关中地区小麦/玉米轮作农田硝态氮淋溶特点

通过田间原位淋溶装置研究了不同施氮量和秸秆覆盖对关中地区小麦/玉米轮作农田90cm深处硝态氮(NO3--N)淋溶量、0～1m土层硝态氮累积及作物产量和氮平衡的影响.试验设不施氮(N1,0kg·hm-2·a-1)、常规施氮(N2,471kg·hm-2·a-1)、推荐施氮(N3,330kg·hm-2·a-1)、减量施氮(N4,165kg·hm-2·a-1)、增量施氮(N5,495kg·hm-2·a-1)和推荐施氮+秸秆覆盖(N3+S)6个不同施肥处理.结果表明:NO3--N淋溶量随施氮量的增加而增大,氮肥的过量施用及秸秆覆盖易造成NO3--N淋溶.N3+S处理90cm处年NO3--N流失量最大,为22.32kg·hm-2,施肥造成的氮流失量为16.44kg·hm-2,比相同施氮量不覆盖处理(N3)高158.9%.NO3--N主要累积在20～60cm土层,年施氮量330kg·hm-2(N3)时,秸秆覆盖与否不影响NO3--N的剖面分布.各施肥处理对作物产量没有显著影响,但减量施氮处理(N4)有减少作物产量的趋势.在本试验条件下,推荐施肥量(小麦施氮150kg·hm-2,玉米施氮180kg·hm-2)在保证作物产量的同时,可减少土壤NO3--N的淋溶和累积.     

不同施肥条件下玉米田土壤养分淋溶规律的原位研究

利用排水采集器法结合田间原位试验,研究了夏玉米不同施肥处理对棕壤土养分淋失的影响.结果表明:在夏玉米生长期内,影响玉米田土壤水分淋溶的主要因素是大量降雨和灌溉,夏玉米生长前期的土壤淋溶水量较大,但随夏玉米生育进程的推进而递减,各处理差异也逐渐减小;与施氮肥处理相比,秸秆还田配施氮肥处理可加剧土壤水淋溶.在夏玉米生长期内,施肥处理的土壤淋溶水硝态氮浓度均呈"双峰"曲线变化趋势,而铵态氮浓度则呈先升后降的变化趋势.玉米田土壤氮素淋失以硝态氮形式为主,其累计淋失量为12.90～46.53 kg·hm-2,铵态氮的累计淋仅为1.66～5.11 kg·hm-2,两种形态氮的淋失量都随施氮量的增加而升高.秸秆还田配施氮肥处理的氮素淋失率比单施氮肥处理高6.53%～13.07%,低氮处理的氮素淋失率比高氮处理高3.66%～10.10%;玉米田土壤速效磷的累计淋失量较小,仅为0.148～0.235 kg·hm-2,而速效钾的累计淋失量较大,为7.08～13.00 kg·hm-2.在夏玉米生长后期,秸秆还田配施氮肥处理使土壤速效磷淋失量升高,并可加剧土壤速效钾的淋失,而单施氮肥处理作用不明显.     

不同施肥对雷竹林径流及渗漏水中氮形态流失的影响

雷竹经营过程中化肥的大量施用,是产区水体污染的主要原因之一,养分管理技术可有效控制面源污染。为了探明减量施肥和有机肥施用对雷竹不同氮形态流失的影响,2012年在浙江省临安市雷竹产区设置了4种施肥处理:对照(CK);常规施肥(CF);减量无机(DI);减量有机无机(DOI),试验于5月18日、9月7日、11月9日分别施用肥料总量的40%,30%和30%,施肥后均进行浅翻,深度5 cm左右。通过建立径流场和土壤渗漏水收集装置,同时在试验田附近布置量雨筒,观察2012年不同氮形态浓度及流失负荷随降雨量的动态变化。研究结果表明:不同施肥处理径流水硝态氮、水溶性有机氮(WSON)以及颗粒态氮的浓度分别在3.82-6.82 mg/L、0.89-1.85 mg/L和0.89-1.83 mg/L,其占总氮的百分比分别为60.9%-68.2%、16.0%-18.1%和15.1%-21.6%。不同施肥处理渗漏水中硝态氮、铵态氮及WSON的浓度分别在26.2-92.5 mg/L、0.50-6.42 mg/L和6.57-12.6 mg/L,其占总氮的百分比分别为75.8%-82.9%、1.50%-6.36%和11.2%-20.6%。不同施肥处理径流水的氮总流失负荷,减量无机和减量有机无机相对于常规施肥来说减少了46.9%和23.1%;不同施肥处理的渗漏水的氮总流失负荷,减量无机和减量有机无机相对于常规施肥来说减少了19.1%和52.1%,可见减量施肥和减量有机无机减少氮流失的效果显著。     

长期施用有机物料下黑土氮素有效性及其与作物产量的关系

利用长期定位施肥试验,于2011年采样研究长期施用不同有机物料(秸秆、有机肥)对东北黑土氮素有效性的影响,并分析氮供应与作物生物量及产量的关系.结果表明:化肥配施有机肥、化肥配施低量秸秆均可显著提高黑土农田土壤无机氮和硝态氮含量,进而提高作物产量;尽管化肥配施高量秸秆提高了土壤氮矿化速率,但可能由于硝态氮淋溶或者其他形式的氮素损失或转化,与化肥配施低量秸秆处理相比,化肥配施高量秸秆下土壤无机氮量并没有增加.可见,适量施用有机物料对提高土壤氮素有效性、提高作物产量及保护环境具有重要意义.     

太湖地区绿肥还田模式下氮肥的深度减量效应

通过绿肥还团条件下免施基肥的氮肥深度减量试验,研究了稻季田面水氮素含量、氮素径流损失及水稻产量的变化.结果表明:在太湖地区绿肥还田模式下,追施150 kg·hm-2无机氮,与施基肥相比,不施基肥可以大大降低田面水的氮素浓度,减少了17.2％的氮素径流流失,且作物产量提高了2.8％.无机氮肥仅作追肥的施肥方式是可行的,但过量减施或增施无机氮肥均不能获得最高的产量.在太湖地区尝试紫云英还田条件下免施基肥,同时补充133kg·hm-2无机氮作追肥,既可以大大减少无机肥的投入、保证水稻产量,也可以减少稻田氮素的排放量,实现水稻产量效应和环境效应的协调.     

小流域内植被类型对土壤NO3-/NH4+空间变化的影响

流域内植被类型、地形地貌特征对土壤氮循环过程有重要的作用,是影响下游水体无机氮素来源以及富营养化的关键因子。通过比较小流域内4种植被类型(落叶松人工林、油松人工林、天然阔叶次生林和农田(玉米))对土壤NO3--N和NH4+-N含量空间变化的影响,揭示流域内不同立地条件下水源涵养林与土壤无机氮变化特征之间的关系。结果表明:4种植被类型土壤NO3--N和NH4+-N含量差异显著(P<0.05);由坡上到坡下土壤NO3--N和NH4+-N含量显著降低;在土壤表层NO3--N和NH4+-N含量最高,随着土层深度增加无机氮含量减少;与水源涵养林天然植被和人工林植被相比,农田土壤NO3--N含量最高(11.86mg·kg-1),有较高的氮流失风险。     

氮肥种类及运筹技术调控土壤氮素损失的研究进展

氮肥的不合理施用导致氮肥利用率低下,大量氮素通过径流、淋溶、氨挥发、硝化-反硝化作用等途径损失到环境中,从而对水体、大气造成污染,带来严重的环境问题,影响人类健康.施氮量、施肥时间和方式,以及肥料种类对氮素流失量的影响显著.土壤氮素浓度过饱和是导致氮素大量流失的最根本原因,充分利用环境供氮量,减少化学氮肥施用量,采用深施等技术,以及配合施用有机肥,可以有效降低氮素的损失,提高氮素利用率.在开发应用新型高效氮肥和强化氮肥高效管理技术研究的同时,加强环境氮素的监测和利用力度,是实现减氮增效的有力手段.     

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.     

施肥措施对河套灌区氮素淋溶和玉米产量的影响

为了解不同施肥措施对氮素淋溶风险的影响,为河套地区基础农田的化肥面源污染防治提供参考,本试验采用田间原位渗漏计法,对河套灌区盐化潮土玉米季连续2年氮素淋溶状况进行监测,研究5种不同施肥措施(不施肥(NF)、农民常规施肥(CK)、农民常规施肥+膨润土(B)、农民常规施肥+生物炭(C)、农民常规施肥+有机肥(F))对氮素淋溶及玉米产量的影响。结果表明:B、C处理下淋溶水总量均较低,比CK平均分别减少了16.4%、15.9%,F处理淋溶水量相对较高;在氮素养分淋溶损失中,硝态氮、铵态氮浓度均在第二次灌水后出现了峰值,B、C处理峰值较低,F处理稍高;除NF外,B处理的无机氮累积淋溶量最低,平均为65 kg·hm~(-2),比CK处理下降了41. 3%; C、F处理依次为73. 4kg·hm~(-2)、96.4 kg·hm~(-2),分别比CK下降了33.7%、12.9%。淋溶水中全氮、可溶性总氮的淋溶量大小顺序均为NF B C F CK; B、C、F的表观淋溶率平均分别为15.3%、16.5%,18.5%,均低于CK处理的25.5%; F、B、C处理的玉米产量显著高于CK(P0.05),其增产率依次为9.8%、8.4%、6.6%,且2年各处理表现出增产的趋势。考虑到F处理下氮素淋溶损失量较大,而膨润土、生物炭有效地抑制了氮素的淋溶损失,提高了氮肥利用率,在一定程度上减少了河套灌区化肥面源污染,故B处理推广施用的可行性较大,C处理次之。     

退化设施蔬菜地修复过程中土壤可溶性有机碳与无机氮动态

土壤强还原处理(reductive soil disinfestation,RSD)可以有效修复退化设施蔬菜地土壤,但实施过程中亦会存在可溶性有机碳(DOC)与无机氮(NO3--N和NH4+-N)的淋溶风险。本研究选用水稻秸秆及其制备的生物质炭(biochar,BC)作为修复材料,采用BC、RSD以及RSD+BC三种方法修复退化蔬菜地土壤,探究修复过程中土壤基本性质、DOC与无机氮的动态变化。结果表明,与对照土壤相比,BC处理显著提高了土壤pH、EC和DOC含量(P<0.05),但对土壤NO3--N和NH4+-N无显著影响。对于RSD和RSD+BC处理,土壤NO3--N含量在1~3 d内快速下降,之后维持在较低水平;土壤DOC含量呈先上升后下降趋势,在整个培养时段均显著高于对照处理(P<0.05)。方差分析表明,BC与RSD处理对土壤DOC、全碳(TC)、全氮(TN)和C/N存在交互作用。可见,RSD和RSD+BC处理能有效去除NO3--N,但DOC含量大幅度增加,存在淋溶风险。     

Inorganic Nitrogen Leaching from Organic and Conventional Rice Production on a Newly Claimed Calciustoll in Central Asia

Characterizing the dynamics of nitrogen (N) leaching from organic and conventional paddy fields is necessary to optimize fertilization and to evaluate the impact of these contrasting farming systems on water bodies. We assessed N leaching in organic versus conventional rice production systems of the Ili River Valley, a representative aquatic ecosystem of Central Asia. The N leaching and overall performance of these systems were measured during 2009, using a randomized block experiment with five treatments. PVC pipes were installed at soil depths of 50 and 180 cm to collect percolation water from flooded organic and conventional paddies, and inorganic N (NH₄-N+NO₃-N) was analyzed. Two high-concentration peaks of NH₄-N were observed in all treatments: one during early tillering and a second during flowering. A third peak at the mid-tillering stage was observed only under conventional fertilization. NO₃-N concentrations were highest at transplant and then declined until harvest. At the 50 cm soil depth, NO₃-N concentration was 21–42% higher than NH₄-N in percolation water from organic paddies, while NH₄-N and NO₃-N concentrations were similar for the conventional and control treatments. At the depth of 180 cm, NH₄-N and NO₃-N were the predominant inorganic N for organic and conventional paddies, respectively. Inorganic N concentrations decreased with soil depth, but this attenuation was more marked in organic than in conventional paddies. Conventional paddies leached a higher percentage of applied N (0.78%) than did organic treatments (0.32–0.60%), but the two farming systems leached a similar amount of inorganic N per unit yield (0.21–0.34 kg N Mg⁻¹ rice grains). Conventional production showed higher N utilization efficiency compared to fertilized organic treatments. These results suggest that organic rice production in the Ili River Valley is unlikely to reduce inorganic N leaching, if high crop yields similar to conventional rice production are to be maintained.     

Nitrogen fate and environmental consequence in paddy soil under rice-wheat rotation in the Taihu lake region, China

Field undisturbed tension-free monolith lysimeters and ¹⁵N-labeled urea were used to investigate the fate of fertilizer nitrogen in paddy soil in the Taihu Lake region under a summer rice-winter wheat rotation system. We determined nitrogen recovered by rice and wheat, N remained in soil, and the losses of reactive N (i.e., NH₃, N₂O, NO₃ ^?, organic N and NH₄ ⁺) to the environment. Quantitative allocation of nitrogen fate varied for the rice and wheat growing seasons. At the conventional application rate of 550 kg N ha^?1 y^?1 (250 kg N ha^?1 for wheat and 300 kg N ha^?1 for rice), nitrogen recovery of wheat and rice were 49% and 41%, respectively. The retention of fertilizer N in soil at harvest accounted for 29% in the wheat season and for 22% in the rice season. N losses through NH₃ volatilization from flooded rice paddy was 12%, far greater than that in the wheat season (less than 1%), while N leaching and runoff comprised only 0.3% in the rice season and 5% in the wheat season. Direct N₂O emission was 0.12% for the rice season and 0.14% for the wheat season. The results also showed that some dissolved organic N (DON) were leached in both crop seasons. For the wheat season, DON contributed 40–72% to the N- leaching, in the rice season leached DON was 64–77% of the total N leaching. With increasing fertilizer application rate, NH₃ volatilization in the rice season increased proportionally more than the fertilizer increase, N leaching in the wheat season was proportional to the increase of fertilizer rate, while N₂O emission increased less in proportion than fertilizer increase both in the rice season and wheat season.     

Effects of forest fertilization on nitrogen leaching and soil microbial properties in the Northern Calcareous Alps of Austria

Several boreal and alpine forests are depleted in nutrients due to acidification. Fertilization may be a remedy, but rapidly-soluble salts (N, P, K, Mg) may pose nitrate problems for the groundwater or decrease microbial activity.With the aim to investigate potential nitrogen leaching after fertilization we set up an experiment employing intact soil cores (11 cm diameter, 20–40 cm long) from a mixed forest and a Picea abies stand (soil type Rendsina) in the Northern Calcareous Alps of Austria. The cores were fertilized with a commercial NPK fertilizer or a methylene-urea-apatite-biotite (MuAB) fertilizer at a rate corresponding to 300 kg N ha^-1 and incubated for 28 weeks together with unfertilized controls. Both soil water (retrieved 5 cm below the soil surface) and leachate were analyzed for nitrate and ammonium in regular intervals. After the incubation, soil microbial biomass and basal repiration were determined and a nitrogen mineralization assay was performed.For the control, in the soil water and leachate maximum NH₄ ⁺ and NO₃ ^- concentrations of 5 and 11 mg N L^-1, respectively, were found. Compared to that, MuAB fertilizer resulted in a slow increase of NH₄ ⁺ and NO₃ ^- in the soil water (up to 11 and 35 mg N L^-1 respectively) and in the leachate (4 mg NH₄ ⁺-N L^-1 and 44 mg NO₃ ^--N L^-1). Highest nitrogen loads were found for the fast release NPK fertilizer, with NH₄ ⁺ and NO₃ ^- concentrations up to 170 and 270 mg N L^-1, respectively, in the soil water. NH₄ ⁺-N levels in the leachate remained below 5, while NO₃-N levels were up to 190 mg L^-1. Fast- release NPK caused a significant decrease of microbial biomass and basal respiration. These parameters were not affected by MuAB fertilizer.The results suggest that the MuAB fertilizer may be an ecologically appropriate alternative to fast-release mineral fertilizers for improving forest soils.     

Fate of urine nitrogen on mineral and peat soils in New Zealand

A field lysimeter experiment was conducted over 150 days to examine the fate of synthetic urinary nitrogen (N) applied to peat and mineral soils, with and without a water table. At the start of the winter season, synthetic urine labelled with ¹⁵N, was applied at 500 kg N ha^–1. Plant uptake, leaching losses and nitrous oxide (N₂O) fluxes were monitored. Total plant uptake ranged from 11% to 35% of the urine-N applied depending on soil type and treatment. Plant uptake of applied N was greater in the presence of a water table in the mineral soil. Nitrate-N (NO₃ ^--N) was only detected in leachates from the mineral soil, at concentrations up to 146 g NO₃ ^--N mL^–1. Presence of a water table in the mineral soil reduced leaching losses (as inorganic-N) from 47% to 6%, incrased plant uptake and doubled apparent denitrification losses. In the peat soils leaching losses of applied urine-N as inorganic-N were low (<5%). Losses of N as N₂O were greater in the mineral soil than in the peat soils, with losses of 3% and <1% of N applied respectively after 100 days. Apparent denitrification losses far exceeded N₂O losses and it is postulated that the difference could be due to dinitrogen (N₂) loss and soil entrapment of N₂.     

滇池流域退耕区植物群落构建对地表径流污染物的削减效应

为探索不同群落的构建在滇池流域的实际应用,以确定削减污染物最优植物群落的配置方式,该研究选取地表径流悬浮物(SS)、COD含量、总氮(TN)、总磷(TP)、氨氮(NH_4~+-N)、硝氮(NO_3~--N)六个指标作为主要的分析对象,在滇池流域退耕区开展了不同植物群落配置对地表径流污染物削减效应的试验研究。结果表明:三个植物群落对SS、COD、TN、TP、NO_3~--N在2014年和2015年间均表现出显著性的削减趋势,且三个植物群落对SS、TP和NO_3~--N的削减率均在45%以上,但并未对NH_4~+-N表现出削减效果。不同植物群落对污染物的削减效应存在一定的差异性,但是三个不同群落与年度的交互作用对SS、COD、TN、TP、NO_3~--N五个养分指标的削减并没有表现出显著的差异性。从整体上来看,三种植物群落类型中,以乔-灌-草构建的立体式植物群落对地表径流污染物的削减效果最佳。     

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。     

不同近地表土壤水文条件下雨滴打击对黑土坡面养分流失的影响

目前,土壤水分饱和和壤中流条件下,雨滴打击对养分流失的影响尚不清楚.通过3个近地表土壤水文条件(自由入渗、土壤水分饱和与壤中流)下,土槽上方架设与不架设尼龙纱网模拟降雨对比试验,研究雨滴打击对黑土坡面侵蚀过程及NO3-N、NH4-N与PO4-P随径流和侵蚀泥沙迁移的影响.结果表明,纱网覆盖消除雨滴打击后坡面侵蚀量和泥沙浓度分别减少59.4％-71.6％和57.3％ -73.0％,不同水文条件下减少量的排序为:自由入渗＞壤中流＞土壤水分饱和.消除雨滴打击后养分随径流流失的减少仅在自由入渗条件下体现较明显,该水文条件下NO3-N、NH4-N与PO4-P流失分别减少33.3％、23.1％和40.7％;3种水文条件下,消除雨滴打击均明显减少养分随泥沙的流失,其中自由人渗条件下减少效果最明显,该水文条件下,NO3-N和NH4-N流失分别减少20.9％ -54.9％和25.0％ -62.3％,而PO4-P流失减少在74.6％以上.雨滴打击增大了NO3-N的淋失,但对NH4-N与PO4-P的淋失几乎无影响.消除雨滴打击后,自由人渗条件下养分的等效径流迁移深度减少26.7％-42.6％,而土壤水分饱和与壤中流条件下基本无变化.以上研究结果为有效防治坡面土壤侵蚀和农业非点源污染提供科学理论依据,尤其是在壤中流出现的地方.     

秸秆和地膜覆盖对渭北旱作玉米农田土壤氮组分与产量的影响

基于田间定位试验,研究了秸秆和地膜覆盖措施对旱作春玉米田土壤氮组分和作物产量的影响。试验包括无覆盖对照,秸秆覆盖和地膜覆盖3个处理,观测指标包括土壤全氮(STN)、颗粒有机氮(PON)、潜在可矿化氮(PNM)、微生物量氮(MBN)、硝态氮(NO_3~--N)、铵态氮(NH_4~+-N)含量及作物产量。结果表明:试验进行5到7年后,与对照相比,秸秆覆盖处理0—10 cm土层STN、PON、PNM、MBN和NO_3~--N含量3年平均分别提高了13.11%、64.29%、17.51%、16.94%和55.37%,10—20 cm土层STN、PON、MBN和NO_3~--N含量3年平均分别提高了5.93%、33.33%、15.78%和27.57%(P0.05)。而地膜覆盖处理0—10 cm和10—20 cm土层NO_3~--N的含量较对照分别提高了189.14%和135.75%(P0.05),其他氮组分与对照处理差异不显著。秸秆和地膜覆盖处理玉米产量较对照处理3年平均分别提高了6.90%和36.74%(P0.05)。玉米产量与0—20 cm土层NO_3~--N含量和NO_3~--N/STN值呈显著正相关关系。总的来看,秸秆覆盖能显著增加旱地土壤全氮和活性有机氮含量,促进氮素固定,但需注意作物生长后期补充氮肥以满足作物生长需要。而地膜覆盖能显著提高土壤氮素有效性和作物产量,但不利于土壤有机氮的固定,且表层土壤存在潜在氮淋失风险。     

典型农作措施对沙溪庙组壤质紫色土坡耕地径流氮流失的影响

明确典型农作措施对紫色土坡耕地径流氮(N)流失的影响可为优化面源污染防控措施提供科学依据。基于2019—2021年沙溪庙组发育的壤质紫色土坡耕地不同降雨等级次降雨产流事件,分析了常规施肥(CK),优化施肥(T1)和优化施肥+秸秆还田(T2)措施下径流、径流中总氮(TN)、硝态氮(NO₃-N)及铵态氮(NH₄-N)流失浓度和流失量的变化特征。结果表明,与CK相比,T1和T2的径流深分别减小了4.24%、12.71%,但减小程度不显著(P>0.05);CK与T1的径流系数相等,且比T2增加了12.5%(P>0.05);相比CK,T1和T2的TN浓度增加了19.35%、25.8%(P>0.05),TN流失量则均增加了11.54%(P>0.05),表明T1和T2的施用也有增加土壤N流失的潜在风险。与中雨、大雨和大暴雨事件相比,暴雨事件的径流深分别增加了6.5%—191.11%(P<0.05),而TN、NO₃-N及NH₄-N的流失量分别增加106.38%—177.14%(P>...