氮素调节玉米幼穗及籽粒发育的生理机制

选用高效吸收利用氮素的氮高效品种,是在适当降低施氮量的条件下维持较高产量水平的重要途径之一。国内外有关氮高效生理、遗传基础研究方面已经开展了多年的工作,在硝酸盐和铵转运蛋白基因克隆与功能分析、氮素调节根系发育、氮素诱导的基因表达谱、氮高效性状QTLs定位等方面都取得了重要进展,但这些研究集中于营养器官,很少涉及到作物产量器官——穗和籽粒。以玉米为例,综述了氮素供应不足对穗、籽粒发育的影响,并重点从氮素代谢相关酶及细胞分裂素信号互作的角度,论述了氮素调节玉米穗和籽粒发育的可能生理机制,提出了一个理论假设。图2,参36。     

氮肥减施下添加硝化抑制剂对夏玉米灌浆期叶片生理特性的影响

为明确氮肥减施条件下添加硝化抑制剂对夏玉米灌浆期叶片生理特性的影响,本研究设置氮肥正常施用量、氮肥不同减施量及其添加硝化抑制剂处理,研究玉米灌浆期叶片SPAD值、荧光特性、氮素代谢关键酶活、籽粒产量及氮效率的变化。结果表明,氮肥减施20%时添加硝化抑制剂处理能够显著增加果穗粒数,籽粒产量为11.59 t·hm^-2,达到正常施氮量水平。与正常施氮处理相比,氮肥减施30%和20%时添加或不添加硝化抑制剂,氮效率均显著提高,其中氮吸收效率和氮利用效率在各处理间表现不一致,氮吸收效率以氮肥减施30%处理最高,为0.72 kg·kg^-1,氮利用效率以氮肥减施30%添加硝化抑制剂最高,为72.23 kg·kg^-1。玉米灌浆期,氮肥减施20%并添加硝化抑制剂处理下穗位叶SPAD值优势明显,最大荧光和PSⅡ综合性能指数等荧光指标明显提高,氮素代谢关键酶硝酸还原酶(NR)和谷氨酰胺合成酶(GS)活性显著增强。综上,在本试验条件下,氮肥减施20%并添加硝化抑制剂能增强玉米灌浆期氮素代谢能力,协调碳氮代谢之间的关系,提高氮效率,增加玉米籽粒产量,达到玉米节本增效的目的。本研究结果为在夏玉米生产上推广施用硝化抑制剂提供了理论依据。     

施氮量和密度互作对玉米产量和氮肥利用效率的影响

【目的】施氮量、种植密度等主要栽培措施的互作效应,往往使氮肥利用效率难以估计和评价,定量分析施氮量和密度互作下玉米产量和氮肥利用效率 (NUE) 响应的生理过程,对玉米高产氮高效栽培具有参考价值。 【方法】以郑单958为材料,在3个种植密度 (4.5、7.5和10.5万株/hm2) 和3个施氮量 (N 0、150和300 kg/hm2) 条件下进行田间试验。在14叶展期 (V14)、吐丝期 (R1)、灌浆期 (R3) 和成熟期 (R6) 取样,采用长宽系数法测定叶面积后,将样品分为叶片、茎秆 (含叶鞘、雄穗) 和雌穗 (R1、R3);在成熟期,将样品分为茎秆 (包括叶片、茎鞘、苞叶、穗轴) 和籽粒两部分,记录干质量,测定植株及籽粒全氮含量。分析了玉米碳氮积累与产量形成和氮肥吸收利用的关系。 【结果】与N150相比,N300既没有提高玉米群体碳氮积累总量,也没有提高个体生产能力,氮肥利用效率较低;N150和D10.5条件下,玉米产量和氮肥利用效率最高,说明减氮增密是协同提高玉米产量和氮肥利用效率的重要途径。施氮和增密的氮素积累优势主要受V14—R3阶段干物质积累的驱动,且这种关系在花前V14前后就已经建立。V14—R3阶段干物质积累速率与氮素积累速率呈显著正相关,施氮和增密明显促进氮素积累对干物质积累的响应强度。施氮和增密下玉米以花前较低氮浓度获得较高氮积累量,也说明其花前氮积累是以花前大量茎叶干物质积累为前提,花后氮积累则主要取决于雌穗干物质积累。氮密互作对氮收获指数 (NHI) 无显著影响,而适宜施氮和增密显著提高HI,说明减氮增密获得较高的氮肥利用效率,而与籽粒中氮素分配多少无关,主要取决于籽粒中干物质分配的多少。 【结论】施氮量和密度互作通过影响干物质积累量、产量和氮积累量影响氮肥利用效率。合理减氮增密通过促进V14—R3阶段作物生长率和花后物质生产,驱动充足的氮素积累和干物质分配,实现产量与氮肥利用效率的协同提高。     

不同包膜控释肥施用对轮作作物养分利用效率的影响

为揭示不同包膜控释肥对轮作作物氮、硫养分利用效率的差异,在池栽条件下,连续2年选用控释掺混肥(SCU+PCU)、硫加树脂包膜控释氮肥(PSCU)和树脂包膜控释氮肥(PCU)在夏玉米-冬小麦体系中,研究不同包膜控释肥对轮作作物籽粒产量的差异及与氮素利用效率和硫素利用效率的关系。结果表明:施用控释掺混肥和PSCU均可明显促进作物生长,增加植株对氮和硫的吸收,使作物氮素利用效率与硫素利用效率协同提高,在保持植株一定氮素和硫素积累量的基础上,通过提高氮素和硫素的收获指数促进籽粒产量的增加,夏玉米季SCU+PCU,PSCU,处理的氮肥利用率均高于Urea处理分别为19.6%,15.65%,实现作物对氮素的高效利用。     

不同氮效率玉米根系时空分布与氮素吸收对氮肥的响应

【目的】 研究玉米根系时空分布对不同供氮水平的响应及其与植株氮素吸收的关系,对于充分挖掘氮高效基因型,探讨氮高效栽培途径具有重要意义。 【方法】 以氮高效玉米品种 (郑单 958、金山 27) 和氮低效玉米品种 (蒙农 2133 、内单 314) 为材料,以不施氮为对照 (N0),施氮 300 kg/hm2 为适量处理 (N300)、450 kg/hm2 为过量处理 (N450),进行了两年田间试验,调查了玉米根重、根长的时空分布及其与植株氮素吸收量的关系。 【结果】 对照 (N0) 和适量施氮 (N300) 条件下,氮高效品种的根系生物量显著高于氮低效品种,过量施氮 (N450) 条件下二者在吐丝前无显著差异,吐丝后氮高效品种根重降低缓慢,根系生物量高于氮低效品种。N0 和 N300 条件下,氮高效品种 0—100 cm 土层根长均显著高于氮低效品种,吐丝期到乳熟期,N0 处理 0—20 cm 耕层和 40 cm 以下土层内,氮高效品种的根系降低比率显著低于氮低效品种;施氮条件下,两类型品种 0—40 cm 土层内根系降低比率无显著差异,但 40 cm 以下土层氮高效品种根系降低比率显著低于氮低效品种。吐丝前氮素吸收量在 N0 和 N300 条件下,单位根长氮吸收速率对氮素吸收的直接作用较大,直接通径系数是 0.590 和 0.649,在 N450 条件下,根长对于氮素吸收的直接作用较大,直接通径系数是 0.536;吐丝后氮素吸收量在 N0 和 N300 条件下,根长对氮素的吸收直接作用较大,直接通径系数是 1.148 和 0.623,在 N450 条件下,单位根长氮吸收速率对氮素吸收的直接作用较大,直接通径系数是 0.858。 【结论】 不同氮效率玉米品种根系分布和氮素吸收对氮肥的响应存在明显差异。在低氮和适量施氮条件下,氮高效品种较氮低效品种表现出较高的根系生物量、根长和较低的根系衰老速率,其吐丝前氮素吸收主要与单位根长氮吸收速率有关,吐丝后则主要与根长有关;过量施氮条件下,其吐丝前氮素吸收主要受根长影响,吐丝后则主要与单位根长氮吸收速率有关。      

施氮模式对玉-麦周年轮作系统产量和氮吸收利用的影响

为明确适宜豫北平原夏玉米-冬小麦一体化种植的高效施氮管理模式,2016—2017年分别在豫北典型高产田区河南省鹤壁市和中产田区河南省原阳县开展了夏玉米-冬小麦周年轮作不同施氮模式对夏玉米与冬小麦产量、氮素吸收和利用效率影响的田间试验。共设5种处理:不施氮肥(T1)、普通尿素按210 kg(N)?hm?2一次性基施(T2)、普通尿素分次施用且总施氮量同T2(T3)、控释尿素与普通尿素配比氮素减量施用(T4)和控释尿素与普通尿素配比氮素足量施用(T5)。分别于夏玉米和冬小麦关键生育期测试叶片SPAD值、植株与籽粒氮含量及生物量等氮营养指标,并于成熟期测定产量和产量构成因子,分析计算植株氮积累量与吸收利用特征。结果表明,处理间,高、中产区夏玉米与冬小麦产量、产量构成因子及氮素营养指标整体变化趋势均为T5T4T3T2T1。产区间,各处理夏玉米和冬小麦产量性状及氮营养指标均表现为高产区显著优于中产区。综合各处理平均值,高产区夏玉米产量、植株氮含量和氮素积累量相比于中产区分别平均提高58.0%、19.2%和47.1%,冬小麦增幅则分别为34.7%、33.3%和85.9%。氮利用效率方面,高、中产田在氮肥表观利用率、氮肥农学效率和100kg籽粒需氮量变化趋势均表现为T5T4T3T2T1,处理间差异显著;氮素收获指数则与此相反。豫北平原夏玉米-冬小麦周年轮作制在作物稳产甚至增产条件下,采用尿素与缓释氮肥掺混配施的氮肥优化施用模式不仅可有效减少肥料用量,还能显著提升肥料利用率,降低氮肥损失。     

施氮量对不同氮效率玉米品种根系时空分布及氮素吸收的调控

【目的】研究不同氮效率夏玉米根系的时空分布、 植株氮素吸收利用特性及其对氮素用量的响应,探讨玉米氮素高效利用的生理基础,以期探明通过采用氮高效品种、 促进根土互作、 提高根系与水肥时空耦合、 提高玉米氮素利用效率,强化环境友好型生产的有效途径。【方法】试验于2011-2012年在山东农业大学黄淮海玉米技术创新中心（N3618,E11712）和作物生物学国家重点实验室进行,以氮高效玉米品种郑单958（ZD958）和氮低效品种玉米秀青73-1（XQ73-1）为试验材料,在大田条件下设置两个氮素水平（0和315 kg/hm2）,采用土壤剖面取样法和系统取样法分别进行根系相关指标、 干物质及氮素积累与分配的测定。【结果】ZD958整个生育期根系相关指标（根系干重、 根长密度、 根系TTC还原量、 根系吸收面积及活跃吸收面积）及其在深层土壤（60-100 cm）中所占的比例、 单株生物量、 单株绿叶面积、 植株氮素积累量、 单株籽粒产量均显著高于XQ73-1（P0.05）,抽雄期和完熟期根系干重、 根长密度、 根系TTC还原量、 根系吸收面积、 根系活跃吸收面积、 单株绿叶面积分别比XQ73-1高12.02%、 8.39%、 25.34%、 34.48%、 29.22%、 7.76%和36.74%、 24.21%、 36.29%、 29.94%、 32.83%、 13.73%,完熟期单株生物量、 植株氮素积累量、 籽粒产量分别比XQ73-1高11.65%、 11.78%、 15.16%。施氮后两品种各指标均显著提高,ZD958和XQ73-1根系干重、 根长密度、 根系TTC还原量、 根系吸收面积、 根系活跃吸收面积、 单株绿叶面积抽雄期分别提高8.13%、 6.12%、 18.08%、 15.10%、 24.71%、 12.06%和7.19%、 4.59%、 10.47%、 10.82%、 13.02%、 7.15%,而完熟期分别提高16.48%、 22.43%、 19.26%、 15.03%、 27.45%、 14.97%和15.02%、 14.59%、 13.01%、 12.81%、 21.95%、 11.06%; 单株生物量、 植株氮素积累量、 单株籽粒产量完熟期分别提高9.40%、 10.08%、 13.43%和5.20%、 8.56%、 9.69%。相关分析表明,植株吸氮量与根长密度、 根系干重、 根系活跃吸收面积呈显著线性正相关（相关系数均在0.8以上）。 ZD958花前根系对氮素的响应度高于XQ73-1,花后则低于XQ73-1。【结论】氮高效玉米品种ZD958根系总量大、 深层土壤根系多、 根系活力高、 氮素吸收能力强; 施氮条件下优势更加明显,对ZD958作用大于XQ73-1,说明氮高效玉米品种发达且分布合理的根系保证了植株对氮素的吸收,有利于进行光合生产、 获得较高籽粒产量。两品种对氮素的响应不同,氮高效品种花前对氮素的响应度高于氮低效品种,花后则相反。因此,可过适度减少氮高效品种花前施氮量、 增加花后施氮量,而适度增加氮低效品种花前施氮量、 降低花后施氮量来促进根系发育,提高氮素利用效率。     

冀东地区晚播春玉米氮素积累、分配与转运特性

为明确冀东地区晚播春玉米氮素积累、分配与转运特性,2017—2018年以京农科728和MC812为供试材料进行了2年的田间试验,以常规播期(5月1日)为对照,分析了冀东地区晚播(5月30日)春玉米氮素积累动态和阶段积累特性及其在各器官中的分配和转运特性。结果表明,冀东地区春玉米氮素的积累动态符合Logistic模型,与常规播期比较,晚播春玉米氮素积累的渐增期和缓增期持续时间缩短,而快增期持续时间延长;氮素平均积累速率、渐增期和缓增期积累速率提高,氮素总积累量增加。晚播显著促进抽雄期-成熟期植株对氮素的吸收,此阶段京农科728和MC812氮素吸收量比常规播期分别增加72.56%和18.39%,阶段吸收百分率均达45%以上。晚播使春玉米茎鞘中氮素分配率提高,叶片的氮素分配率降低,同时还促进了叶片向籽粒转运氮素,使其转运量、转运率以及对籽粒的贡献率提高;成熟期晚播春玉米籽粒氮素分配比例达73.82%~77.41%。另外,晚播提高了春玉米产量,使氮素收获指数和氮素偏生产力同步提高;百公斤籽粒氮素吸收量基本不受播期的影响。综上可知,在晚播春玉米生产中,应注意增加氮肥施用量,选择基施肥效较长的缓释肥或在春玉米生长后期追施氮肥,以保证春玉米生育后期土壤有效氮的充足供应,保持叶片活力,维持叶片光合能力,促进春玉米增产。本研究对冀东地区晚播春玉米氮肥合理施用具有一定的指导意义。     

氮肥运筹对黄土高原春玉米产量形成和氮代谢的调控效应

为明确黄土高原旱地春玉米减肥增效的科学生产模式,采用完全随机裂区试验设计,以氮肥梯度(N1:225 kg/hm²;N2:275 kg/hm²;N3:325 kg/hm²)为主区,在播种前、大喇叭口期追肥分别占总施氮量的20%、40%条件下,以氮肥后移比例(传统追肥M1:拔节期40%;氮肥后移10% M2:拔节期30%+开花后10 d 10%;氮肥后移20% M3:拔节期20%+开花后10 d 20%;氮肥后移30% M4:拔节期10%+开花后10 d 30%)为副区,测定玉米不同生育阶段硝酸还原酶(NR)活性、花期和成熟期茎秆叶片氮含量变化、花后氮素转运特征和籽粒产量。结果表明:M4处理显著增加了拔节期之后玉米叶片NR活性,同一氮肥运筹模式下,中氮(N2)提高了灌浆期及灌浆期之后玉米叶片NR活性,高氮(N3)反而抑制NR活性。氮肥后移提高了花期、成熟期玉米茎秆叶片氮含量,成熟期N3处理下氮肥后移处理M2、M3、M4较传统追肥M1处理分别高10.1%、14.7%和23.5%。同一施氮水平下,氮肥后移比例越大,玉米茎秆氮素转运量、转运率和对籽粒的贡献率越高,而N2水平下,M4处理显著增加了叶片对籽粒的贡献率。N2和N3水平下M4处理籽粒产量无显著差异,但N2处理纯利润显著高于N3处理。施氮275 kg/hm²且氮肥后移30%(拔节期追肥27.5 kg/hm²+开花后10 d追肥82.5 kg/hm²)有利于玉米增产,促进农户增收。     

实现黑土玉米高产和养分高效的控释氮肥与尿素掺混比例

  【目的】  控释氮肥与普通尿素配合施用是东北黑土区实现轻简化施肥的有效技术途径之一。研究控释氮肥与普通尿素适宜的掺混比例,以实现氮肥一次性施用获得高产高效和可持续利用。  【方法】  于2017—2019年在吉林省公主岭市,以玉米品种‘富民108’为试材,在施N 210 kg/hm2条件下,共设置6个普通尿素与控释氮肥掺混比例处理,分别为:10∶0 ( RU)、8∶2 (CRU20%)、6∶4 (CRU40%)、4∶6 (CRU60%)、2∶8 (CRU80%)、0∶10 (CRU100%),并以不施氮肥(N0)为对照。于玉米主要生育期调查植株生物量、氮含量和土壤无机氮含量,并于成熟期测定产量及其构成因素,计算作物氮积累量、氮素利用率和土壤?作物系统氮素平衡状况。  【结果】  控释氮肥与普通尿素掺混各处理玉米穗粒数和百粒重均高于RU处理,显著提高了玉米产量(P<0.05),其中以CRU60%处理增幅最高,3年平均产量提高了17.3%。与RU处理相比,控释氮肥与普通尿素掺混显著提高了玉米开花期至成熟期土壤无机氮含量,增加了开花期至成熟期氮素积累及其占总生育期氮素积累比例,进而提高了玉米开花后氮素积累对籽粒氮的贡献率。控释氮肥与普通尿素掺混各处理氮素回收率、农学利用率和偏生产力均随控释氮肥比例的增加呈先增后减趋势,其中以CRU60%处理最高,较RU处理分别提高36.1%、66.9%和17.3%。土壤?作物系统氮素平衡状况表明,氮素表观损失量随控释氮肥比例的增加先降后升,以CRU60%处理氮素表观损失量最低,较RU处理降低了28.8%。将控释氮肥与普通尿素掺混比例与产量、氮素利用率、土壤无机氮含量和氮素表现损失量分别进行拟合,得出当控释氮肥的掺混比例为63.4%时,玉米理论产量最高,为11059 kg/hm2,相对应的氮素回收率为42.4%、农学利用率为17.1 kg/kg、偏生产力为53.2 kg/kg;土壤无机氮含量为20.8 mg/kg;3年累计氮素表观损失量为223.1 kg/hm2;其结果与得到最高产量处理(CRU60%)相对应的玉米产量、土壤无机氮含量和氮素利用率结果相近。以理论最佳控释氮肥比例的95%作为置信区间,求得适宜控释氮肥掺混比例为61%～67%。  【结论】  在东北黑土区,60%控释氮肥与40%普通尿素配合一次施用可提高玉米生育后期土壤无机氮供应能力,促进玉米氮素吸收,进而显著提高玉米产量和氮素利用率,并降低氮素损失量。     

不同氮效率玉米杂交种的根系生长、氮素吸收与产量形成

以氮效率不同的4个玉米杂交种(组合)为材料,在两个氮水平下分析了根系大小与氮素累积及产量形成方面的相互关系。结果表明,氮高效杂交种(NE1和ND108)吸氮量显著高于氮低效品种,但这种差异主要来自于吐丝后氮累积量,而在前期不同基因型间氮素累积差异不显著。两个氮水平下,氮高效品种NE1和ND108都具有较大的根系;在不施氮条件下,氮低效品种209115的根系干重与ND108相近,而其氮累积量及产量均最低。说明根系大小是决定氮累积量的主导因素,但氮吸收速率的作用也不可忽视。     

甜玉米氮素吸收利用的基因型差异

以近年来育成的22个甜玉米品种为材料,在同一供氮水平下对其氮素吸收利用的基因型差异进行了研究。结果表明,不同品种产量、氮素积累量和氮素利用效率都存在着显著差异。氮素积累量变幅为126.6～243.8 kg/hm2,鲜果穗和鲜子粒氮素利用效率的变幅分别为43.5～62.0 kg/kg和28.4～46.0 kg/kg。聚类分析结果看出,鲜果穗、鲜子粒均表现为高产、氮素积累量大、氮素利用效率高的品种是金凤5号、穗美9701和金师王,其氮素积累量均值为214.4kg/hm2,鲜果穗和鲜子粒的氮素利用效率分别为50.8kg/kg和38.2kg/kg。通径分析表明,氮素积累量对不同品种产量的作用大于氮素利用效率对产量的作用,说明鲜食甜玉米品种的高产关键在于改良品种的氮素积累量,并在此基础上提高氮素的利用效率。     

川中丘区玉米氮高效品种筛选及增产潜力分析

为探究高产氮高效玉米品种在减肥增效措施中的增产潜力,本研究通过对川中丘陵区近十年11个主推玉米品种在2个环境(简阳和中江)和3个氮水平[0(LN)、150(MN)和300 kg·hm^-2(HN)]下的田间产量及产量构成因子等进行方差和相关性分析,依据产量的基因型×氮互作效应对玉米品种进行氮效率分类,研究不同类型玉米的增产潜力以及与增产潜力有关的产量性状。结果表明,基因型、氮、环境及其互作显著影响玉米产量,基因型×氮互作显著影响穗粗和百粒重;11个试验玉米品种存在氮效率的基因型差异,包括双高效型、高氮高效型、耐低氮型和双低效型4种类型,其中双高效型和高氮高效型占总数的45.5%,其在HN和LN的增产潜力分别为6.74%~7.54%和9.88%~13.45%;高产氮高效品种(双高效型和高氮高效型)在2个试验点的节氮潜力差异较大,HN的节氮潜力可达19.18%以上;增产潜力与穗粗、百粒重等产量构成因子显著正相关;正红311、川单189和绵单1256在2个环境下均表现出高产氮高效品种特征。在川中丘陵区不同肥力的土壤上选择种植高产氮高效或耐低氮的玉米品种,通过合理施肥,可以达到增产/稳产和节氮增效的目的。本研究对川中丘陵区玉米高产氮高效品种的选育和推广应用具有重要理论意义。     

Durum Wheat Genotypic Variation of Yield and Nitrogen use Efficiency and Its Components Under Different Water and Nitrogen Regimes in the Mediterranean Region

Farmers in dry areas of the Mediterranean region are reluctant to apply nitrogen (N) fertilizer to rainfed wheat because of frequent drought. So, it is desirable to select varieties with high nitrogen use efficiency (NUE). The objectives of this study, conducted in 2009/10 and 2010/11 in Syria, were to study the response of genotypes of durum wheat to low and high N applications and to evaluate the contribution of N uptake efficiency and utilization efficiency to NUE under rainfed and supplemental irrigation conditions. Under the rainfed regime, grain yield decreased significantly in year 1 and year 2 when applying N fertilizer at a high rate. The early maturing genotypes gave the highest average yields under rainfed and irrigated regimes. High N fertilizer rate decreased significantly NUE from 36.1 to 24.3 in year 1 and 37.0 to 5.8 in year 2. Under irrigation, NUE fell from 84.6 to 67.1 in year 1 and from 117.7 to 33.3 in year 2. The contribution of N uptake efficiency and utilization efficiency to NUE varied from one year to another. In year 1, the contribution of N utilization efficiency was more important at all nitrogen levels; while the opposite was observed in year 2 when more N was applied. The fractions of the genotype sum of squares, respectively, for N uptake efficiency and utilization efficiency were in average 0.15 and 0.78 in year 1 and 0.75 and 0.25 in year 2. From this study we conclude that high N levels in the soil exacerbate the effect of water stress on productivity and NUE of wheat. Early maturing new genotypes tend to be better adapted and to use nitrogen more efficiently under limited water conditions. N utilization efficiency contributes more to NUE under high N availability than N uptake efficiency and vice-versa.     

SUBSOIL ROOT GROWTH OF FIELD GROWN SPRING WHEAT GENOTYPES (TRITICUM AESTIVUM L.) DIFFERING IN NITROGEN USE EFFICIENCY PARAMETERS

In a two-year (1999–2000) field experiment four Swiss spring wheat (Triticum aestivum L.) genotypes (cvs. ‘Albis’, ‘Toronit’ and ‘Pizol’ and an experimental line ‘L94491’) were compared for genotypic differences in the root parameters that determine uptake potential and nitrogen use efficiency (NUE):root surface area (RSA) and its components, root length density (RLD) and the diameter of the roots. The genotypes were grown under no (N0) and under ample fertilizer nitrogen (N) [ammonium nitrate (NH₄NO₃); N1; 250 kg N ha^?1] supply. Root samples were taken from all the genotypes at anthesis from the subsoil (30–60 cm). Genotypic effects on RLD and RSA were evident only in 2000 and large amounts of N fertilizer usually diminished root growth. Adequate soil moisture in 1999 may have favored the establishment of the root system of all the genotypes before anthesis. Parameters of NUE for each genotype were also determined at anthesis and at physiological maturity. ‘Albis’ the least efficient cv. in recovering fertilizer N (ranged from 36.5 to 61.1%) with the lowest N uptake efficiency (0.47 to 0.79 kg kg^?1) had the lowest RLD and RSA in both seasons. Among genotypes ‘Toronit’, a high-yielding cv., efficient in recovering fertilizer N, exhibited the higher NUE (22.4 to 29.3 kg kg^?1) and tended to have the highest values of RLD and RSA. Nitrogen fertilization also led to an increase in the proportion of roots with diameters less than 300 μm and decreased the proportion of roots with diameters of 300 to 700 μm. These trends were more pronounced for cv. ‘Pizol’ in 1999 and for cv. ‘Toronit’ in 1999 and 2000. By anthesis in a humid temperate climate, there are no marked differences in the subsoil root growth of the examined genotypes. Some peculiarities on the root growth characteristics of the cultivars ‘Albis’ and ‘Toronit’ may partially explain their different NUE performance.     

Deep root growth and nitrogen uptake by rocket (Diplotaxis tenuifolia L.) as affected by nitrogen fertilizer,plant density and leaf harvesting on a coarse sandy soil

This study investigated management strategies to increase deep root growth and crop nitrogen (N) uptake by rocket grown as baby leaf in coarse sandy soil. Stage I (sowing to first harvest) measured the effects of two sowing densities and two N fertilizer rates on root growth and total N uptake. In Stage II (first to second harvest), effects of leaf harvesting and late season N fertilizer application on root growth, total N uptake and deep ¹⁵N uptake were measured. At the end of Stage I, root depth was 0.68–0.90 m, and the large fertilizer application increased N uptake. Plant density increased root depth, N uptake and nitrogen use efficiency (NUE) early in this stage and biomass production at harvest. Leaf harvesting in Stage II affected root density but not root depth that reached 1.4 m. The ability for N uptake was greater from 0.6 m due to more roots and larger N inflow than from 1.1 m depth. Late season fertilizer increased N concentration and uptake but did not affect NUE and deep N uptake. During the growing season, 330–349 kg N_inorg/ha was lost from 0 to 1.0 m depth most likely by leaching. Management practices that increased root growth and N uptake were found to increase NUE in rocket production early in the season. The production system used N inefficiently and smaller applications, plant density, leaf harvesting and other changes of management are required to reduce leaching.     

Phosphorus Enriched Organic Amendments can Increase Nitrogen Use Efficiency in Wheat

Although nitrogen (N) has the highest requirement for plant growth, N use efficiency (NUE) seldom exceeds 40%. NUE may be improved by integrated application of fertilizer N and enriched organic amendments. The present experiment aimed to test the extent of increase in NUE by integrated application of fertilizer N farmyard manure (FYM) and rock phosphate enriched compost (RPEC). Mineralization kinetics and N release from FYM and RPEC were studied by an incubation experiment. Results revealed that maximum potentially mineralizable N as well as N release (283.9, 186.7 mg kg^?1 soil, respectively) were from RPEC + fertilizer N treated soils, followed by FYM + fertilizer N. Maximum yield, N uptake, and N recovery were obtained from RPEC + fertilizer N treated soils followed by FYM + fertilizer N. Soils treated with RPEC had shown significantly higher dehydrogenase activity than FYM treated soils. Thus, RPEC might increase yield as well as NUE over FYM. N uptake by plant at maximum tillering stage and flowering stage of wheat correlated positively (R² > 0.85) with the decay rate (k and kN₀) parameter of incubation experiment suggesting their relevance as indicators of plant available N.     

Effect of nitrogen supply on leaf traits related to photosynthesis during grain filling in two maize genotypes with different N efficiency

In the present study, plant traits related to the photosynthetic capacity at the whole plant level were compared during grain filling in two maize genotypes with different nitrogen (N) efficiency. The plants were grown in a greenhouse in large root containers and supplied either with suboptimal or optimal rates of N fertilizer. Suboptimal N supply reduced total plant biomass at maturity (47 days (d) after flowering) by 29 % for the efficient genotype and by 36 % for the inefficient genotype. Suboptimal N supply reduced leaf growth of both genotypes. The reduction of leaf area was less severe in the N‐efficient genotype, despite of lower N content in the leaves. This indicates lower sensitivity of leaf growth towards internal N limitation in the efficient genotype. At low N supply, the green leaf area per plant gradually decreased after flowering in both genotypes, because of loss of chlorophyll during leaf senescence. The rate of net photosynthesis per unit leaf area (A) was reduced at low in comparison with high N supply. The ratio of A/leaf N content or leaf chlorophyll content was higher in the efficient genotype, indicating more efficient utilization of internal N for photosynthesis. At the end of grain filling, low N supply led to enhanced intercelluar CO₂ concentrations (Ci) in the leaves, indicating limitation of CO₂ assimilation by carboxylation rather than by stomatal resistance. The N deficiency‐induced increase of Ci was less pronounced in the efficient genotype. Furthermore, higher photosynthetic rate of the efficient genotype at suboptimal N supply was associated with lower contents of reducing sugars and sucrose in the leaves, whereas starch content was higher than in the inefficient genotype. The ability to avoid excessive sugar accumulation in the leaves under N deficiency might be related to higher photosynthetic N efficiency.     

Effect of time of application on nitrogen uptake,partitioning, and remobilization in walnut trees

Walnut tree requires a relatively high amount of nitrogen (N). To avoid loss in the environment, N uptake efficiency (NUE) should be optimized. The aims of this study were to evaluate the effect of time of N application on NUE, partitioning, and remobilization in walnut trees. Two-year-old trees were planted in 40-L pots and fertilized with 1 g of ¹⁵N-enriched (5 atom %) N at: 1) bud burst, 2) pistillate flower maturity, and 3) late summer. One week after fertilization, the percentage of N derived from fertilizer and NUE were higher in trees fertilized in late summer, than other timings. N uptake was linearly related to root dry weight. At May 2008 harvest, the N stored in trunk and twigs was remobilized to the developing leaves and to the roots. Late summer N application appeared to be the most effective in providing N for walnut spring new growth.