Towards a better understanding of the genetic and physiological basis for nitrogen use efficiency in maize

To enhance our understanding of the genetic basis of nitrogen use efficiency in maize (Zea mays), we have developed a quantitative genetic approach by associating metabolic functions and agronomic traits to DNA markers. In this study, leaves of vegetative recombinant inbred lines of maize, already assessed for their agronomic performance, were analyzed for physiological traits such as nitrate content, nitrate reductase (NR), and glutamine synthetase (GS) activities. A significant genotypic variation was found for these traits and a positive correlation was observed between nitrate content, GS activity and yield, and its components. NR activity, on the other hand, was negatively correlated. These results suggest that increased productivity in maize genotypes was due to their ability to accumulate nitrate in their leaves during vegetative growth and to efficiently remobilize this stored nitrogen during grain filling. Quantitative trait loci (QTL) for various agronomic and physiological traits were searched for and located on the genetic map of maize. Coincidences of QTL for yield and its components with genes encoding cytosolic GS and the corresponding enzyme activity were detected. In particular, it appears that the GS locus on chromosome 5 is a good candidate gene that can, at least partially, explain variations in yield or kernel weight. Because at this locus coincidences of QTLs for grain yield, GS, NR activity, and nitrate content were also observed, we hypothesize that leaf nitrate accumulation and the reactions catalyzed by NR and GS are coregulated and represent key elements controlling nitrogen use efficiency in maize.     

施氮量对小麦叶片硝酸还原酶活性、一氧化氮含量和气体交换的影响

研究了不同施氮量对冬小麦分蘖到抽穗期叶片硝酸还原酶(NR)活性、一氧化氮(NO)含量、气体交换参数和籽粒产量的影响.结果表明:叶片光合速率（P_n）、蒸腾速率（T_r）、瞬时水分利用效率（IWUE）和产量均随施氮量的增加呈先升高后降低的趋势,在180 kg·hm^-2氮处理时达到最高.随施氮量的增加,叶片NR活性提高; 在分蘖期和拔节期,叶片NR活性与NO含量呈显著线性相关（R²≥0.68,n=15）,NO含量和气孔导度（G_s）呈显著正二次相关（R²≥0.43,n=15）;低氮处理下,NR活性较低使叶片NO含量维持在较低水平,促进气孔开放,高氮处理下,NR活性较高使叶片NO含量增加,诱导气孔关闭;在抽穗期叶片NR活性和NO含量无显著相关关系,虽然NO含量和G_s也呈显著正二次相关（R²≥0.36,n=15）,但不能通过施氮提高NR活性来影响叶片NO含量,进而调节叶片气孔行为.合理施氮使小麦叶片NO含量维持在较低水平,可提高叶片G_s、T_r和IWUE,增强作物抗旱能力,促进光合作用,提高小麦产量.     

Genetic analysis of grain and malt quality in an elite barley population

Quantitative trait loci (QTLs) associated with grain weight, grain width, kernel hardness and malting quality were mapped in a doubled haploid population derived from two elite Australian malting barley varieties, Navigator and Admiral. A total of 30 QTLs for grain weight, grain width and kernel hardness were identified in three environments, and 63 QTLs were identified for ten malting quality traits in two environments. Three malting quality traits, namely β-amylase, diastatic power and apparent attenuation limit, were mainly controlled by a QTL linked to the Bmy1 gene at the distal end of chromosome 4H encoding a β-amylase enzyme. Six other malting quality traits, namely α-amylase, soluble protein, Kolbach index, free amino-acid nitrogen, wort β-glucan and viscosity, had coincident QTL clustered on chromosomes 1HS, 4HS, 7HS and 7HL, which demonstrated the interdependence of these traits. There was a strong association between these malt quality QTL clusters on chromosomes 1HS and 7HL and the major QTL for kernel hardness, suggesting that the use of this trait to enable early selection for malting quality in breeding programs would be feasible. In contrast, the majority of QTLs for hot-water extract were not coincident with those identified for other malt quality traits, which suggested differences in the mechanism controlling this trait. Novel QTLs have been identified for kernel hardness on chromosomes 2HL and 7HL, hot-water extract on 7HL and wort β-glucan on 6HL, and the resulting markers may be useful for marker-assisted selection in breeding programs.     

Characterisation of grain yield and nitrogen level in relation to flag leaf senescence of wheat varieties

Three wheat cultivars ( Triticum aestivum L.), Splendeur, Hobbit and Maris Huntsman grown in pots were compared. Especially when compared to Splendeur, the flag leaf senesced most rapidly in Maris Huntsman, which presented the most rapid loss of moisture, chlorophyll and nitrogen. The uptake of exogenous nitrogen during the post-anthesis period was lower in the rapidly than in the slowly senescing variety. A higher concentration of free amino nitrogen in the flag leaf at a given sampling date was associated with a lower percentage decrease of soluble proteins at the following date. Acid proteinase activity in the flag leaf was inversely related to moisture percentage and free amino nitrogen level, but unrelated to the nitrogen loss of the flag leaf. Acid proteinase activity in the flag leaf was directly related to grain nitrogen percentage, but inversely related to grain yield. Grain yield was also directly related to the mean soluble protein content of the flag leaf through senescence.     

干旱胁迫对不同耐旱性玉米杂交种产量和根系生理特性的影响

通过盆栽人工模拟干旱试验,研究了全生育期中度干旱胁迫对不同耐旱性玉米杂交种（耐旱：京科628;不耐旱：农大95）产量及根系生理特性的影响.结果表明：干旱胁迫下,耐旱玉米产量比对照减少33.7%,不耐旱玉米则比对照减少62.3%.干旱胁迫下,玉米根系生物量降低且最大值出现时间提前,与对照相比,不耐旱玉米根冠比升高,耐旱玉米根冠比前期升高后期降低;根系活力降低,不耐旱玉米根系活力降低幅度大于耐旱玉米;根系超氧化物歧化酶（SOD）活性前期高于对照后期低于对照,耐旱玉米根系SOD活性开始低于对照的时间比不耐旱玉米晚;根系丙二醛（MDA）含量升高,随干旱胁迫处理时间的延长,不耐旱玉米MDA含量比对照升高的幅度大于耐旱玉米;根系可溶性蛋白含量降低,不耐旱玉米的降低幅度大于耐旱玉米.干旱胁迫下耐旱玉米杂交种根系活力﹑根系SOD活性及可溶性蛋白含量较高,减缓了根系的衰老进程,延长了根系功能期,这可能是耐旱玉米杂交种在干旱胁迫下仍能获得较高产量的重要原因之一.     

Alleu cropping sequentially cropped maize and cowpea with Leucaena on a sandy soil in Southern Nigeria

Summary The potential of alley cropping maize and cowpea with the giant Leucaena (Leucaena leucocephala (Lam) de Wit) cultivar K-28 was studied on an Entisol (Psammentic Ustorthent) in Southern Nigeria. In this trial the crops were grown in 4 m wide alleys formed by periodically pruned leucaena hedgerows. The effect of application of leucaena prunings, nitrogen fertilizer and tillage was studied.Despite the very intensive pruning regime (five prunings/year) for a six-year period, the leucaena hedgerows continue to produce substantial amounts of prunings, nitrogen yield and stakes. Application of nitrogen to the maize crop increased dry matter and nitrogen yield from the leucaena prunings. Although high nitrogen yield was obtained from the prunings, the application of low nitrogen rates was still needed for obtaining a high maize yield. Maize grain yield can be sustained at about 2.0 t/ha with continuous application of leucacna prunings only. Without application of leucaena prunings and nitrogen maize yield continued to decline with subsequent croppings. Cowpea grain yield was not affected either by leucaena prunings or by residual nitrogen. Tillage (rototilling) resulted in either higher or the same maize and cowpea yields as compared with no-tillage.Application of leucaena prunings resulted in higher soil moisture retention, organic matter, exchangeable K, Ca, Mg, and also nitrate levels in the soil solution. Leucaena and maize appear to extract soil moisture from different zones in the soil. Timely pruning of hedgerows is necessary to minimize shading.     

深松与包膜尿素对玉米田土壤氮素转化及利用的影响

耕作方式和氮肥施用是影响土壤中氮肥转化、利用效率和作物产量的重要因素。通过夏玉米田的2a(2011—2012)定位试验,研究了两种耕作方式(深松、旋耕)配合不同尿素类型(包膜尿素、普通尿素)的施用对玉米田土壤硝态氮和铵态氮含量、脲酶活性、硝化细菌和反硝化细菌数量、玉米产量以及氮肥农学效率的影响。研究结果表明:相同耕作方式下,包膜尿素处理土壤中脲酶活性较稳定,且增加了旱田土壤亚硝酸细菌数量而降低了反硝化细菌数量,有利于土壤硝态氮含量的提高,尤其是作物生长的中后期;包膜尿素处理的产量比普通尿素提高7.25%—10.82%,同时提高氮肥农学效率。深松处理增加了土壤中的反硝化细菌数量,配合施用包膜尿素进一步提高了土壤脲酶活性,增加了亚硝酸细菌数量;旋耕与包膜尿素配合施用在一段时期内能显著增加土壤硝态氮含量,减少反硝化细菌数量。深松配合包膜尿素处理能够显著的增加玉米产量,2a分别比旋耕配合包膜尿素增加1.41%和10.62%。因此,深松措施配合施用包膜尿素能够增强土壤脲酶活性,增加亚硝酸细菌数量,提高氮素转化速率,增加作物产量和氮肥农学效率,其稳产效果在干旱年份尤为显著。     

Changes in the uptake and assimilation efficiency for sulfate and nitrate in maize hybrids selected during the period 1930 through 1975

Sulfate and nitrate uptake capacity, ATP sulfurylase (ATPS) and nitrate reductase (NR) activity were determined in a set of maize hybrids representative of selection cycles carried out during the period 1930 through 1975. All the above metabolic parameters together with the grain yield were improved by the selection. The annual rate of the improvement was higher (double) for sulfate uptake than for ATPS and similar for NR and nitrate uptake. Significant correlations were evidenced between the uptake efficiency of the roots and the enzyme activity in the leaves both for sulfate and nitrate pathways, and also between the uptake and enzyme steps of nitrate and those of sulfate. This offered good evidence of a coupled genetic regulation between nitrogen and sulfur metabolism in maize.     

间作对玉米品质、产量及土壤微生物数量和酶活性的影响

为了进一步深入了解禾本科作物和豆科作物间作的优势机理,研究了在不同施肥条件下玉米单作、玉米‖花生间作和玉米‖大豆间作对玉米籽粒品质、单株经济产量和生物产量﹑产量及土壤中细菌、真菌、放线菌和固氮菌数量及酶活性的影响。结果表明,在不施肥条件下玉米间作可以显著提高玉米籽粒蛋白质、油分和赖氨酸含量,但对淀粉含量影响不显著;在施肥条件下玉米间作可以显著提高淀粉和赖氨酸含量,但对油分和蛋白质含量的增加却影响不显著;间作在提高玉米籽粒淀粉、蛋白质和赖氨酸含量方面的效果没有该施氮水平(50kg/km²)显著。间作可以增加玉米产量及其单株经济产量和生物产量,其中在不施肥和施肥条件下产量分别比单作增加了3.7％、9.7％、19.0％和18.6％,但间作在增加产量方面的效果没有该施氮水平显著。间作在不同施肥条件下可明显增加土壤中细菌、真菌、放线菌和固氮菌的数量,且效果达到显著水平。土壤中的酶活性也显著受到间作的影响,在不施肥条件下玉米间作和单作土壤中的转化酶活性差异达到显著水平,在施肥条件下间作和单作土壤中转化酶和磷酸酶活性差异达到显著水平。4种微生物数量和4种酶活性之间呈显著或极显著正相关,玉米籽粒品质、产量及单株生物产量除与转化酶及磷酸酶活性部分相关不显著外,与土壤中的其它酶活性及微生物数量皆显著或极显著正相关。     

大田增温对夏玉米产量和品质的影响

研究了大田条件下增温（3 ℃）对夏玉米产量和品质的影响. 结果表明：增温条件下玉米的籽粒产量显著降低,农大108（ND108）和掖单13号（YD13）分别减产46.6%和45.1%.增温也显著影响了玉米的籽粒品质,与对照相比,ND108和YD13的粗蛋白含量分别提高了11.6%和2.02%;粗脂肪含量分别降低了38.9%和9.6%;淀粉含量分别降低了7.0%和8.4%,且主要降低了支链淀粉的含量;赖氨酸含量则分别降低了58.9%和51.2%.     

Breeding progress,genotypic and environmental variation and correlation of quality traits in malting barley in German official variety trials between 1983 and 2015

Key message

Evaluation of breeding progress for spring barley varieties in Germany showed that both grain yield and malting quality were considerably improved during the last 33 years, and that genetic effects of protein concentration and malting traits were not associated.

Abstract

Based on historical data, this study aimed to investigate yield potential and malting quality of 187 varieties tested and released in German registration trials to evaluate the value for cultivation and use (VCU) during 1983–2015, and to quantify the environmental variability and the association among traits. We used mixed linear models with multiple linear regression terms to dissect genetic and non-genetic trend components. Grain yield increased by 43% (23.4 dt ha^?1) in VCU trials and 35% (14.0 dt ha^?1) on-farm relative to 1983. All yield components contributed significantly. Malting quality was also considerably improved by 2.3% for extract content up to 25.1% for friability, relative to 1983, nearly completely due to new varieties. Total variability of individual traits was very different between traits (2.4–24.4% relative to 1983). The relative influence of genotypes on total variation was low for grain yield and its components, whereas it was considerably larger for other traits. We found remarkable differences between phenotypic and genetic correlation coefficients for grain yield and protein concentration with malting traits. The observed positive phenotypic relation between grain yield and malting quality can be attributed to a shift of selection and environmental effects, but genetic correlations showed a negative association. Genetic effects of protein concentration and malting quality were not correlated indicating that both were not genetically linked. Considerable yield progress and improvement of malting quality were achieved despite of their weak to moderate negative genetic dependence.

     

Mildew-resistant mutants induced in North American two- and six-rowed malting barley cultivars

Mildew-resistant mutants were induced with sodium azide in three North American malting barley cultivars, two in the six-rowed Ursula (URS1 and URS2), one in the six-rowed Gertrud (GER1), and one in the two-rowed Prudentia (PRU1). Two of the mutants, URS1 and PRU1, showed complete resistance and were shown to have two new alleles at the mlo locus; these were designated, respectively, mlo31 and mlo32. Mutant URS2, showing partial resistance, was inherited as a dominant gene, but was not an allele at the Mla locus. The mean yield of each mutant was higher than that of its parental line, but yield levels varied across environments, although this was independent of the severity of the mildew attack. Other reasons, for example, the severity of the necrotic lesions in the mutants, may account for yield variations. The malting quality of the GER1 mutant proved similar to that of Gertrud, but both URS1 and URS2 showed lower malt extract than Ursula. This lower extract might be due to the smaller grain size of the mutants that could, in turn, result from necrotic lesions in the leaves, as implied by the effects on grain yield.Communicated by G. Wenzel     

氮肥水平对不同基因型水稻氮素利用率、产量和品质的影响

以不同基因型的水稻品种日本晴、N70、N178和OM052为供试品种,氮肥采用尿素,按基肥(70%)和蘖肥(30%)两次施用,设置3个施氮水平(N用量设0、120、270 kg·hm^-2)的田间小区试验,研究氮素水平对水稻产量、氮素利用效率和稻米品质的影响,以期为氮肥合理施用和氮高效水稻品种创制提供科学依据.结果表明:施氮能增加水稻品种产量的原因是提高了有效穗数和每穗实粒数;与对照(0 kg·hm^-2)相比,当施氮量为120和270 kg·hm^-2时,OM052籽粒产量在4个品种中增幅最大,分别为41.1%和76.8%;品种产量增幅不同是由于氮素利用效率的差异,在120、270 kg·hm^-2氮处理下,4个供试品种中,日本晴籽粒产量和氮素农学利用率(40.90 g·g^-1、18.56 g·g^-1)都最低,为氮低效品种,OM052籽粒产量和氮素农学利用率(145.9 g·g^-1、81.24 g·g^-1)都最高,为氮高效品种.施N能够增加各品种的直链淀粉和蛋白质含量,使胶稠度变长,降低垩白率、垩白度和碱消值;随施氮量增加,热浆黏度、峰值黏度、回复值和崩解值递减,而消碱值递增.相关性分析表明,低N水平下,供试品种产量及产量构成因子与外观品质、蒸煮食味的相关性更显著.综上,OM052是一个籽粒产量和氮素利用效率“双高”基因型品种,合理施用氮肥可以显著增加水稻的有效穗数和每穗粒数,改善稻米籽粒品质,实现高产和优质的协同.     

有机肥和化肥配施对不同熟期大白菜土壤生物特性及产量品质的影响

以早熟和晚熟品种大白菜为试材,根据化肥氮(尿素)、有机肥氮(生物有机肥)配施比例设置4个施肥处理,测定不同施肥处理下不同熟期大白菜土壤酶活性、可培养微生物数量及产量、品质的变化特征.结果 表明:早熟品种'德高16'大白菜莲座期和结球紧实期均以配施1/2生物有机肥(T2)处理的土壤蔗糖酶、土壤脲酶、土壤过氧化氢酶活性较强...     

密度与氮肥对关中灌区夏玉米(Zea mays L.)群体光合生理指标的影响

合理的密度是玉米构建良好群体结构、优化群体光合生理功能的基础,适宜的氮肥施用量是玉米进行光合生产的营养物质保障.运用作物群体生理学的方法,采用二次饱和D试验设计,研究了关中灌区夏玉米密度与氮肥耦合和群体光合生理指标的关系及其效应,明确了在关中灌区夏播条件下,在45000～75000株/hm2的密度范围内,密度与玉米籽粒产量、总干物质积累量(DMA)、吐丝期叶面积指数(MLAI)、总光合势(LAD)、平均作物生长率(CGR)为正相关,在45000～60000株/hm2的密度范围内,密度与玉米叶片平均净同化率(NAR)为正相关,而在60000～75000株/hm2的密度范围内,密度与玉米NAR为负相关;在氮素施用量≤600.0 kg/hm2的范围内,氮素施用量与玉米籽粒产量、DMA、CGR为正相关,在氮素施用量≤260.55 kg/hm2的范围内,氮素施用量与玉米MLAI、LAD为正相关,与玉米NAR为负相关,而在氮素施用量260.55～600.0kg/hm2的范围内,氮素施用量与玉米MLAI、LAD为负相关,与玉米NAR为正相关.密度对其影响较大的指标为:籽粒产量、DMA、LAD、CGR和MLAI , 影响较小的指标为:NAR;氮肥对其影响较大的指标为:DMA、CGR、籽粒产量、NAR,影响较小的指标为:LAD和MLAI .对籽粒产量和群体生理指标的综合影响效应,密度显著大于氮肥,玉米生产中,尤其要重视合理密植.通过对回归模型的解析,筛选确定了陕单8806玉米在关中灌区夏播中,实现高产的密度与氮肥耦合优化技术方案:合理密度为61713～66177株/hm2,适宜纯氮施用量为309.88～569.02kg/hm2.     

控释尿素施用方式及用量对夏玉米氮肥效率和产量的影响

在大田条件下以不施氮为对照,研究了施氮量为75和150 kg N·hm^-2条件下,普通尿素底施、控释尿素底施和侧施对夏玉米光合性能、氮肥效率和产量的影响.结果表明：与普通尿素相比,相同施氮水平下,包膜控释尿素处理玉米果穗叶光合速率、叶绿素含量、硝酸还原酶活性、籽粒灌浆速率均显著提高,玉米籽粒产量比普通尿素平均提高9.5%;与控释尿素侧施相比,底施使玉米籽粒产量提高6.2%.包膜控释尿素处理的氮肥农学利用率（AE）和偏生产力（PFP）比普通尿素平均分别提高74.5%和11.0%;与包膜控释尿素侧施相比,底施使AE和PFP分别提高26.8%和5.7%.控释尿素施用量较高时,玉米光合性能得到改善,产量、AE和PFP显著提高;与控释尿素侧施相比,底施对玉米产量、AE和PFP的增加效果更显著.     

Evaluation of nigerian millet (pennisetum typhoideum) as a raw material for beer production

Millet (Pennisetum typhoideum) its malt and wort were evaluated to ascertain the suitability of the grain for beer production. Thousand grain weight was 8.03 g while foreign material and broken cernels represented 3.23%. Germination energy, germination capacity and moisture content of the grain were 75.67, 92.33 and 10.43%, respectively, while the carbohydrate, total nitrogen and protein contents were 53.88, 1.34 and 8.40%, respectively. Millet malt had a moisture content of 5.03% while its carbohydrate, total nitrogen, protein content and malting loss were 48.47, 1.87, 11.7 and 8.3%. pH and specific gravity of the worth were 5.70 and 1.5927, respectively; its protein content was negligible while % titratable acidity was 1.35. The low nitrogen and protein contents of the grain as well as the low malting loss make millet an attractive alternative cereal for beer production in Nigeria.     

不同沼液用量对夏玉米源库代谢关键酶及产量的影响

以玉米杂交种郑单958为材料,研究了3个不同沼液用量（15000、22500、30000 kg·hm^-2）对夏玉米源库代谢关键酶和产量构成因素的影响.结果表明：与对照和施氮肥相比,田间浇灌沼液不仅可提高夏玉米地上部干物质量、叶面积指数和叶绿素含量,而且可提高叶片中硝酸还原酶（NR）、谷氨酰胺合成酶（GS）、蔗糖磷酸合成酶（SPS）和籽粒中蔗糖合成酶（SS）活性,从而显著增加了玉米穗粗、穗长、穗行数、穗粒数、穗粒重、千粒重和单位面积产量.在3个沼液用量中,以22500 kg·hm^-2处理(拔节期、大口期、抽雄期各追施7500 kg·hm^-2)对提高玉米酶活性和产量的效果最好,其产量可达14006.7 kg·hm^-2,比对照增产40.7％.     

微灌与播前深松对根际土壤酶活性和夏玉米产量的影响

为探明微灌与播前深松耕作对夏玉米根际土壤酶活性和产量的影响,以大田夏玉米为研究对象,设计微灌灌溉方式(地表滴灌、地下滴灌和微润灌)、灌水量(分别控制土壤含水量下限为田间持水率的50%、65%和80%)和深松深度(20、40、60 cm)3因素、3水平正交田间试验.结果表明: 夏玉米全生育期内,土壤过氧化氢酶和脲酶活性均呈先增加后减小趋势,磷酸酶活性则呈先减小后增加趋势.地下滴灌0~80 cm生育期平均土壤含水率比地表滴灌和微润灌高6.3%和1.8%,且显著提高土壤脲酶活性、夏玉米根系体积和产量;随着灌水量的增加,土壤磷酸酶活性呈先减小后增加趋势,脲酶活性和产量均呈先增加后减小趋势,生育期平均土壤含水率与根系体积均呈增加趋势;深松40 cm比20 cm的产量和根系体积增加量大于深松60 cm比40 cm的增加量,深松40 cm土壤酶活性较高.从提高水资源、氮肥利用率及作物产量角度考虑,该地区夏玉米种植的最优组合应为地下滴灌、灌水下限为田间持水率的65%与播前深松40 cm.     

玉米-大豆间作和施氮对玉米产量及农艺性状的影响

为研究玉米-大豆间作模式和施氮水平对玉米产量、主要农艺性状及生长动态的影响,进行2个种植模式(玉米单作和玉米-大豆间作)和2个施氮水平(0 kg/hm2,150 kg/hm2)的双因素随机区组试验,以期揭示施氮和间作对玉米产量的影响规律,为提高玉米-大豆间作系统产量提供一定的理论依据。研究结果表明:(1)与不施氮相比,施氮显著增加了春秋两季间作玉米产量,分别达到23.81%和40.99%。施氮处理下的间作玉米地上部生物量较不施氮提高了29.91%,单作模式下显著提高了40.34%,两者差异均达到显著水平。(2)与不施氮相比,施氮150 kg/hm2条件下春玉米单作和间作模式百粒重分别提高了18.92%和19.23%,秋玉米单作和间作模式百粒重分别提高了31.03%和32.75%,差异均达到显著水平。与不施氮相比,施氮150 kg/hm2条件下,单作和间作模式均显著提高秋玉米穗长。与不施氮相比,施氮150 kg/hm2条件下,单作秋玉米的穗粗提高了18.67%,差异显著。(3)施氮和间作均能促进玉米干物质累积、提高株高和叶绿素(SPAD值),且表现为施氮效果高于间作效果。总体来看,种植模式和施氮水平对玉米产量、主要农艺性状和生长动态均有一定影响,且施氮效果优于间作效果。由于土壤具有一定的供氮能力,而间作豆科能为玉米供给一定量的氮素,故对于春玉米而言,施氮效果仅在百粒重中表现,随着土壤原有氮素被玉米吸收利用减少后,供氮能力下降,在秋玉米中施氮效果显著提高。