Effects of P fertilization level on phosphorus uptake and agronomic traits under deficit irrigation in winter wheat (T. aestivum L.)

Abstract

Enhancing the phosphorus (P) use efficiency is critical for the sustainable cultivation of winter wheat. In this study, we investigated the effects of P fertilization level on plant P-uptake and agronomic traits under deficit irrigation, by using two wheat cultivars sharing contrasting water responses (i.e., Jimai 585 and Shimai 22). The high P level treatment (P120) improved plant biomass and P accumulation at each growth stage, grain yields, P remobilization amount to grain (PRA), P remobilization rate (PRR), and P contribution rate (PRR) of the cultivars with respect to the low P treatments (i.e., P90 and P60). Compared with Jimai 585, a cultivar acclimated to affluent water, the drought tolerant cultivar Shimai 22 exhibited similar behaviors on plant biomass, P-associated traits at each stage, and agronomic traits at maturity under P120. However, Shimai 22 was more improvement on P-associated and agronomic traits than Jimai 585 under P60 and P90. P contents were increased whereas moisture contents decreased in soil profile treated by P120 with respect to those by P60. Meanwhile, the soil profile cultivated by Shimai 22 displayed reduced moisture and P contents under P deprivation (i.e., P90 and P60) respect to that by Jimai 585, suggesting the contribution of more consumption of soil P and water storage to improved agronomic traits of Shimai 22. Together, our investigation suggested that suitable P input management positively mediates plant P-associated traits and grain formation capacity under deficit irrigation by improving supply and internal translocation of P across tissues in winter wheat plants.     

The yields,agronomic, and nitrogen use efficiency traits of wheat cultivars in north China under N-sufficient and -deficient conditions

In this study, the yields, yield components, agronomic, and nitrogen use efficiency (NUE) traits of the eighty-four winter wheat cultivars were investigated under nitrogen (N)-sufficient and -deficient conditions. Dramatic variations were observed in the yield and agronomic traits among the cultivars. Based on absolute yields under the N treatments, the cultivars were categorized into N efficiency groups of high, close high, medium, and low, in which the high efficiency group cultivars generally exhibited improved agronomic traits under these contrasting N-supply conditions. Additionally, the wheat cultivars were classified into various N response groups, including toleration, relative toleration, sensitive, and most sensitive based on the ratios of yield under N deficiency to that under N sufficiency. Regression correlation analyses revealed that straw biomass, total biomass, grain N amount, and straw N amount were significantly correlated with yield, suggesting that these traits can be acted as indices in evaluating yield potentials in wheat.     

Nitrogen Leaching Of Spring Wheat Genotypes (Triticum Aestivum L.) Varying In Nitrogen-Related Traits

Efficient use of nitrogen (N) by wheat crop and hence prevention of possible contamination of ground and surface waters by nitrates has aroused environmental concerns. The present study was conducted in drainage lysimeters for three years (1998–2000) to identify whether spring wheat genotypes (Triticum aestivum L.) that differ in N-related traits differ in N leaching and to relate parameters of N use efficiency (NUE) with parameters of N leaching. For this reason two spring wheat cultivars (‘Albis’ and ‘Toronit’) and an experimental line (‘L94491’) were grown under low (20 kg N ha^?1) and ample N supply (270 kg N ha^?1). The genotypes varied in parameters of NUE but not in N leaching. Grain yield of the high-protein line (‘L94491’) was, on average, 11% lower than that of ‘Toronit’ but among genotypes had significantly higher N in the grain (%), grain N yield, and N harvest index. Nitrogen lost through leaching was considerably low (0.42–0.52 g m^?2) mainly due to low volume of percolating water or the ability of the genotypes to efficiently exploit soil mineral N. There were no clear relationships between N-related genotype traits and N leaching, but across all treatments significantly negative correlations between volume of leachate and the amount of N in the total biomass and grain N yield existed.     

不同氮肥水平下水稻产量以及氮素吸收、利用的基因型差异比较

采用田间试验在施氮量为06、0、120、1802、40、3003、60.kg/hm27个水平下研究了不同水稻子粒产量、产量构成因子以及氮素吸收和利用的差异。结果表明,水稻品种4007的子粒产量在各个施氮水平下显著高于品种ELIO对氮肥的响应度高。施氮水平显著影响子粒产量构成因子。有效穗数与子粒产量存在显著正相关:ELIO和4007的相关系数(r)分别为0.839**和0.933**,表明有效穗数对水稻子粒产量起着非常重要的作用。本试验条件下,ELIO和4007获得最高产量所需的有效穗数分别为332、561个/m2;两者的氮素吸收效率在各施氮素水平下差异很小,均随着施氮量的增加而增加,而氮素利用效率均随着施氮量的增加而下降。4007的氮素利用效率在各个施氮水平下显著高于ELIO,较高的氮素收获指数(NHI)是主要原因之一。水稻氮素利用效率与成熟期茎秆、叶片的氮含量显著负相关,说明开花期后植物将吸收的氮素从营养器官有效地转运到子粒中是氮素利用效率高的重要原因之一。     

Choice of nitrogen fertilizer affects grain yield and agronomic nitrogen use efficiency of wheat cultivars

Abstract

Nitrogen use efficiency (NUE) is low in cereals especially in wheat. Different wheat cultivars may vary in NUE due to inherited biological nitrification inhibition (BNI) potential. In this study, three wheat cultivars (Punjab-2011, ARRI-2011 and Millat-2011) were fertilized at the rate of 140?kg ha^?1 with three N sources [nitrophos (NP), urea and calcium ammonium nitrate (CAN)]. The soil nitrate (NO₃^?)-N contents were significantly enhanced coupled with simultaneous decrease in ammonium (NH₄⁺)-N contents in the rhizosphere of cultivar Punjab-2011, fertilized with NP; however, cultivar Millat-2011 receiving urea behaved in contrast. Wheat cultivar Punjab-2011 fertilized with NP had the highest grain yield and agronomic NUE than other treatments due to significant increase in chlorophyl contents, allometric and yield parameters. The highest net benefit was recorded from the cultivar Punjab-2011 fertilized with CAN. In conclusion, use of NP in Punjab-2011 enhanced the grain yield and agronomic NUE.     

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.     

Response of Wheat Cultivars to Nitrogen and Sulfur for Crop Yield,Nitrogen Use Efficiency,and Protein Quality in the Semiarid Region

ABSTRACT

The effects of nitrogen (N at 0, 100 and 180 kg N ha-1) and sulfur (S at 0, 20, 40 and 60 kg S ha-1) on crop yield, nutrient uptake, nitrogen use efficiency (NUE), and amino acid composition of two bread wheat cultivars, ‘Shehan’ and ‘Enkoy,’ grown in Andisols and Cambisols in randomized blocks with three replications were evaluated. Both cultivars responded significantly (P < 0.05) to N and S applications and S application with N improved the NUE by 28%. The yield increase for the two cultivars by N and S application ranged between 0.8 to 2.4 Mg ha^?1. The N concentration increased significantly from N0 to N2 in both cultivars. Sulfur fertilization increased the concentration of cysteine and methionine by 27% and 14%, respectively, as compared to N alone. The grain yield, NUE, N, and S uptake, and the S-amino acid concentration of ‘Enkoy’ were significantly higher than ‘Shehan’ cultivar.     

Developing nitrogen management strategies under drip fertigation for wheat and maize production in the North China Plain based on a 3‐year field experiment

The intensive winter wheat (Triticum aestivum L.)–summer maize (Zea mays L.) cropping systems in the North China Plain (NCP) rely on the heavy use of mineral nitrogen (N) fertilizers. As the fertigated area of wheat and maize in the NCP has grown rapidly during recent years, developing N management strategies is required for sustainable wheat and maize production. Field experiments were conducted in Hebei Province during three consecutive growth seasons in 2012–2015 to assess the influence of different N fertigation rates on N uptake, yield, and nitrogen use efficiency [NUE: recovery efficiency (RE_N) and agronomic efficiency (AE_N)]. Five levels of N application, 0 (FN₀), 40 (FN_40%), 70 (FN_70%), 100 (FN_100%), and 130% (FN_130%) of the farmer practice rate (FP: 250 kg N ha^?1 and 205.5 kg N ha^?1 for wheat and maize, respectively), corresponding to 0, 182.2, 318.9, 455.5, and 592.2 kg N ha^?1 y^?1, respectively, were tested. Nitrogen in the form of urea was dissolved in irrigation water and split into six and four applications for wheat and maize, respectively. In addition, the treatment “drip irrigation + 100% N conventional broadcasting” (DN_100%) was also conducted. All treatments were arranged in a randomized complete block design with three replications. The results revealed the significant influence of both N fertigation rate and N application method on grain yield and NUE. Compared to DN_100%, FN_100% significantly increased the 3‐year averaged N recovery efficiency (RE_N) by 0.09 kg kg^?1 and 0.04 kg kg^?1, and the 3‐year averaged N agronomic efficiency (AE_N) by 2.43 kg kg^?1 and 1.62 kg kg^?1 for wheat and maize, respectively. Among N fertigation rates, there was no significant increase in grain yield in response to N applied at a greater rate than 70% of FP due to excess N accumulation in vegetative tissues. Compared to FN_70%, FN_100%, and FN_130%, FN_40% increased the RE_N by 0.17–0.57 kg kg^?1 and 0.03–0.34 kg kg^?1and the AE_N by 4.60–27.56 kg kg^?1 and 2.40–10.62 kg kg^?1 for wheat and maize, respectively. Based on a linear‐response relationship between the N fertigation rate and grain yield over three rotational periods it can be concluded that recommended N rates under drip fertigation with optimum split applications can be reduced to 46% (114.6 kg N ha^?1) and 58% (116.6 kg N ha^?1) of FP for wheat and maize, respectively, without negatively affecting grain yield, thereby increasing NUE.     

Wheat Yield Differences between Two Cropping Systems in Permanent Raised-Beds as Affected by Components of Nitrogen Use Efficiency

Permanent raised-bed is an alternative planting system for wheat (Triticum aestivum L.) in rain-fed areas. However, this system in monoculture conditions produces lower yields compared with wheat in rotation. Our objective was to estimate these yield differences as affected by nitrogen (N) use efficiency (NUE). Wheat in monoculture and in rotation with maize (Zea mays L.) was evaluated for eight years (2002–2009) with four N rates (0, 40, 80 or 120 kg ha^?1). Yield response to N in monoculture was consistently lower than for wheat in rotation. Yield reduction in monoculture at low and high N rate was 81 and 99% attributed to NUE out of which 70 and 82% was due to the uptake efficiency (UPE) and 30 and 19% to the utilization efficiency (UTE), respectively. Total N uptake proved to be the parameter that needs to be improved to enhance wheat yield in monoculture.

Abbreviations: NUE: nitrogen use efficiency; UPE: uptake efficiency; UTE: utilization efficiency; Ns: nitrogen supply; NDVI: normalized difference vegetation index     

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.     

Nitrogen Use Efficiency of Rice Under Cadmium Contamination:Influence of Rice Cultivar Versus Soil Type

There is a need for rice cultivars with high yields and nitrogen (N) use efficiency (NUE), but with low cadmium (Cd) accumulation in Cd-contaminated paddy soils. To determine the relative effects of rice genotype, soil type, and Cd addition on rice grain yield and NUE, a pot experiment consisting of nine rice cultivars was conducted in two types of paddy soils, red soil (RS) and yellow soil (YS), without or with Cd spiked at 0.6 mg kg^-1. The N supply was from both soil organic N pools and N fertilizers; thus, NUE was defined as the grain yield per unit of total crop-available N in the soil. Cd addition decreased grain yield and NUE in most rice cultivars, which was mainly related to reduced N uptake efficiency (NpUE, defined as the percentage of N taken up by the crop per unit of soil available N). However, Cd addition enhanced N assimilation efficiency (NtUE, defined as the grain yield per unit of N taken up by the crop) by 21.9% on average in all rice cultivars. The NpUE was mainly affected by soil type, whereas NtUE was affected by rice cultivar. Hybrid cultivars had higher NUEs than the japonica and indica cultivars because of their greater biomass and higher tolerance to Cd contamination. Reduction of NUE after Cd addition was stronger in RS than in YS, which was related to the lower absorption capacity for Cd in RS. Canonical correspondence analysis-based variation partitioning showed that cultivar type had the largest effect (34.4%) on NUE, followed by Cd addition (15.2%) and soil type (10.0%).     

Phenotypic diversity of durum wheat (<Emphasis Type="Italic">Triticum durum</Emphasis> Desf.) from Jordan

Durum wheat landrace genotypes are disappearing from the main wheat areas in Jordan, because of spreading of new uniform cultivars and the serious reduction in wheat cultivation. This study was conducted to evaluate genetic diversity in durum wheat landraces from Jordan and to identify desirable agronomic traits. Landraces were collected from two target areas: Ajloun and Karak. The collected material was grown under rainfed conditions using an augmented design with five blocks and four repeated check cultivars. Data were collected for 14 morphological and agronomic traits. Phenotypic diversity index (H′) was estimated, and the relationships among accessions were measured using cluster analysis and dendrogram similarity matrix. The results revealed the presence of a wide range of variability among landraces., which possess high levels of variability for biological yield, fertile tillers, number of seeds per spike, seed weight per spike and weight of 1000 seeds. These landraces must be considered as a reservoir of genes that plant breeders need in their wheat improvement programs and should be conserved both ex situ and in situ.     

施磷对小麦旗叶氮代谢关键酶活性和子粒蛋白质含量的影响

在田间试验条件下,以强筋品种济麦20和弱筋品种山农1391为材料,研究了不同施磷水平对2类型品种小麦旗叶氮代谢关键酶活性和子粒蛋白质积累的效应。结果表明,在P2O5 0～135 kg /hm2范围内,施磷明显提高济麦20灌浆前期旗叶硝酸还原酶（NR）和谷氨酰胺合成酶（GS）活性;但却降低山农1391旗叶NR、GS活性。强筋品种济麦20在灌浆中、后期旗叶内肽酶（EP）、羧肽酶（CP）活性和蛋白质含量因施磷而提高;而弱筋品种山农1391的EP、CP活性和子粒蛋白质含量则降低。施磷使济麦20子粒清蛋白、醇溶蛋白和谷蛋白的含量提高,球蛋白含量有所降低;但弱筋品种山农1391子粒球蛋白、醇溶蛋白和谷蛋白的含量因施磷而降低,清蛋白含量未见显著变化。说明小麦施磷应考虑不同品质类型品种氮代谢及子粒蛋白质含量对施磷的反应。     

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.     

强筋和中筋小麦氮肥适宜基追比例研究

  【目的】  研究不同氮肥基追比例对小麦籽粒蛋白组分、氮素利用效率和产量的影响,为黑龙港流域小麦高效施用氮肥提供理论依据。  【方法】  以济麦22和藁优2018为供试品种进行了2年小麦田间试验。以不施氮肥(N₀)为对照,在等氮肥用量条件下设氮肥基追比3∶7 (N_3:7)、4∶6 (N_4:6)、5∶5 (N_5:5)和6∶4 (N_6:4) 4个处理,氮肥追施在拔节期随灌溉一起进行。分析小麦生长关键时期的植株干物质和氮素积累量、籽粒总蛋白质含量及蛋白组分含量、氮肥效率和籽粒产量。  【结果】  随氮肥基追比例的提升,两小麦品种的植株干物质和氮素积累量均呈先增后减的趋势。随生育期的推进,两小麦品种的植株干物质积累速率呈先升后降的趋势,而氮素积累速率呈“升―降―升”的趋势。拔节至挑旗期是小麦干物质和氮素积累的主要阶段,至成熟期藁优2018和济麦22分别以N_4:6和N_5:5处理的干物质和氮素积累量最高。N_4:6处理的藁优2018具有最高的籽粒清蛋白、球蛋白、谷蛋白含量,籽粒总蛋白质含量较其他处理显著增加3.66%～10.76%,籽粒产量是其他处理的1.07～1.13倍,氮肥偏生产力、氮肥回收率和氮肥农学效率均显著提升。N_5:5处理的济麦22籽粒清蛋白、球蛋白、醇溶蛋白、谷蛋白和总蛋白质含量分别较其他处理高2.55%～4.78%、4.11%～16.92%、3.42%～10.39%、1.35%～10.32%和2.95%～10.06%,籽粒产量是其他氮肥处理的1.03～1.08倍,氮肥回收率显著增加。在挑旗—成熟期,藁优2018的氮素积累速率与济麦22相比较高,籽粒蛋白组分含量较济麦22高出1.17%～5.72%;而济麦22各氮肥处理的籽粒产量比藁优2018增加5.4%～15.21%。  【结论】  满足小麦氮素积累特性的氮肥基追比有利于小麦的高产优质。中筋小麦 (济麦22) 品种在挑旗至成熟期氮素积累速率变小,氮肥基追比为5∶5较为适宜,而强筋小麦 (藁优2018) 品种氮素积累速率大,氮肥基追比提高到4∶6,可以促进小麦高产和增加蛋白含量。     

Effect of crop‐residue management on the production and agronomic nitrogen efficiency in a rice–wheat cropping system

The rice–wheat cropping system (RWCS), producing about 5–10 Mg ha^–1 y^–1 of grain, is the backbone of food‐crop production in South‐East Asia. However, this system shows signs of fatigue as indicated by declining yields, negative nitrogen (N) balances, and reduced responses to applied fertilizer at some research centers. The return of rice and wheat residues can recycle up to 20%–30% of the N absorbed by the crops. However, their wide C : N ratio can temporarily immobilize native and applied N. To overcome this immobilization, wheat‐straw application was supplemented with the incorporation of Sesbania green manure and mungbean residues, and their effects on productivity, agronomic N efficiency, and system's apparent N balances were studied. Combining the application of wheat straw with Sesbania green manure or mungbean residues increased cereal grain yield and agronomic N efficiency and improved the generally negative apparent N balances. The combined use of wheat straw and mungbean produced an additional 0.5–0.6 t ha^–1 protein‐rich grain and thus appears to be the most promising residue‐management option for rice–wheat cropping systems in South Asia, provided that the transition cropping season between wheat harvest and rice transplanting is long enough.     

小麦硒敏感性的基因型差异分析

土壤中硒分布不均匀,富硒土壤中硒含量可达1 200 mg/kg,硒含量过高对大多数植物均有毒害作用。小麦是我国重要的主要粮食作物,筛选硒耐性强的小麦品种有利于实现小麦在富硒地区更好的推广。本研究选择99份小麦品种(系)进行盆栽试验,在拔节期进行处理设置(硒处理每盆硒酸钠用量120 mg/L,记作Se120;以硒酸钠0 mg/L处理为对照,记作CK),比较不同品种(系)小麦硒处理下农艺性状的变化。结果表明:与CK相比,过量施硒后小麦籽粒千粒重显著提高(P0.01),株高、有效叶面积、单株叶片数和功能叶片数均显著下降(P0.01),SPAD值(叶绿素相对含量)则没有显著变化。以Se120和CK之间农艺性状的差异作为小麦的耐硒性指标,通过马氏距离综合评估不同小麦品种对硒的耐受性和敏感性差异,结合聚类分析,发现X325、淮麦18、扬麦15号、淮9440、扬麦11是典型的耐硒品种,而扬麦2号和Corrine是典型的硒敏感型品种。     

Effects of Stoichiometric Traits of Nitrogen and Phosphorus in Soil on Photosynthetic Characteristics of Wheat

ABSTRACT

To improve the use efficiency of fertilizer in agricultural production, effects of stoichiometric traits of soil available nitrogen (N) and phosphorus (P) on photosynthetic gas exchange parameters and fluorescence parameters of wheat were revealed in a full factorial pot experiment with our N and P fertilizer rates each. Results showed that at the same level of soil available N, the net photosynthetic rate (Pn), stomatal conductance (Cond), photochemical quenching (qP), the quantum yield of PSII photochemistry (ΦPSII), and apparent electron transport rate (ETR) of wheat generally increased with a decline of soil N/P ecological stoichiometric ratio (by increasing soil available P), whereas the intercellular CO₂ concentration (Ci) and nonphotochemical quenching (NPQ) of wheat decreased with a decline of soil N/P. At the same level of soil available P, Pn, Cond, qP, ΦPSII, and ETR of wheat initially increased and then decreased with an increase of soil N/P ecological stoichiometric ratio (by increasing soil available N), whereas the dynamics of Ci and NPQ of wheat were exactly opposite to those of the above parameters. A limiting effect of soil available P on the photosynthesis of wheat occurred during the entire experiment. It was deduced that the cultivated soil, with the available N of 258.4 mg·kg^?1, available P of 89.6 mg·kg^?1, and stoichiometric N/P of 2.88, was suitable for weak gluten wheat cultivar Yangmai15. Therefore, another approach to improves nutrient use efficiency was provided on the basis of ecological stoichiometry theory.     

Comparison of nitrogen accumulation and nitrogen utilization efficiency between elite inbred lines and the landraces of maize

Abstract

Inadequate supply of nitrogen (N) fertilizers results in lower N use efficiency (NUE) and higher N losses which cause environmental deterioration, such as nitrate pollution of groundwater and emission of nitrous greenhouse gases. One way to increase NUE is to use N-efficient cultivars, which grow better under reduced N supplies. Both elite inbred lines and landraces are the basis for hybrid breeding in maize. While inbred lines are mostly selected from high N input conditions, landraces are historically distributed in poor soils with low N availability. Therefore, some potential NUE-related traits conserved in the landraces may have been lost during modern breeding processes. In the present study, the N accumulation and utilization efficiency of 15 elite inbred lines and four landraces of maize were compared at low (LN) and high N (HN) input conditions. In general, the grain yields of the inbred lines and the landraces were similar at both N rates. However, nitrogen accumulation ability in landraces was much higher than that of the inbred lines. The high N accumulation of landraces was closely related to their higher biomass, indicating that growth potential is the main driving force for N accumulation. Nevertheless, N utilization efficiency (grain produced per unit N absorbed) of the landraces was significantly lower than that in inbred lines. Correspondingly, assimilation allocation for grain formation, as indicated by the harvest index, was much lower in landraces than in inbred lines. The higher growth potential, and hence, the ability of N accumulation in landraces may be a valuable trait in breeding programs aiming to further improve N use efficiency.     

Effects of three N strategies on tillering and yield of low shoot density winter wheat

Abstract

Application of nitrogen (N) in early spring is often recommended for low shoot density winter wheat in northern temperate areas such as Sweden. Regional N-strategy field trials in such areas generally show no relationship between early N and grain yield but the effects on shoot numbers and other yield components are seldom investigated. This study quantified the effect of three N fertilization strategies on the number of tillers at GS30-31 and the grain yield of winter wheat with low shoot density in early spring, in order to evaluate the importance of early N application. The investigations were carried out from 1999–2002 in four annual field experiments on a clay soil in south-west Sweden using winter wheat (cvs. Kosack and Tarso) with shoot densities in early spring ranging from 360–850 shoots m^?2. A positive relationship between time of first N application as number of days before GS30 and increase in number of shoots from GS20-21 to GS30-31 was observed. The relationship was strongest in experiments with the lowest shoot density in early spring (360–560 shoots m^?2) and the additional increase with each day of earlier availability of N before GS30 was 11 shoots m^?2. In wheat with this low shoot density in early spring, N was needed before GS30 to avoid yield reductions. Whether N was applied and available 24 or 13 days before GS30 did not affect yield, despite significantly more shoots being present at GS30-31 with earlier N application.