黄土高原旱地夏季休闲期15N标记硝态氮的去向*

2017-11-01 09:21夏梦洁陈竹君刘占军周建斌
土壤学报 2017年5期
关键词:旱地硝态田块

夏梦洁 陈竹君 刘占军 周建斌

(西北农林科技大学资源环境学院,农业部西北植物营养与农业环境重点实验室,陕西杨凌 712100)

黄土高原旱地夏季休闲期15N标记硝态氮的去向*

夏梦洁 陈竹君 刘占军 周建斌†

(西北农林科技大学资源环境学院,农业部西北植物营养与农业环境重点实验室,陕西杨凌 712100)

夏季休闲是黄土高原旱地小麦常见的蓄纳雨水、恢复地力的措施。随着氮肥用量的增加,一季小麦收获后,旱地土壤剖面累积的硝态氮量不断增加,休闲期间降雨量高,残留硝态氮的去向是值得研究的问题。利用15N标记法研究小麦收获后残留肥料氮在黄土高原旱地(陕西长武)夏季休闲期间的去向,即小麦收获后在微区土壤表层(0~15 cm)施入15N标记的硝态氮肥(30 kg hm-2(以纯氮计),约相当于当地小麦一季作物收获后土壤残留肥料氮量),休闲结束后,采集0~200 cm土壤样品,测定了土壤全氮、硝态氮含量及其15N丰度。结果表明,小麦收获(即休闲开始)时0~200 cm土壤剖面硝态氮累积量在205~268 kg hm-2之间(平均244 kg hm-2),累积量较高。夏季休闲期间降水量为157 mm,属欠水年,但休闲结束后,15N标记肥料氮向下迁移已达80 cm土层,下移深度在45~65 cm之间,说明,旱地休闲期间硝态氮的淋溶作用不可忽视。夏季休闲结束后,加入的15N标记肥料氮平均损失率为28%,损失机理值得进一步研究。

旱地;夏季休闲;15N标记法;残留肥料氮;硝态氮淋溶

中国干旱、半干旱地区面积占国土面积的52.5%[1],旱地小麦在我国小麦生产中占有重要地位。黄土高原是我国旱地集中分布的区域,该区域的旱地小麦面积占全国的27%~29%[2-4]。水分是制约旱地小麦生产的关键因素之一。为了蓄水保墒,旱地小麦收获后多采取夏季休闲的措施[5],即小麦收获后翻耕土壤,一方面蓄纳雨水,另一方面,夏季高温多湿可促进土壤有机质矿化,增加土壤有效养分含量,这在传统的旱地农业生产中对提高作物产量具有重要意义。自20世纪80年代以来,我国旱地农田中氮肥用量不断增加[6],一季小麦收获后,土壤残留的肥料氮量不断增加,有研究发现,小麦收获时,当季施入氮肥的83.7%残留在0~200 cm土壤剖面中,且多以硝态氮形态存在[7-8];Dai等[9]研究发现,黄土高原长期施氮量为240 kg hm-2时,小麦收获后,0~300 cm土壤剖面硝态氮累积高达326 kg hm-2。Zhou等[10]指出小麦地0~400 cm土壤剖面硝态氮累积量高达453 kg hm-2。夏季休闲期地表裸露,降雨量高,短短的2~3个月期间的降雨量占年降水量的60%左右,因此,休闲期旱地残留肥料氮的损失是值得研究的问题[11-15]。

20世纪60年代,彭琳等[16]最早关注了夏季休闲对陕西关中塿土硝态氮淋溶的影响,发现该地区集中降雨的6—9月份土壤剖面硝态氮累积和下渗现象非常明显,平均10 mm降水可使硝态氮下渗3~5 cm。近年来,随着该地区旱地氮肥用量的增加,夏季休闲期间硝态氮的淋溶损失问题开始引起学者的广泛关注。如有研究指出,夏季降水为364 mm的黄土高原南部,可使休闲后0~100 cm土层的硝态氮淋溶至220 cm土层[17]。戴健等[18]的研究也指出,每10 mm降水使塿土剖面硝态氮下移2~4 cm,说明,旱地夏季休闲期间硝态氮淋溶风险大。而已有的研究均采用比较休闲前后土壤剖面硝态氮含量变化的方法评价硝态氮在土壤剖面迁移及淋溶情况,由于土壤剖面迁移及淋溶的硝态氮既可能来自残留的肥料氮,也可能来自夏季休闲期间土壤有机态氮矿化,因此,该方法难以定量一季小麦收获后以硝态氮形态残留在土壤中的肥料氮在土壤剖面的淋溶及损失特性。

15N稳定同位素标记法是定量氮素去向的有效方法[19]。因此,本文采用在夏季休闲小麦田块中加入15N标记硝态氮的方法,研究黄土高原旱地夏季休闲期间残留肥料氮的去向,旨在定量评价该地区夏季休闲期残留肥料氮的去向,为旱地氮素有效管理提供理论依据。

1 材料与方法

1.1 试验地概况

试验地位于黄土高原的陕西省长武县洪家镇王东村,该地处于黄土高原中南部,海拔1 227 m,属暖温带半湿润大陆性季风气候,年均降水量580 mm,主要集中在7—9月,年均温度9.1℃,属典型的旱作雨养农业区。供试土壤为黑垆土(堆垫干润均腐土)。2014年长武夏季休闲期间降水量和蒸发量以及常年(1957—2014年)同期降水量见图1。

图1 2014年长武夏季休闲期间降水量和蒸发量以及常年(1957—2014)同期降水量Fig. 1 Rainfalls and evaporations during the summer fallow season in Changwu in 2014 and in the year of 1957—2014

1.2 试验方案

本文采取土壤中外加15N标记硝态氮的田间微区法研究旱地小麦收获后残留在土壤中硝态氮在夏季休闲期间的去向。试验设施氮和不施氮两个处理(分别以N及CK表示),所有氮肥形态为15N标记的硝酸钾(15N丰度为10.28%),用量为30 kg hm-2(以纯氮计),约相当于当地旱地小麦一季作物收获后土壤残留的肥料氮量。微区采用聚氯乙烯(Polyvinylchloride,以下简称PVC)管,将直径25 cm,长25 cm的PVC管插入表层土壤,插入深度22 cm。然后,将PVC管中表层(0~15 cm)土壤取出,与1.0623 g K15NO3充分混匀后再重新回填、压实,各处理重复3次。试验分布在研究区域的5个农户田块(分别用a、b、c、d、e代表)进行,以代表不同的肥力状况;不同田块0~20 cm土层土壤基本理化性质见表1。试验于2014年7月15日开始,同年9月5日结束。

1.3 样品采集与测定

试验开始前,在每个田块中采集3个0~200 cm土壤样品组成混合样(每20 cm为一层),剔除作物根系后带回实验室,测定土壤基础理化性质。试验结束时从每个微区中采集1个0~200 cm土壤样品(每20 cm为一层),剔除作物根系后密封,带回实验室,一部分4℃保存,另一部分风干磨细过0.25 mm筛备用。

土壤含水量采用烘干法(105℃下烘干8 h)测定。硝态氮测定:1 mol L-1KCl溶液浸提(水土比10∶1),振荡1 h,过滤,自动化连续流动分析仪(AA3,Bran+Luebbe,德国)测定。土壤全氮及15N丰度:半微量凯氏法测定土壤全氮,15N丰度采用同位素比值质谱仪(EA-IRMS,Sercon Ltd,Cheshire,英国)测定。硝态氮15N丰度:氨扩散法[20-21]收集,具体方法为,取适量浸提液(含氮100 μg左右),放入扩散容器中,将加有30 μl 2.5 mol L-1KHSO4的玻璃纤维滤纸,挂在扩散容器中(始终不接触浸提液),向浸提液中加入0.4 g戴氏合金,再加入2 ml 5 mol L-1NaOH,迅速密封扩散容器,在培养箱25℃下放置1周,以充分反应。7d后取出玻璃纤维滤纸,干燥后用锡囊包裹,用同位素比值质谱仪测定15N丰度。所有15N丰度测定均在美国加州大学戴维斯分校同位素分析中心完成。

表1 供试土壤基本理化性质(0~20 cm)Table 1 Physico-chemical properties of the tested soil(0~20 cm)

1.4 数据处理

土壤硝态氮含量(kg hm-2)=硝态氮含量(mg kg-1)×土壤容重(kg m-3)×面积(m2)×0.2(m)/1 000 000

土壤硝态氮累积量(kg hm-2)=每20 cm土层土壤硝态氮含量之和

15N标记硝态氮含量(kg hm-2)=土壤硝态氮含量×15N原子百分超/15N标记硝酸钾原子百分超

15N标记肥料氮残留量(kg hm-2)=全氮(g kg-1)×土壤容重(kg m-3)×面积(m2)×0.2(m)/1 000 000×15N原子百分超/15N标记硝酸钾原子百分超

15N标记肥料氮损失率(%)=(标记肥料氮施用量-0~100 cm土壤剖面标记肥料氮残留量)/标记肥料氮施用量×100

数据计算采用Excel 2007,数据统计分析采用SPSS 20.0,多重比较采用邓肯(Duncan)法。图表绘制采用Excel 2007和SigmaPlot 12.0。

2 结 果

2.1 小麦收获后硝态氮累积及休闲期间降水情况

小麦收获后5个试验田块0~200 cm土壤剖面硝态氮累积量在205~268 kg hm-2之间,平均244 kg hm-2(图2)。试验期间降水量为157 mm,蒸发量为100 mm。2014年降水量明显低于1957—2014年同期降水量的平均值(188mm),属欠水年[22]。同时,这期间的降水集中在8月5日—15日之间,达105 mm,其他时期降水量相对较少(图1)。

图2 五个田块收获后0~200 cm土壤剖面硝态氮累积量Fig. 2 NO3--N accumulation in the 0~200 cm soil layer in all the five tracts of cropland in the experiment after winter wheat was harvested

2.2 夏闲前后不同处理土壤剖面硝态氮含量变化

与休闲前相比,休闲后土壤剖面硝态氮累积峰并未发生明显下移(图3f),这与试验期间降水量(仅157 mm)低于多年同期(1957—2014年7月15日—9月5日期间降水量均值为188 mm)有关。休闲后5个田块施氮处理相比不施氮处理在0~100 cm土壤剖面中存在明显的硝态氮累积峰。但5个田块间存在一定差异,田块a~d休闲后施氮处理硝态氮累积峰位于40~60 cm土层,而田块e则达到了80~100 cm。同时,剖面中硝态氮含量存在差异,b和e田块较高,其余3个田块较低。

图3 休闲后0~200 cm土壤剖面硝态氮含量分布Fig. 3 NO3--N distribution in the 0~200 cm soil layer after summer fallow

2.3 夏闲后土壤剖面15N丰度的变化

15N的自然丰度为0.366%[23]。由图4可以看出,休闲后施氮处理0~100 cm土壤剖面15N丰度明显增加。5个田块0~100 cm土壤剖面中15N丰度分布趋势相同,均在60 cm处为最高,但丰度值存在差异,田块a和e中15N丰度较低,田块d则较高(图4),这与不同田块土壤剖面性质不同有关。各田块微区60 cm处15N丰度为0.408%~0.482%,平均为0.429%,80 cm处平均为0.372%,均高于土壤本底值,而100 cm深度其值为0.369%,与土壤本底值无异(表2)。可见,休闲初期加入的硝态氮深度为0~15 cm,经过一个夏季休闲已经下移至80 cm深处,下移深度为45~65 cm。

2.4 夏闲后肥料氮在土壤剖面分布与损失

经过一个休闲季后5个田块施氮处理在0~100 cm土壤剖面残留肥料氮的量为20.80~22.86 kg hm-2,平均21.58 kg hm-2,占施入肥料氮的71.9%。在0~20 cm残留有4.50 kg hm-2的标记肥料氮,其中2.9%仍是以硝态氮的形式存在。残留的肥料氮主要集中在40~60 cm土层,总含量为17.7 kg hm-2,占施入肥料氮的52.8%,其中标记硝态氮含量为6.85 kg hm-2,占施入肥料氮的22.8%(表2)。可见,休闲前以硝态氮形式存在于土壤的氮素经过休闲季节后会有较大一部分转化为其他形态氮素被土壤固持。在5个试验田块中,田块b微区残留肥料氮中以硝态氮形态存在的量最大,尤其是在60 cm处,残留的肥料氮主要是硝态氮,其次为c、d微区,a和e微区最少(图5)。

图4 夏季休闲后0~100cm土壤剖面15N丰度Fig. 4 15N abundance in the 0~100cm soil layer after summer fallow

表2 土壤剖面15N丰度和硝态氮15N丰度、15N标记肥料氮和硝态氮含量Table 2 15N abundance,nitrateabundance and contents of 15N labeledN fertilizerN and nitrate-N in thesoil profile

经过一个休闲季,5个田块施入肥料氮的损失率分别为30.4%、23.8%、29.4%、26.1%和30.8%,平均为28.1%(图6)。

图5 施氮处理0~100 cm剖面15N标记硝态氮和全氮含量Fig. 5 Contents of NO3--15N and total N in the 0~100 cm soil layer in Treatment N30

图6 施氮处理夏季休闲后肥料氮损失率Fig. 6 Loss rate of applied N fertilizer after summer fallow

3 讨 论

3.1 夏闲期残留肥料氮的迁移与损失

夏季休闲期间的降水量是影响氮素在土壤剖面移动的主要驱动因素[24]。本试验夏闲期间总降水量为157 mm,显著低于多年同期降水量(1957—2014年期间平均降水量为188mm),属欠水年。即使如此,休闲结束后肥料氮在土壤剖面向下迁移仍然较为明显,迁移的距离平均超过45 cm(图4)。黄土高原旱地一般出现欠水年的概率为27%,而平水、丰水年的概率则为73%。由此可知,肥料氮在旱地夏季休闲期间实际淋溶深度会更大,所以,夏季休闲期间残留肥料氮通过淋溶损失值得关注。

硝态氮在土壤剖面的移动与土壤水分状况及土壤质地[25]有密切关系。从机理上看,硝态氮以离子形态由土壤高湿度(低吸力)区域会向低湿度(高吸力)区域运移[26-27]。试验的2014年属欠水年,夏季休闲期间肥料氮在土壤剖面的向下移动很明显。这一方面与休闲期间总的降水量(157 mm)大于总蒸发量(100 mm)有关;同时,也与降水量的分布有关。休闲后至8月5日之前、8月15日—8月25日之间降水量小于蒸发量;而8月5日—8月15日期间出现集中降雨,仅8月5日—8月6日两天的降水量就达69 mm,远远大于蒸发量(5 mm),这可能是欠水年发生硝态氮在土壤剖面随降水向下层迁移的主要因素。黑垆土黏粒相对含量较少,质地较轻,也是发生肥料氮向下淋溶的因素之一。夏季休闲结束后5个田块中肥料氮的回收率平均为71.9%,损失率平均为28.1%。反硝化损失可能是夏季休闲期间氮素损失的途径之一。Nosalewicz等[28]指出,在0~30 cm土壤深度,随着温度或土壤含水量上升,N2O的释放量增加。Laville等[29]指出,温度一定,当土壤孔隙含水量达到68%时,土壤N2O释放量为最大。本研究施入的氮肥形态为硝态氮肥,夏季休闲期间高温多雨,可能会造成部分肥料氮发生反硝化作用,进而导致肥料氮的气态损失。此外,本研究采用微区为PVC管,其插入土壤的深度为22 cm,肥料氮下移深度大于60 cm,所以存在肥料氮横向迁移的可能。如Follett[30]曾指出,15N标记微区试验存在边界效应,会导致部分肥料氮进入微区以外的土体。因此,本研究存在高估肥料氮损失的可能。

3.2 夏闲期残留肥料氮的固持

本研究中加入的肥料氮形态为15N标记的硝态氮,但休闲结束后,0~100 cm土壤剖面以硝态氮存在的肥料氮仅占肥料氮的2.9%~46.6%,其中,0~20 cm土壤残留的肥料氮占0~100 cm土壤剖面残留肥料氮的14.3%,但以硝态氮形式存在的仅占这一土层肥料氮的2.9%(表2),说明加入的硝态氮在休闲期间有相当一部分转化成其他形态的氮素。其中的一个机理可能是,小麦收获后,残茬(包括地上部分及根茬)进入或保留在土壤中的有机物促进了土壤微生物对施入肥料氮的固持。有研究[31]指出,土壤微生物对氮肥的利用很迅速,施肥后5d土壤微生物对氮肥的固持达到最高,其固持量是施用肥料氮(150 kg hm-2)的5.4%。本研究中残留在0~100 cm土壤剖面的肥料氮主要累积在20~60 cm土层,该层次残留的肥料氮以硝态氮残留的比例在40.0%~46.5%之间,显著高于0~20 cm土层;但残留的肥料氮更多仍以其他形态氮存在。由于在该土层深度,通过根茬补充的有机物相对较少,再加上微生物活动相对较弱,因此,微生物的固持作用应该有限。

近来,关于硝态氮歧化还原为铵态氮的现象受到关注。Minick等[32]和Rütting等[33]均指出,氧化还原状况是影响硝态氮歧化还原为铵态氮的关键;在还原条件下培养,硝态氮歧化还原量占矿化产生的硝态氮的比例能超过60%[32]。本试验在8月5日—8月15日之间出现大量降水,且有几次单次降水量相对较高(图1),会使施入的肥料氮迅速下移;同时,短期大量降水的出现使40~60 cm土层处于还原状态,这两个条件可能满足了硝态氮歧化还原为铵态氮的要求,生成的铵态氮被土壤晶格固定,这可能是该层次硝态氮固持的另一个机理。

本研究采用施入15N标记硝态氮肥的方法模拟了夏季休闲期间土壤残留硝态氮的去向,与常规的测定土壤剖面硝态氮含量方法相比,15N方法可以区分肥料氮及土壤有机质矿化的氮素,进而可定量评价施入硝态氮的去向。但研究中15N标记氮肥的加入深度为0~15 cm土层,与作物收获后残留在土壤剖面的肥料氮累积的深度存在差异。Ju等[34]15N标记试验指出,氮素存在深度会影响硝态氮的垂直运移程度,硝态氮残留的深度越深,随水下移的程度越小。当然,为更加准确地研究旱地夏季休闲期间残留硝态氮的去向,下一步研究有必要将15N标记氮肥在小麦季直接施入,然后观测。

4 结 论

黄土高原旱地小麦收获后0~200 cm土壤剖面硝态氮累积量较高,在205~268 kg hm-2之间(平均244 kg hm-2)。2014年属欠水年,但休闲结束后,标记肥料氮向下迁移的深度达80 cm土层,主要集中在40~60 cm土层,说明,旱地休闲期间硝态氮的淋溶作用不可忽视。夏季休闲结束后,加入的15N标记肥料氮平均损失率为28%,损失机理值得进一步研究。

[1] 高焕文,李问盈,李洪文. 中国特色保护性耕作技术.农业工程学报,2003,19(3):1—4 Gao H W,Li W Y,Li H W. Conservation tillage technology with Chinese characteristics(In Chinese).Transactions of the Chinese Society of Agricultural Engineering,2003,19(3):1—4

[2] Gao Y J,Li Y,Zhang J C,et al. Effects of mulch,N fertilizer,and plant density on wheat yield,wheat nitrogen uptake,and residual soilnitrate in a dryland area of China. Nutrient Cycling in Agroecosystems,2009,85(2):109—121

[3] TurnerN C,Li F M,Xiong Y C,et al. Agricultural ecosystem management in dry areas:Challenges and solutions. Plant and soil,2011,347(1):1—6

[4] He G,Wang Z H,Li F C,et al. Soil nitrate-N residue,loss and accumulation affected by soil surface management and precipitation in a winter wheatsummer fallow system on dryland. Nutrient Cycling in Agroecosystems,2016,106(1):31—46

[5] 山仑. 旱地农业技术发展趋向. 中国农业科学,2002,35(7):848—855 Shan L. Development trend of dryland farming technologies(In Chinese). Scientia Agricultura Sinica,2002,35(7):848—855

[6] 闫湘,金继运,何萍,等. 提高肥料利用率技术研究进展. 中国农业科学,2008,41(2):450—459 Yan X,Jin J Y,He P,et al. Recent advances in technology of increasing fertilizer use efficiency(In Chinese). Scientia Agricultura Sinica,2008,41(2):450—459

[7] 王西娜,王朝辉,李华,等. 旱地土壤中残留肥料氮的动向及作物有效性. 土壤学报,2016,53(5):1202—1212 Wang X N,Wang Z H,Li H,et al. Dynamics and availability to crops of residual fertilizer nitrogen in upland soil(In Chinese). Acta Pedologica Sinica,2016,53(5):1202—1212

[8] 赵伟,梁斌,周建斌. 施入15N标记氮肥在长期不同培肥土壤的残留及其利用. 土壤学报,2015,52(3):587—596 Zhao W,Liang B,Zhou J B.Residual of applied15N fertilizer in soilsunder long-term different patterns of fertilization and its utilization(In Chinese). Acta Pedologica Sinica,2015,52(3):587—596

[9] Dai J,Wang Z H. Li F C,et al. Optimizing nitrogen input by balancing winter wheat yield and residual nitrate-N in soil in a long-term dryland field experiment in the Loess Plateau of China. Field Crops Research,2015,181:32—41

[10] Zhou J Y,Gu B J,Schlesinger W H,et al. Significant accumulation of nitrate in Chinese semi-humid croplands. Scientific Reports,2016,6:Article number:25088

[11] Conway G R,Pretty J N. Unwelcome harvest:Agriculture and pollution. London:Earthscan Publications,1991

[12] 巨晓棠,谷保静. 我国农田氮肥施用现状、问题及趋势. 植物营养与肥料学报,2014,20(4):783—795 Ju X T,Gu B J. Status-quo,problem and trend of nitrogen fertilization in China(In Chinese). Plant Nutrition and Fertilizer Science,2014,20(4):783—795

[13] Galloway J N,Aber J D,Erisman J W,et al. The nitrogen cascade. Bioscience,2003,53(4):341—356

[14] Wang G L,Chen X P,Cui Z L,et al. Estimated reactive nitrogen losses for intensive maize production in China. Agriculture,Ecosystems & Environment,2014,197:293—300

[15] Kanter D R,Zhang X,Mauzerall D L. Reducing nitrogen pollution while decreasing farmers’costs and increasing fertilizer industry profits. Journal of Environmental Quality,2015,44(2):325—335

[16] 彭琳,彭祥林,卢宗藩. 塿土旱地土壤硝态氮季节性变化与夏季休闲的培肥增产作用. 土壤学报,1981,18(3):211—222 Peng L,Peng X L,Lu Z F.NO3--N seasonal change in dryland and fertilization production role during summer fallow of Lou soil(In Chinese). Acta Pedologica Sinica,1981,18(3):211—222

[17] Darwiche-Criado N,Comín F A,Sorando R,et al.Seasonal variability of NO3-mobilization during flood events in a Mediterranean catchment:The influence of intensive agricultural irrigation. Agriculture,Ecosystems & Environment,2015,200:208—218

[18] 戴健,王朝辉,李强,等. 氮肥用量对旱地冬小麦产量及夏闲期土壤硝态氮变化的影响. 土壤学报,2013,50(5):956—965 Dai J,Wang Z H,Li Q,et al. Effects of nitrogen application rate on winter wheat yield andsoil nitrate nitrogen during summer fallow season on dryland(In Chinese). Acta Pedologica Sinica,2013,50(5):956—965

[19] Hauck R D,Bremner J M. Use of tracers for soil and fertilizer nitrogen research. Advances in Agronomy,1976,28:219—266

[20] Sebilo M,MayerB,Grably M,et al. The use of the ammonium diffusion method for δ15N-NH4+and δ15N-NO3-measurements:Comparison with other techniques. Environmental Chemistry,2004,1(2):99—103

[21] Brooks P D,Stark J M,McInteer B B,et al. Diffusion method to prepare soil extracts for automated nitrogen-15 analysis. Soil Science Society of America Journal,1989,53(6):1707—1711

[22] 吴义城,袁业畅,任耀武,等. 农业气候影响评价:农作物气候年型划分方法(GB/T 21986-2008). 北京:中国标准出版社,2008 Wu Y C,Yuan Y C,Ren Y W,et al. Assessment of agroclimate impact:Classification method of annual crop climate type(GB/T 21986-2008)(In Chinese).Beijing:Standards Press of China,2008

[23] Högberg P. Tansleyreview No. 95∶15N natural abundance in soil-plant systems. The New Phytologist,1997,137(2):179—203

[24] 郭胜利,吴金水,郝明德,等. 长期施肥对 NO3--N 深层积累和土壤剖面中水分分布的影响. 应用生态学报,2003,14(1):75—78 Guo S L,Wu J S,Hao M D,et al. Effect of longterm fertilization on NO3--N accumulation and moisture distribution in soil profiles(In Chinese). Chinese Journal of Applied Ecology,2003,14(1):75—78

[25] 刘愫倩,徐绍辉,李晓鹏,等. 土体构型对土壤水氮储运的影响研究进展. 土壤,2016,48(2):219—224 Liu S Q,Xu S H,Li X P,et al. Effects of soil profile configuration on soil water and nitrogen storage and transportation:A review(In Chinese). Soils,2016,48(2):219—224

[26] 郭大应,熊清瑞,谢成春,等. 灌溉土壤硝态氮运移与土壤湿度的关系. 灌溉排水,2001,20(2):66—68 Guo D Y,Xiong Q R,Xie C C,et al. Feasibility analysis on irrigation return flow reuse system in Hetao irrigation district in Inner Mongolia(In Chinese).Irrigation and Drainage,2001,20(2):66—68

[27] 陈效民,邓建才,柯用春,等. 硝态氮垂直运移过程中的影响因素研究. 水土保持学报,2003,17(2):12—15 Chen X M,Deng J C,Ke Y C,et al. Study on influence factors in process of nitrate vertical transport(In Chinese). Journal of Soil and Water Conservation,2003,17(2):12—15

[28] Nosalewicz M,Stepniewska Z,Nosalewicz A. Effect of soil moisture and temperature on N2O and CO2concentrations in soil irrigated with purified wastewater.International Agrophysics,2013,27(3):299—304

[29] Laville P,Lehuger S,Loubet B,et al. Effect of management,climate and soil conditions on N2O and NO emissions from an arable crop rotation using high temporal resolution measurements. Agricultural and Forest Meteorology,2011,151(2):228—240

[30] Follett RF. Innovative15N microplot research techniques to study nitrogen use sufficiency under different ecosystems. Communications in Soil Science and Plant Analysis,2001,32(7/8):951—979

[31] 韩晓日,郭鹏程,陈恩芬,等. 土壤微生物对施入肥料氮的固持及其动态研究. 土壤学报,1998,35(3):412—418 Han X R,Guo P C,Chen E F,et al. Immobilization of fertilizer nitrogen by soil microbes and its changes(In Chinese). Acta Pedologica Sinica,1998,35(3):412—418

[32] Minick K J,PandeyC B,Fox T R,et al. Dissimilatory nitrate reduction to ammonium and N2O flux:Effect of soil redox potential and N fertilization in loblolly pine forests. Biology and Fertility of Soils,2016,52(5):601—614

[33] Rütting T,Boeckx P,Müller C,et al. Assessment of the importance of dissimilatory nitrate reduction to ammonium for the terrestrial nitrogen cycle.Biogeosciences,2011,8(7):1779—1791

[34] Ju X T,Gao Q,Christie P,et al. Interception of residual nitrate from a calcareous alluvial soil profile on the North China Plain by deep-rooted crops:A15N tracer study. Environmental Pollution,2007,146(2):534—542

Fate of15N Labeled Nitrate in Dryland under Summer Fallow on the Loess Plateau

XIA Mengjie CHEN Zhujun LIU Zhanjun ZHOU Jianbin†
(College of Natural Resources and Environmental,Northwest A&F University,Key Laboratory of Plant Nutrition and the Agrienvironment in Northwest China,Ministry of Agriculture,Yangling,Shaanxi712100,China)

【Objective】Summer fallow after winter wheat is harvested in dryland on the Loess Plateau is a very common practice to save rain water,and restore soil fertility for the next crop. Nowadays,the content of nitrogen(N)(mainly in nitrate form)in the soil of the dryland as residue of the fertilizer applied to winter wheat is increasing steadily. As summer is the rainy season in this region,whether or not the high rainfall would increase NO3--N leaching loss is an important issue deserving further study. The method of adding15N labeled nitrate after winter wheat is harvested in dryland is one to quantitativelyexplore fate of the residual fertilizer N in the dryland under summer fallow in the Loess Plateau,and hence to provide a scientific basis for managing Nin dryland.【Method】The15N labeled fertilization micro-plot(Polyvinylchloridecolumn,25 cm diameter and 25 cm long)method was used to study fate of the residual fertilizer N in the dryland under summer fallow in a field experiment,which hadfive tracts of cropland and two N treatments set up with and without N application(0 and 30 kg N hm-2).15N labeled nitrate was mixed with the surface soil(0~15 cm)in the micro-plot at a rate equal to the content of the residual fertilizer N in the field after winter wheat was harvested. At the end of the summer fallow,soil samples throughout the soil profile(0~200 cm)were taken fromthe micro-plots,for analysis the contents of soil total nitrogen,NO3--N,and their15N abundance.【Result】Results show that at the beginning of the summer fallow,the content of NO3--N accumulated in the 0~200 cm soil was quite high,ranging between 205 and 268 kg hm-2and averaging 244 kg hm-2;At the end of the summer fallow,apparent NO3--N accumulation peaks were found in the soil,40~80 cm in depth,and15N abundance ranged between 0.408% and 0.482% and averaged 0.429%,being the highest in the soil 60 cm in depth,averaged 0.372% in the soil 80 cm in depth,being higher than the background value of15N abundance in the soil(0.36715N atom%),and was 0.369 % in the soil 100 cm in depth,more or less the same as the background value,in Treatments N30 in all the five tracts of cropland. In the five tracts of cropland,15N labeled nitrate abundance was the highest in the 40~60 cm soil layer in the soil profiles(0~100 cm),averaging 2.151%;and the lowest abundance was in the 80~100 cm soil layer,averaging 0.407%,both significantly higher than the background value. Although the rainfall during the summer fallow season was only 157 mm,making it a dry year,it still leached15N labeled nitrate down to 80 cm in depth,through a 45~65 cm thick soil layer,and even15N labeled nitrate was found in 100 cm depth. At the end of the fallow,the content of residual N averaged 21.6 kg hm-2or ranged between 20.8 and 22.9 kg hm-2in the 0~100 cm soil profile,accounting for 71.9% of the applied N fertilizer in all the five tracts of cropland.The content of residual labeled N was 4.5 kg hm-2,2.9% of which was in the form of NO3-- N in the 0~20 cm soil layer;Residual fertilizer N was mainly distributed in the 40~60 cm soil layer,and averaged 17.7 kg hm-2in content,accounting for 52.8% of the total N fertilizer applied,in which15N labeled nitrate content was 6.8 kg hm-2. After the summer fallow,the applied15N labeled N fertilizer was found lost at a rate of 23.8%~30.8%(averaging 28.1%).【Conclusion】Residual fertilizer N accumulated significantly in the 0~200cm soil layer of the dryland after wheat was harvested,posing a potential risk of leaching. In 2014,though it was a dry year,the effect of rain water leaching NO3--N was still quite significant,indicating that the NO3--N leaching in the dryland during the summer fallow season should not be ignored and further studies should be done on mechanisms of its leaching loss.

Dryland;Summer fallow;15N labeled fertilization method;Residual fertilizer N;Nitrate leaching

S158.5

A

10.11766/trxb201704120060

* 国家自然科学基金项目(31372137)资助 Supported by the National Natural Science Foundation of China(No. 31372137)

† 通讯作者 Corresponding author,E-mail:jbzhou@nwsuaf.edu.cn

夏梦洁(1990—),女,浙江嘉兴人,博士研究生,主要研究植物营养与调控。E-mail:xmj629@126.com

2017-04-12;

2017-05-12;优先数字出版日期(www.cnki.net):2017-05-24

(责任编辑:陈荣府)

猜你喜欢
旱地硝态田块
“施肥宝” 微信小程序端设计与实现
旱地麦田夏闲期复种绿肥 保持土壤的可持续生产力
电化学法去除硝态氮的研究
水稻-红螯螯虾共作模式下不同虾苗放养模式对比试验
旱地冰球运动开展价值的研究
田块尺度上的农田土壤Cd污染分布不均匀性*
旱地冰球运动推广及发展策略
活性碳源显著降低蔬菜地土壤硝态氮
滴灌施氮对高垄覆膜马铃薯产量、氮素吸收及土壤硝态氮累积的影响
长期施肥下红壤旱地土壤CO2排放及碳平衡特征