Nitrification activities and N mineralization in paddy soils are insensitive to oxygen concentration

Oxygen concentration is considered to be the most important factor influencing nitrification and mineralization rates in agricultural soils. However, the sensitivities of nitrification and N mineralization in paddy soils to oxygen concentrations are not well known. We examined nitrification activities and N mineralization rates of six paddy soils with pH ranging from 5.23 to 7.83 and incubated at 25°C and 60% water-holding capacity in laboratory after ammonium was added at concentrations of 10, 30 and 50?mg?N?kg^?1 of soil and the headspace gases were replaced with stock gases whose oxygen concentrations were 20%, 10% and 2%, respectively. The tested paddy soils had a very wide range of nitrification activities so that the nitrate ratio in inorganic N varied from >?95% after 1 day incubation to?相似文献   

Long-Term Nitrate Export Pattern from Hubbard Brook Watershed 6 Driven by Climatic Variation

From 1964 through 1994, the pattern of nitrate (NO₃ ^?) export from Watershed 6 at Hubbard Brook Experimental Forest (HBEF) in New Hampshire, U.S.A., exhibited 10 years of high export (1968–1977) followed by 12 years of low export (1978–1989), with four ‘spikes’ in 1970, 1973, 1976, and 1990. Disruptions of N cycling by soil freezing, insect defoliation, or drought have been suggested to explain this pattern. We developed a model of nitrogen dynamics demonstrating that most of the long-term pattern can be reproduced without explicit consideration of these events. Comparisons of simulated N fluxes between high and low export years suggested that inorganic N input to the soil, from both atmospheric N deposition and N mineralization, was significantly higher during periods of high streamflow NO₃ ^? flux than in low periods. Simulated inorganic N pools (ammonium and nitrate) and fluxes (nitrification, plant uptake, denitrification, and ammonia volatilization) were also significantly higher in these periods. By swapping the time sequences of inorganic N input between high and low export years, it was shown that N mineralization, not atmospheric N deposition, drives the simulated long-term pattern. Although simulated nitrification showed a stronger relationship with measured streamflow NO₃ ^? flux than did N mineralization, nitrification rate depended upon availability of soil ammonium supplied from N mineralization. Because N mineralization in the model varies only with soil temperature and moisture, we conclude that shifts in the interaction of these two variables over time produced the shifts in NO₃ ^? stream exports.     

Effect of Land Use,Seasonality, and Hydrometeorological Conditions on the K<Superscript>+</Superscript> Concentration–Discharge Relationship During Different Types of Floods in Carpathian Foothills Catchments (Poland)

The purpose of the study was to determine the role of land use, seasonality, and hydrometeorological conditions on the relationship between stream water potassium (K⁺) concentration and discharge during different types of floods—short- and long-duration rainfall floods as well as snowmelt floods on frozen and thawed soils. The research was conducted in small catchments (agricultural, woodland, mixed-use) in the Carpathian Foothills (Poland). In the woodland catchment, lower K⁺ concentrations were noted for each given specific runoff value for summer rainfall floods versus snowmelt floods (seasonal effect). In the agricultural and mixed-use catchments, the opposite was true due to their greater ability to flush K⁺ out of the soil in the summer. In the stream draining woodland catchment, higher K⁺ concentrations occurred during the rising limb than during the falling limb of the hydrograph (clockwise hysteresis) for all flood types, except for snowmelt floods with the ground not frozen. In the agricultural catchment, clockwise hystereses were produced for short- and long-duration rainfall floods caused by high-intensity, high-volume rainfall, while anticlockwise hystereses were produced for short- and long-duration rainfall floods caused by low-intensity, low-volume rainfall as well as during snowmelt floods with the soil frozen and not frozen. In the mixed-use catchment, the hysteresis direction was also affected by different lag times for water reaching stream channels from areas with different land use. K⁺ hystereses for the woodland catchment were more narrow than those for the agricultural and mixed-use catchments due to a smaller pool of K⁺ in the woodland catchment. In all streams, the widest hystereses were produced for rainfall floods preceded by a long period without rainfall.     

Seasonal dynamics of the mineral nitrogen forms in mountain-meadow alpine soils

The good agreement between the changes in the concentrations of ammonium and nitrate nitrogen, on the one hand, and the mineralization and nitrification activities, on the other hand, was shown in the annual dynamic cycle of the mobile mineral nitrogen concentrations, the net mineralization of its organic compounds, and the net nitrification in mountain-meadow soils of different ecosystems of the Teberda Reserve. The low nitrification activity in the mountain-meadow soils results in the predominance of ammonium nitrogen in its mineral forms during the entire vegetation period. The importance of the fall-winter-spring period, when the mineralization of organic nitrogen compounds proceeds actively and results in the accumulation of ammonium nitrate in the soil up to the beginning of the vegetation period, was emphasized. Due to the long duration of this period, its average contribution to the total annual mineralization is comparable to that of the vegetation period.     

土地利用方式对湿润亚热带土壤硝化作用的影响

在土壤最大持水量60%和30℃条件下对采自江西的自然土壤(森林和灌丛)和农业利用土壤(稻田、旱地和茶园)进行了实验室培养,研究土地利用对硝化作用的影响。结果表明,由于土壤呈酸性(pH4.2～6.3,平均为4.9),供试土壤的硝化作用很弱甚至缺失。当无外加铵态氮时,土壤的硝化速率与有机氮矿化速率呈显著的线性关系(p<0.01),而与土壤pH无关;当外加铵态氮使基质饱和时,硝化速率与土壤pH显著相关(p<0.01)。农业利用显著提高土壤的硝化作用能力,绝大部分自然土壤(78%)的净硝化速率小于净矿化速率,无机氮以铵态氮为主,而绝大部分农业利用土壤(74%)的净硝化速率大于净矿化速率。农业利用通过提高土壤pH、氮肥施用刺激硝化作用及改善土壤磷素供应状况等途径促进土壤的硝化作用。农业利用土壤硝化作用能力的提高增加了氮肥以硝态氮形态淋失的风险。     

Nitrate leaching from a small catchment in central England

Abstract. Flow and nitrate concentrations were measured weekly for four years at twelve stream-water monitoring sites in a catchment in the English Midlands designated as a Nitrate Advisory Area. Farm surveys and satellite images have provided soil and land use information. Measurements show the nitrate load to be dominated by discharge, with large variability due to differing weather conditions from year to year. Within-year variability in nitrate concentrations is also related to weather conditions, with high concentrations when field capacity is reached if this occurs late in the year. There is also clear evidence of dilution of nitrate during intense storms. The effect of changing weather conditions makes it impossible to identify catchment-scale changes in leaching due to changes in agricultural practice over a period as short as four years. Measurements from a major spring in the catchment show an increasing trend in nitrate concentrations through the period. There is some evidence that the greatest N leaching to streams in the catchment is associated with intensive grassland on soils which are naturally poorly drained.     

植物类型与改良方式对重构土壤氮转化速率的影响

[目的] 研究不同植物与改良方式对重构土壤氮转化率的影响,为提高矿区重构土壤可利用氮素含量提供理论依据。[方法] 以取自内蒙古自治区通辽市扎哈淖尔露天煤矿的采矿剥离物为基质配制重构土壤,分别以鸡粪肥、自制改良剂对其进行改良,并选取4种类型的植物,研究这两个因素对无机氮存在形式、氮净矿化率、净氨化率和净硝化率的影响。[结果] 硝态氮是重构土壤中无机态氮存在的主要形式,改良剂、植物及其交互作用对重构土壤氮净矿化率、净氨化率和净硝化率有极显著影响,自制改良剂改良可以显著提高重构土壤中铵态氮、硝态氮和亚硝态氮的含量及净硝化率,紫花苜蓿可以显著提高重构土壤中硝态氮含量及氮净矿化率。90 d时重构土壤的氮净矿化率最高。[结论] 播种90 d内,重构土壤中无机态氮存在形式由铵态氮向硝态氮转化,添加自制改良剂能够提高重构土壤中无机态氮含量,对矿区重构土壤的净氨化率、净硝化率及氮净矿化率的提高有促进作用。     

林地改为茶园对土壤净硝化速率及N2O排放的影响

以我国江南茶区(安徽、浙江)和华南茶区(福建)典型茶园土壤及各自相邻的林地土壤为研究对象,在25oC和60%田间持水量条件下,通过28 d的室内培养试验,研究了林地改为茶园后对土壤净硝化速率及N_2O排放规律的影响。结果表明:安徽地区林地改种茶园显著抑制了净硝化速率;与安徽地区的林地和茶园土壤相比,浙江和福建地区林地和茶园土壤净硝化速率很低(N,0.2 mg/(kg·d)),且林地改为茶园后对土壤净硝化速率没有显著影响。安徽地区植茶年限超过10 a的茶园土壤N_2O累积排放量均显著低于邻近的林地土壤,而植茶年限为10 a的茶园土壤与邻近的林地土壤差异不显著。浙江和福建茶园土壤N_2O累积排放量均高于各自对照的林地土壤。安徽地区土壤的N_2O累积排放量与p H呈显著的正相关关系,这表明林地改为茶园后,随着植茶年限的增加和氮肥的施用,p H降低抑制了净硝化速率,进而降低N_2O排放。     

Nitrate Leaching from Compost-Amended Soils

Nitrate in ground water was measured for three years beneath a sandy terrace soil with high conductivity which had been amended yearly with spent mushroom compost (SMC) and chicken manure compost (CMC) at rates of 25 and 50 T/A. The compost provided all the fertilizer requirements for intensive vegetable production. Nitrate concentrations in ground water from beneath all compost-amended plots remained below 10 ppm during the course of the study while concentrations beneath the fertilized control climbed to 14.7 ppm in an unusually wet spring. After heavy rains, control plots were more susceptible to nitrate leaching than compost-amended plots in the first two years of the study. The overall mean of the control (4.2 ppm) was significantly higher than all the other compost-amended plots except SMC amended at 25 T/A (3.4 ppm). Nitrate concentrations in ground water from CMC plots amended at 50 T/A peaked at 9.2 ppm after three consecutive years of compost application indicating a cumulative effect in the soil that was substantiated by soil analysis. The results indicate that composts can be applied for three successive years at rates high enough to supply the fertilizer requirement of most vegetables without excessively contaminating the ground water with nitrate. Because of the cumulative effect, it appears that lower rates could be applied in subsequent years to lessen nitrate leaching, especially with nitrogen-rich composted chicken manure.     

Impact on Water Quality of High and Low Density Applications of Spent Mushroom Substrate to Agricultural Lands

We studied the influence of spent mushroom substrate (SMS) land application on water resources. Four study sites, including mushroom farms with low or high density land applications of SMS, and two controls, an alfalfa field and a woodland, were instrumented with soilwater lysimeters and groundwater monitoring wells. Water samples were collected during the dormant season (winter) and growing season (spring). Samples were analyzed for a number of water quality parameters, including dissolved organic carbon (DOC), dissolved organic nitrogen (DON), ammonia, chloride, nitrate, nitrite, phosphate, sulfate, aluminum, cadmium, calcium, chromium, copper, iron, lead, magnesium, manganese, mercury, nickel, potassium, silicon, sodium, and zinc. Additional analyses were performed for pesticides commonly used in the cultivation of alfalfa or corn, or for insect control, including methomyl, dimethoate, hexazinone, atrazine, diuron and permethrin.

All agricultural sites had elevated salt concentrations relative to the woodland site. The mushroom farm where SMS was applied in high concentrations had salt concentrations in the soilwater that were 10 to 100 times higher than the other agricultural sites. Of particular note were ammonium, nitrate, chloride, sulfate, calcium, magnesium, sodium, and potassium. Each of these were also elevated in the groundwater. The high salt concentrations were reflected in measurements of electrical conductivity. DOC and DON concentrations were also elevated in the soilwater and groundwater. Groundwater from each agricultural site, including the agricultural control, exceeded the primary drinking water standard for nitrate.

No pesticide residues were detected in well or lysimeter water collected at either site amended with SMS. Water samples collected from the woodland and at the alfalfa field not receiving SMS contained part per trillion quantities of a few pesticides.     

Carbon and nitrogen mineralization in cultivated and natural savanna soils of Northern Tanzania

In the present study, soil C and N mineralization and nutrient availability were compared: (1) in savanna woodland soils under natural acacia vegetation; (2) at termite sites; (3) in degraded woodland where acacias were selective logged for charcoal production; (4) in agricultural fields which were cultivated for 3 and 15 years, and (5) in traditional homestead fields which regularly received animal manure for about 10 years. Soil C and N mineralization dynamics were measured by incubation under controlled conditions for 120 days. Labile and stable soil C and N pools were determined by fitting double-exponential models to the measured cumulative mineralization. Selective removal of acacias from the woodland and short-term cultivation for 3 years did not affect available nutrient contents but significantly decreased total C and N contents and mineralization (P<0.05). Mainly the labile soil N pool decreased during the first 3 years of continuous cropping, whereas after 15 years the stable N pool, total S, available Ca and Zn contents were also depleted. Even after 15 years, however, the decrease of nutrient availability (apart from N) was less severe than that of soil organic matter stability. Additionally, not only the labile but also the more stable soil C and N pools decreased and controlled total mineralization as determined by the incubation experiments. Homestead fields with manure additions were shown to have elevated soil nutrient and organic matter contents. However, the manure should be mixed into the soil to improve organic matter stabilization. Soil regeneration in degraded savannas and recently cultivated fields might rapidly be achieved, whereas the 15-years-cultivated fields may require longer fallows to restore soil fertility.     

Changes in soil chemical properties following a 12-year fallow: A 2-year comparison of conventional tillage and no-tillage agroecosystems

Soil chemical parameters including total N, exchangeable ammonium, soluble nitrate, and extractable phosphate, potassium, calcium and magnesium, were compared between conventional and no-tillage treatments on land which had been left fallow in old-field vegetation for 12 years. Tillage treatments were also compared to an adjacent old-field which was not cropped. The study was carried out on the Georgia Piedmont for 2 years following the fallow period. Soil nutrient availability was related to chemical concentrations in the soil solution, plant nutrient uptake and litter decomposition. During 1978–1979, soil nitrate concentrations were highest in plowed systems and lowest in the old field. Extractable cation concentrations were generally higher in conventional tillage than in no-tillage soil during the 1st year after fallow (1978). However, during the 2nd year, higher cation concentrations in no-tillage soil prevailed. Nitrate concentrations in the soil solution at 60 cm depth were generally highest in conventional tillage, followed by no-tillage and lowest in old-field systems. During 1978–1979, total nutrient uptake by crops (grain sorghum and rye) and weeds was higher in conventional than in no-tillage systems. From 1978–1979 to 1979–1980, uptake decreased in both cropping systems, but proportionately more in conventional tillage systems so that uptake in 1979–1980 was similar in the two cropping treatments. Higher nitrate concentrations in leachate of conventional than in no-tillage and old-field systems suggested that plowing stimulated nitrification processes.     

Modeling of Nitrate Leaching from a Potato Field using HYDRUS-2D

Excessive use of nitrogen (N) fertilizers is likely to be responsible for the increasing nitrate in groundwater. Thus, appropriate water and nutrient management is required to minimize groundwater pollution and to maximize the nutrient-use efficiency. In this study HYDRUS-2D software package was applied to simulate nitrate leaching from a drip-irrigated sandy agricultural soil for varying emitter discharges and various amounts of fertilizer. It was found that for small emitter discharge values free drainage increased significantly with increase in discharge, whereas the increase was leveled out at greater discharge values. Nitrate leaching increased with an increase in emitter discharge and amount of fertilizer, but the rate of increase was most significant for low emitter discharges. Based on the results, with regard to the selection of emitter discharge and the amount of appropriate fertilizer amount, nitrate leaching from a potato field can be minimized even in a sandy soil.     

Soil nitrate sources and nitrate leaching losses, Slapton, South Devon

Abstract. Concentrations of soil nitrate were measured in areas of different land use within a small drainage basin. From previous work on nitrate losses from subcatchments, soil nitrate levels were expected in the order arable > grassland > woodland. Although differences were detected, they were not consistent and seasonal variations in soil nitrate for the same land use were greater than those between land uses. Seasonal fluctuations in stream nitrate loads were not strongly related to the seasonal differences in soil nitrate levels but were more closely related to stream discharge and antecedent climatic conditions. Losses of nitrate from the catchment seemed to be transport limited and independent of variations in soil nitrate supply; the implication is that water quality control by land use manipulation will only be successful in supply limited situations when leaching losses are sensitive to variations in soil nitrate supply.     

黄土高原北部生长季土壤氮素矿化对植被和地形的响应

氮素矿化是陆地生态系统氮循环的重要过程,对氮素有效性有着重要影响。本文在黄土高原北部六道沟小流域选取退耕年限相近的油松和柠条坡地,用原位培养法测定生长季节(4—10月)不同坡位冠层下和冠层外0~10 cm和10~20 cm土层土壤氮素矿化速率,以确定该区氮素矿化的季节动态特征和主要影响因素。结果表明,研究区生长季土壤矿质氮以铵态氮为主,其含量在0~10 cm和10~20 cm土层分别占矿质氮总量的61%和70%,并随生长季的推移而升高。油松林上坡位和中坡位土壤铵态氮显著高于下坡位土壤,柠条林不同坡位铵态氮差异不显著。土壤硝态氮和矿质氮不受坡位的影响,但与林型和采样位置有关,冠层下硝态氮在油松林与冠层外相近,在柠条林则高于冠层外。生长季土壤氮素矿化在0~10 cm土层由硝化作用引起,在10~20 cm土层则由硝化和铵化作用共同引起。铵化速率在生长季初期较高,中期较低,并受坡位、林型和采样位置的影响。土壤硝化和矿化速率在油松林不受采样位置影响,但是在柠条林则以冠层下较高。硝化和矿化速率在冠层下以下坡位土壤最高,在冠层外则以下坡位土壤最低。柠条林促进了冠层下土壤氮素的硝化和矿化过程,有利于矿质氮的积累;油松林对矿质氮和氮素矿化的影响不受采样位置影响。     

Nitrogen inputs and outputs in a small agricultural catchment in the eastern part of the United Kingdom

Abstract. Nitrate concentrations measured in an ephemeral stream draining a 170 ha clay catchment in eastern England, with about 23% arable land, were greater than 11.3 mg N 1–¹ on the resumption of flow each autumn but then declined. There was also a spring peak in two years out of seven, 1978–1984, which depend on the length of time soils was at field capacity in the preceding winter. Mean annual load measured in rain was 19 kg N ha^-1 and loss of nitrate in the stream 34 kg N ha^-1. A catchment nitrogen balance suggested that inputs, which averaged 130 kg N ha yr^-1, were generally more than outputs, average 108 kg N ha yr^-1', but gaseous losses were not taken into account.     

Soil response to canopy position and feral pig disturbance beneath Quercus agrifolia on Santa Cruz Island,California

We assessed the effects of canopy position and feral pig disturbance on soil moisture, pH, and inorganic nitrogen concentrations beneath canopies of Quercus agrifolia and surrounding grasslands on Santa Cruz Island, California. Percent soil moisture, pH, nitrate-N, and total inorganic nitrogen varied significantly with canopy position. Soil moisture decreased, and pH increased along transects from the subcanopy trunk position to the open grassland outside the canopy. Nitrate and total nitrogen increased from the trunk position to midcanopy and then decreased from midcanopy to the open grassland position. The ratio of nitrate to ammonium varied with canopy position, even after controlling for the effects of soil moisture and pH, both of which strongly influence rates of nitrogen mineralization. Temporally, soil pH, soil moisture, nitrate-N, and total carbon all varied significantly between drought and non-drought years. Soils from fenced exclosures that removed feral pig disturbance did not exhibit significant differences in any soil property compared to control plots where pig access was permitted. The results of our analysis suggest that the primary factors influencing spatial and temporal variability in oak woodland soils on Santa Cruz Island were subcanopy position and climate variability, respectively. Biotic disturbance by feral pigs did not cause a significant cause in soil properties over the spatial and temporal domains examined in this study.     

Nutrient And Particulate Inputs Into The Mar Menor Lagoon (Se Spain) From An Intensive Agricultural Watershed

The Mar Menor is a Mediterranean coastal lagoon of high conservation interest, but highly threatened by non-point pollution derived from agricultural lands. This is the first comprehensive study that evaluates the inputs into the Mar Menor from a drainage channel and the Albujón wadi, the main watercourse, and their influence on the trophic state of the lagoon. Discharge variation during the study period was closely related to the precipitation pattern. Suspended sediments and particulate organic matter loads greatly increased with flash floods. Nitrate concentrations, too, increased after heavy autumn rains through washing of the nitrates accumulated in soils, although no significant correlations were found between nitrate concentrations and precipitation or discharge. The nitrate load depended on several factors including the intensity and frequency of precipitation, and the nitrates accumulated in soils as a result of fertilisation. Phosphate concentrations decreased with higher flows. The total input into the lagoon from the two discharges estimated for the period September 2002–October 2003 were 10,142 t.yr^?1of suspended sediments, 389 t.yr^?1 of particulate organic matter, 2,010 t.yr^?1 of dissolved inorganic nitrogen (93 % as NO^? ₃) and 178 t.yr^?1 of soluble reactive phosphorus. The Albujón wadi exported about 80% of the N load and 70% of the P load. Higher flows contributed approximately 80% of the total discharge and nutrient loads, 99% of suspended sediment and 88% of the particulate organic matter. Mean suspended solids and nutrient concentrations in the lagoon followed a spatial pattern, decreasing with distance from the mouth of the Albujón wadi. Water nitrate and phosphate concentrations in the Mar Menor lagoon were lower than reference limits for eutrophic conditions, except after heavy rains. Nutrient concentrations were positively correlated with precipitation variables and particulate and nutrient inputs. Phosphorus was the most limiting nutrient in the Mar Menor, the DIN:SRP ratios found being higher than the Redfield ratio on all sampling dates. Phytoplankton bloom in the lagoon was only found next to the Albujón mouth during late summer and extending 5000 m into the lagoon in autumn as a consequence of large freshwater discharge caused by flash floods. Around 53.6% of the variation in chlorophyll a in the lagoon was explained by the NH₄ and NO₃ inputs and distance from the Albujón mouth. A good deal of P input into the lagoon is retained in the sediments, supporting a high biomass of the benthic macroalga Caulerpa prolifera in spring and summer.     

Effect of rewetting air-dried soils on pH and accumulation of mineral nitrogen

The effect of rewetting a number of air-dried soils on pH and on accumulation of mineral-N was examined in a laboratory incubation study. When rewetted-soils were incubated at 25°C three patterns of change in soil _pH and in accumulation of mineral-N were observed. Ammonification and nitrification proceeded together in soils with pH values greater than 6.0; soil pH decreased whilst concentrations of nitrate rose and those of ammonium remained low. By contrast, in soils with pH values less than 5.0, although ammonification proceeded there was no appreciable nitrification; soil pH increased whilst concentrations of ammonium rose and those of nitrate remained very low. In a third group of soils with pH values between 5.0 and 5.5, there was a delay in nitrification, but ammonification was not retarded; soil _pH initially rose as concentrations of ammonium increased, but when nitrification subsequently commenced the _pH decreased, concentrations of nitrate rose and those of ammonium declined. When microbial activity in rewetted soils was inhibited by incubation at 3°C, or in a chloroform atmosphere at 25°C, there was little change in concentrations of ammonium and nitrate, and soil pH remained relatively constant.
Such changes in soil _pH, induced by ammonification and nitrification, are likely to have important consequences to soil chemical studies where _pH-dependent reactions are being studied using rewetted soils. Changes in pH can be minimized by using field moist rather than air-dried soils.     

Volatile and water-soluble inhibitors of nitrogen mineralization and nitrification in a ponderosa pine ecosystem

Summary Bioassay experiments were performed to test for inhibition of the processes of nitrogen mineralization and nitrification by organics in the forest floor of a ponderosa pine ecosystem. Water-extractable organics in the forest floor were tested by applying filtered extracts to the assay soil. The extract decreased nitrate production by 17.0% and decreased net mineralization by 4.1%. Inhibition by volatile organics was tested by placing vials containing forest floor or selected terpenoids of ponderosa pine in sealed jars containing the assay soil. Nitrate production was inhibited by 87.4% and 100%, and net nitrogen mineralization was inhibited by 73.3% and 67.7% in the jars with forest floor and terpenoids, respectively. Organics which are partially water-soluble and are volatile (such as terpenoids) would be very effective inhibitors of nitrogen cycling processes.