绿洲农田氮素积累与淋溶研究述评

作物对氮素的吸收利用及氮素在土壤中的积累和运移,制约着绿洲农田生产力并对农田环境造成影响,是绿洲农田生态系统可持续发展和绿洲稳定性研究的一个重要方面。针对农田氮素积累和淋溶这一绿洲资源消耗量增加、耕作方式粗放结果下的环境问题,对其特征及引发的环境效应进行了详细阐述,并从不同的角度综述了缓减绿洲氮素淋失及环境污染的对策。指出在未来还需加强绿洲地下水氮污染调查及农田氮素积累和淋溶现状的区域评价,并针对一些在绿洲大面积推广的农田管理技术开展其对农田氮素积累和淋溶影响的研究,并强调人文因素在绿洲农田氮素积累与淋溶调控中的重要性。     

Nitrogen input together with ecosystem nitrogen enrichment predict nitrate leaching from European forests

The IFEF database (Indicators of Forest Ecosystem Functioning), consisting of nitrogen deposition, nitrate leaching fluxes, and soil and ecosystem characteristics, is analysed to evaluate the C/N ratio in the organic horizon as an indicator of nitrate leaching. One hundred and eighty one forests are examined, from countries across Europe ranging from boreal to Mediterranean regions, encompassing broadleaf and coniferous sites and plot and catchment studies. N input in throughfall ranges from less than 1 kg N ha^?1 y^?1 in northern Norway and Finland to greater than 60 kg N ha^?1 y^?1 in the Netherlands and Czech Republic. The amount of NO₃^– leached covers a smaller range, between 1 and 40 kg N ha^?1 y^?1. Nitrate leaching is strongly dependent on the amount of nitrogen deposited in throughfall (N input) and simply adding the C/N ratio in the organic horizon to a regression equation does not improve this relationship. However, when the data are stratified based on C/N ratios less than or equal to 25 and greater than 25, highly significant relationships (P < 0.05) are observed between N input and NO₃^– leached. The slope of the relationship for those sites where C/N ratio is ≤ 25 (′nitrogen enriched′ sites) is twice that for those sites where C/N ratio is > 25. These empirical relationships may be used to identify which forested ecosystems are likely to show elevated rates of nitrate leaching under predicted future nitrogen deposition scenarios. Elevated NO₃^– leaching also shows a relationship with soil pH, with high rates of NO₃^– leaching only observed at sites with a pH < 4.5 and N inputs > 30 kg N ha^?1 y^?1. Tree age and species have no significant impact on the ecosystem response to N input at a regional scale.     

氮添加对沙质草地氨挥发及硝态氮淋溶的影响

采用密闭室法和离子交换树脂袋法,研究了科尔沁沙质草地不同处理(水添加、氮添加、水氮添加)氧挥发的损失量和硝态氮的淋溶量.结果表明:氮添加处理和水氮添加处理显著促进了氨挥发(P＜0.05),最大氨挥发速率显著高于对照;氮添加处理和水氮添加处理的氨挥发累积量为111.80和148.64 mg·m-2,分别占氮添加量的1.1％和1.5％;水氮同时添加条件下,氨挥发累计量显著高于氨添加处理(P＜0.05),水添加处理和对照相比没有显著差异(P＞0.05);水氮添加处理显著增加了土壤深度20 cm处的硝态氮淋溶量(P＜0.05),氮添加处理和水氮添加处理的硝态氮淋溶量分别是对照的1.96和4.22倍,然而在土壤深度40 cm处各处理硝态氮淋溶量差异不显著(P＞0.05);可见,氮添加和水氮添加均促进了土壤的氧挥发,对硝态氮的淋溶没有显著影响.     

Effects of carbon and nitrate additions to soil upon leaching of nitrate,microbial predators and nitrogen uptake by plants

Amendments with glucose significantly reduced the amount of nitrate leached from a sandy soil amended with nitrate. The decrease was most likely caused by immobilisation of the nitrate into microbial cells. Populations of ciliates and flagellates and amoebae, but not nematodes, increased 7–14 days following glucose amendments. Mineralisation of the immobilised nitrate occurred during this period. Some of the mineralised nitrogen appeared to be available to ryegrass plants only if the roots exploited most of the soil during the period of maximum predator activity. After 28 days, 44% of the organic N remaining in the soil after leaching was taken up by the plants. The difference developed over the last 2 weeks when amoebal populations were large.     

生物炭对黄壤中氮淋溶影响:室内土柱模拟

土壤氮素的淋失作用不仅造成土壤营养元素的损失,而且对河流和湖泊等环境水体的富营养化具有重要贡献.采用土柱室内模拟方法,通过模拟降雨淋滤,研究了生物炭对土壤淋溶液体积、pH和电导率以及NH4+-N和NO3--N淋溶的影响.试验中所用的生物炭是以桉树木屑为原料制成,分别按照炭土质量比1％、2％、4％、10％施用于土壤中.结果显示,与对照相比,向土壤添加10％、4％、2％、1％生物炭分别减少土壤水分损失14％、0.03％、0.02％和0.01％;随生物炭添加量增加,淋溶液的pH和电导率也逐渐增加;土壤生物炭添加量为10％、4％、2％时,NH4+-N淋溶量分别增加235％、28.1％、31.6％,NO3--N淋溶量分别增加4.2％、14.5％、25.6％;但生物炭添加量为1％的土柱NH4+-N淋溶量减少15.8％,NO3--N淋溶量减少19.2％.本研究表明,桉树生物炭对土壤氮淋溶与其施用量有关,1％施用量能减少氮淋溶,过量施用将增加氮淋溶,这种作用是否与生物炭种类有关有待进一步研究.     

Effects of a catch crop on leaching of nitrogen from a sandy soil: Simulations and measurements

The effects of an undersown catch crop on the dynamics and leaching of nitrogen in cropping systems with spring cereals were investigated in southern Sweden. Field measurements of soil mineral nitrogen and nitrogen concentrations in drainage water were made for 4 years in a sandy soil. The experiment was performed on four tile-drained field plots sown with spring cereals. On two of the plots, Italian rye grass was undersown and ploughed down the following spring during three of the years. The other two plots were treated in a conventional way and served as controls. Soil nitrate levels were substantially reduced in the catch-crop treatment, but increased during the fourth year when no catch crop was grown. The differences between the treatments in soil nitrate were reflected in the nitrate concentrations measured in the drainage water. A mathematical model was used to simulate nitrogen dynamics in corresponding treatments. There was good agreement between measurements and simulations with regard to patterns of change in soil mineral nitrogen and nitrate concentrations in drainage water for each treatment. Simulated leaching of nitrate in the conventional treatment was 1.9–3.9 g N m^–2 y^–1 during the first three years while calculated leaching based on the measurements was 2.7–4.4 g N m^–2 y^–1. In the catch-crop treatment leaching of nitrate was reduced by 1.4–2.6 g m^–2 y^–1 according to the simulations and by 2.2–4.1 g m^–2 y^–1 according to calculations based on the measurements. Measurements showed that leaching of nitrogen compounds other than nitrate was hardly affected by the catch crop. In the simulations the ploughed-down catch crop resulted in temporary increases of the litter pool, a net increase of the humus pool and a reduced C-N ratio of the litter pool. Simulated net mineralization from the litter pool was substantially higher in the catch-crop treatment compared with the conventional treatment. In the fourth year, the yield of the main crop was 20–25% higher in the catch-crop treatment, and leaching was higher than in the conventional treatment.     

Effect of one year rotational set-aside on immediate and ensuing nitrogen leaching loss

This paper reports results from a 3-year field experiment which examined Nitrogen (N) leaching loss from land under various set-aside managements. Four treatments were examined: three ploughed plots which were sown with wheat, ryegrass or maintained fallow; the fourth treatment was unploughed and natural weed growth (volunteers) permitted. The l-year set-aside was followed by two winter wheat test crops. Ceramic suction cups were installed at a depth of 90 cm and used to collect drainage water. N leaching loss was calculated by multiplying drainage volume, calculated from meteorological data, by its inorganic N concentration.Set-aside management significantly affected N leaching loss over the three years. During the set-aside year, the peak nitrate concentration from the unploughed treatment growing volunteer weeds was significantly lower than that from ploughed plots. Of the latter, by the spring, crop (i.e. wheat and ryegrass) assimilation of N significantly reduced N concentration compared to the fallow. The four set-aside treatments had a carry-over effect to the following year (first wheat test crop) resulting in significant differences in N losses. Leaching following the ryegrass treatment was very small and we believe that the grass residues minimised rates of net-N mineralization.The influence of set-aside management continued to the second wheat test crop where N loss was greater under the all wheat rotation because take-all had reduced yield and therefore crop N uptake.     

宁夏引黄灌区猪粪还田对稻作土壤硝态氮淋失的影响

以宁夏引黄灌区稻田为例,探索猪粪还田条件下稻田土壤硝态氮淋失规律。试验设置3个处理:常规施肥300 kg纯N kg/hm2(CK)、常规施肥条件下施用4500kg/hm2(T1)和9000 kg/hm2(T2)猪粪。利用树脂芯法吸附稻田30cm、60cm和90cm土层的硝态氮流失量。结果表明:在常规施肥的基础上增施猪粪,可以减少稻田生育期内60cm与90cm处土壤硝态氮淋失量,与CK相比,T1、T2在两个土层处淋失量的减少比例分别为4.93%、13.92%与7.48%、13.77%。同一土层不同处理之间差异显著性比较看(P0.05),30cm处T1、T2与CK相比没有达到显著性差异;60cm处,T1与CK未达到显著差异,T2与CK达到显著差异;90cm处,T1、T2与CK相比达到显著差异;60cm和90cm土层处的T2与T1之间均达到显著差异。T1和T2在30cm处的淋失量高于CK,但增加不明显,处理之间以及处理与对照相比差异不显著。稻田生育期内不同土层硝态氮淋失量在13.61—17.77 kg/hm2(纯N)。硝态氮淋失集中在插秧至分蘖期(5月中旬—6月下旬),该阶段的硝态氮淋失量占生育期内总淋失量的61.62%—72.84%;后期淋失量明显减少。处理T1、T2的水稻产量增产率分别为15.86%与12.85%。由此可见,在引黄灌区稻田,一定数量的猪粪还田,不仅能够减少土壤硝态氮向深层淋失,防控地下水污染,还有利于水稻增产。     

一次性施肥技术对水稻-油菜轮作系统氮素淋失特征及经济效益的影响

一次性施肥技术是指在作物根际附近只进行一次基施肥的新技术,具有简化施肥管理、降低劳动成本等优点,但其对环境的影响如氮素淋失等仍需进一步分析.本研究以长江中下游地区典型的水稻-油菜轮作模式为例,设置了空白对照(CK)、农民习惯施肥(FP)、优化施肥(OPT)、一次性基施尿素(UA)、一次性基施控释肥(CRF)5个处理,采用地下淋溶原位监测的方法,获取了不同处理下水稻-油菜轮作系统土壤90 cm深度处氮素(N)淋失特征,评估了一次性施肥技术对氮素淋失的影响,并综合分析了其经济效应.结果表明: 油菜季和水稻季土壤渗漏液中氮素的主要形态不同,油菜季渗漏液中以NO₃^--N为主,水稻季渗漏水中NO₃^--N和NH₄⁺-N各占约50%.从整个轮作周期看,氮素淋失主要发生在水稻季,与FP、OPT和UA相比,CRF氮淋失总量分别显著减少33.7%、20.8%和20.7%;但各施肥处理对油菜季氮素淋失影响不显著.在相同施氮量的条件下,与OPT相比,UA不仅保证油菜和水稻均稳产,而且使油菜季氮肥农学效率显著提高了15.1%,但是没能提高水稻季氮肥农学效率;CRF水稻产量和氮肥农学效率均差异不显著,但油菜产量和氮肥农学效率分别显著提高10.7%和18.9%.经济效益上,与OPT相比,UA和CRF处理油菜分别增收3660和3048 元·hm^-2,水稻分别增收3162和2220元·hm^-2.因此,对于长江中下游典型种植系统而言,综合考虑对氮素淋失、作物产量和经济效益的影响,一次性基施控释肥技术能在保证作物稳产或增产、提高农民经济效益的同时显著降低氮淋失量,是未来水稻-油菜轮作系统值得推荐的一种生产技术.     

氮肥配施生化抑制剂组合对黄泥田土壤氮素淋溶特征的影响

揭示尿素类肥料添加生化抑制剂组合后,在黄泥田土壤中硝态氮(NO~-_3-N)和铵态氮(NH~+_4-N)的淋溶损失规律。采用室内土柱淋溶培养试验,研究脲酶抑制剂N-丁基硫代磷酰三胺(NBPT)和硝化抑制剂2-氯-6-(三氯甲基)吡啶(CP)单独添加及配合施用对尿素和尿素硝铵(300 kg N/hm~2)中氮(N)素在土体中淋溶损失的影响。结果表明:尿素和尿素硝铵处理淋溶液中NH~+_4-N和NO~-_3-N浓度均呈先升后降的变化趋势,而出峰时间不一。NH~+_4-N和NO~-_3-N淋失量随着时间的延长,处理间差异逐渐变大。NBPT处理可以减缓尿素水解,有效抑制NH~+_4-N生成,延缓其出峰时间,减少NH~+_4-N流失;CP处理可以有效抑制NH~+_4-N向NO~-_3-N转化,减少NO~-_3-N流失。与单独添加NBPT和CP处理相比,两者配施对N素淋溶损失有明显的协同抑制效果在黄泥田土壤中,既能减缓尿素水解,保持土壤中较高NH~+_4-N含量,又能降低淋溶液中NO~-_3-N浓度。培养结束时(第72天),UAN处理中NO~-_3-N、NH~+_4-N、矿质态N淋失总量及硝化率较U处理高34.39%、5.32%、31.72%和15.71%。U+NBPT、U+CP和U+NBPT+CP处理较U处理分别显著降低NO~-_3-N淋失总量达15.58%、114.77%和73.45%;UAN+NBPT、UAN+CP和UAN+NBPT+CP处理较UAN处理分别显著降低达15.88%、54.87%和37.46%。不同处理NO~-_3-N淋失总量大小表现为:UAN UAN+NBPT U UAN+NBPT+CP U+NBPT UAN+CP U+NBPT+CP U+CP CK。在一定施肥量条件下,NBPT和CP单独施用或配施均可降低黄泥田土壤中NO~-_3-N累积淋失量。对各处理淋溶液中NO~-_3-N淋失量(y)随时间(x)的变化进行拟合,其中以线性方程(y=ax+b)的拟合度较高,且各抑制剂处理a、b值均存在明显差异。总体认为,在黄泥田土壤中施用CP及其与NBPT配施可以显著降低土壤NO~-_3-N淋溶损失,减少N素淋失风险,提高肥料利用率。     

Dissolved inorganic nitrogen concentrations and fluxes in three British Sitka Spruce plantations

A catchment approach was used to estimate mean dissolved inorganic-N concentrations and fluxes through three mature Sitka spruce plantations at Beddgelert (north Wales), Plynlimon (mid-Wales) and Kershope (Cumbria). Dissolved inorganic-N in bulk precipitation, throughfall, stemflow, soil water at 4 or 5 depths, and streamwater was measured every two weeks for periods of 1 or 2 years at all three sites. Bulk precipitation inputs at the three sites varied from 6 to 10.4 kg N ha^-1 a^-1 and stream outputs varied from 6.4 to 13.6 kg N ha^-1 a^-1. Beddgelert Forest had the highest inputs and outputs and is Nitrogen saturated according to certain Scandinavian criteria (Nilsson, 1986). All three sites had much higher outputs than might be expected from the magnitude of the inputs, since conifer forests are normally regarded as being conservative with respect to N. Only at Plynlimon were reductions in dissolved inorganic N flux or concentration observed from bulk precipitation to throughfall and soil waters. At the other two sites, the tree canopies did not assimilate N in incoming rainfall, and active nitrification resulted in high concentrations of nitrate in soil and streamwater. It is proposed that many mature western upland Sitka spruce plantations may behave in a similar manner with respect to dissolved N, in contrast to sites in eastern Scotland where rates of nitrification are slower and nitrogen appears to be less available to plantation trees.     

Modelling and measuring the effect of nitrogen catch crops on the nitrogen supply for succeeding crops

Nitrogen catch crops are grown to absorb nitrogen from the rooting zone during autumn and winter. The uptake of N (N_upt) from the soil inorganic N pool (N_min) to a pool of catch crop nitrogen, will protect the nitrogen against leaching. After incorporation, a fraction (m) of the catch crop nitrogen is mineralized and becomes available again. However, not all available nitrogen present in the soil in the autumn is lost by leaching during winter. A fraction (r) of the nitrogen absorbed by the catch crop would, without a catch crop, have been retained within the rooting zone. The first year nitrogen beneficial effect (N_eff) of a catch crop may then be expressed b N _eff = m*N _upt - r* N _upt The soil-plant simulation model DAISY was evaluated for its ability to simulate the effects of catch crops on spring N_min and N_eff. Based on incubation studies, parameter values were assigned to a number of catch crop materials, and these parameter values were then used to simulate spring Nmin. The model was able to predict much of the vairiation in the measured spring Nmin (r² = 0.48***) and there was good agreement between the measured and the simulated effect of winter precipitation on spring N_min and Neff.Scenarios including variable soil and climate conditions, and variable root depth of the succeeding crop were simulated. It is illustrated that the effect of catch crops on nitrogen availability for the succeeding crop depends strongly on the rooting depth of the succeeding crop. If the succeeding crop is deep rooted and the leaching intensity is low, there is a high risk that a catch crop will have a negative effect on nitrogen availability. The simulations showed that the strategy for the growing of catch crops should be adapted to the actual situation, especially to the expected leaching intensity and to the rooting depth of the succeeding crop.     

铲草和施肥对降香黄檀与印度檀香混交林土壤氮素矿化淋溶的影响

珍贵树种降香黄檀与印度檀香混交种植是当前华南地区人工林发展的一种重要模式.本研究设置对照(不做处理)、铲草、施肥、铲草+施肥4个处理,研究抚育措施对林地土壤净矿化速率、净硝化速率、净铵化速率和氮素淋溶速率的影响.结果表明:4个处理0~10 cm土层在春、秋季有最大净氮矿化速率,分别为18.92、18.13 mg·kg^-1·month^-1;在春、秋季有最大硝化速率,分别为20.35、18.85 mg·kg^-1·month^-1;夏、冬季有最大铵化速率,分别为0.22、0.26 mg·kg^-1·month^-1;秋季的氮素淋溶最严重,为15.98 mg·kg^-1·month^-1,全年最大淋溶为86.69 mg·kg^-1.铲草、施肥、铲草+施肥都在一定程度上抑制了土壤氮的净矿化和硝化速率,铲草、施肥、铲草+施肥处理年氮矿化量分别下降26.2%、16.1%、6.3%,年氮硝化量分别下降17.1%、16.6%、1.4%,同时也抑制了土壤铵态氮的累积.铲草、施肥、铲草+施肥处理全年氮素淋溶量依次减少25.2%、8.6%、6.1%.相对于铲草、施肥、铲草+施肥抚育措施,季节因素对土壤氮素矿化和淋溶过程的影响更显著.铲草、施肥、铲草+施肥措施在一定程度上抑制了土壤氮素硝化和铵化过程,减少了土壤氮素的矿化和淋溶损失量,有利于土壤肥力的保存和氮素的累积.     

Evaluation of a nitrogen leaching/mineralization model for sugar beet

Tests were made of the ability of a leaching/mineralization model to predict the amounts of mineral N in the soil in spring as a step towards estimating the nitrogen fertilizer requirement of sugar-beet crops. There was good agreement between predicted and measured values, both under conditions of natural winter rainfall and when the soil was covered to prevent leaching. The model also successfully predicted leaching losses of soil mineral N soon after drilling in a year in which early season irrigation and heavy rain induced considerable leaching.     

Changes in soil mineral nitrogen during and after 3-year and 5-year set-aside and nitrate leaching losses after ploughing out the 5-year plant covers in the UK

The management and effects of 3-year and 5-year set-aside covers on soil mineral nitrogen (SMN, 0.0–0.9 m) were studied at six sites in England. Soil mineral N was measured annually in autumn and spring during the period of set-aside cover, with more frequent SMN sampling over the first winter after ploughing out the covers. Spring SMN was measured in the second year after set-aside. Nitrate leaching losses were also measured at three sites in the first winter after destruction of the 5-year set-aside covers. Winter cereals were grown in both test years after each set-aside period.Amounts of both autumn and spring SMN in the perennial rye-grass (PRG), perennial rye-grass/white clover (PRG/WC) and natural regeneration (NR) covers were generally less than, or similar to those in the continuous arable treatment during each year of set-aside, indicating a slightly smaller nitrate leaching risk under set-aside management. Slight increases in autumn SMN, and hence leaching potential were, however, observed under PRG/WC in the fourth and fifth years, compared with continuous arable cropping.Ploughing out of both 3-year and 5-year covers increased soil N supply and potential nitrate leaching losses over winter, compared with continuous arable cropping. By the following spring, mean increases across all sites in amounts of SMN after 3-year covers of PRG, NR and PRG/WC were 14, 18 and 33 kg ha^–1 N, respectively, compared with the arable rotation. Equivalent increases in spring SMN following destruction of the 5-year set-aside covers were almost identical, at 17, 19 and 33 kg ha^–1, respectively, although only the ploughed-out PRG/WC covers increased SMN at the clay sites. Measured nitrate leaching losses in the first winter after 5-year set-aside were greatest after PRG/WC at two sites on shallow chalk but greatest after NR, which had a naturally large clover content, at the third site which was on a sandy soil. However, the leaching losses after set-aside were relatively small, relative to typical losses after ploughing out intensively managed grass or grass/clover swards, and would have been compensated for by potentially less leaching during set-aside.Spring SMN measurements in the second year after ploughing out the set-aside covers, showed negligible or, for PRG/WC, only slight increases (12 – 18 kg ha^–1) in residual soil N supply after both 3-year and 5-year covers, compared to continuous arable cropping. The extra N mineralisation after cover destruction justified small reductions in fertiliser N inputs for the first, but not second crop following either 3- or 5-year set-aside, unless the cover had contained a large clover content. Both 3-year and 5-year set-aside covers had minimal or no effect on either organic matter content, apart from a slight increase in the PRG/WC treatments, or extractable phosphorus, potassium and magnesium status in the topsoil.     

Physical and biogeochemical controls over terrestrial ecosystem responses to nitrogen deposition

Anthropogenic perturbations to the global nitrogen (N) cycle nowexceed those to any other major biogeochemical cycle on Earth, yet ourability to predict how ecosystems will respond to the rapidly changing Ncycle is still poor. While northern temperate forest ecosystems haveseen the greatest changes in N inputs from the atmosphere, other biomes,notably semi-arid and tropical regions of the globe, are nowexperiencing increases in N deposition. These systems are even less wellunderstood than temperate forests, and are likely to respond to excess Nin markedly different ways. Here, we present a new integratedterrestrial biophysics-biogeochemical process model, TerraFlux, and usethis model to test the relative importance of factors that may stronglyinfluence the productivity response of both humid tropical and semi-aridsystems to anthropogenic N deposition. These include hydrological lossesof dissolved inorganic and organic N, as well as multiple nutrientinteractions with deposited inorganic N along the hydrological pathway.Our results suggest that N-rich tropical forests may have reducedproductivity following excess N deposition. Our simulations of semi-aridsystems show increases in productivity following N inputs if wateravailability is sufficient and water losses are moderate. The mostimportant model controls over the carbon cycle response in eachsimulation were interactions that are not represented in the most commonterrestrial ecosystem models. These include parameters that control soilsolute transport and nutrient resorption by plants. Rather than attemptprognostic simulations, we use TerraFlux to highlight a variety ofecological and biogeochemical processes that are poorly understood butwhich appear central to understanding ecosystem response to excessN.     

Uptake and leaching of nitrogen from artificial urine applied to grassland on different dates during the growing season

Artificial urine, equivalent to 30 g N m^-2, was applied to replicated plots in a perennial ryegrass (Lolium perenne L.) sward, each plot receiving a single application on one of six dates between July and November 1990. Recoveries of urine-N in herbage up to the end of the growing season in November decreased linearly for consecutive application dates, ranging from 40% of the urine-N applied in July to a negligible proportion of the final application. In contrast, contents of urine-derived N remaining in the soil (to 1-m depth) in November increased from 3% of the N applied in July to 66% for the final application. Almost all of this was present as nitrate + nitrite-N. Only soils that had received urine in September or later contained significantly greater quatities of mineral-N than the control plots. The mineral-N content of soils collected the following April indicated that most of this urine-derived N had been lost from the soil over the winter. Estimates of the quantities of N leached ranged from 0.7 g N m^-2 from untreated plots to 18.6 g N m^-2 from plots treated with urine in November. Although grass yields and N uptakes in March and April provided evidence of a residual effect from the previous year's urine applications, contents of mineral-N and of potentially mineralisable N in urine-treated soils in April were not significantly different from those in untreated soils.     

降水变化对科尔沁沙地樟子松人工林土壤氮矿化和淋溶的影响

为研究降水量减少对沙地森林土壤氮循环过程的影响,以科尔沁沙地15年生樟子松人工林为研究对象,野外模拟不同降水量（自然降水、减少30%和50%）对沙地樟子松人工林土壤无机氮（SIN）含量、氮矿化速率和淋溶动态的影响。研究结果发现,沙地樟子松人工林SIN主要以硝态氮形态存在,模拟降水减少降低土壤硝态氮含量（P<0.05）和硝态氮/SIN值（P<0.001）,而增加土壤铵态氮含量（P<0.05）。与自然降水相比,降水减少降低土壤净硝化速率和净矿化速率（P=0.002）,但不同降雨处理的土壤净氨化速率差异不显著（P=0.86）。科尔沁沙地樟子松人工林土壤以硝态氮淋溶为主,不同降雨处理土壤硝态氮淋溶量差异不显著（P=0.09）,但模拟降水减少降低土壤铵态氮淋溶（P=0.04）。此外,沙地樟子松人工林SIN含量、净氮矿化速率和淋溶量具有明显月动态特征,与降雨月动态规律基本一致。降水处理和采样时间对SIN含量和净氮矿化速率具有显著交互作用,但土壤氮淋溶量的交互作用不显著。可见,降水变化能够显著影响科尔沁沙地樟子松人工林土壤氮有效性、氮矿化速率和淋溶等过程,未来干旱加剧可能降低科尔沁沙地樟子松人工林土壤氮的可利用性。     

Simulated and measured nitrogen conditions in a manured and fertilised soil

The governing factors for soil nitrogen dynamics were identified with a simulation model. In addition, the model was used to interpret measurements from a plot fertilisation experiment in southwest Sweden.Simulated moisture and temperature conditions were the driving variables for the simulation of soil nitrogen dynamics and leaching during a 6-year period. The results of the simulation were compared with monthly observations on two plots with grain crops, one with liquid manure and commercial fertilisers applied and one with commercial fertilisers only.Simulated temporal variations of the nitrate and ammonium storages generally agreed with observations. The dominant role of the crops as a determinant of soil nitrogen conditions was demonstrated. A higher leaching loss from the plot with application of commerical fertilisers only occurred both in simulations and measurements compared to the plot with application of both commercial fertilisers and manure. The main reason was the higher N-application in the former treatment.The effect of water flows in macropores was interpreted as a delay of simulated leaching compared to observed leaching on some occasions in summer and early autumn. No direct effect of the macropores on the yearly rates of leaching could be seen.