚稻、休闲期取0—20 cm 土样,动态监测稻田土壤几种重要活性碳、氮成分,包括无机态氮 (NH₄+-N、NO₃–-N),可溶性有机碳、氮 (DOC、DON) 和微生物生物量碳、氮 (MBC、MBN) 的周年动态变化。 【结果】 稻田土壤NH₄+-N含量在早稻期间呈下降状态,晚稻期间变化较平缓,休闲期呈先上升后下降的趋势。土壤无机氮主要以NH₄+-N形式存在,其含量范围为14.9～31.6 mg/kg,其休闲期含量略低于生育期 (P > 0.05);周年土壤NO ₃–-N含量 (< 3 mg/kg) 远小于NH₄+-N含量,与NH₄+-N含量呈现此消彼长的趋势 (P < 0.01)。稻田土壤DOC、DON周年变化趋势相似 ( P < 0.01),在生育期呈下降状态,休闲期呈先上升后下降趋势,休闲期土壤DOC、DON含量略低于生育期 ( P > 0.05)。休闲期土壤MBC、MBN含量分别为463～701 mg/kg、31.1～52.4 mg/kg,比生育期分别提高25.4%～36.9%和62.8%～125.9%。总体来看,稻田休闲期土壤活性碳 (DOC+MBC)、氮 (NH ₄+-N+NO₃–-N+DON+MBN) 含量高于生育期含量,较生育期增幅分别为10.8%～19.6%、10.3%～34.8%。不同施肥处理结果表明,仅施用化肥 (NPK处理) 对活性碳、氮影响较小 (P > 0.05),有机物还田能显著提高水稻生育期和休闲期的土壤活性碳、氮含量 ( P < 0.05),NPKM与CK相比活性碳、氮在水稻生育期分别提高53.8%和81.2%,而在休闲期分别提高了43.5%和63.2%。相关性分析结果表明,稻田休闲期土壤NH ₄+-N、DOC、DON含量不仅与土壤SOC、TN含量密切相关 (P < 0.05 或 P < 0.01),还受温度、水分含量等环境因子影响,如休闲期土壤NH ₄+-N含量与5 cm处土壤温度呈极显著负相关关系 (P < 0.01),而土壤NO ₃–-N含量与该土层温度呈显著正相关关系 (P < 0.05),土壤DOC和DON与土壤含水量呈显著正相关关系 ( P < 0.05)。 【结论】 长期化肥配施紫云英及秸秆还田能显著提高稻田土壤周年活性碳、氮含量,其活性含量与土壤有机碳、全氮含量呈显著正相关关系;休闲期稻田能维持较高的活性碳、氮含量,且比水稻生育期有一定程度增加。休闲期土壤无机氮含量变化主要受土壤温度影响,土壤可溶性碳、氮含量变化主要受土壤含水量的影响。      

Influence of moisture regime on inhibition of nitrification by DCD

A laboratory study at the Indian Agricultural Research Institute, New Delhi showed that DCD was an efficient nitrification inhibitor under field capacity moisture (???30 kPa) but not so under submerged soil conditions. Nitrification inhibition by DCD was 79.6% after 1 week of incubation and decreased to 59.3% after 3 weeks of incubation under field capacity moisture, while it was only 19.3% after 1 week of incubation and 10.6% and 18.4% after 2 and 3 weeks of incubation under submergence, respectively. DCD can play an important role in reducing N losses from agricultural fields.