Suspending Nitrogen Fertilization Reduces Residual Soil Nitrates in Dryland Cotton

Nitrogen (N) fertilizer use in cotton (Gossypium hirsutum L.) production is a potential source of nitrate (NO₃ ^?) contamination of soils, groundwater, and streams. The McConnell–Mitchell plots, a long-term study of cotton responses to N-fertilization and irrigation methods, were utilized to determine the NO₃ ^?-N in soil cropped to continuous cotton. The McConnell–Mitchell plots had a split-block experiential design. The main blocks of this test were irrigation methods. Each block of plots was irrigated using a single irrigation method for the entirety of the testing. Nitrogen fertilization rates were tested within each irrigation block. The soil NO₃ ^?-N content of two irrigation blocks, furrow flow (FI) and center pivot (CP), were compared to the dryland (DL) control block. Nitrogen treatments tested within each irrigation block ranged from 0 to 168.0 kg N ha^?1 in 33.6-kg N ha^?1 increments. Nitrogen treatments were tested for 18 years (1982 through 1999), discontinued for 4 years (2000 through 2003), and resumed in 2004. Soil samples were taken in the early spring (2000 and 2004) to a depth of 1.50 m in 0.15 m increments and analyzed for NO₃ ^?-N. Soil samples taken in 2004 were prior to any fertilization treatment. Irrigation method was found to influence the distribution of soil NO₃ ^?-N. Little accumulation of soil NO₃ ^?-N was observed in either irrigation block or under dryland production when N rates were less than 67.2 kg N ha^?1. Distribution of soil NO₃ ^?-N in the FI block was significantly different with sample depth and N treatment but not the interaction of depth and treatment in both 2000 and 2004. Presumably, the small and close values of the means and the greater variability of interactions compared to main effects precluded significant interactions. Differences in soil NO₃ ^?-N in the FI block after suspending N treatments for 4 years were similar to those found in 2000, although the soil NO₃ ^?-N was generally depleted in 2004 compared to 2000. The distribution of soil NO₃ ^?-N in the CP-irrigated block was dependent on the interaction of sample depth with N treatment in both 2000 and 2004. Soil NO₃ ^?-N values and differences tended to be too small to be of discernable or practical importance under CP irrigation. The distribution of soil NO₃ ^?-N in the DL block was dependent on the interaction of sample depth with N treatment in 2000 and 2004. Soil NO₃ ^?-N was minimal in the three lowest N treatments (0, 33.6, and 67.2 kg N ha^?1) in 2000. Greatest amounts of soil NO₃ ^?-N were found in conjunction with the 134.4 and 168.0 kg N ha^?1 treatments both years. Depletion of soil NO₃ ^?-N was evident in the surface 0.45 m of the 100.8, 134.4, and 168.0 kg N ha^?1 treatments under DL conditions in 2004.     

Irrigation and Nitrogen Fertilization Effects on Soil Chemical Properties and Cotton Yield

A 2-year field experiment was conducted in central Greece (Platykampos, Larissa) to investigate productivity parameters of cotton under conditions of water stress. A Latin square split-plot design with three replications was used to evaluate the effect of three irrigation levels (250, 350, and 450 mm) and three fertilization rates (60, 110, and 160 kg N ha^–1), where irrigation level was the whole-plot factor and the fertilizer was the split-plot factor. The results showed that irrigation level had no significant effect on soil chemical properties, but these only changed with fertilizer application. Concentration of soil nitrates increased in proportion to the amount of applied fertilizer in early July. The associated rise in electrical conductivity (EC) was not sufficiently high as to adversely affect salt-tolerant cotton. The soil acidity produced during formation of nitrate was evident by a soil pH decrease of 0.2 units in the high fertilizer application. A great decline of nitrate N and EC and a rise of pH in all treatments in early August indicated rapid N uptake by the crop during the late stage of vegetative growth. In contrast, cotton yield was not affected by the rate of fertilizer application but by the level of irrigation. This is the reason that correlations between soil properties and yield were insignificant in early July and August. It appears that there was sufficient N available to the crop from sources other than fertilizer N (soil-derived N and irrigation N). Preplant soil nitrates were greater than residual nitrates in the second growing season and indicated depletion of soil mineral N pools of the order of 36 kg N ha^–1 in the 0- to 25-cm depth. Significant negative correlations between soil properties and cotton yield appeared only at the end of the season and indicated that depletion of soil mineral N increased with increasing crop N requirement or irrigation level.     

不同施氮量对棉花产量和棉田土壤养分的影响

为探讨连续定位试验条件下不同施氮水平对棉花产量和棉田土壤养分含量及养分利用效率的影响,于2018—2020年连续3年在阿拉尔开展田间试验,设置6个纯氮处理:0(N0)、90(N1)、180(N2)、270(N3)、360(N4)、450 kg·hm^-2(N5),研究了定点定量施氮对棉花土壤有机质、全氮、速效养分、植株干物重及含氮量、产量和氮肥利用效率的影响。结果表明,各处理土壤有机质、全氮及速效养分含量均随土层加深而减少。随施氮水平的提高,收获期棉田0~60 cm各土层土壤有机质含量基本无显著差异,全氮、碱解氮含量整体表现为N0、N1和N2处理低于N3、N4和N5处理,速效磷含量变化则反之;不同年限处理间速效钾含量基本以N3处理最低,至2020年N3处理0~60 cm土层速效钾平均含量较其他处理低23.49%~51.13%。棉花地上部单株干物重和单株含氮量均以棉铃占比最高,不同处理分别为59.04%~62.91%和56.48%~65.16%。各处理地上部单株干物重、单株含氮量、皮棉产量和氮肥表观利用率均随施氮量的增加呈先增后降的趋势,且均在N3处理达到最大,试验年内N3处理平均单株干物重和单株含氮量分别为117.25和1.96 g,皮棉产量2 419.39 kg·hm^-2,较其他处理分别高出29.75%、14.32%、8.18%、8.54%和10.21%,氮肥表观利用率也最高,为47.26%。因此,综合考虑产量及氮肥利用效率,推荐南疆阿拉尔地区棉花氮肥适宜用量为270 kg·hm^-2。在此施用量下可获得棉花高产,并减少收获期土壤养分残留。本研究结果为棉花精准施肥提供了理论依据。     

滴灌条件下秸秆覆盖与施肥对夏玉米水肥利用效率的影响

为探索秸秆覆盖与滴灌施肥结合栽培模式下夏玉米水肥利用效率和增产效果,于2014—2015年在北京市大兴区进行无施肥覆盖(T1)、无施肥不覆盖(T2)、中肥覆盖(T3)、中肥不覆盖(T4)、高肥覆盖(T5)和高肥不覆盖(T6)6种试验。结果表明:表层土壤温度和气温具有高度线性相关关系,秸秆覆盖可降低夏玉米生长季土壤温度的增温速率,T1、T3和T5较T2、T4和T6处理的土壤增温速率分别降低23.62%,13.65%和11.47%,全生育期秸秆覆盖较不覆盖日均土壤温度平均降低1.75℃;滴灌条件下秸秆覆盖影响0—60cm土层的水分分布变化,对0—20cm土层土壤含水率保水效果明显,2014年秸秆覆盖较不覆盖土壤含水率平均提高11.73%,2015年平均提高9.56%;秸秆覆盖下E/ET较不覆盖平均减少6.99%,生育期内抽雄—灌浆阶段夏玉米耗水强度最高;2年试验T3获得籽粒产量最高,较T2提高27.62%,较T6提高15.83%,同时水分利用效率和肥料偏生产力表现最优,分别为23.73kg/(hm2·mm)和40.33kg/kg。本研究表明滴灌条件下中肥覆盖对表层土壤具有降低增温速率的效应,起到增产的同时对提高水分利用效率和肥料偏生产力的作用较优。     

减氮和秸秆还田对旱地土壤微生物和硝化潜势的影响

通过3年田间试验,研究减氮和秸秆还田对黄土高原南部旱地春玉米产量、硝态氮残留量及微生物学特性等指标的影响。研究共设置不施肥（CK）、传统施氮（N250）、传统施氮配合秸秆还田（N250+S）、减氮20%（N200）、减氮20%配合秸秆还田（N200+S）5个处理。结果表明：（1）连续3年减氮20%和秸秆还田可以提高玉米产量,阻控土壤硝态氮淋溶,N200较N250处理玉米增产5.9%,N200+S较N200处理玉米增产7.4%,N250+S较N250处理玉米增产9.1%;0－300 cm土层,N200较N250处理硝态氮残留量减少51.3%,N200+S较N200处理硝态氮残留量减少18.0%,N250+S较N250处理硝态氮残留量减少41.2%。（2）减氮和秸秆还田是调控土壤硝化潜势的有效措施,N200较N250处理硝化潜势降低8.8%,N250+S较N250处理硝化潜势降低14.2%,N200+S较N200处理硝化潜势降低20.4%。（3）秸秆还田显著提高土壤微生物量碳氮（SMBC、SMBN）含量,N250+S较N250处理SMBC、SMBN分别显著增加17.5%和24.0%,N200+S较N200处理SMBC、SMBN分别显著增加18.4%和31.3%。（4）施氮和秸秆还田对氨氧化古菌（AOA）影响较小,但增加了氨氧化细菌（AOB）数量。（5）氨氧化细菌（AOB）丰度与硝态氮、铵态氮、土壤微生物量碳氮（SMBC、SMBN）和硝化潜势均呈极显著正相关,而氨氧化古菌（AOA）丰度和影响因子没有明显的相关性。研究结果可为黄土旱塬春玉米种植区氮肥管理和农业可持续发展提供科学依据。     

基施缓释肥等氮替代化肥对径流氮素流失和青贮玉米生长的影响

[目的]探究配施两种释放方式不同的缓释氮肥对滇中地区坡耕地径流氮素流失及青贮玉米生长的影响,为滇中坡耕地水土保持提供理论依据和支持。[方法]通过研究自然降雨条件下的径流槽模拟试验,在等氮条件下设置普通尿素(CK),40%添加了硝化抑制剂的速溶诺泰克^?21+60%普通尿素(处理I)和40%包膜缓释氮肥聚谷氨酸增效3代+60%普通尿素(处理Ⅱ)3个处理。[结果]生育期内各处理氮素流失呈先上升后下降的趋势,其中CK流失量最高,处理I和处理Ⅱ较CK有显著减少,总氮流失量分别下降了29.95%和16.77%,硝态氮分别减少了14.55%和6.53%,铵态氮分别减少了16.08%,8.24%。尿素配施缓释氮肥能够有效提高土壤全氮和铵态氮含量,减少硝态氮含量。处理I,Ⅱ较CK相比土壤全氮含量增加了3.25%和0.87%,铵态氮含量分别显著增加了30.57%,25.70%;较CK相比,处理I、处理Ⅱ硝态氮含量分别减少了22.49%和16.61%。[结论]3个处理间青贮玉米的产量无显著性差异,但配施缓释肥可以在保证土壤肥力和满足青贮玉米正常生长需求的同时减少坡耕地径流养分流失,其中...     

长期定位施肥对旱作农田土壤全氮及其组分的影响

基于田间定位试验,研究了长期施肥对旱作冬小麦农田土壤全氮及其组分的影响,试验设4个处理(对照不施肥CK、氮磷配施NP、化肥与有机肥配施NPM以及长期休闲地BL),测定了0—15,15—30,0—30cm土壤全氮、微生物量氮、潜在矿化氮和颗粒有机氮含量。结果表明,长期持续施肥30a后,在0—30cm土层,NPM处理土壤全氮、微生物量氮、潜在矿化氮分别较CK提高了35.0%,27.0%和48.9%(P0.05),且这种增加作用在15—30cm更明显,土壤全氮增幅达到41.3%(P0.05),但颗粒有机氮差异并不显著;此外,NPM处理微生物量氮、颗粒有机氮含量较NP处理分别提高了35.2%,307.5%(P0.05),而NP处理与CK仅潜在矿化氮差异显著。与种植作物相比,长期休闲降低了土壤全氮、微生物量氮、潜在矿化氮和颗粒有机氮含量,差异分别为15.0%,1.8%,31.3%和33.6%,但均未达到显著水平。相关性分析表明,土壤全氮、潜在矿化氮、微生物量氮和颗粒有机氮两两之间存在着显著的正相关关系。总的来说,长期持续施入有机肥能够有效地增加旱作农田土壤全氮,同时增加其组分含量,有助于维持土壤健康,保持其供氮能力。     

地膜覆盖对黄土高原旱作春玉米田土壤碳氮组分的影响

基于2年田间试验,研究了地膜覆盖对旱作春玉米田土壤有机碳、全氮及其组分的影响,试验包括地膜覆盖玉米田、无覆盖玉米田和裸地休闲3个处理,分层测定了0—40cm土层有机碳、全氮、颗粒有机碳氮、潜在矿化碳氮和微生物量碳氮含量。结果表明:在0—40cm土层,各处理间土壤有机碳和全氮含量均无显著差异。与不覆盖相比,地膜覆盖处理0—40cm土层颗粒有机碳氮及其所占比例分别降低了29.0%,33.3%,29.9%,35.7%;0—10cm土层潜在可矿化碳及其所占比例分别降低了17.8%和16.1%,潜在可矿化氮和微生物量碳及其所占比例无显著差异,但在0—10cm土层地膜覆盖微生物量氮含量及其所占比例分别较不覆盖处理提高了10.6%和10.5%(p0.05)。与裸地休闲相比,无覆盖处理0—40cm土层潜在可矿化碳氮分别提高了12.8%和14.7%,地膜覆盖处理则分别提高了7.8%和6.5%(p0.05),但种植玉米降低了微生物量碳氮含量及其所占比例。在0—40cm土层覆盖与否对潜在可矿化碳氮和微生物量碳氮影响不显著。总体来看,地膜覆盖能够在一定程度上提高表土微生物量氮组分及其所占比例,但显著降低了中活性碳氮组分含量及其比例,不利于长期的土壤碳氮固定。     

年际间周年覆盖保水对旱地小麦植株氮素利用的调控研究

为深入探索旱地小麦覆盖保水、增产、高效栽培技术途径,于2011—2014年在山西农业大学闻喜试验基地,以夏季覆盖渗水地膜与不覆盖为主区,以生育期膜际条播、常规条播为副区,研究年际间周年覆盖对麦田土壤水分运行和植株氮素积累、利用及氮效率的影响。结果表明:夏季覆盖提高播前3m内土壤水分,其保水效果可至孕穗期,且采用膜际条播效果更佳。夏季覆盖提高各生育时期植株氮素积累量,丰水年效果显著,提高27~31kg/hm~2,且采用膜际条播,夏季覆盖条件下欠水年提升空间较大,提高2~8kg/hm~2。夏季覆盖促进丰水年花前叶片和穗中氮素运转,促进平水年和欠水年茎秆+茎鞘中氮素运转,提高花前氮素运转量及对籽粒的贡献率,尤其欠水年;且采用膜际条播促进平水年茎秆+茎鞘和欠水年叶片中氮素运转,提高花后氮素积累量及对籽粒的贡献率。夏季覆盖提高氮素利用效率和氮素生产效率,欠水年采用膜际条播氮素吸收效率效果更佳;且采用膜际条播提高氮素吸收效率,欠水年夏季覆盖条件下氮素生产效率影响较大。结果还表明,夏季覆盖后,丰水年和平水年单位花后氮素积累量的增产效果较好,每增加1kg/hm~2可增产176~224kg/hm~2,而欠水年单位花前氮素运转量的增产效果较好,每增加1kg/hm~2可增产142~185kg/hm~2;采用膜际条播较常规条播,丰水年和平水年单位花前氮素运转、单位花后氮素积累的增产量均较大,欠水年夏季覆盖条件下采用膜际条播单位花后氮素积累量的增产量较大,每增加1kg/hm~2可增产234kg/hm~2。总之,周年覆盖有利于植株氮素吸收、运转,实现旱地小麦高产高效。     

Yield,Petiole Nitrate,and Node Development Responses of Cotton to Early Season Nitrogen Fertilization

Abstract

Nitrogen (N) fertilization continues to be of primary importance in the economically successful production of cotton (Gossypium hirsutum L.). Profit margins of producers might be expanded by increasing the uptake efficiency of applied N. Recently, N fertilization of crops grown in the Mississippi River Delta has been suspected to impact water quality in the Gulf of Mexico. Improving efficiency of N uptake could alleviate some environmental concerns by increasing the retention of N at the site of application. The objective of this study was to determine the impact of replacing preplant N applications with postemergent N applications on the growth and yield characteristics of cotton. Delayed applications of the recommended rate of N fertilizer (112 kg N ha^?1) were tested for four years under irrigated and dry land production conditions. The N rate was applied either preplant, after crop emergence, or at first square. Further, 112 kg N ha^?1 was split applied evenly at preplant + first square, and after emergence + first square. The five 112 kg ha^?1 N treatments were compared to an unfertilized control. Yield tended to be maximized with N treatments that included a first square application. Yields were usually lowest in the unfertilized control and the 112 kg N ha^?1 preplant treatments. Not surprisingly, both yield and plant growth was influenced more by irrigation than N fertilization. Years when drought conditions caused water stress and limited plant growth, dry land cotton had only limited response to the N fertilization treatments. Irrigated cotton responded to N treatments all years with increased growth and yield. Optimizing agronomic considerations, the best N fertilization timing was an after emergence + first square split application.

     

过量施肥下氮素形态对旱地土壤细菌多样性的影响

采用细菌16SrDNA的PCR-RFLP技术,以西北地区土垫旱耕人为土为材料,模拟田间过量施肥水平,经室内恒温短期培养,研究了过量施肥下酰胺态氮、硝态氮和铵态氮对土壤细菌多样性的影响。结果显示：PCR-RFLP分析酰胺态氮（T1）、硝态氮（T2）和铵态氮（T3）过量施肥处理的细菌16SrDNA克隆文库,分别得到17、25和130个酶切分型,不施肥对照（CK1）和正常施肥对照（CK2）分别得到119和187个酶切分型,表明正常施肥处理的酶切分型最多,过量使用酰胺态氮和硝态氮减少了酶切类型,而过量施用铵态氮可以维持与不施肥对照相近的酶切类型数量。采用α多样性测度对试验结果进行分析统计表明,不同处理间土壤细菌的多样性指数（H＇、Ds）和物种丰富度指数（dM）a均为CK2〉T3〉CK1〉T2〉T1处理,表明合理施肥可显著增加土壤中细菌的多样性,而过量施用酰胺态氮则减少细菌的多样性,使用铵态氮处理可维持细菌多样性;除正常施肥对照（CK2）外,其余各处理都出现了优势菌种。通过对优势菌的16SrDNA序列比对发现,酰胺态氮处理都为未培养细菌,硝态氮处理和铵态氮处理的优势菌呈现了菌属多样性,前者包括变形菌门的假单胞菌属和寡养单胞菌属、芽单胞菌门的未培养芽单胞菌属和未培养土壤细菌,后者为未培养酸杆菌属、变形菌门寡养单胞菌属和厚壁菌门芽孢杆菌属,表明不同施肥方式改变了土壤细菌的群落结构。     

秸秆和地膜覆盖对黄土高原旱作小麦田土壤团聚体氮组分的影响

利用田间定位试验研究旱作农田不同覆盖措施对土壤团聚体氮组分的影响。基于黄土高原8年冬小麦覆盖定位试验,试验设置生育期秸秆覆盖(SM)、生育期地膜覆盖(PM)和无覆盖对照(CK)3个处理。采用干筛法测定团聚体分布特征及不同粒径团聚体中全氮(STN)、微生物量氮(MBN)和潜在可矿化氮(PNM)含量。结果表明:(1)与CK处理相比,2种覆盖处理均未在各粒径团聚体全氮含量有显著变化,但SM处理相较于PM处理提高了0—10 cm土层的1.00～0.25 mm粒径团聚体STN含量(12.88%,P0.05)。(2)与CK处理相比,SM处理在0—10 cm土层中2.00,2.00～1.00,0.25 mm粒径团聚体MBN含量分别提高18.67%,24.05%,20.08%(P0.05),且各粒径团聚体PNM含量分别提高35.13%,30.03%,42.88%(P0.05);SM处理在10—20 cm土层中2.00 mm粒径团聚体MBN含量提高23.02%(P0.05),分别提高2.00,2.00～1.00,0.25 mm粒径团聚体PNM含量28.59%,31.31%,32.48%(P0.05)。(3)PM处理较CK处理提高0—10 cm土层中0.25 mm粒径团聚体PNM含量(32.34%,P0.05)。(4)微团聚体(0.25 mm)氮组分含量均高于大团聚(0.25 mm)氮组分含量,但大团聚体氮组分贡献率为81.88%～87.66%。可见,SM处理可提高土壤表层大团聚体氮组分的贡献率,使更多的氮素储存在大团聚体中,而PM处理对团聚体氮素贡献率的影响作用较小。总体而言,与CK和PM处理相比,SM处理可提高总土壤氮组分含量,提高微团聚体和大团聚体氮组分含量,使更多的氮储存在大团聚体中,促进土壤氮素周转。     

秸秆与地膜覆盖条件下旱作玉米田土壤氮组分生长季动态

研究不同覆盖措施下农田土壤全氮及其活性和半活性组分在作物生长季的动态变化,有助于深入理解农田土壤氮循环过程。基于黄土高原8年春玉米覆盖定位试验,系统分析了土壤全氮、矿质氮、微生物量氮、潜在可矿化氮以及颗粒有机氮在玉米不同生育期的动态特征。试验包括全生育期9 000kg/hm2秸秆覆盖、全生育期地膜覆盖和不覆盖对照3个处理。结果表明:(1)除硝态氮和铵态氮在苗期上升外,秸秆和地膜覆盖下土壤全氮及其组分含量在春玉米生育期基本呈苗期下降、拔节期上升、大喇叭口—抽雄期下降、灌浆和收获期回升的变化趋势;(2)与对照相比,秸秆覆盖提高了大多数生育时期0—40cm土层全氮和硝态氮含量及0—20cm土层铵态氮含量,提高各生育时期0—40cm土层微生物量氮、潜在可矿化氮以及颗粒有机氮含量;(3)地膜覆盖较对照提高大多数生育时期0—40cm土层硝态氮和0—20cm土层铵态氮含量,降低作物生育后期0—20cm土层全氮和0—40cm土层颗粒有机氮含量,降低大多数时期0—40cm土层微生物量氮和10—20cm土层潜在可矿化氮含量;(4)除了地膜覆盖下20—40cm土层颗粒有机氮相对含量在作物不同生育期差异不显著外,秸秆和地膜覆盖下0—40cm土层微生物量氮、潜在可矿化氮、颗粒有机氮对土壤全氮的动态均有重要贡献。总之,黄土高原的春玉米田秸秆覆盖具有明显的提升土壤全氮及其组分含量的作用,有助于培肥地力和土壤固氮;地膜覆盖则降低了作物生育后期土壤全氮及其组分含量,同时显著提高了土壤硝态氮水平,导致农田土壤氮素淋溶风险提高。     

不同施肥措施对旱地采煤塌陷区复垦土壤结构及玉米品质的影响

研究不同施肥措施对复垦土壤结构及玉米品质的影响,以期深入理解采煤塌陷区复垦土壤有机碳固持机制.采集复垦1年的定位试验各处理耕层(0—20 cm)土样以及玉米籽粒,分析土壤水稳性团聚体(>2,0.25～2,0.053～0.25 mm)及粉黏粒组分(<0.053 mm)中有机碳(SOC)及全氮(TN)含量、玉米籽粒蛋白质、...     

Soil Salinity Dynamics under Drip Irrigation and Mulch Film and Their Effects on Cotton Root Length

A field experiment based on a monolith method using flooding irrigation under mulch film (FI) as a control was conducted to investigate soil salinity dynamics under drip irrigation with mulch film (DI) and its effects on cotton root length. The average soil salinity increased with duration of irrigation, but salt distribution in the soil profile was uneven and showed strong accumulation in the soil between adjacent mulch films. With advancing growth of cotton plants, the area of salt accumulation gradually expanded, especially from 110 to 125 days after sowing (DAS), when salinity distinctly increased in the 0- to 40-cm soil depth and at distances 30–70 cm from drip lines; the electrical conductivity (EC) under DI in all soil samples was at least 3 mS cm^?1 and in some cases exceeded 5 mS cm^?1. Root length declined significantly by 18.1% from 110 to 125 DAS under DI. The soil area showing the greatest decline in root length under DI coincided with the main site of salt accumulation. Correlation analysis of soil EC and root length density indicated the root length declined when soil salt content exceeded 2.8 mS cm^?1. However, under FI salt accumulation barely exceeded 2.8 mS cm^?1 and no reduction in root length was observed. The results indicated that the main reason for decreased root length in cotton under DI was localized accumulation of salinity.     

增氧灌溉对棉花营养特征及土壤肥力的影响

以新陆早41号为材料,通过模拟试验和田间小区试验,研究增氧对灌溉水溶解氧的影响,以及增氧灌溉对棉田土壤养分、土壤微生物数量、棉花养分吸收和产量的影响。增氧灌溉模拟试验设计4个充氧浓度(CK-0%、O_2-21%、O_2-30%、O_2-50%),连续测定主管道和滴灌带不同监测点位灌溉水溶解氧浓度;田间试验设计3种增氧灌溉方式,物理增氧PO、化学增氧CO和常规滴灌CK。结果表明,增氧灌溉能够明显提高灌溉系统内灌溉水的溶解氧浓度,并且随着溶解氧浓度的增加衰变增加,灌溉水溶解氧浓度增加至12~14 mg L~(-1)较为适宜;增氧灌溉显著促进棉花增产,PO、CO棉花产量分别较对照增加11.39%、11.42%;增氧灌溉能促进棉花对土壤养分的吸收,从而降低土壤中养分含量,棉田土壤速效氮、有效磷、速效钾、有机质含量均有所降低,CO处理土壤速效氮、有机质含量与对照之间的差异达到显著水平,分别降低27.23%、9.61%,PO处理速效钾含量与对照之间的差异达到显著水平,较对照降低5.78%;增氧灌溉对棉田土壤细菌、真菌、微生物数量有促进作用,PO、CO处理细菌数分别较对照提高28.38%、21.05%,微生物总量分别提高27.86%、20.63%,处理间差异均达到显著水平。说明棉花根系对氧敏感,增氧灌溉能够进一步挖掘棉花生产潜能,不同增氧措施均能在一定程度上促进棉花生长和促进棉花对土壤养分的吸收,能加速土壤有机质分解和养分释放。     

减氮配施缓释氮肥对棉田土壤酶活性和氮素吸收利用的影响

为探明减氮配施缓释氮肥对棉田土壤酶活性和氮素吸收利用的影响,通过试验研究减氮、配施不同比例缓释氮肥对棉花土壤理化性质、酶活性、无机氮含量、氮肥利用率及棉花产量的影响。试验选用新陆早64号棉花品种,设置2种施氮方式,分别为常规全施尿素(T2)和缓释氮肥与尿素不同比例配施(US),配施处理按照施氮量设3个水平,分别为不减氮U_0.8S_0.2(T3)、U_0.6S_0.4(T4),减氮20% U_0.6S_0.2(T5)、U_0.4S_0.4(T6),减氮40% U_0.4S_0.2(T7)、U_0.2S_0.4(T8),不施氮肥(T1)为对照,共8个处理。对棉花不同生育期内土壤的理化性质、酶活性、无机氮含量及成熟期棉花氮素含量和产量进行测定与分析,并计算氮肥利用率。结果表明:与常规全施尿素相比,配施缓释氮肥能显著提高土壤含水量和全氮含量,其中,以缓释氮肥与尿素4∶6配施(T4)处理的土壤含水量最大,较常规全施尿素(T2)在棉花苗期、蕾期、花期、铃期和吐絮期分别提高了14.07%,11.05%,7.58%,6.22%,6.65%;T4处理的土壤全氮在花期显著高于常规全施尿素(T2)处理,达到1.24 g/kg。减氮20%配施缓释氮肥(T5、T6)处理各生育时期的土壤脲酶活性、蔗糖酶活性、过氧化氢酶活性、碱性磷酸酶活性和铵硝态氮含量与常规全施尿素(T2)间无显著差异,减氮20%配施缓释氮肥(T5、T6)处理成熟期土壤脲酶活性与硝态氮含量较不减氮T4处理分别减少了28.20%,26.40%和11.13%,8.32%。此外,减氮20%(T5、T6)处理的氮肥利用率显著高于常规全施尿素(T2)处理,分别为62.09%和62.43%,产量及其构成因素与常规全施尿素(T2)间无显著差异。综上,减氮20%配施缓释氮肥(T5、T6)处理与常规全施尿素(T2)处理相比土壤酶活性、无机氮含量及产量差异不显著,氮肥利用率显著高于T2处理,可以确保棉花全生育期的氮素供给,避免[JP]氮素的大量浪费,达到棉花高产及氮肥高效利用的目的。     

水稻秸秆还田配施肥料对小麦产量和氮素利用的影响

为了解高C/N比秸秆还田与肥料施用对金坛地区小麦产量和氮素利用的影响，通过设置大田试验，研究了稻秸还田与肥料施用对麦季土壤养分、微生物生物量、作物产量和氮肥利用率的影响。结果表明：稻秸还田配施肥料能够提高土壤速效养分含量。单施肥仅显著影响拔节期微生物生物量碳，单施稻秸显著影响拔节期和抽穗期微生物生物量氮，稻秸还田和肥料施用的交互作用在拔节期显著影响土壤微生物生物量和微生物熵。单施肥、稻秸配施肥料处理的氮肥表观利用率分别为31%和37%，稻秸配施肥料后的氮肥农学利用率和偏生产力表明每kg纯氮增产幅度约为6.86 kg籽粒。单施肥和稻秸配施肥料显著增加了小麦每穗粒数及千粒重，并且理论产量分别增加211%和319%，实际产量则分别增加119%和231%，而单施稻秸处理的实产却减产21%。综合分析认为，稻秸还田搭配肥料施用，能够保证当季土壤有效氮供应，促进土壤有机质转化为更易被微生物利用的形态，提高养分有效性，促进小麦对氮素的吸收利用，有利于每穗粒数和千粒重的增加，从而最终提高小麦的产量。     

渭北旱塬小麦不同栽培模式对土壤硝态氮残留的影响

在陕西渭北旱塬进行了4年田间小麦试验,研究了旱地不同栽培模式、施氮量和种植密度对土壤硝态氮残留累积的影响。结果表明,种植小麦4年后,0-200 cm土壤剖面中残留硝态氮为29.87~462.59 kg/hm2,且主要积累在80-160 cm土层,土壤氮库不仅明显,且残留比前3年土壤剖面显著下移(前3年主要累积在100 cm),差异达显著和极显著水平;不同栽培模式和种植密度0-200 cm土层硝态氮残留累积规律及其小麦籽粒吸氮量基本相似,排序均为:地膜覆盖>常规种植>秸秆覆盖>垄沟种植;随施氮量的增加土壤硝态氮残留量也相应增加,N0处理0-200 cm土壤平均硝态氮残留量为57.69 kg/hm2,N120处理平均为97.04 kg/hm2,虽然高于无氮处理,但两者差异未达到显著水平,N240处理平均为355.43 kg/hm2,比前者增加的幅度更大,其差异达到极显著水平。因施氮肥而增加的土壤硝态氮残留量为14.9~401.18 kg/hm2,平均占4年施氮量的19.59%,其中地膜覆盖占26.07%,常规种植占20.98%,秸秆覆盖占17.46%,垄沟种植种植占13.87%。     

减氮配施氮肥增效剂对土壤速效氮和玉米产量的影响

过量施氮一直是玉米生产中存在的主要问题,而配施氮肥增效剂可作为减氮条件下玉米实现高产和稳产的一种重要技术措施。2016—2017年在四川省德阳市中江县合兴乡新建村设置田间试验,研究不同施氮量与氮肥增效剂配施对土壤速效氮含量和玉米干物质积累及产量的影响,为玉米减氮增产栽培技术提供科学依据。结果表明:减氮配施增效剂能够增强土壤速效氮供应能力,促进玉米干物质积累,改善产量构成,提高玉米产量,实现玉米减氮不减产。常规氮和减氮20%配施增效剂增产幅度分别为5.53%～13.97%和10.24%～17.05%,减氮配施增效剂的增产效果更好。减氮20%条件下A_2B_4脲酶活性和土壤硝态氮含量较A_2B_2、A_2B_32年平均分别降低了19.00%,15.65%和-2.97%,57.24%,土壤铵态氮含量和产量2年平均提高11.48%,248.50%和3.71%,6.18%。综上,减氮20%条件下硝化抑制剂(DCD)和脲酶抑制剂(HQ)复配土壤速效氮的供应能力最强,可实现玉米减氮不减产。