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1.
Nitric oxide (NO) plays a central role in the formation of tropospheric ozone, hydroxyl radicals, as well as nitrous and nitric acids. There are, however, large uncertainties around estimates of global NO emissions due to the paucity of data. In particular, there is little information on the rate of NO emission and its sensitivity to processes such as land use changes in dry environments. Here we report on a two-year study on the influence of afforestation on soil NO fluxes in the semi-arid afforestation system in Southern Israel (Yatir forest, mean annual precipitation ∼280 mm). Laboratory incubations were carried out under seasonally defined conditions of soil moisture and temperature using soils sampled in different seasons from the native shrubland (taken both under shrub canopy and in the inter-shrub areas), and from the adjacent ∼2800 ha, 40-year-old pine afforestation site. Combining laboratory results with field measurements of soil moisture and temperature, we up-scaled soil-atmosphere NO fluxes to the ecosystem level. The different microsites differed in their annual mean NO release rates (0.04, 0.14 and 0.03 mg m−2 d−1 for the shrubland under and between shrubs and for the forest, respectively), and exhibited high inter-seasonal variability in NO emission rates (ranging from zero up to 0.25 mg m−2 d−1 in the wet and dry-rewetting seasons, respectively), as well as in temperature responses. Up-scaling results to annual and ecosystem scales indicated that afforestation of the semi-arid shrubland could reduce soil NO emission by up to 65%.  相似文献   

2.
为了更好地对太子河上游区域河流硝酸盐污染进行防治,联合硝酸盐氮氧同位素(δ15 N-NO-3和δ18O-NO-3)、水的氧同位素(δ18O-H2O)、氯离子(Cl-)、硝酸盐(NO-3)、氨氮(NH+4-N),对不同水文期太子河上游区域河流硝酸盐来源进行了识别。结果表明:枯水期ρ(Cl-),ρ(NO-3),ρ(NH+4-N)和δ18O-NO-3显著高于丰水期,δ15 N-NO-3无显著时间差异。空间上,枯水期,太子河北支ρ(NO-3)显著高于南支。丰水期,太子河南支ρ(Cl-)显著高于北支。太子河北支ρ(Cl-)和ρ(NO-3)在丰水期和枯水期的空间变化呈相反趋势。丰水期太子河南支ρ(Cl-)和ρ(NO-3)的空间变化趋势与枯水期一致。枯水期太子河上游地区NO-3主要来源于土壤有机氮。可见,丰水期的主要来源是土壤有机氮、复合肥料。另外,丰水期上游区域土壤中的大气沉降可能也是河流硝酸盐的一个主要来源。丰水期硝酸盐从土壤冲刷进入河流过程中发生了硝化作用。枯水期太子河北支河流内硝化过程影响着硝酸盐浓度变化。  相似文献   

3.
干湿交替程度对土壤速效养分的影响   总被引：1，自引：0，他引：1  
降雨和灌溉引起的干湿交替显著影响土壤速效养分的转化和迁移。为了探究干湿交替程度对土壤速效养分的影响,采用室内模拟干湿交替试验,设置轻度(DW1,复水至60%WHC)、中度(DW2,复水至45%WHC)、重度(DW3,复水至30%WHC)3种干湿交替程度,并以恒湿处理(CM,恒定60%WHC)为对照,探究试验前后土壤pH、水溶性有机碳(dissolved organic carbon,DOC)、铵态氮、硝态氮、速效磷及速效钾的变化。结果表明:DW1土壤pH比其他各组低0.25~0.45,其余各组间差异不显著;培养后CM组DOC下降20.01%,DW组下降37.04%~41.36%,不同程度干湿交替处理间差异不显著。土壤铵态氮含量在培养后下降18.19%~42.02%,各处理间表现为DW3>DW2>DW1;土壤硝态氮含量较培养前急剧增长,表现为DW1>DW2>DW3,DW2的铵态氮和硝态氮含量与CM组基本一致。土壤速效钾和速效磷培养前后变化不大,但DW2速效磷含量较其他各处理减少2.93~4.00 mg/kg,而DW3的速效钾含量较其他各处理减少3.69~14.72 mg/kg。干湿交替显著降低土壤DOC和铵态氮含量,增加土壤硝态氮含量,对土壤pH、速效磷、速效钾影响不大。干湿交替程度的增强能提高土壤pH,促进铵态氮的产生,抑制硝态氮和速效钾的生成,但对DOC和速效磷影响不大。  相似文献   

4.
Northern Australian tropical savannas are subjected to pressures from both grazing and planned and unplanned burning. We know little about the effects of these processes on the below-ground environment. The aim of this study was to investigate the effects of fire, grazing and season on environmental and biological properties of the soil at the base of grass tussocks in a semi-arid savanna rangeland of north Australia. A long-term fire and grazing exclusion experiment was used to test the effects of season, fire and grazing on soil physicochemical factors (soil organic carbon, total nitrogen, ammonium, nitrate levels and bulk density) and soil mite abundance and diversity. Grazed plots were associated with small but significant reductions in total soil nitrogen and organic carbon when compared to 30 year old plots where grazing and fire had been excluded. This suggests slow, long-term losses of nitrogen and soil carbon from an ecosystem with limited available nutrients. Fire had a limited impact on soil properties, but this may reflect the modest experimental fire intensity resulting from fuel reduction due to grazing. Treatment effects on soil bulk density were also negligible. Season had a significant impact on total soil mite abundance and diversity, whereas burning and grazing treatments had no impact on soil mites. Only two morpho-species, one each from the families Cunaxidae and Stigmaeidae, decreased in abundance as a result of grazing. Increased moisture levels in the wet season were associated with increased total nitrogen and the highly mobile nitrate. Changes in mite abundance and diversity reflected these changes in levels of nitrogen and it is possible that increasing total nitrogen availability and soil moisture, is a determinant of mite abundance.  相似文献   

5.
Sudden pulse-like events of rapidly increasing CO2-efflux occur in soils under seasonally dry climates in response to rewetting after drought. These occurrences, termed “Birch effect”, can have a marked influence on the ecosystem carbon balance. Current hypotheses indicate that the “Birch” pulse is caused by rapidly increased respiration and mineralization rates in response to changing moisture conditions but the underlying mechanisms are still unclear. Here, we present data from an experimental field study using straight-forward stable isotope methodology to gather new insights into the processes induced by rewetting of dried soils and evaluate current hypotheses for the “Birch“-CO2-pulse. Two irrigation experiments were conducted on bare soil, root-free soil and intact vegetation during May and August 2005 in a semi-arid Mediterranean holm oak forest in southern Portugal. We continuously monitored CO2-fluxes along with their isotopic compositions before, during and after the irrigation. δ13C signatures of the first CO2-efflux burst, occurring immediately after rewetting, fit the hypothesis that the “Birch” pulse is caused by the rapid mineralization of either dead microbial biomass or osmoregulatory substances released by soil microorganisms in response to hypo-osmotic stress in order to avoid cell lyses. The response of soil CO2-efflux to rewetting was smaller under mild (May) than under severe drought (August) and isotopic compositions indicated a larger contribution of anaplerotic carbon uptake with increasing soil desiccation. Both length and severity of drought periods probably play a key role for the microbial response to the rewetting of soils and thus for ecosystem carbon sequestration.  相似文献   

6.
Extensive research has focused on the temperature sensitivity of soil respiration. However, in Mediterranean ecosystems, soil respiration may have a pulsed response to precipitation events, especially during prolonged dry periods. Here, we investigate temporal variations in soil respiration (Rs), soil temperature (T) and soil water content (SWC) under three different land uses (a forest area, an abandoned agricultural field and a rainfed olive grove) in a dry Mediterranean area of southeast Spain, and evaluate the relative importance of soil temperature and water content as predictors of Rs. We hypothesize that soil moisture content, rather than soil temperature, becomes the major factor controlling CO2 efflux rates in this Mediterranean ecosystem during the summer dry season. Soil CO2 efflux was measured monthly between January 2006 and December 2007 using a portable soil respiration instrument fitted with a soil respiration chamber (LI-6400-09). Mean annual soil respiration rates were 2.06 ± 0.07, 1.71 ± 0.09, and 1.12 ± 0.12 μmol m−2 s−1 in the forest, abandoned field and olive grove, respectively. Rs was largely controlled by soil temperature above a soil water content threshold value of 10% at 0-15 cm depth for forest and olive grove, and 15% for abandoned field. However, below those thresholds Rs was controlled by soil moisture. Exponential and linear models adequately described Rs responses to environmental variables during the growing and dry seasons. Models combining abiotic (soil temperature and soil rewetting index) and biotic factors (above-ground biomass index and/or distance from the nearest tree) explained between 39 and 73% of the temporal variability of Rs in the forest and olive grove. However, in the abandoned field, a single variable - either soil temperature (growing season) or rewetting index (dry season) - was sufficient to explain between 51 and 63% of the soil CO2 efflux. The fact that the rewetting index, rather than soil water content, became the major factor controlling soil CO2 efflux rates during the prolonged summer drought emphasizes the need to quantify the effects of rain pulses in estimates of net annual carbon fluxes from soil in Mediterranean ecosystems.  相似文献   

7.
Abstract

Leaf N and soil nitrate and ammonium levels were monitored in 1986 and 1987 following N fertilization of 8–9 year old highbush blueberries. Urea was applied at 76 kg N/ha in a single application at bud break or in two applications (split) at bud break and petal fall. Controlled release fertilizers (CRF), of two different residual effects (Osmocote 3 mo., Osmocote 8 mo.) were applied at 38 kg N/ha or 76 kg N/ha at bud break. Compared to controls, N applications increased soil ammonium and nitrate levels early in the season and leaf N levels throughout the season. Urea provided a greater increase in leaf N and soil ammonium levels than CRF. Split urea applications increase leaf levels slightly over single urea treatments. Fertilizers increased soil ammonium and nitrate levels below the root zone, indicating that some leaching losses occurred.  相似文献   

8.
《Applied soil ecology》2001,16(3):219-227
Significant variations were found in soil texture, levels of organic carbon, microbial biomass carbon, nitrate, and nitrification rates in the upper 20 cm of soil from three distinct Uplands forest, Cohune Palm forest, and Bajo forest habitats within the subtropical rainforest of Northwestern Belize. The Cohune Palm forest soils had the most organic carbon, microbial biomass carbon, nitrate, and highest nitrification rates, while the soils from the Bajo forests had the lowest levels of these parameters. The heterogeneity in the soil composition is even more significant given that the three habitats studied are part of the same ‘forest’ and are within 2 km of each other.The first rains at the beginning of the wet season had a rapid and significant effect on various components in the soil. A rapid increase in the microbial biomass carbon, organic carbon, and nitrification rates and a decrease in nitrate occurred in the soil from all three habitats within hours after what locals anecdotally consider the start of the wet season. The greatest percent change in all factors following the rains occurred within the soil from the Bajo forests, while the smallest percent change occurred within soil from the Uplands forest.There were also significant correlations found between soil moisture levels and organic carbon, microbial biomass carbon, and nitrification rates. The variations in the measured parameters were also associated with the amount of clay in the soil. It appears, then, that the amounts of moisture and clay are most critical soil composition factors which when combined with microbial biomass carbon, organic carbon, and nitrification rates may be good predictors of soil quality in these forests.  相似文献   

9.
Forest floors in the temperate climate zone are frequently subjected to strong changes in soil moisture, but the consequences for the soil N cycle are poorly known. In a field experiment we tested the hypotheses that soil drying leads to a decrease of gross N turnover and that natural rewetting causes a pulse of gross N turnover and an increase of N leaching from the forest floor. A further hypothesis was that optimal water availability induced by irrigation causes maximum N turnover and N leaching. Replicated control, throughfall exclusion and irrigation plots were established in a Norway spruce forest to simulate different precipitation patterns during a growing season. Gross N turnover rates were determined in undisturbed soil cores from Oi + Oe and Oa + EA horizons by the 15N pool dilution technique. Forest floor percolates were periodically collected by suction plates. After 142 mm throughfall was excluded, the median soil water potential at the throughfall exclusion plots increased from pF 1.9 to 4.5 in the Oi + Oe horizon and from pF 1.8 to 3.8 in the Oa + EA horizon. Gross ammonification ranged from 14 to 45 mg N kg−1 soil day−1 in the Oi + Oe horizon and from 4.6 to 11.4 mg N kg−1 soil day−1 in the Oa + EA horizon. Gross ammonification of both horizons was smallest in the throughfall exclusion plots during the manipulation, but the differences between all treatments were not statistically significant. Gross nitrification in both horizons was very small, ranging from 1.6 to 11.1 mg N kg−1 soil day−1. No effects of decreasing water potential and rewetting on gross nitrification rates were observed because of the small rates and huge spatial variations. Irrigation had no effect as the differences from the control in soil water potential remained small. N leaching from the forest floor was not affected by the treatments. Our findings suggest that ammonification in forest floors continues at considerable rates even at small water potentials. The hypotheses of increased N turnover and N leaching following rewetting of dry forest floor or irrigation were not confirmed.  相似文献   

10.
Except where nitrate is added to the soil artificially, nitrate is leached from forest soils only if it is produced. Although the factors influencing nitrification have been widely studied, nitrification activity still cannot be simply predicted from ecosystem characteristics. In France, about half of the present forest area was agricultural in 1850. Previous work suggested that former cultivation could be a major factor influencing nitrogen availability in forest soils. Using laboratory incubations, we compared the net production of ammonium and nitrate in soils from formerly manured lands planted with conifers 70–100 years ago with that in soils of surrounding ancient coniferous forests. Net nitrate production, available P content, and natural abundance of nitrogen 15, δ15N, were greater in soils from formerly manured plots than other land, whereas the C:N ratio of the soil was less. The difference in net nitrate production between previously manured sites and adjacent ancient forests was related to differences in δ15N values in the soil but not evidently to other soil properties. Because soil δ15N increases with the intensity of organic manuring, these results suggest that nitrification in forest soils depends on previous manurial practices under agriculture. In this context, the soil δ15N might be used as an indicator of both previous agricultural land use and potential nitrification. Because a significant proportion of West European forests grow on previously cultivated soils, past land use should be taken into account when evaluating the risks of nitrate leaching from forests.  相似文献   

11.
研究森林土壤团聚体酶活性对氮沉降的响应差异以及团聚体酶活性的影响因素，以滇中亚高山云南松林和华山松林为研究对象，于2020年6月至2021年5月通过野外模拟氮沉降试验，设置对照[CK,0 g/(m2·a)N]、低氮[LN,10 g/(m2·a)N]、中氮[MN,20 g/(m2·a)N]、高氮[HN,25 g/(m2·a)N],分别采集旱季(2021年2月)和雨季(2020年8月)的土壤样品，分析土壤团聚体中脲酶(Ure)、蔗糖酶(Inv)和酸性磷酸酶(AP)的变化特征，以及与环境因子的交互作用，阐明不同筛分方式下土壤团聚体酶活性对氮沉降的响应特征。结果表明：(1)氮沉降对2种林分下土壤团聚体的分布未造成显著影响，而不同筛分方式则影响显著；不同氮沉降水平下，土壤团聚体中3种酶活性均表现出LN促进，MN与HN抑制；(2)与干筛法相比，湿筛法下土壤团聚体中酶活性均有显著下降，Inv和Ure的团聚体酶活性的降幅均在20%以上，AP的降幅可达57.55%;(3)土壤干筛、湿筛团聚体酶活性的几何平均数(GMe...  相似文献   

12.
The choice of manure application technique can affect both the spatial distribution of ammonium in soil and net nitrogen (N) mineralization, and thereby N availability to crops. In this study we compared net N mineralization and spatial ammonium distribution after different degrees of incorporation of solid chicken manure and cattle slurry into soil. Ammonium‐specific fluorescing optodes were assembled with manure applied to soil in closed chambers and the spatial distribution of ammonium in different treatments was measured for 2 weeks. The results indicated that much ammonium from the manures was quickly adsorbed to clay particles. Consequently, the ammonium concentration in the soil solution was threefold higher in the sandy soil than in the clay soil studied. Ammonium was distributed over a larger soil volume from manure applied below the soil surface than from manure applied above. Because the optodes excluded ammonium adsorbed to soil particles, net N mineralization was instead studied in separate incubations using extraction with potassium chloride solution for determination of ammonium and nitrate. When manure was kept concentrated in lumps rather than being mixed with soil, nitrate levels were about five times smaller after 1 week and 5–10% more of the manure N occurred as mineral N after 2 weeks. There were no differences in net N mineralization between surface application and subsurface incorporation. In this study a new technique to visualize and measure ammonium patterns around manure in soil proved to be useful for evaluating ammonium distribution and adsorption, but net N mineralization required incubations.  相似文献   

13.
We applied digestate generated from the anaerobic digestion of slurry, undigested slurry, or inorganic N (ammonium nitrate) or NPK compound fertilizer to pots of grass and a grass–clover mix grown in two soils. Crop yields were equal or enhanced with digestate, and analysis of soil water showed that there was less potential for loss of nutrients via leaching. Replacing inorganic fertilizer with digestate may therefore maintain grassland productivity but with less impact on the environment.  相似文献   

14.
As a part of an ongoing investigation into urban acidic deposition in Greater Manchester, a wet-only collector was collocated with a bulk collector in the city centre of Manchester, one of 18 sites of an urban precipitation monitoring network. A comparison of data from these collocated bulk and wet-only collectors allowed estimates of the contribution of dry deposition to the bulk collector to be made. Dry deposition was found to contribute between 15 and 17% to elevated deposition and concentrations of non marine sulphate, nitrate and ammonium in the bulk collector. By a statistical analysis between ion concentrations with gas concentrations and an evaluation of the available literature, the form of the dry deposited material was inferred. The contribution of dry deposited Ca2+ to concentration and deposition in the bulk collector was found to be 46%. Calcium species are suggested as being those which reduce acidity most. Statistical analyses revealed significant differences between concentrations of ions found in the bulk and wet-only collectors. An evaluation of the data from the collocated collectors has identified possible sampling artifacts introduced by the use of bulk collectors in urban areas.  相似文献   

15.
Seven grassland experiments on sandy and clay soils were performed during a period of 4 years to estimate the nitrogen (N) fertilizer replacement value (NFRV) of concentrated liquid fractions of separated pig slurry (mineral concentrate: MC). The risk of nitrate leaching when applying MC was compared to when applying mineral fertilizers. Grassland yields in 2009–2012 fertilized with MC were compared with grassland fertilized with two mineral fertilizers: granulated calcium ammonium nitrate and liquid ammonium nitrate (LAN). The mineral fertilizers comprised 50% nitrate-N and 50% ammonium-N, and MC comprised 95–100% ammonium-N. Treatment application rates included zero N and three incremental rates of N fertilization. The liquid fertilizers were shallow injected (0–5 cm). The NFRV of MCs was 75% on sandy and 58% on clay soil with granulated ammonium nitrate as reference, and 89% on sandy and 92% on clay soil with LAN as reference. Risk of nitrate leaching after application of MC, measured in residual soil mineral N post-growing season and N in the upper groundwater in the following spring, was equal to that for mineral fertilizers.  相似文献   

16.
Variations in patterns of ammonification and nitrification among and within four sites at each of three stages of old field succession (old field to pine to deciduous hardwoods) were evaluated by laboratory incubations in May and August 1979. Each experiment included mineral nutrient-minus-nitrogen (?N) and supplemental ammonium (+ N) treatments to examine limitations on nitrification.In general, nitrate production was highest and ammonium accumulation was lowest in old field soils compared to pine or hardwood soils. However, there was considerable overlap in response, and variation due to locality within site and site within successional stage exceeded that attributable to successional stage alone.Ammonium addition enhanced nitrification in soil from all old field sites, only one pine forest site and no hardwood site. Addition of nutrients less nitrogen (?N) had no effect in any soil. Correlations between other soil variables and changes in ammonium and nitrate during incubation varied among successional stage and in some instances between dates.  相似文献   

17.
Soil microbial activity is greatly affected by soil water content. Determining the appropriate moisture content to rewet soils that have been dried in preparation for laboratory incubations to determine microbial activity can be laborious and time-consuming. The most common methods used achieve sufficient moisture content for peak microbial respiration are gravimetric water content, soil matric potential, or percentage of water-filled pore space (WFPS). Alternatively, a fast, simple, and accurate way to ensure that a given soil receives the appropriate amount of water for peak soil microbial respiration is to rely on natural capillary action for rewetting the dry soil. The capillary method is related to the gravimetric method for water uptake and has a strong correlation with WFPS. A microbial respiration test was conducted to compare rewetting methods. The 24-h carbon dioxide (CO2) / carbon (C) results were very similar and strongly correlated using the gravimetric method and the capillary method for rewetting dried soil.  相似文献   

18.
研究苗期干旱胁迫下施氮对东北春玉米氮素吸收利用和土壤生物化学性质的影响,为区域玉米养分管理与逆境调控提供依据。研究设置水、氮二因素盆栽试验,土壤水分包括3个水平:田间持水量的30%(W0),50%(W1)和70%(W2);施氮量包括2个水平:不施氮(N0)和施氮0.24 g/kg(N1),测定不同水氮条件下玉米苗期的植株干重和氮素吸收、根际和非根际土壤的化学性质、微生物量碳、氮(MBC、MBN)及土壤酶活性。结果表明:干旱胁迫显著降低玉米苗期植株干重和氮素吸收量,其中W0条件降幅最大(分别为51.1%,43.8%)。施氮促进各水分条件下植株生长,且与水分存在显著交互作用,W2条件下施氮后植株干重和氮素吸收量的增幅最高(分别为53.7%,83.2%)。干旱胁迫提高植株的水分利用效率,但降低氮肥利用效率。施氮显著提高W2条件植株的水分利用效率,但干旱条件下则无显著影响。水、氮及其交互作用对土壤性质的影响较为复杂。总体上,苗期干旱胁迫暂时提高了根际和非根际土壤pH,显著增加根际土壤的铵态氮和硝态氮含量。MBC、MBN对干旱胁迫的响应在根际与非根际土壤之间存在相反趋势,根际土壤随干旱程度增加而提高,非根际土壤则随之下降。土壤酶活性方面,干旱胁迫显著影响根际土壤的硝酸还原酶和亚硝酸还原酶活性。施氮增加所有水分条件下根际和非根际土壤的pH和铵态氮、硝态氮含量,其中根际土壤的增幅高于非根际土壤。施氮显著增加各水分条件下根际和非根际土壤的MBC、MBN、脲酶和硝酸还原酶活性,但显著降低根际和非根际土壤亚硝酸还原酶活性。水氮交互作用显著影响根际土壤的亚硝酸还原酶、非根际土壤的脲酶、亚硝酸还原酶和FDA水解酶活性。根际、非根际土壤各生物化学性质之间均存在显著的相关关系,而且根际土壤除土壤亚硝酸还原酶外的各指标均与植株氮素吸收和氮肥利用效率呈正相关。苗期干旱显著抑制玉米植株生长和氮素吸收,并对土壤生物、化学性质造成显著影响。施氮对植株和土壤性质的影响在不同水分条件下存在差异,而且植株表现与土壤生物、化学性质之间存在显著相关关系。  相似文献   

19.
Concentrations of dissolved ions from samples collected by wet/dry collectors were compared to those collected by bulk collectors at Halfmoon Creek and Ned Wilson Lake in western Colorado to determine if bulk collectors can be used to monitor wet deposition chemistry in remote, high-altitude regions in winter. Hydrogen-ion concentration was significantly lower (p <0.05) in the bulk collectors. All other ion concentrations were significantly higher (p <0.05) in the bulk collectors except for ammonium (p >0.05) at Halfmoon Creek. Wet deposition concentrations were predicated from bulk deposition concentrations through linear regression analysis. Results indicate that anions (chloride, nitrate and sulfate) can be predicted with a high degree of confidence. Lack of significant differences between seasonal (winter and summer) ratios of bulk to wet deposition concentrations indicates that at sites where operation of a wet/dry collector during the winter is not practical, wet deposition concentrations can be predicted from bulk collector samples through regression analysis of wet and bulk deposition data collected during the summer.  相似文献   

20.
滴灌均匀系数对土壤水分和氮素分布的影响   总被引：10，自引：4，他引：6  
为了确定滴灌均匀系数的设计与评价标准,在日光温室内研究了滴灌施肥灌溉均匀性和施氮量对土壤水氮分布特性的影响。试验中滴灌均匀系数（Cu）设置0.62、0.80和0.96 3个水平,施氮量设置150和300 kg/hm2 2个水平。土壤含水率和电导率采用沿毛管均匀布置的TDR探头（Hydra Probe）连续监测,并定期取土样测试土壤硝态氮和铵态氮含量。结果表明,在作物生育期内3种滴灌均匀系数处理的土壤含水率一直保持很高的均匀系数,滴灌均匀系数和施氮量对土壤含水率均值及其均匀系数的影响均不显著（α=0.05）。土壤电导率及硝态氮含量的均匀性在很大程度上取决于土壤初始氮素含量的均匀性,其均匀系数低于土壤含水率的均匀系数,滴灌均匀系数的影响也不显著。从获得均匀的土壤水氮分布的角度出发,现行滴灌均匀系数标准尚有降低的空间。  相似文献   

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