Sulfur fertilization improves nitrogen use efficiency in wheat by increasing nitrogen uptake

Nitrogen (N) fertilization plays a central role for improving yield in wheat and high N use efficiency (NUE) is desired to protect ground and surface waters. Several studies showed that sulfur (S) fertilization may increase NUE, but no attempts have been made to explain whether this increase is due to greater recovery efficiency (RE), an enhanced internal efficiency (IE) or by an improvement of both efficiencies. The aim of this study was to analyze the effects of different N and S fertilizer rates, and their interaction on N uptake, its partition at maturity, NUE and its main components. Field experiments were carried out during two consecutive growing seasons in the Argentinean Pampas using a single bread-wheat genotype grown under different combinations of N and S fertilizer rates. Additional experiments were performed in farmer fields using N and S fertilization evaluating different genotypes in order to analyze the components of NUE in other environmental conditions. Plant N uptake increased linearly in response to N addition until rates of ca. 80 kg N ha⁻¹. Sulfur addition showed no effect at the lowest N fertilizer rate, but N uptake was increased when S was applied at the highest N rate, revealing a synergism between both nutrients. At the lowest S rate RE was 42%, and increased to 70% when S fertilizer was added. No changes in IE in response to S fertilization were observed. These results were also observed in farmer field experiments, in genotypes that showed different IE. This study showed that S addition increased NUE mainly by increasing the N recovery from the soil. Thus, the concurrent management of N and S is important for reducing the potential pollution of residual soil nitrate by increasing N recovery from the soil while sustaining high nitrogen use efficiency.     

种植密度和施氮量耦合对夏玉米干物质积累及氮肥利用率的影响

以郑单958和中单909为试验材料,设4.5万、6.75万、9.0万株/km~2 3个种植密度和0、100、300、500 kg/km~2 4种施氮水平,分析种植密度与施氮量对夏玉米干物质积累量和氮肥利用率的影响。结果表明,玉米在种植密度9.0万株/hm~2,其叶面积指数、群体干物质积累量、总氮素积累量以及产量均显著高于4.5万株/hm~2密度处理。增施氮肥可显著增加玉米叶面积指数、单株干物质积累量、群体干物质积累量、总氮积累量和子粒产量。当施氮量为300~500 kg/hm~2时,叶面积指数、群体干物质积累量及产量不再提加,氮肥利用率和氮肥偏生产力大幅降低。结果表明,郑单958和中单909种植适宜模式为施氮量300~500 kg/hm~2、种植密度9.0万株/hm~2。     

Optimization of nitrogen rate and seed density for safflower (Carthamus tinctorius L.) production under low-input farming conditions in temperate climate

Field experiments under low-input farming conditions were conducted in South West Germany (lhinger Hof) and North Switzerland (Wil) in 2004 and 2005 aimed at optimizing nitrogen rate and seed density for the production of the newly introduced safflower (Carthamus tinctorius L.). The experiments were laid out in a four-replicated-split plot design with three nitrogen fertilizer rates (0, 40, 80 kg/ha) as main plots and cultivars (Sabina, Saffire, BS-62915) and seed densities (50, 100, 150 seeds/rn2) randomized in split plots. It was shown that many traits responded differentially across environments to rate of nitrogen and seed density. Application of 40 and 80 kg N/ha did not significantly affect most of the investigated traits. At Ihinger Hof, the total nitrogen fertilizer needed to maximize safflower yield was estimated to be 86 kg N/ha. At Wil, residual soil nitrogen alone resulted in satisfactory seed yield when safflower followed a crop fertilized at a commercial rate. The nitrogen rate × seed density interaction was only significant for seed yield and Alternaria leaf spot disease. Nitrogen rates provided significant increases in seed yield at high seed density compared to low seed density. Seed density did not reveal any significant variation in seed yield, oil content, and oil yield. On average, the low seed density produced substantially higher numbers of heads/plant and seeds/plant compared to medium and high densities. These results demonstrate the ability of safflower to use residual soil nitrogen efficiently and to compensate for low plant density.     

Inter-plant competition for resources in maize crops grown under contrasting nitrogen supply and density: Variability in plant and ear growth

Increased plant population density in irrigated and fertilized maize crops enhances plant-to-plant variability since early vegetative stages, because the most suppressed individuals of the stand intercept less radiation per unit leaf area than the dominant ones (i.e. a size-asymmetric competition for light). Contrarily, a size-symmetric competition has been proposed for the acquisition of soil resources in a plant community (e.g. N capture per unit root length is similar among plants of different size). Hence, N fertilization effect on the variability of maize plants would depend on the initial plant-to-plant variability or on that promoted by a high plant population density. Two maize hybrids with contrasting tolerance to crowding (tolerant AX820 and intolerant AX877) were cultivated under different combinations of stand densities (6, 9 and 12 plants m⁻²) and N supplies (0 and 200 kg N ha⁻¹) without water restrictions. Variability in plant growth rate among plants was computed along the cycle, especially after fertilizer was applied (i.e. the early reproductive period; PGR_ER) and during the critical period around silking (PGR_CP). Plant-to-plant variability in biomass partitioning to the ear (partition index; PI), ear growth rate during the critical period (EGR_CP) and kernel number per plant (KNP) was also established. Reduced N supply increased the coefficient of variation (CV) of PGR_ER, PGR_CP, EGR_CP and KNP (0.05 < P < 0.10). The CVs of PGR_CP, PI, EGR_CP and KNP augmented (0.001 < P < 0.10) at the highest stand density. The CVs of PGR_ER, PGR_CP, PI and KNP were larger for hybrid AX877 than for hybrid AX820 (0.001 < P < 0.10). N fertilization smoothed the initial plant-to-plant variability, but the extent of this benefit in a maize crop is genotype dependent; it was much larger in the hybrid tolerant to crowding stress than in the intolerant one. For the latter, the variability held during the critical period around silking and produced a high CV of KNP.     

Biomass production and nitrogen accumulation and remobilisation by Miscanthus × giganteus as influenced by nitrogen stocks in belowground organs

The nitrogen (N) requirement of dedicated crops for bioenergy production is a particularly significant issue, since N fertilisers are energy-intensive to make and have environmental impacts on the local level (NO₃ leaching) and global level (N₂O gas emissions). Nitrogen nutrition of Miscanthus × giganteus aboveground organs is assumed to be dependent on N stocks in belowground organs, but the precise quantities involved are unknown. A kinetic study was carried out on the effect of harvest date (early harvest in October or late harvest in February) and nitrogen fertilisation (0 or 120 kg N ha⁻¹) on aboveground and belowground biomass production and N accumulation in established crops. Apparent N fluxes within the crop and their variability were also studied.Aboveground biomass varied between 24 and 28 t DM ha⁻¹ in early harvest treatments, and between 19 and 21 t DM ha⁻¹ in late harvest treatments. Nitrogen fertilisation had no effect on crop yield in late harvest treatments, but enhanced crop yield in early harvest treatments due to lower belowground biomass nitrogen content. Spring remobilisation, i.e. nitrogen flux from belowground to aboveground biomass, varied between 36 and 175 kg N ha⁻¹, due to the variability of initial belowground nitrogen stocks in the different treatments. Autumn remobilisation, i.e. nitrogen flux from aboveground to belowground organs, varied between 107 and 145 kg N ha⁻¹ in late harvest treatments, and between 39 and 93 kg N ha⁻¹ in early harvest treatments. Autumn remobilisation for a given harvest date was linked to aboveground nitrogen accumulation in the different treatments. Nitrogen accumulation in aboveground biomass was shown to be dependent firstly on initial belowground biomass nitrogen stocks and secondly on nitrogen uptake by the whole crop.The study demonstrated the key role of belowground nitrogen stocks on aboveground biomass nitrogen requirements. Early harvest depletes belowground nitrogen stocks and thus increases the need for nitrogen fertiliser.     

不同玉米自交系氮效率的分析

试验在4个氮处理水平上对8个玉米自交系的氮效率进行了研究。结果表明,玉米自交系在产量、生物量和氮累积量上存在显著的差异。据氮效率分析,黄C属低氮、高氮处理下产量均较高的双高效型,340属低氮高效型自交系,00冬属高氮高效型自交系,C8605属低氮、高氮处理下产量均较低的双低效型自交系。通径分析表明,在3个施氮处理中氮吸收效率对氮效率的作用均大于氮利用效率对氮效率的作用,且低氮下吸收效率对氮效率的作用大,高氮下利用效率对氮效率的作用大。     

不同氮肥模式对夏玉米产量、蛋白质品质和氮素利用特性的影响

以高产玉米品种郑单958和先玉335为供试材料,在大田生产条件下设置4个施氮水平,研究不同氮肥模式对两个高产玉米品种子粒产量、蛋白质产量及氮素利用特性的影响。结果表明,两个玉米品种子粒产量随施氮量的增加显著增加,均以240 kg/hm~2处理最高,先玉335子粒产量显著高于郑单958;两个玉米品种子粒蛋白质含量及其产量随施氮量的增加显著增加,先玉335的蛋白质含量及其产量均高于郑单958;两个玉米品种氮素利用效率、氮肥生产效率和氮肥农学利用效率随施氮量的增加而显著降低,均以180 kg/hm2处理最高,先玉335的氮素利用效率、氮肥生产效率和氮肥农学利用效率均高于郑单958。综合分析认为,两个玉米品种均以240 kg/hm~2处理可以同步协调实现较高的子粒产量、蛋白质含量和氮素利用效率,获得产量、品质和高氮素利用效率的协调统一。     

玉米秸秆还田条件下冬灌时间与施氮方式对冬小麦生长发育及水肥利用效率的影响

为给玉米秸秆还田条件下冬小麦的水氮运筹提供依据,以小麦品种临优2069为材料,研究了山西省小麦-玉米一年两熟区玉米秸秆还田条件下冬灌时间和施氮方式对冬小麦生长发育及水氮利用效率的影响。结果表明,随着冬前灌水时间的推迟,小麦总茎数、单株分蘖数、成穗数、产量、籽粒水分生产率、氮肥表观利用率均呈先升高后降低趋势,以11月25日冬灌的最高。在施氮量相同条件下,氮肥一次性底施(N10∶0)的拔节期总茎数、成穗数、产量、籽粒水分生产率和氮素吸收量、表观利用率高于氮肥70%底施+30%拔节期追施(N7∶3)处理,冬前总茎数、单株分蘖数则相反。冬前灌水时间提前和氮肥一次性底施有利于提高小麦前期单株干重;冬前灌水时间推迟和后期追氮则有利于灌浆期穗部和总干物质的积累。因此,山西省小麦-玉米一年两熟区,秸秆还田条件下氮肥采取一次性底施,并于11月25日冬灌,可实现冬小麦的高产高效栽培。     

不同氮肥施用量对东北玉米田杂草发生的影响

利用吉林省梨树县黑土区氮肥长期定位试验田(施氮水平为0、60、120、180、240、300 kg/hm2),2019～2020两年调查玉米田杂草种类、密度和生物量及其与玉米生物量和产量的关系.结果表明,试验条件下玉米田杂草主要是禾本科杂草,尤其是水稗草Echinochloa oryzoides.与不施肥相比,60 k...     

Nitrogen uptake,fixation and response to fertilizer N in soybeans: A review

Although relationships among soybean (Glycine max [L.] Merr) seed yield, nitrogen (N) uptake, biological N₂ fixation (BNF), and response to N fertilization have received considerable coverage in the scientific literature, a comprehensive summary and interpretation of these interactions with specific emphasis on high yield environments is lacking. Six hundred and thirty-seven data sets (site–year–treatment combinations) were analyzed from field studies that had examined these variables and had been published in refereed journals from 1966 to 2006. A mean linear increase of 0.013 Mg soybean seed yield per kg increase in N accumulation in aboveground biomass was evident in these data. The lower (maximum N accumulation) and upper (maximum N dilution) boundaries for this relationship had slopes of 0.0064 and 0.0188 Mg grain kg⁻¹ N, respectively. On an average, 50–60% of soybean N demand was met by biological N₂ fixation. In most situations the amount of N fixed was not sufficient to replace N export from the field in harvested seed. The partial N balance (fixed N in aboveground biomass − N in seeds) was negative in 80% of all data sets, with a mean net soil N mining of −40 kg N ha⁻¹. However, when an average estimated belowground N contribution of 24% of total plant N was included, the average N balance was close to neutral (−4 kg N ha⁻¹). The gap between crop N uptake and N supplied by BNF tended to increase at higher seed yields for which the associated crop N demand is higher. Soybean yield was more likely to respond to N fertilization in high-yield (>4.5 Mg ha⁻¹) environments. A negative exponential relationship was observed between N fertilizer rate and N₂ fixation when N was applied on the surface or incorporated in the topmost soil layers. Deep placement of slow-release fertilizer below the nodulation zone, or late N applications during reproductive stages, may be promising alternatives for achieving a yield response to N fertilization in high-yielding environments. The results from many N fertilization studies are often confounded by insufficiently optimized BNF or other management factors that may have precluded achieving BNF-mediated yields near the yield potential ceiling. More studies will be needed to fully understand the extent to which the N requirements of soybean grown at potential yields levels can be met by optimizing BNF alone as opposed to supplementing BNF with applied N. Such optimization will require evaluating new inoculant technologies, greater temporal precision in crop and soil management, and most importantly, detailed measurements of the contributions of soil N, BNF, and the efficiency of fertilizer N uptake throughout the crop cycle. Such information is required to develop more reliable guidelines for managing both BNF and fertilizer N in high-yielding environments, and also to improve soybean simulation models.     

Comparison of Nitrogen Uptake,Transpiration Rate and Exudation Rate between Upland NERICAs and Japanese Cultivars

Abstract

Our previous study revealed that upland cultivars of New Rice for Africa (NERICAs) exhibited superior biomass production and N uptake compared with selected Japanese cultivars under upland conditions. The objective of this study was to examine whether the N uptake ability of upland NERICAs is attributable to their transpiration and exudation rates. Two NERICA cultivars (NERICA 1 and NERICA 5), two Japanese upland cultivars (Toyohatamochi and Yumenohatamochi), and a Japanese lowland cultivar Hitomebore were grown under rainfed upland conditions at two N levels. The NERICAs exceeded Japanese cultivars in the increment of aboveground dry weight and N content during the ripening stage. The transpiration rate and exudation rate of NERICAs tended to be higher than those of Japanese cultivars during the ripening stage. These results suggest that NERICAs are capable of maintaining higher water uptake ability during the ripening stage, leading to greater N uptake and biomass production at maturity.     

Estimating maize nutrient uptake requirements

Generic, robust models are needed for estimating crop nutrient uptake requirements. We quantified and modeled grain yield–nutrient uptake relations in maize grown without significant biotic and abiotic stresses. Grain yield and plant nutrient accumulation in above-ground plant dry matter (DM) of commercial maize hybrids were measured at physiological maturity in on-station and on-farm experiments in Nebraska (USA), Indonesia, and Vietnam during 1997–2006. These data were used to model the nutrient requirements for yields up to 20 Mg ha⁻¹ using the QUEFTS (QUantitative Evaluation of the Fertility of Tropical Soils) approach. The model required estimation of two boundary lines describing the minimum and maximum internal nutrient efficiencies of N, P and K (IE, kg grain per kg nutrient in plant DM), which were estimated at 40 and 83 kg grain kg⁻¹ N, 225 and 726 kg grain kg⁻¹ P and 29 and 125 kg grain kg⁻¹ K, respectively. The model predicted a linear increase in grain yield if nutrients are taken up in balanced amounts of 16.4 kg N, 2.3 kg P and 15.9 kg K per 1000 kg of grain until yield reached about 60–70% of the yield potential. The corresponding IEs were 61 kg grain kg⁻¹ N, 427 kg grain kg⁻¹ P and 63 kg grain kg⁻¹ K. The model predicted a decrease in IEs when yield targets approached the yield potential limit. A spherical model was derived from QUEFTS model outputs and found to be particularly suitable for practical applications such as estimating fertilizer needs. The proposed spherical model offers generality across environments and management practices, allowing users to estimate the optimal N, P and K uptake requirements based on two inputs: estimated yield potential and yield target. Further improvements in modeling the relationship between N uptake and grain yield can be made by taking into account differences in harvest index. Accuracy in the simulation of N uptake using the spherical model was improved from an RMSE of 35 kg N ha⁻¹ to 25 kg N ha⁻¹ when harvest index was accounted for, suggesting that the relationship between N uptake and actual yield is affected by both yield potential and efficiency in biomass partitioning.     

Effect of winter cover crop species and planting methods on maize yield and N availability under irrigated Mediterranean conditions

Under semiarid Mediterranean conditions irrigated maize has been associated to diffuse nitrate pollution of surface and groundwater. Cover crops grown during winter combined with reduced N fertilization to maize could reduce N leaching risks while maintaining maize productivity. A field experiment was conducted testing two different cover crop planting methods (direct seeding versus seeding after conventional tillage operations) and four different cover crops species (barley, oilseed rape, winter rape, and common vetch), and a control (bare soil). The experiment started in November 2006 after a maize crop fertilized with 300 kg N ha⁻¹ and included two complete cover crop-maize rotations. Maize was fertilized with 300 kg N ha⁻¹ at the control treatment, and this amount was reduced to 250 kg N ha⁻¹ in maize after a cover crop. Direct seeding of the cover crops allowed earlier planting dates than seeding after conventional tillage, producing greater cover crop biomass and N uptake of all species in the first year. In the following year, direct seeding did not increase cover crop biomass due to a poorer plant establishment. Barley produced more biomass than the other species but its N concentration was much lower than in the other cover crops, resulting in higher C:N ratio (>26). Cover crops reduced the N leaching risks as soil N content in spring and at maize harvest was reduced compared to the control treatment. Maize yield was reduced by 4 Mg ha⁻¹ after barley in 2007 and by 1 Mg ha⁻¹ after barley and oilseed rape in 2008. The maize yield reduction was due to an N deficiency caused by insufficient N mineralization from the cover crops due to a high C:N ratio (barley) or low biomass N content (oilseed rape) and/or lack of synchronization with maize N uptake. Indirect chlorophyll measurements in maize leaves were useful to detect N deficiency in maize after cover crops. The use of vetch, winter rape and oilseed rape cover crops combined with a reduced N fertilization to maize was efficient for reducing N leaching risks while maintaining maize productivity. However, the reduction of maize yield after barley makes difficult its use as cover crop.     

苗期甘蔗氮高效基因型评价指标的筛选

本研究通过低氮压力选择,筛选出甘蔗氮高效种质,分析影响甘蔗氮高效的重要指标,为甘蔗氮高效育种及栽培提供理论依据。以58份甘蔗种质资源为材料,在苗期采用正常供氮（2 mmol/L N）和低氮（0.2 mmol/L N）处理,分析甘蔗植株形态、干重及氮素在各器官中累积分配的特征。通过主成分分析方法筛选影响甘蔗氮高效利用的重要指标,通过聚类分析对58份种质进行聚类。结果表明,低氮（0.2 mmol/L N）处理可以明显从植物形态区分不同种质的氮利用差异,58份种质低氮条件下的干重范围为0.64~14.75 g/株,氮累积量为5.53~63.00 mg/株,氮利用率范围为115.40~279.30 g/g。对低氮压力下甘蔗干重及氮累积等25个指标进行主成分分析后,提取出4个主要成分,总贡献率为92.35%。通过高、低氮条件下与氮利用效率有关的氮转移系数及基因潜力等19个指标分析后提取出5个主成分,总贡献率为82.21%。影响甘蔗氮高效的重要指标有甘蔗的干重（全株、叶、根）、氮累积量（全株、叶、茎）、氮利用率（全株、叶）、叶的相对氮利用率、茎的基因潜力、茎的相对干物质量和茎的相对氮累积量。经聚类分析后初步将58份甘蔗种质分为氮高效基因型、偏氮高效基因型、偏氮低效基因型和氮低效基因型。     

不同基因型玉米氮素吸收利用效率研究进展

玉米氮效率的评价方法与指标不尽一致,导致对玉米基因型不同的分类结果。玉米氮效率研究主要集中于根系对氮素的吸收、叶片对氮素的还原同化、氮素在植株体内的积累和分配以及地上部生长势与氮效率的关系方面。以子粒为主要收获对象的玉米,穗、子粒发育状况对玉米产量起着关键作用,有关穗、子粒发育对玉米氮效率贡献率的大小、不同氮效率基因型玉米穗、子粒发育的差异以及内在生理生化机制研究较少。对不同氮效率基因型玉米子粒发育与氮效率之间关系、子粒发育尤其是顶部子粒的早期发育(决定穗粒数的形成)对氮素的反应、氮高效品种顶部子粒的早期发育是否优于氮低效型、氮素对不同氮效率基因型玉米子粒发育的影响机制等问题有待进一步研究。     

膜下滴灌春玉米氮素吸收规律与增产效应

研究春玉米膜下滴灌条件下氮肥对玉米氮素吸收、干物质积累以及氮肥的增产作用,提出试验条件下的最佳施氮量.结果表明,增加施氮量能够增加膜下滴灌春玉米地上部干物质积累及氮素吸收能力,过量施氮导致干物质及氮素累积降低;玉米产量随着施氮量增加而增加,300 kg/hm²时达到最高产量,此时氮肥农学效率、氮肥利用率以及生理利用率均达到最大.采用二次曲线拟合,计算最佳施氮量为291.80 kg/hm²,此时最高产量为14 964.54 kg/hm².     

Identification of traits to improve the nitrogen-use efficiency of wheat genotypes

Nitrogen (N) fertilizer represents a significant cost for the grower and may also have environmental impacts through nitrate leaching and N₂O (a greenhouse gas) emissions associated with denitrification. The objectives of this study were to analyze the genetic variability in N-use efficiency (grain dry matter (DM) yield per unit N available from soil and fertilizer; NUE) in winter wheat and identify traits for improved NUE for application in breeding. Fourteen UK and French cultivars and two French advanced breeding lines were tested in a 2 year/four site network comprising different locations in France and in the UK. Detailed growth analysis was conducted at anthesis and harvest in experiments including DM and N partitioning. Senescence of either the flag leaf or the whole leaf canopy was assessed from a visual score every 3-4 days from anthesis to complete canopy senescence. The senescence score was fitted against thermal time using a five parameters monomolecular-logistic equation allowing the estimation of the timing of the onset and the rate of post-anthesis senescence. In each experiment, grain yield was reduced under low N (LN), with an average reduction of 2.2 t ha⁻¹ (29%). Significant N × genotype level interaction was observed for NUE. Crop N uptake at harvest on average was reduced from 227 kg N ha⁻¹ under high N (HN) to 109 kg N ha⁻¹ under LN conditions while N-utilization efficiency (grain DM yield per unit crop N uptake at harvest; NUtE) increased from 34.0 to 52.1 kg DM kg⁻¹ N. Overall genetic variability in NUE under LN related mainly to differences in NUtE rather than N-uptake efficiency (crop N uptake at harvest per unit N available from soil and fertilizer; NUpE). However, at one site there was also a positive correlation between NUpE and NUE at LN in both years. Moreover, across the 2 year/four site network, the N × genotype effect for NUpE partly explained the N × genotype effect for grain yield and NUE. Averaging across the 16 genotypes, the timing of onset of senescence explained 86% of the variation in NUtE amongst site-season-N treatment combinations. The linear regression of onset of senescence on NutE amongst genoytpes was not significant under HN, but at three of the four sites was significant under LN explaining 32-70% of the phenotypic variation amongst genotypes in NutE. Onset of senescence amongst genotypes was negatively correlated with the efficiency with which above-ground N at anthesis was remobilized to the grain under LN. It is concluded that delaying the onset of post-anthesis senescence may be an important trait for increasing grain yield of wheat grown under low N supply.     

The effects of nitrogen and iron fertilization on growth,yield and fertilizer use efficiency of soybean in a Mediterranean-type soil

Poor seed yield of soybean in Mediterranean-type environments may result from insufficient iron (Fe) uptake and poor biological nitrogen (N) fixation due to high bicarbonate and pH in soils. This study was conducted to evaluate the effects of N and Fe fertilization on growth and yield of double cropped soybean (cv. SA 88, MG III) in a Mediterranean-type environment in Turkey during 2003 and 2004. The soil of the experimental plots was a Vertisol with 176 g CaCO₃ kg⁻¹ and pH 7.7 and 17 g organic matter kg⁻¹ soil. Soybean seeds were inoculated prior to planting with commercial peat inoculants. N fertilizer rates were 0, 40, 80, and 120 kg N ha⁻¹ of which half was applied before planting and the other half at full blooming stage (R2). Fe fertilizer rates were 0, 200 and 400 g Fe EDTA (5.5% Fe and 2% EDTA) ha⁻¹. It was sprayed as two equal portions at two trifoliate (V2) and at five trifoliate stages (V5). Plants were sampled at flower initiation (R1), at full pod (R4) and at full seed (R6) stages. Application of starter N increased biomass and leaf area index at R1 stage whereas Fe fertilization did not affect early growth parameters. N application continued to have a positive effect on growth parameters at later stages and on seed yield. Fe fertilization increased growth parameters at R4 and R6 stages, and final seed yield in both years. This study demonstrated an interactive effect of N and Fe fertilization on growth and yield of soybean in the soil having high bicarbonate and pH. There was a positive interaction between N and Fe at the N rates up to 80 kg N ha⁻¹. However, further increase in N rate produced a negative interaction. Fertilization of soybean with 80 kg N ha⁻¹ and 400 g Fe ha⁻¹ resulted in the highest seed yield in both years. We concluded that application of starter and top dressed N in combination with two split FeEDTA fertilization can be beneficial to improve early growth and final yield of inoculated soybean in Mediterranean-type soils.     

Key Indicators for Assessing Nitrogen Use Efficiency in Cereal-Based Agroecosystems

SUMMARY

Improving nitrogen use efficiency (NUE) is an important objective of agroecosystem management. We define and demonstrate key indicators of NUE that enable a broader assessment of N management strategies. Nitrogen efficiency components and indexes were defined to assess soil and crop physiological processes, and agronomic and environmental factors related to N use. Measurements of grain yield, grain N, aboveground plant N, applied N, post-harvest root-zone soil N, and N losses via subsurface drains were used to assess N retention efficiency, available N uptake efficiency, N utilization efficiency, N harvest index, N yield efficiency, N reliance index, grain N accumulation efficiency, N balance index, N fertilizer utilization efficiency, and N loss index. Nitrogen use indicators were evaluated for two field studies: (1) hard red spring wheat with four N levels and two tillage treatments: no-tillage (NT) and conventional tillage (CT); and (2) corn in crop sequences of continuous corn (C-C), corn-soybean (C-S), two years of corn following alfalfa (ALF-C-C), and two years of corn following perennial grass (CRP-C-C). Tillage, crop rotation, and applied N had large and variable effects on different indicators of N use. N efficiency components and indexes were useful for monitoring cropping system N use, assessing N management strategies, and identifying key areas for improvements in NUE.     

Ecophysiological traits in maize hybrids and their parental inbred lines: Phenotyping of responses to contrasting nitrogen supply levels

Maize (Zea mays L.) breeding based primarily on final grain yield has been successful in improving this trait since the introduction of hybrids. Contrarily, understanding of the variation in ecophysiological processes responsible of this improvement is limited, especially between parental inbred lines and their hybrids. This limitation may hinder future progress in genetic gain, especially in environments where heritability estimation is reduced because grain yield is severely affected by abiotic stresses. The objective of this study was to analyze the genotypic variation between inbred lines and derived hybrids in the physiological determinants of maize grain yield at the crop level, and how differences among hybrids and parental inbreds may effect contrasting responses to N stress. Special emphasis was given to biomass production and partitioning during the critical period for kernel number determination. Phenotyping included the evaluation of 26 morpho-physiological attributes for 6 maize inbred lines and 12 derived hybrids, cropped in the field at contrasting N supply levels (N₀: no N added; N₄₀₀: 400 kg N ha⁻¹ applied as urea) during three growing seasons. Tested genotypes differed in the response to reduce N supply for most measured traits. Grain yield was always larger for hybrids than for inbreds, but N deficiency affected the former more than the latter (average reduction in grain yield of 40% for hybrids and of 24% for inbreds). We also found (i) a common pattern across genotypes and N levels for the response of kernel number per plant to plant growth rate during the critical period, (ii) a reduced apical ear reproductive capacity (i.e., kernel set per unit of ear growth rate) of inbreds as compared to hybrids, (iii) similar RUE during the critical period and N absorption at maturity at low N levels for both groups of genotypes, but enhanced RUE and N absorption of hybrids at high N supply levels, and (iv) an improved N utilization efficiency of hybrids across all levels of N supply. Results are indicative of a more efficient use of absorbed N by hybrids than by parental inbreds. Larger grain yield of hybrids than of inbreds at N₀ was associated to (i) enhanced dry matter accumulation due to improved light interception during the life cycle and (ii) enhanced biomass partitioning to the grain.