玉米叶片SPAD值、全氮及硝态氮含量的品种间变异

研究比较两种土壤肥力条件下,4个春玉米品种在喇叭口期至成熟期间叶片SPAD值、全氮及硝态氮含量的变异程度、及其与氮素积累和产量形成的关系,以期为不同品种植株的氮素营养测试指标的优化提供依据。结果表明,叶片SPAD值与产量、吸氮量及生物量呈显著相关,该值主要受氮肥水平影响,并因土壤肥力而变异。从喇叭口期至灌浆期间平均变异幅度为17.7%,但品种间变异很小,平均仅为4.3%。说明利用SPAD值诊断玉米氮素营养时,其诊断指标不需要因品种而调整,但需要因不同肥力而调整。在新立城低肥力条件下,喇叭口期(V12)和抽雄期(VT)的SPAD临界值指标分别为46.1和57.8;在德惠高肥力条件下,两个时期的SPAD值临界值较为接近,分别为59.9和60.3。植株叶片硝态氮含量在土壤肥力间及品种间变异均较大,变异幅度分别为43.1%和29.3%,且与产量、吸氮量及生物量的相关性均较差,不适于在大面积范围内单独作为玉米氮素营养状况的评价指标。     

相对SPAD值用于不同品种夏玉米氮肥管理的研究

采用田间试验研究了不同氮肥处理、不同玉米品种及关键生育期间的SPAD值差异和基于相对SPAD阈值的氮肥管理对氮肥用量、子粒产量、氮肥利用率和土壤氮素变化的影响。结果表明,两品种玉米各关键生育期的SPAD值开始随施氮量的增加而显著增加,施氮量超过N 210 kg /hm2后不再显著增加;郑单958和冀农一号大喇叭口期的相对SPAD值与产量的关系符合线性加平台模型,其平台相对SPAD值分别为0.976和0.981;两玉米品种和不同生育期间的绝对SPAD值差异显著,利用相对SPAD值可消除品种和生育期间的SPAD值差异。玉米关键生育期追肥量和总施氮量均随预设相对SPAD阈值的增加而增加,基于相对SPAD阈值的氮肥管理能在保持高产的同时较农民习惯施肥显著降低氮肥用量、田间氮素表观损失和收获后土壤无机氮残留、提高氮肥利用率;本试验条件下,保持玉米高产高效的适宜相对SPAD阈值为0.95～0.98,此阈值管理下,郑单958和冀农一号的产量较农民习惯施肥没有降低,而氮肥用量降低了42%,氮肥回收利用率和农学效率分别增加了18.6、20.0个百分点和6.0、6.5 kg/kg。     

实时实地氮素管理对水稻产量和氮素吸收利用的影响

以扬两优6号和培两优3076水稻为材料,通过田间试验比较研究了基于SPAD值的氮素管理对水稻氮素吸收、产量和氮肥利用率的影响。结果表明,随着SPAD预设阈值的增加,氮肥用量增加,籽粒产量和氮素吸收也随之增加。实时氮素管理条件下,水稻扬两优6号和培两优3076均以SPAD值为41处理获得较高的籽粒产量和氮素利用率,该处理在籽粒产量不降低的同时节约了氮肥用量12. 8% ～33.3%;而实地氮素管理条件下,水稻扬两优6号和培两优3076均以SPAD值为39～41处理获得较高的籽粒产量和氮素利用率,该处理在籽粒产量不降低的同时节约了23.1%的氮肥用量。鉴于实地氮素管理在田间易于操作,因此建议采用39～41作为水稻关键生育期指导氮肥施用的SPAD阈值。     

Corn nitrogen management using NDVI and SPAD sensor-based data under conventional vs. reduced tillage systems

Present analyses to calculate nitrogen fertilizer recommendations are time consuming and costly. Therefore, a field study determining the efficiency of SPAD and NDVI meters to calculate soil N deficiency and guide fertilizer application timing and rate was completed. Reduced vs. conventional tillage at various N application rates was studied. Regardless of tillage system, both NDVI and SPAD were able to detect N deficiency at early growth stages, however, SPAD measurements better reflected plant N status regarding N application rates. A modified Michaelis-Menten model was used to illustrate the relationship between N rates and grain yield, as well as grain N content and leaf N content, and both showed acceptable goodness of fit. Grain yield under reduced tillage was significantly higher than that of conventional tillage. The combination of leaf nitrogen, SPAD, and NDVI data may become a tool to manage corn field nitrogen status and predict grain yield.     

Response of low-nitrogen tolerant maize genotypes to nitrogen application in a tropical Alfisol in northern Nigeria

In the dry savannas of west and central Africa, where low soil fertility is major constraint to maize production, the development of tropical maize genotypes with high and stable yield under low-nitrogen condition is very important, since access to these improved genotypes may be the only affordable alternative to many small scale farmers.

Field trials were conducted at Samaru (Typic Haplustalfs) to investigate the response of low-N tolerant maize cultivars to nitrogen (N) fertilizer. Nitrogen application rates were 0, 30, 60, 90 kg N ha⁻¹ and four maize cultivars (Low-N pool C2, ACR 8328 BN C7, Super Oba II and TZR-SR). Maize leaf area index, intercepted radiation, leaf area and stover weights were increased due to nitrogen application at flowering. For most of the parameters, 60 kg N ha⁻¹ appeared to have the significantly high values. However, there was no significant difference between application rates of 60 and 90 kg N ha⁻¹ in stem weight, stover weight, grain yield and shelling percent at harvest. Genotypic variation observed in the maize agronomic traits were not significant except in leaf weight and grain yield. The amount of nitrogen taken by maize increased with increase in fertilizer rates. Application of 30 and 90 kg N ha⁻¹ to soil increased the maize grain N concentration and total N uptake. About 45.3 kg ha⁻¹ and 8.8 g N kg⁻¹ nitrogen uptake was obtained in maize shoot and grain, respectively, at the application of 90 kg N ha⁻¹. Low-N pool C2 genotype had the highest grain N concentration and shoot uptake significantly higher than TZB-SR. Nitrogen fertilizer applied accounted for 97% variation in soil nitrate. There existed a positive and significant correlation between maize grain yield and leaf nitrogen uptake (r = 0.33, P < 0.01). Averagely, nitrogen fertilizer applied accounted for 86% variations in maize grain yield.     

氮肥运筹对水稻农学效应和氮素利用的影响

通过田间试验,以不同氮肥量级为参照,结合关键生育期叶片叶绿素含量（SPAD值）指导氮肥施用,以探明潜江地区水稻关键生育期的氮肥适宜用量。结果表明,在施N 90～180kg/hm2间水稻产量差异不显著,当超过N 180 kg/hm2,产量降低。根据水稻产量（y）和施氮量（x）拟合得出一元二次关系式:y = -0.0728x2 + 22.335x + 6811.5,R2 = 0.9442。结合当年水稻价格肥料投入费用等计算出水稻的经济效益（Y）和施氮量（X）之间的函数式:y = -0.134x2 + 37.097x + 12533-M,R2 = 0.9331;由此得出经济效益最大时水稻的施氮量是N 138 kg/hm2。该施氮量下水稻的氮肥表观利用率,农学利用率和氮肥偏生产力可保持在40.9%,11.5 kg/ kg和63.2 kg/ kg,与完全依据SPAD值指导关键生育期的氮肥施用量相近似（N 140 kg/hm2）,保证了水稻最大的经济效益,同时也保持了较高的氮肥利用率,降低氮素表观损失。     

Functional traits associated with nitrogen use efficiency in wheat

The association between functional traits and nitrogen use efficiency (NUE) was investigated to assist the breeding of nitrogen (N) use-efficient bread wheat (Triticum aestivum ssp. aestivum) varieties. This study combined results from a climate chamber experiment involving 41 spring wheat varieties and a field experiment involving six winter and six spring wheat varieties grown with and without the application of mineral N fertiliser. The climate chamber experiment was analysed by partial least squares (PLS) regression, with several predictors and NUE as response, to identify traits related to NUE. Specific hypotheses were then tested in the field experiment. The PLS indicated six traits of particular importance for overall NUE: leaf chlorophyll (SPAD value) of the top leaf at stem elongation, grains ear^?1, ears pot^?1, straw biomass pot^?1, days between emergence and anthesis, and days between emergence and completed senescence. In the field experiment, the SPAD value of flag leaves of winter wheat around anthesis was positively correlated with NUE and total grain N, at both N levels. Fast development was positively correlated with high NUE and N uptake efficiency in spring wheat. Early senescence of the flag leaf was positively correlated with grain N concentration and negatively correlated with grain-specific N efficiency in winter wheat at low N fertilisation levels. The results indicate that high SPAD value of the top leaf might be a candidate trait that could be used in wheat breeding for improved NUE, while genetic variation in senescence could possibly be used to tailor varieties for different end-use quality when grown at low N. More studies are needed to validate these findings in other environments and for other genotypes.     

Tomato leaf chlorophyll meter readings as affected by variety,nitrogen form,and nighttime nutrient solution strength

Leaf chlorophyll content is closely related to leaf nitrogen (N) content, so it is reasonable to assume that ammonium‐N (NH₄‐N): nitrate‐N (NO₃‐N) ratio in the nutrient solution used to grow tomatoes (Lycopersicon esculentum Mill.) hydroponically may affect leaf greenness, and consequently chlorophyll meter (SPAD) readings. It has also been shown that increasing nutrient solution strength (NSS) increases tomato productivity, but there are no reports regarding how NSS affects SPAD readings under greenhouse conditions. Genotype may also influence SPAD readings, and standardization for cultivar and sampling time may be needed. The objective of this study was to characterize SPAD readings for five tomato cultivars and SPAD reading response to a combination of two NSS (1X and 4X Steiner solution strength daily applied 18 days after transplanting at 7 p.m.) and two concentrations of NH₄‐N in solution (0 and 25%) in order to evaluate the potential of SPAD readings as a tomato yield predictor in greenhouse production systems. The SPAD readings were not uniform across tomato varieties tested, being consistently higher for ‘Max’ and lower for the other varieties. Initially, SPAD readings for tomato varieties used in this study were low at the vegetative stage, and increased up to 40 DAT, but subsequently decreased at 49 DAT, or the fruit set of the first and second clusters. After this time, SPAD readings showed no variation. Chlorophyll meter readings for ‘Max’ were higher in the top plant layers, but decreased in the top plant layer of the other tomato varieties. The SPAD readings were higher for plants supplied with 25% NH₄‐N than those without NH₄‐N in solution, but the use of a nighttime nutrient solution did not affect SPAD readings. None of the possible interactions among tomato variety, NH₄‐N: NO₃‐N ratio, and NSS were consistently significant.     

不同施肥处理对夏玉米产量及活性氧代谢的影响

以2009年建立的肥料定位试验为研究平台,于2013年进行了不同施肥处理对夏玉米产量及活性氧代谢影响的研究。结果表明,氮磷钾均衡施肥对夏玉米籽粒产量有显著的增产作用,产量达到9 299.85 kg/hm2,NPK处理的穗粒数和千粒重最高,NP处理的穗长、穗重与NPK处理没有显著差异;氮能有效地提高玉米穗位叶叶绿素含量和籽粒的灌浆速率;氮对玉米穗位叶过氧化物酶活性的影响最大,氮钾配施能够有效地提高玉米穗位叶超氧化物歧化酶活性,增加穗位叶可溶性蛋白质含量,降低穗位叶丙二醛含量。合理配施氮钾能够有效地提高玉米穗位叶光合效率,延缓叶片衰老,提高玉米籽粒产量。     

施氮量对夏玉米碳氮代谢和氮利用效率的影响

本试验研究了施氮量（0、90、180、270 kg/hm2）对夏播玉米CF008、金海5号和郑单958碳氮积累、运转及氮肥利用的影响。结果表明,3个品种的茎叶碳氮积累量、成熟期地上部总氮量均为在施氮量180 kg/hm2或270 kg/hm2下较高,但是最终碳氮运转率、氮素吸收效率、氮素利用效率和氮肥利用率均在施氮量90 kg/hm2下较高。本试验中,碳运转率与产量呈正相关,氮运转率与氮肥利用率呈正相关,表明较高的碳氮运转率可以促进产量和氮肥利用率的提高。本研究在施氮量90 kg/hm2下,CF008和金海5号茎鞘的C/N值在吐丝期和成熟期分别为22.11～22.91、35.66～54.23,叶片的C/N值分别为4.32～5.11、9.06～10.57;在施氮量90～180 kg/hm2下,3个品种夏玉米产量达到了10688～11461 kg/hm2;CF008和金海5号的氮肥利用率达到了31.55%～49.33%,而郑单958的氮肥利用率仅为15.11%～19.20%。     

Leaf Color Chart and Chlorophyll‐Meter‐Based Leaf Nitrogen Estimation and Their Threshold Values for Real‐Time Nitrogen Management in Cassava

The critical leaf and the threshold values of leaf color chart (LCC) and chlorophyll meter (SPAD‐502) for cassava have been evaluated. The nitrogen (N) rates and cultivars had a significant effect on LCC score, SPAD values, and leaf N concentration of leaf 1 in most cases. Among the three leaf positions studied, the youngest fully expanded leaf (YFEL) blade (leaf 1) had significant, positive correlation of tuber yield with LCC score, SPAD value, and leaf N concentration. The regression between LCC score and leaf N concentration of leaf 1 was LCC = 0.358 (Leaf N) + 0.78 (r² = 0.81) and that between LCC score and SPAD value was SPAD = 10.981 (LCC) – 3.51 (r² = 0.82). A threshold LCC score of 2.65 and threshold SPAD value of 25 were suitable to determine the optimal timing of N top‐dressing for cassava.     

低氮胁迫对耐低氮玉米品种苗期光合及叶绿素荧光特性的影响

【目的】叶绿素荧光参数经常用来评价光合器官的功能和环境压力的影响,不同玉米基因型耐低氮胁迫能力差异较大,与光合及叶绿素荧光特性对低氮胁迫的响应机制有关。本文以耐低氮能力差异较大的4个玉米杂交种为试验材料,研究了低氮胁迫对不同耐低氮性玉米品种苗期光合及叶绿素荧光特性的影响,以期明确耐低氮胁迫玉米品种的光合机制。【方法】采用二因素完全随机设计盆栽试验,因素A为不同耐低氮性玉米品种:‘正红311’、‘成单30’和不耐低氮品种‘先玉508’、‘三北2号’;因素B为不同氮素水平:正常氮CK(霍格兰完全营养液,N 15 mmol/L)、低氮胁迫LN1(N 0.5 mmol/L)、极低氮胁迫LN2(N 0.05 mmol/L)。测定了苗期单株干物质积累量,单株氮素积累量,叶片叶绿素含量与荧光特性,以及光合效率指标。【结果】低氮胁迫下玉米苗期单株干物质积累量、单株氮素积累量、叶片叶绿素含量等生理指标显著下降,但耐低氮品种的下降幅度显著低于不耐低氮品种;低氮胁迫下玉米苗净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)显著降低,胞间CO2浓度(Ci)显著升高,净光合速率(Pn)、气孔导度(Gs)和蒸腾速率(Tr)的降幅及胞间CO2浓度(Ci)的增幅耐低氮品种均显著低于不耐低氮品种;低氮胁迫下可变荧光(Fv)、最大荧光(Fm)、PSⅡ潜在活性(Fv/F0)、PSⅡ最大光化学效率(Fv/Fm)、PSⅡ有效光量子产量(Fv'/Fm')和光化学猝灭系数(q P)等叶绿素荧光特性也均显著降低,耐低氮品种下降幅度显著低于不耐低氮品种;低氮胁迫下耐低氮品种PSⅡ实际光量子产量(ΦPSⅡ)降低,不耐低氮品种有所增加;而耐低氮品种非光化学猝灭系数(NPQ)升高,不耐低氮品种有所降低。【结论】耐低氮玉米品种能够减缓低氮胁迫对植株光合系统的影响,进而保证植株较高的氮素积累,提高叶片叶绿素含量,维持较高的PSⅡ有效光量子产量(Fv'/Fm')和光化学猝灭系数(q P),为光合作用提供充足的光能;从而保持了较高的净光合速率(Pn),保证了耐低氮品种在低氮条件下保持较高的干物质生产。     

氮锌配施对不同玉米品种灌浆期生理特性和籽粒氮锌含量的影响

提高粮食作物中可食部分的锌生物有效性是解决人体缺锌的重要措施。为研究氮锌肥料施用对玉米籽粒锌营养的影响,本研究以郑单958和谷神玉66为试验材料,在大田条件下研究3个氮水平(90、180 和225 kg N·hm^-2)和2个喷锌处理(0和4.5 kg·hm^-2 ZnSO₄·7H₂O)下玉米籽粒产量和氮锌含量以及灌浆期叶片生理特性的变化。结果表明,吐丝后,与施氮量90 kg·hm^-2处理相比,施氮量180和225 kg·hm^-2处理提高了吐丝后穗位叶SPAD值及硝酸还原酶(NR)、谷氨酰胺合成酶(GS)、碳酸酐酶(CA)、超氧化物歧化酶(SOD)活性和灌浆后期PSⅡ综合性能指数(PI),降低了丙二醛(MDA)含量。施锌能提高吐丝后穗位叶CA、SOD、过氧化物酶(POD)、过氧化氢酶(CAT)活性和灌浆后期SPAD值和PI,降低MDA含量。2个品种相比,谷神玉66灌浆后期穗位叶SPAD值、叶片初始荧光(F_o)和最大荧光(F_m)较高,而灌浆前期穗位叶PI和吐丝后NR、CA、SOD以及POD活性则以郑单958较高。施氮量为90 kg·hm^-2时,玉米籽粒产量平均为8.55 t·hm^-2,随着施氮量增加,玉米籽粒产量显著提高。籽粒中氮含量以施氮量180 kg·hm^-2时最高,为14.85 g·kg^-1。施氮量90和180 kg·hm^-2时,籽粒锌含量平均为27.2 mg·kg^-1,显著高于施氮量225 kg·hm^-2处理。与不施锌相比,喷锌后玉米籽粒产量未有显著变化,籽粒中氮、锌含量分别增加了11.7%和18.0%。郑单958籽粒产量较谷神玉66提高了3.8%,籽粒氮锌含量则分别减少了11.9%和5.3%。综合来看,施氮量为180 kg N·hm^-2时,与喷施ZnSO₄·7H₂O 4.5 kg·hm^-2 配合施用能够增强玉米灌浆期叶片SPAD和荧光特性,提高氮锌代谢关键酶活性,增强氧自由基清除系统酶活性,减弱膜脂过氧化作用的伤害,促进籽粒中氮、锌的吸收和累积。本研究结果可为玉米生产中优化锌生物强化措施提供理论依据。     

陕A群、陕B群选育的玉米自交系氮效率评价

为阐明不同类型玉米自交系氮效率差异特征,筛选氮高效的玉米自交系,以陕A群、陕B群选育的33份玉米自交系为材料,以4份骨干自交系(‘郑58’、‘昌7-2’、‘PH6WC’和‘PH4CV’)为对照,调查了2种施肥条件下[0 kg(N)·hm?2、180 kg(N)·hm?2]玉米自交系的穗位叶SPAD值、叶面积、干物质积累量、叶片、茎秆和籽粒氮含量等生理指标。利用主成分分析和模糊隶属函数,采用逐步回归分析方法建立最优回归方程,筛选耐低氮性综合评价指标。结果表明:穗位叶SPAD值、吐丝期绿叶面积、吐丝期茎干重、吐丝期叶干重和籽粒氮含量,可作为玉米自交系耐低氮能力的第2性状筛选指标。以产量作为第1性状指标,可将37份玉米自交系划分为14份高产氮高效型,5份低产氮高效型,15份低产氮低效型和3份高产氮低效型。以耐低氮能力综合值D值筛选,将37份玉米自交系可分成3种类型,其中耐低氮能力较强的15份(D值≥0.5),耐低氮能力中等的15份(0.35≤D值0.5),耐低氮能力较差的7份(D值0.35)。综合分析,2种施氮条件下,‘KB215’、‘KB417’、‘KA225’、‘KB081’和‘L123098-2’5份玉米自交系具有吐丝期绿叶面积大,吐丝期茎叶干重、籽粒氮含量高和籽粒产量高,耐低氮能力强的特点。因此,强化育种环境的选择压力,实施低氮选择策略,可有效提高玉米种质对氮肥的利用效率。     

施氮对不同肥力土壤小麦氮营养和产量的影响

【目的】农田养分供应是由土壤基础肥力和肥料投入共同决定的,不同土壤肥力下土壤养分供应能力和特征也不同。本文研究了河南省高、低肥力田块下,不同施氮量对小麦主要生育时期植株氮素营养和土壤硝态氮及产量的影响,以期为河南省同类生产条件下氮肥的合理施用和产量的提升提供参考和依据。【方法】2015—2016年,以小麦品种矮抗58为供试材料进行大田试验,分别设置0、120、225、330 kg/hm^2 4个施氮处理(表示为N0、N1、N2、N3),在开花期到成熟期调查施氮量对土壤硝态氮及产量的影响;在开花期、花后10天和花后20天,测定施氮量对小麦旗叶到倒4叶的叶片氮含量、SPAD值和氮素积累量,以及对植株和所有叶片氮含量的影响。【结果】从开花期到成熟期土壤中硝态氮含量随着施氮量的增加而增加,高肥力田块的土壤硝态氮含量显著高于低肥力田块的土壤硝态氮含量。施氮能显著增加低肥力田块产量,但是高肥力田块的产量均高于低肥力田块,与不施氮相比,低肥力田块的产量最大增幅是高肥力田块产量最大增幅的2.63倍。N1和N2处理下,在开花期和花后10天倒2叶的SPAD值高肥力田块显著高于低肥力田块,但在花后20天低肥力田块显著高于高肥力田块。在N1、N2和N3处理下,旗叶的氮含量在花后10天高肥力田块显著高于低肥力田块,但在花后20天则显著相反。开花期到花后20天,对于低肥力田块旗叶的氮素积累量对上4叶的贡献率最大(N0除外),最高达52.6%;高肥力田块,旗叶和倒2叶对上4叶的氮素积累量贡献率处在同等重要的位置,最高分别达39.9%和39.7%。花后10天到花后20天,高肥力田块不同叶位的氮素转运量和转运率均高于低肥力田块(N0除外)。【结论】增施氮肥可以通过提高土壤硝态氮含量来提高土壤供氮能力,高肥力田块的叶片转运量和转运率比低肥力田块高,低肥力田块通过提高施氮量增加的产量低于高肥力田块下的产量,因此,需改善农田基础肥力来提高产量。通过对高、低肥力条件下产量的分析发现,达到最高产量时的施氮量分别为213kg/hm^2和287 kg/hm^2。     

硝酸盐反射仪和SPAD法对玉米氮素营养诊断的比较

精准的营养诊断是了解作物氮素营养及推荐施肥的基础。本文在田间滴灌条件下利用SPAD叶绿素仪(SPAD-502 Plus)和硝酸盐反射仪(RQ flex10)两种诊断方法对玉米关键生育时期的氮素营养诊断进行研究,旨在筛选出适宜的诊断方法,并依据诊断值建立滴灌玉米不同生育时期的施肥模型。试验设置0 kg(N)·hm~(-2)(N0)、225 kg(N)·hm~(-2)(N225)、330 kg(N)·hm~(-2)(N330)、435 kg(N)·hm~(-2)(N435)和540 kg(N)·hm~(-2)(N540)5个施氮水平,在不同生育时期测定了玉米叶片SPAD值和叶鞘NO_3~-含量,并分别与施氮量、植株全氮含量、产量进行方程拟合,比较两种诊断方法对玉米氮素营养的响应。研究结果表明:1)玉米叶片SPAD值和叶鞘NO_3~-含量均随施氮量的增加而显著升高,且在拔节期对施氮量的响应最敏感。叶鞘NO_3~-含量对施氮量变化的响应较SPAD值大,其与施氮量及玉米产量的拟合度均高于SPAD值,说明硝酸盐反射仪法对滴灌玉米氮素丰缺的反应更灵敏。2)玉米全氮含量与叶片SPAD值呈显著线性关系,而与叶鞘NO_3~-含量则以线性加平台表示。当叶鞘NO_3~-含量小于186 mg·L~(-1)时,植株全氮与NO_3~-间呈显著线性相关;当叶鞘NO_3~-含量大于186 mg·L~(-1)时,植株全氮随NO_3~-含量增加趋于不变。3)本农作区滴灌玉米最佳经济施氮量为402.5 kg·hm~(-2),对应的玉米产量为17 049 kg·hm~(-2)。玉米拔节期、抽雄吐丝期和灌浆期的临界叶鞘NO_3~-含量分别为729.3 mg·L~(-1)、536 mg·L~(-1)和81.2 mg·L~(-1)。SPAD叶绿素仪和硝酸盐反射仪均可对滴灌玉米进行氮素营养诊断,但硝酸盐速测值能更敏感地反映氮素丰缺状况,基于硝酸盐反射法进行作物氮素营养诊断及推荐施肥具有较好的准确性与适用性。     

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 nitrogen rate on plant nitrogen loss in winter wheat varieties 1

Gaseous nitrogen (N) loss from winter wheat (Triticum aestivum L.) plants has been identified, but has not been simultaneously evaluated for several genotypes grown under different N fertility. Two field experiments were initiated in 1993 and 1994 at the Agronomy Research Station in Stillwater and Perkins to estimate plant N loss from several cultivars as a function of N applied and to characterize nitrogen use efficiency (NUE). A total of five cultivars were evaluated at preplant N rates ranging from 30 to 180 kg·ha^‐1. Nitrogen loss was estimated as the difference between total forage N accumulated at anthesis and the total (grain + straw) N at harvest. Forage, grain, straw yield, N uptake, and N loss increased with increasing N applied at both Stillwater and Perkins. Significant differences were observed among varieties for yield, N uptake, N loss, and components of NUE in forage, grain, straw, and grain + straw. Estimates of N loss over this two‐year period ranged from 4.0 to 27.9 kg·ha^‐1 (7.7 to 59.4% of total forage N at anthesis). Most N losses occurred between anthesis and 14 days post‐anthesis. Avoiding excess N application would reduce N loss and increase NUE in winter wheat varieties. Varieties with high harvest index (grain yield/total biomass) and low forage yield had low plant N loss. Estimates of plant loss suggest N balance studies should consider this variable before assuming that unaccounted N was lost to leaching and denitrification.     

Assessment of nitrogen uptake and utilization in drought tolerant and Striga resistant tropical maize varieties

Maize (Zea mays L.) is an important food crop in the Guinea savannas of Nigeria. Despite its high production potential, drought, Striga hermonthica parasitsim, and poor soil fertility particularly nitrogen deficiency limit maize production in the savannas. Breeders at IITA have developed drought- and Striga-tolerant cultivars for testing, dissemination, and deployment in the region. Information on the response of these cultivars to N fertilization is, however, not available. This study evaluated grain yield, total N uptake (TNU), N uptake (NUPE), N utilization (NUTE), and N use efficiency (NUE) of selected maize cultivars along with a widely grown improved maize cultivar at two locations in the Guinea savannas of northern Nigeria. Maize grain yield increased with N application. The average grain yield of the maize cultivars was 76% higher at 30, 156% higher at 60, and 203% higher at 120 kg N ha^?1 than at 0 kg N ha^?1. This suggests that N is a limiting nutrient in the Nigerian savannas. Five drought-tolerant cultivars produced consistently higher yields when N was added at all levels. These cultivars had either high NUPE or NUTE confirming earlier reports that high N uptake or NUTE improves maize grain yield. The study also confirms earlier reports that maize cultivars that are selected for tolerance to drought are also efficient in uptake and use of N fertilizer. This means that these cultivars can be grown with application of less N fertilizer thereby reducing investment on fertilizers and reduction in environmental pollution.     

两个玉米品种灌浆期叶片氮转移效率差异的分子机制

【目的】 提高玉米氮效率是实现农业高产高效的重要措施,而花后叶片的衰老和玉米的氮效率密切相关。为此,在田间条件下研究了叶片衰老过程与氮转移效率的关系,尤其是不同玉米品种氮转移效率差异的分子机制。 【方法】 田间试验选择中度绿熟玉米品种先玉335 (XY335) 和持绿玉米品种NE9为供试作物,设施N 45,120和240 kg/hm2三个水平。测定了玉米吐丝期以及吐丝后7 d、14 d、21 d、28 d、35 d、42 d和成熟期茎、叶、籽粒氮含量和花后绿叶面积,吐丝期及吐丝后14 d、28 d、42 d和成熟期叶片氮浓度,以及吐丝期和灌浆期叶片中SPAD、可溶性蛋白浓度、游离氨基酸浓度和ZmSee2β (玉米叶片中协同衰老的蛋白酶–豆荚蛋白的基因) 基因表达的变化,计算了叶片氮转移效率。 【结果】 品种XY335具有比品种NE9更高的产量,随施氮量的增加品种XY335的籽粒产量较品种NE9增加更加显著。虽然两个品种的收获指数没有差异,但是品种XY335的氮素收获指数高于品种NE9,并且品种XY335营养器官的氮转移效率高于品种NE9,整体高8.28个百分点 (P < 0.05)。品种XY335叶片氮转移效率比品种NE9高出12.89个百分点,而二者茎的氮转移效率没有差异。品种XY335花后叶片中氮浓度开始降低的时间早于品种NE9,在低氮条件下尤为明显。成熟期时,三个氮水平处理下品种XY335叶片中的氮含量均低于品种NE9。从吐丝期到灌浆期,品种XY335叶片中可溶性蛋白的降解率高于品种NE9,其中N45处理下高16.5个百分点,N120处理下高6.2个百分点。从吐丝期到灌浆期叶片中游离氨基酸的浓度不断增加,而品种XY335叶片中的增加幅度大于品种NE9。从吐丝期到灌浆期叶片中 ZmSee2β基因表达量增加,而随施氮量减少品种XY335叶片中表达量高于品种NE9,表明品种XY335叶片中蛋白降解得更加迅速。 【结论】 相对于绿熟品种NE9,品种XY335具有籽粒产量高和籽粒氮素积累强的特点。这不仅由于吐丝后品种XY335具有较强的氮素吸收能力,而且因为品种XY335有更高的叶片氮转移效率。品种XY335叶片氮转移效率高可能是因为控制蛋白质降解的ZmSee2β基因表达能力强,提高了叶片中蛋白质的降解速度。