我国设施菜地表观氮平衡分析及其空间分布特征

为定量评估区域设施菜地土壤氮素的输入输出平衡状况,探明土壤中氮素的基本去向和氮素潜在污染,从CNKI中文数据库和Web of Science等英文数据库中检索筛选出针对设施菜地氮循环研究的可用数据648组,对我国设施菜地表观氮素平衡进行了分析,并根据《全国设施蔬菜重点区域发展规划(2015—2020年)》中的蔬菜分区,探索了不同区域的氮平衡分布特征。结果表明,我国设施菜地每一生长季总体上表观氮平衡为正值,盈余量为49～1154 kg N·hm~(-2),均值为324 kg N·hm~(-2),氮肥利用率平均为18.6%。从氮素的输入途径来看,每季氮素总投入约为863 kg N·hm~(-2),以化肥和有机肥投入为主,分别为471、306 kg N·hm~(-2),灌溉水带入的氮也不容忽视,达到86 kg N·hm~(-2)。从氮素的支出途径来看,每季氮素总支出为539 kg N·hm~(-2),其中除了作物生长从土壤中吸取大量的氮素(230 kg N·hm~(-2))外,以淋溶、硝化反硝化和氨挥发等形式损失的氮达到309 kg N·hm~(-2),占输出量的57.4%,超过了作物吸收带走的氮(42.6%)。每季区域氮平衡差异显著,其中,黄淮海与环渤海暖温区氮素盈余最高,达到441 kg N·hm~(-2),其较高氮投入和较低的作物吸收是造成农田土壤氮素大量盈余的主要原因,同时也存在较高的氮素损失,通过淋溶流失的氮达到186 kg N·hm~(-2)。总体上,当前我国设施菜地整体表观氮平衡为正盈余,主要由于化肥和有机肥投入量大,但同时存在较高的氮素损失风险。降低氮素投入水平和提高作物的吸收利用率是有效的氮优化管理途径,尤其是在黄淮海与环渤海暖温区,应减少氮素投入,重点关注氮素淋溶损失。     

基于GIS技术的中国农田氮素养分收支平衡研究

该文基于统计数据、调查数据、图形数据以及已经公开发表的文献资料中的数据，详细研究了中国2000多个县域单元农田氮素养分的收支平衡状况，并将研究结果利用GIS技术进行了空间表达。研究发现，中国农田氮素投入总量为34.22×10⁶ t，农田氮素支出总量为31.57×10⁶ t，农田氮素处于盈余状态，盈余总量为2.65×10⁶ t；在县域层面上，农田氮素处于亏缺的县域单元数占全部县域单元数的37.68%，其耕地面积占全国总耕地面积的43.10%，农田氮素处于盈余的县域无论在数量上还是在耕地面积上都占有绝对优势，亏缺的县域单元离散分布在几乎全国的每个省份；在全国层面上，化学氮肥、有机氮肥、生物固氮、其他来源的氮素养分投入分别占全部氮素投入的76.54%、16.26%、3.10%、4.09%，化学氮肥在所有氮肥总投入中占有绝对优势；人畜粪尿是有机氮肥投入的主要来源；全国农田氮素生物产出总量为19.87×10⁶ t，占农田氮素总支出的比重为62.85%，在省域水平上，黑龙江省农田氮素生物产出占全部氮素生物产出的比例最高，达85%。     

基于Nufer模型的京津冀农牧系统氮素平衡状况及化学氮肥减施潜力分析

  【目的】   明确京津冀地区农牧系统氮素流动及平衡特征，解析化学氮肥减施潜力，从而为该地区化肥零增长和农业绿色发展提供依据。   【方法】   通过收集文献数据及2017年统计数据，采用Nufer (nutrient flows in food chain, environment and resources use) 模型，以“农田–畜牧”系统为研究对象，量化京津冀地区农牧系统氮素流动特征及利用效率，并针对输入输出平衡施氮和增加畜禽粪便还田量替代化肥两种措施，通过情景分析评估该地区化学氮肥减施潜力。   【结果】   京津冀地区农田系统和畜牧系统氮素输入量分别为296.1万t和133.6万t，农牧系统氮素总体输入量为306.6万t，其中化学氮肥是最大的输入项，占总输入量的62.5%。农田系统、畜牧系统氮素利用率分别为40.6%和25.0%，农牧系统整体氮素利用率为33.8%，农牧系统氮素循环再利用率为55.2%，生产单位氮含量食物产品所需氮素投入量为3.0 kg/kg。在该地区，土壤氮素累积量为51.2万t (占总输入量的16.7%)，环境排放总量为140.4万t (占总输入量的45.8%)。环境排放中，氨挥发 (包括农田和畜禽粪便氨挥发)和畜禽粪便水体排放与堆置为占比最大的两种损失途径，分别占总氮投入量的21.0%和9.5%。氮素土壤累积和畜禽粪便水体排放与堆置为两种最易调控的损失途径。通过输入输出平衡降低氮素土壤累积量，此地区有40%的氮肥减施潜力，此时，农牧系统氮素总投入量为230.0万t，农田和农牧系统氮素利用率分别较当前增加14.1和11.3个百分点；继续优化氮素管理，增加部分畜禽粪便还田量 (减少水体排放与堆置部分) 以替代化肥，则该地区有50%的氮肥减施潜力，且在此状态下，农牧系统氮素总投入量为210.8万t，较当前降低31.2%，农田系统和农牧系统氮素利用率分别增加15.3和15.4个百分点，氮素环境排放量降低36.2%，氮素循环再利用率增加20.0%，食物氮代价降低33.3%。   【结论】   化学氮肥施用量大，农牧分离是京津冀地区农牧系统氮素利用效率低的主要原因。在农牧系统氮素管理中，通过平衡作物生产中的氮素投入，系统氮素投入的减少潜力为40%。如果能进一步合理利用有机资源，增加畜禽粪便还田率，化学氮肥减施的总潜力可达50%，并可提高氮素利用效率，有效降低氮素的环境排放总量。     

三峡重庆库区柑橘园氮素平衡状况研究

以三峡重庆库区柑橘种植农户调研资料和土壤测试分析数据为基础,从区域角度出发,分析了柑橘园生产体系中的氮肥施用特征和氮素平衡状况。结果表明: 果园氮肥投入量为409.7 kg/hm2,主要来源于复合肥和尿素; 其中通过有机肥投入的氮素水平为 76.51 kg/hm2,主要来源于畜禽粪尿; 柑橘园的总体氮盈余量为 363.9 kg/hm2,盈余量以奉节、江津和永川区较高; 果园氮素投入与氮养分盈余量之间存在极显著的正相关关系。说明过量施用氮肥是氮盈余量高的主要原因。随着氮盈余量增加,果园土壤全氮呈增加趋势,而土壤C/N呈下降趋势, 氮素盈余对土壤全氮的影响大于土壤有机质的影响。     

传统和优化施氮对春玉米产量、氨挥发及氮平衡的影响

【目的】本文通过在陕西省长武县(CW)和吉林省梨树县(LS)的春玉米田间试验,研究了传统和优化施氮对春玉米产量、土壤氨挥发及氮平衡的影响,以探讨春玉米氮肥优化的潜力及其对农田氨减排的效果。【方法】试验设对照、传统施氮(长武N 250 kg/hm2,梨树N 300 kg/hm2)及优化施氮(N 200 kg/hm2)3个处理,分别以N0、Ncon、Nopt表示。氨挥发采用德尔格氨管法(简称DTM法)进行原位测定,通过田间气象因素的校正计算氨挥发累积量。【结果】长武和梨树点不同施氮处理下春玉米的产量结果表明,除对照(长武7.9 t/hm2、梨树3.8 t/hm2)外,传统和优化施氮处理间均无显著差异(长武10.6 10.8 t/hm2,梨树9.5 9.6 t/hm2)。玉米氮肥利用率表现为优化施氮(44.3%44.5%)显著高于传统施氮(33.6%36.4%),其中长武点氮肥利用率提高了8.1个百分点,梨树点氮肥利用率增加了10.7个百分点。氨挥发田间监测结果显示,基肥翻耕入土后,伴随降雨的产生,长武和梨树点均未产生氨挥发。喇叭口追肥期表施氮肥后,长武和梨树点均产生大量氨挥发(占追施尿素氮量的16%22%),减少追肥用量N 30 kg/hm2(长武点)和N 100 kg/hm2(梨树点)能显著减少氨挥发损失N 8和15 kg/hm2。土壤-春玉米系统氮平衡估算的结果显示,与长武点氮素表观矿化N 97 kg/hm2相比,梨树点仅为N 16 kg/hm2。优化施氮比传统施氮处理显著降低表观氮素盈余N 48 88 kg/hm2。长武点各施氮处理的表观氮素盈余中,约46%的氮素残留在0—1 m的土壤中,54%损失到环境中,氨挥发占总损失的15%30%;梨树点表观氮素盈余中,35%损失到环境中,其中氨挥发占总损失的54%75%,约有65%残留在0—1m的土壤中。梨树点传统施氮处理0—1 m土层的氮素残留达N 140 kg/hm2,部分残留在土壤中的氮素也将面临淋洗、硝化和反硝化等损失的风险。与优化施氮相比传统施氮氮素表观损失增加了约N 30 40 kg/hm2,除氨挥发损失外,淋洗和硝化/反硝化等也是土壤-春玉米系统中不可忽视的氮素损失途径。【结论】我国春玉米主产区农民传统的氮肥用量偏高,增产效应不明显,氮肥损失风险加剧,尤其是氨挥发损失较大,氮肥的优化潜力高达20%33%,相当于可减少施氮N 50 100kg/hm2。     

新疆石河子地区玉米产量及氮素平衡的施氮量阈值研究

【目的】合理施用氮肥不仅会提高肥料利用率,还会降低氮素面源污染的风险。通过2年田间肥料定位试验,研究北疆灰漠土区不同氮肥用量下,土壤无机氮积累量、 氮素平衡和玉米产量间的相互关系,为氮肥合理施用提供依据。【方法】研究采用肥料田间定位试验,小区试验于2011-2012年开展,设计6个氮肥（N）用量水平: 0、 225、 300、 375、 450、 600 kg/hm2,分别以N0、 N225、 N300、 N375、 N450、 N600表示,其中300 kg/hm2为当地玉米农田氮肥推荐用量,磷肥（P2O5）施用量为75 kg/hm2,钾肥（K2O）施用量为37.5 kg/hm2。【结果】 1）施用氮肥增加了土壤硝态氮和铵态氮残留量,硝态氮主要残留于060 cm土层,铵态氮主要分布在020 cm土层深度。2011年试验中,土壤无机氮残留量随氮肥用量增加而显著增加,与对照相比,施氮处理无机氮残留量增幅为12%~102%,与施氮量呈指数增长关系。2012年氮肥用量对土壤无机氮残留量的影响与2011年相似。2）施氮量 225 kg/hm2时,0100 cm土层深度土壤无机氮积累量降低,表现为负积累效应,N0和N225处理下2012年土壤无机氮积累量分别较2011年降低165%和170%; 施氮量高于 300 kg/hm2时,土壤无机氮积累量显著增加,表现为富集现象,其中,N375、 N450和N600处理下2012年土壤无机氮积累量分别较2011年增加17%、 388%、 170%。土壤无机氮积累量与施氮量显著呈二次抛物线关系,2011年回归方程为y=0.0001x2 + 0.1013x－22.537（R2 = 0.9288）,无机氮无积累时施氮量为187 kg/hm2; 2012年为 y = 0.0003x2 + 0.1417x - 52.78（R2 = 0.9583）,无机氮无积累时施氮量为245 kg/hm2。土壤氮素表观损失量和氮素盈余量的增加幅度随氮肥用量增加而显著加大。3）氮肥投入可提高玉米产量,产量与施氮量呈显著的二次抛物线或线性加平台的关系,施氮量高于300 kg/hm2时,玉米产量与最高产量差异不显著; 产量与无机氮积累量呈二次抛物线形关系,当土壤无机氮达到平衡时,玉米产量显著低于最高产量,当玉米产量达到最大时,土壤无机氮有一定积累。氮肥利用率则随氮肥用量增加呈指数关系显著降低。施氮量270 kg/hm2为产量与氮肥利用率的交点,施氮量340 kg/hm2 是土壤无机氮残留量与氮肥利用率的交点。【结论】利用产量效应、 环境效应与肥料效应函数的交点确定氮肥投入阈值,是较为优化的方法。合理的氮肥投入不仅能获得玉米高产,降低氮素面源污染风险,还能获得较高的氮肥利用率。因此,施氮量260340 kg/hm2为本研究区玉米高产与环境友好的氮肥投入阈值。     

不同施氮水平对冬小麦季化肥氮去向及土壤氮素平衡的影响

采用田间微区15N示踪技术,研究了冬小麦季化肥氮去向及土壤氮素平衡。结果表明,在供试土壤肥力水平和生产条件下,N 150 kg/hm2的施肥量已达到较高产量,再增加氮肥用量小麦产量不再增加。随着施肥量的增加,地上部吸氮量有所增加,氮肥的表观利用率和农学利用率持续下降,而生理利用率则表现为低—高—低的变化趋势。在低施氮条件下,小麦主要吸收土壤氮的比例高于化肥氮;在高施氮条件下,小麦吸收土壤氮的比例下降。冬小麦收获后,仍有26.7%4~0.6%的氮肥残留在0—100 cm土层中,17.4%2~4.8%的氮肥损失。残留在土壤剖面中的氮肥主要分布在表土层。随着施氮量的增加,土壤氮素总平衡由亏缺转为盈余;土壤根区硝态氮也由播前消耗转为在播前的基础上累加,两个小麦品种表现为相同的趋势。     

不同供氮水平下幼龄苹果园氮素去向初探

以2年生红富士/平邑甜茶为试材,采用田间小区和15N微区相结合,研究了不同供氮水平下幼龄苹果园氮素去向。结果表明,施用氮肥显著增加了植株生物量和吸氮量,而氮肥利用率随施氮量的增加显著降低;N75、N150和N225的氮肥利用率分别为31.28%、22.95%和19.38%。土壤残留氮量随施氮量的增加而显著增大,且残留氮素主要分布于060 cm土层,深层渗漏量很小。整个作物土壤体系氮素回收率随施肥量的增加显著降低,损失率显著增高。N75处理的氮素回收率为60.41%,显著高于N150（46.41%）和N225处理（40.88%）;且损失率最低（39.59%）,显著低于其它两个处理。氨挥发损失随施氮量的增加显著升高,N2O损失量各处理间无明显差异;氮素损失中氨挥发和N2O损失所占比例较低,较多的氮素通过反硝化和径流等途径损失。     

基于氮收支平衡的河套灌区春小麦农田灌溉和施氮策略

针对中国黄河中上游河套灌区不合理灌溉和施肥造成的土壤氮素流失严重及氮收支不平衡等问题,该研究于2019－2021年开展田间试验,探讨不同灌溉和施肥策略对土壤氮损失、作物氮吸收及氮收支的影响。试验设置了3个灌溉水平（高水I1：450 mm,中水I2：315 mm,低水I3：180 mm）和2个施氮水平（高氮N1：340 kg/hm2,低氮N3：170 kg/hm2）,此外,2020和2021年在中等灌溉水平I2下补充了中等施氮水平（250 kg/hm2,N2）,对不同处理的土壤氮损失、作物氮吸收及氮收支等指标进行了对比分析。结果表明,肥料氮是农田氮输入的主要来源,其次是灌溉水、大气沉降和非豆科作物固定。作物吸氮占土壤氮输出的比例最大,其次是NO3--N淋失、NH3挥发和N2O排放。对于氮输入而言,其值随着灌水量和施氮量的减少而降低。对于土壤氮输出而言,减少灌水量和施氮量可显著降低土壤总氮损失量,但过低的灌水量和施氮量将导致小麦吸氮量的降低。传统的N1施氮处理可导致土壤氮素盈余,而施氮量降低50%的N3处理则导致土壤氮素大量亏缺。对照处理（I1N1）的土壤氮损失量最高,该处理氮损失占土壤氮输出的比例高达23%～41%,其中NO3--N淋失和NH3挥发占总氮损失的95%以上。与对照处理相比,I2N2处理可减少21%～29%的氮损失,且作物吸氮几乎未受到影响。同时,该处理土壤氮素处于轻度亏缺状态,其亏缺量为28～50 kg/hm2,占总施氮量的11%～20%。若在收获后将4～8 t/hm2的小麦秸秆还田,则可保持麦田土壤的氮收支平衡。因此,通过改善灌溉和施肥策略并配合适当的秸秆还田可以有效缓解河套灌区春小麦农田的氮损失且实现土壤氮平衡,该研究可为干旱半干旱地区春小麦农田可持续生产和氮污染物减排提供科学依据。     

基于DNDC模型的环渤海典型小流域农田氮素淋失潜力估算

为了定量评价流域尺度氮素污染的可能性并探明氮素污染的主要来源,以期指导农业生产实际保护农田生态环境,该文主要运用农业生态系统生物地球化学模型(DNDC)模拟的方法,以环渤海典型小流域——小清河流域为例,在GIS流域数据库支持下对该流域氮素淋失潜力进行了估算。研究结果表明,2006年小清河流域年均氮淋失负荷范围为10.44×103～36.86×103t,平均为23.65×103t。以当年氮肥投入总量222.2×103t计算,该流域平均氮素流失量占氮肥投入的10.6%。不同地区氮素淋失空间分布差别较大,与氮肥施用量的空间分布规律大体一致。其中,44%和27%的地区氮素潜在淋失量分别集中在20～40和>40～80kg/hm2,这些地区主要分布在小清河两侧沿岸及寿光市大部分地区,给流域水环境造成了较大影响。研究结果显示流域氮淋失存在较大的空间区域差异,根据不同地区的实际情况进行水氮管理,减少氮素的无效丢失十分必要。     

华北地区冬小麦-夏玉米轮作体系的氮素循环与平衡

对华北地区冬小麦-夏玉米轮作体系农田氮素输入输出的数量特征、平衡状况进行了分析,并评估其优化潜力。研究表明,华北地区冬小麦-夏玉米轮作体系农田每年的氮素输入中,化学氮肥、农家肥、降水、灌溉、非生物固氮和种子带入农田的氮分别为545、68、21、15、15和5kghm-2a-1,氮素年输入总量为669kghm-2a-1;每年的氮素输出中,作物收获带走的氮为311kghm-2a-1,而氨挥发、反硝化和淋洗损失的氮分别为120、16和136kghm-2a-1,氮素年输出总量为583kghm-2a-1;氮素年盈余量为86kghm-2a-1。目前我国华北地区冬小麦-夏玉米轮作体系农田氮素处于大量赢余状态,从而导致氮素大量损失。因此,加强氮肥管理,提高氮肥利用率,加大有机肥施用的力度,是华北地区农田氮素资源管理的长期任务。     

Optimum N concentration in winter wheat grown in the coastal plain region of Virginia

Abstract

Limited information is available on optimum N levels in winter wheat (Triticum aestivum L.), particularly at higher yield levels. Three experiments were conducted in the Coastal Plain region of Virginia where N was applied at rates of 0, 67, 90 and 112 kg/ha to Wheeler, Mc Nair 1003 and Coker 747 soft red winter wheat varieties. Yields ranged from 2.33 to 5.83 Mg/ha in the study. Nitrogen fertilization increased yield up to the 67 kg/ha rate and increased N concentration in the plant tissue up to 67 or 112 kg of N/ha, depending on variety. Optimum N concentration, i.e., N concentration at maximum (100%) yield for Wheeler, Mc Nair 1003 and Coker 747, over the three experiments, was 4.54%, 4.52% and 4.81%, respectively, for entire above‐ground plant samples collected at Feekes growth stage 4 and 4.72%, 4.73% and 4.44% for flag leaf samples collected at Feekes growth stage 10. A N sufficiency range of 4.00–5.00% is suggested for use for the plant parts sampled for both growth stages.     

Mid-Season Recovery from Nitrogen Stress in Winter Wheat

ABSTRACT

Although spring-applied nitrogen (N) has been shown to be most efficient, the technique of delaying all N applications until mid-season, and the resultant effect on maximum yields, has not been thoroughly evaluated. This experiment was conducted to determine if potential yield reductions from early-season N stress can be corrected using in-season N applications. Data from three experimental sites and two growing seasons (six site-year combinations) were used to evaluate three preplant N rates (0, 45, and 90 kg ha^?1) and a range of in-season topdress N rates. Topdress N amounts were determined using a GreenSeeker hand-held sensor and an algorithm developed at Oklahoma State University. Even when early-season N stress was present (0-N preplant), N-applied topdress at Feekes 5 resulted in maximum or near-maximum yields in four of six site-year combinations when compared with other treatments receiving both preplant and topdress N.     

黑垆土有机氮组分对可矿化氮的关系

Mineralizable N and organic N components in different layers (0-15, 15-30, 30-45, 45-60, 60-80 and 80-100 cm) of six soils with different fertilities sampled from Yongshou County, Shaanxi Province, China,were determined by the aerobic incubation method and the Bremner procedure, respectively. Correlation,multiple regression and path analyses were performed to study the relation of minerallzable N to organic N components. Results of correlation and regression analyses showed that the amounts of the N mineralized were parallel to, and significantly correlated with, the total acid hydrolyzahle N, but was not so with the acid-insoluble N. Of the hydrolyzable N, the amino acid N and the ammonia N had a highly consistent significant correlation with the mineralized N, and their partial regression coefficients were significant in the regression equations, showing their importance in contribution to the mineralizable N. The amino sugar N, on the other hand, had a relatively high correlation with the mineralized N, but their partial regression coefficients were not significant in the regression equations. In contrast, the hydrolyzable unknown N had no such relations.Path analysis further indicated that the amino acid N and ammonia N made great direct contributions to the mineralized N, but the contributions of the amino sugar N were very low. These strongly suggested tha tthe mineralized N in the soils tested was mainly from the hydrolyzable N, particularly the amino acid N and ammonia N which are the major sources for its production.     

Apparent availability of nitrogen in composted municipal refuse

The use of composted municipal refuse on agricultural land requires prior knowledge of the interactions among compost, soil, and plants. Research into the availability of N in highly matured municipal refuse compost is particularly important considering the current concern about groundwater contamination by NO _inf3 ^sup- -N. A greenhouse pot bioassay was conducted to determine the percentage of short-term apparent bioavailable N of a highly matured refuse compost and its relative efficiency in supplying inorganic N to the soil-plant system in comparison with NH₄NO₃. Municipal refuse (after 165 days of composting) was applied at rates equivalent to 10, 20, 30, 40, and 50 t ha^-1 to a ferrallitic soil from Tenerife Island (Andeptic Paludult). NH₄NO₃ was applied at rates equivalent to the total N content of the compost treatments. Perennial ryegrass (Lolium perenne L.) was grown in 3-kg pots and the tops were harvested at regular intervals after seedling emergence. The compost increased dry matter yield, soil mineral N, and plant N uptake proportional to the applied rate. These increases were significantly higher than the control at an application rate of 20 t ha^-1. After 6 months the apparent bioavailable N ranged from 16 to 21%. The relative efficiency was 43% after 30 days. This suggests that large inputs of inorganic N into soil can be obtained with high rates of this kind of compost, with a potential for NO _inf3 ^sup- -N contamination. However, applied at moderate rates in our bioassay (<50 t ha^-1), compost showed a low N-supplying capacity to ryegrass, i.e. a small fraction of the mineralized compost N was used by plants in the course of time. This was ascribed to a partial biological immobilization. This pattern of N availability in highly matured municipal refuse compost, positive net mineralization but partial immobilization, is similar to the pattern of N availability in biologically active soils and is therefore extremely interesting for the conservation of N in agro-ecosystems.     

Immobilization of ammonium and nitrate and their interaction with native N in three Illinois Mollisols

Summary Three Illinois Mollisols were incubated for 2 weeks at 25°C after treatment with different amounts of glucose and/or ¹⁵N-labelled (NH₄)₂SO₄ or ¹⁵N-labelled KNO₃. The objectives were: (1) to compare the immobilization and interaction of NH _inf4 ^sup+ –N and NO _inf3 ^sup- –N with the native soil N, and (2) to study the relationship between immobilization of applied N and the added N interaction. As determined, immobilized N refers to forms not extractable with 2 MKCl (immobilized ¹⁵N+clay-fixed ¹⁵NH _inf4 ^sup+ ). In all cases, both NH _inf4 ^sup+ –N and NO _inf3 ^sup- –N were actively immobilized and transformed into organic forms in the presence of glucose. In the absence of glucose, a higher proportion of NH _inf4 ^sup+ than NO _inf3 ^sup- was recovered in organic forms. Although the three soils differed considerably in the amounts of applied N immobilized, similar trends in N immobilization were observed. A positive added N interaction occurred with all soils, the magnitude increasing with the rate of N addition. In the absence of glucose, higher added N interactions were obtained for NH _inf4 ^sup+ than NO _inf3 ^sup- , whereas there was very little difference between NH _inf4 ^sup+ and NO _inf3 ^sup- in the presence of glucose. The results indicate that under conditions of rapid immobilization (e.g., in the presence of glucose), NH _inf4 ^sup+ and NO _inf3 ^sup- will show comparable interaction with the native soil N, whereas in unamended soil, the extent of this interaction will be greater with NH _inf4 ^sup+ than with NO _inf3 ^sup- . Significant correlations were observed between applied N immobilized and the added N interaction only in one soil having a high initial mineral N content.     

Comparison of Chemical Methods for Assessing Nitrogen Mineralization in Two Calcareous Soils Treated with Organic Materials

Reliable and quick methods for measuring nitrogen (N)–supplying capacities of soils (NSC) are a prerequisite for using N fertilizers. This study was conducted to develop a routine method for estimation of mineralizable N in two calcareous soils (sandy loam and clay soils) treated with municipal waste compost or sheep manure. The methods used were anaerobic biological N mineralization, mineral N released by 2 M potassium chloride (KCl), ammonium (NH₄ ⁺) N extracted by 1 N sulfuric acid (H₂SO₄), NH₄ ⁺-N extracted by acid potassium permanganate (KMnO₄), and NH₄ ⁺-N released by oxidation of soil organic matter using acidified potassium permanganate. The results showed that oxidizable N extracted by acid permanganate, a simple and rapid measure of soil N availability, was correlated with results of the anaerobic method. Oxidative 0.05 N KMnO₄ was the best method, accounting for 78.4% of variation in NSC. Also, the amount of mineralized N increased with increasing level of organic materials and was greater in clay soil than sandy loam soil.     

提高高产玉米氮素利用效率的根层氮素管理技术

Many recently developed N management strategies have been extremely successful in improving N use efficiency.How-ever,attempts to further increase grain yields have had limited success.Field experiments were conducted in 2007 and 2008 at four sites to evaluate the effect of an in-season root-zone N management strategy on maize (Zea mays L.).According to the in-season root-zone N management,the optimal N rate (ONR) was determined by subtracting measured soil mineral N (NH + 4--N and NO 3--N) in the root zone from N target values.Other treatments included a control without N fertilization,70% of ONR,130% of ONR,and recommended N rate (RNR) by agronomists in China that have been shown to approach maize yield potentials.Although apparent N recovery for the ONR treatment was significantly higher than that under RNR in 2007,grain yield declined from 13.3 to 11.0 Mg ha 1 because of an underestimation of N uptake.In 2008,N target values were adjusted to match crop uptake,and N fertilization rates were reduced from 450 kg N ha-1 for RNR to 225 to 265 kg N ha-1 for ONR.High maize yields were maintained at 12.6 to 13.5 Mg ha 1,which were twice the yield from typical farmers’ practice.As a result,apparent N recovery increased from 29% to 66%,and estimated N losses decreased significantly for the ONR treatment compared to the RNR treatment.In conclusion,the in-season root-zone N management approach was able to achieve high yields,high NUE and low N losses.     

Optimal Management Practices for Nitrogen Application in Corn Cultivated During Summer and Fall in the Tropics

Optimal management practices for nitrogen (N) fertilization is well defined for corn (Zea mays) cultivated during summer (“summer” corn), but not for corn cultivated during the fall (“fall” corn) in the tropics. Two experiments were carried out to evaluate N rates (50, 100, 200, and 300 kg N ha^?1), N application timing (pre-planting – PP, V2–V3, and V5–V6) and N split application, once (at PP, V3, and V6), two (at V3+ V6) and three times (at PP+ V3+ V6) in corn cultivated during summer (2014/2015) and fall (2015/2016). Data on corn grain yield (CGY), weight of 1000-grains, leaf N content and values of soil-plant analyses development (SPAD) were collected and analyzed using univariate, multivariate (principal component analysis, PCA) and regression analysis. Results showed that corn growth was affected by N rates and splitting. Corn cultivated during summer presented higher CGY and weight-1000 g than corn cultivated during the fall. The highest yields were obtained with higher N rates on “summer” corn (125 kg N ha^?1) than “fall” corn (50 kg N ha^?1). Split N-application at vegetative growth stages, V3+ V6, or PP+ V2+ V6, provided higher yields for “summer” corn, while only PP application was a reliable period of N fertilization for “fall” corn. The finding is that corn cultivated during the fall presented a lower response to N and no obvious advantages to split N fertilization when compared to corn cultivated during summer. These optimal management practices for N fertilization in corn production in the tropics depend on soil water availability.     

洞庭湖区不同土地利用方式耕作土壤氮素含量与循环

通过对洞庭湖典型地区的密集采样分析和农户调查,研究了4种利用方式耕作土壤全N、微生物生物量氮(MB-N)含量、两者关系和N素循环特征。结果表明:耕作土壤全N、MB-N含量平均值为3.00±0.48g/kg和101.4±49.2mg/kg。双季稻、一季稻、水田旱作和旱地全N平均含量依次为3.12±0.40g/kg、3.03±0.39g/kg、2.79±0.43g/kg2、.10±0.46g/kg。4种利用方式的MB-N含量分别为124.0±56.6mg/kg、96.4±39.2mg/kg、108.0±48.6mg/kg、75.2±30.5mg/kg。除水田旱作外,MB-N与全N之间存在极显著的正相关关系(P<0.01)。土壤N素盈余量依次为双季稻(105.0kg/hm2.a)>一季稻(75.1kg/hm2.a)>水田旱作油菜(64.5kg/hm2.a)>旱地苎麻(51.9kg/hm2.a)。