Transgenic approaches for improving use efficiency of nitrogen, phosphorus and potassium in crops

The success of the Green Revolution largely relies on fertilizers, and a new Green Revolution is very much needed to use fertilizers more economically and efficiently, as well as with more environmental responsibility. The use efficiency of nitrogen, phosphorus, and potassium is controlled by complex gene networks that co-ordinate uptake, re-distribution, assimilation, and storage of these nutrients. Great progress has been made in breeding nutrient-efficient crops by molecularly engineering root traits desirable for efficient acquisition of nutrients from soil, transporters for uptake, redistribution and homeostasis of nutrients, and enzymes for efficient assimilation. Regulatory and transcription factors modulating these processes are also valuable in breeding crops with improved nutrient use efficiency and yield performance.

Effect of various crop rotations on rice yield and nitrogen use efficiency in paddy–upland systems in southeastern China

To evaluate the effects of various rotation systems on rice grain yield and N use efficiency, a paddy–upland cropping experiment(2013–2016) was conducted in southeastern China. The experiment was designed using six different rice––winter crop rotations: rice–fallow(RF),rice–wheat(RW), rice–potato with rice straw mulch(RP), rice–green manure(Chinese milk vetch; RC–G), rice–oilseed rape(RO), and rice–green manure crop(oilseed rape with fresh straw incorporated into soil at flowering; RO–G) and three N rates, N0(0 kg N ha-1), N1(142.5 kg N ha-1), and N2(202.5 kg N ha-1). Average rice yields in the RF(5.93 t ha-1) rotation were significantly lower than those in the rotations with winter crops(7.20–7.48 t ha-1)under the N0 treatment, suggesting that incorporation of straw might be more effective for increasing soil N than winter fallow. The rice yield differences among the rotations varied by year with the N input. In general, the grain yields in the RP and RO–G rotations –were respectively 11.6–28.5% and 14.80–37.19% higher than those in the RF in plots with N applied. Increasing the N rate may have tended to minimize the average yield gap between the RF and the other rotations; the yield gaps were 18.55%, 4.14%, and 0.23% in N0, N1, and N2, respectively. However, the N recovery efficiency in the RF was significantly lower than that in other rotations, except for 2015 under both N1 and N2 rates, a finding that implies a large amount of chemical N loss. No significant differences in nitrogen agronomic efficiency(NAE) and physiological efficiency(NPE) were found between the rotations with legume(RC–G) and non–legume(RO and RW) winter crops, a result that may be due partly to straw incorporation. For this reason, we concluded that the return of straw could reduce differences in N use efficiency between rotations with and without legume crops. The degree of synchrony between the crop N demand and the N supply was evaluated by comparison of nitrogen balance degree(NBD) values. The NBD values in the RP and RW were significantly lower than those in the other rotations under both N1 and N2 rates. Thus,in view of the higher grain yield in the RP compared to the RW under the N1 rate, the RP rotation might be a promising practice with comparable grain yield and greater N use efficiency under reduced N input relative to the other rotations. The primary yield components of the RF and RP were identified as number of panicles m-2 and numbers of kernels panicle-1, respectively. The NAE and NPE were positively correlated with harvest index, possibly providing a useful indicator for evaluating N use efficiency.

Grain Yield and Nitrogen Use Efficiency Vary with Cereal Crop Type and Nitrogen Fertilizer Rate in Ethiopia: A Meta-Analysis

The crop production in Ethiopia is markedly constrained by soil nutrient depletion and limited fertilizer input. Nitrogen is among the most yield-limiting factors of cereal crops, especially in sub-Saharan Africa (SSA). A meta-analysis of 82 studies was carried out to evaluate the response of major cereal crops, viz. wheat, maize, barley, teff, and sorghum, to nitrogen fertilization in Ethiopia. The results showed that N-application significantly increased yields of all the five crops examined herein. The average yields of the treatment effects over controls for the five crops were 3775.8 kg∙ha−1 and 2593.3 kg∙ha−1, respectively. The overall yield response to nitrogen treatments for all the crops was 64.8% (wheat, 96.5%;maize, 40.65%;barley 84.36%;teff, 50.48%;and sorghum;23%). Overall, nitrogen agronomic efficiency (AEN) and partial factor productivity (PFPN) were 18.2 and 71.81 kg∙kg−1, respectively. A downtrend of nitrogen use efficiency with an increase in N rate was realized. The yield response was higher for the nitrogen treatment effects of >100 kg∙N∙ha−1 (123.9%), clay soils (75.46%), low initial soil organic carbon (SOC) and available phosphorous (AP) (92.4% and 101.6%), respectively, Therefore, we recommend the application of nitrogen fertilizer (>100 kg∙N∙ha−1), especially on infertile soils for improved grain yield and NUE in aforementioned cereal crops in Ethiopia and similar regions in sub-Saharan Africa (SSA).

Effects of Growing of Different Types of Crops on Constitution of Soil Available Nitrogen and Conversion and Utilization of Nitrogen Fertilizer

The soybean, cotton, maize and sorghum were planted in pot under low nitrogen, high nitrogen treatments, the soil available nitrogen constitution and con- version and utilization of nitrogen fertilizer were determined, so as to provide techni- cal guidance for reasonable use and improving use efficiency of nitrogen fertilizer for different types of crops. Compared with the control with nitrogen but unplanted crop, growing soybean, cotton, maize, sorghum significantly decreased the soil available N contents by 53. 48%, 51.54%, 33.10%, 55.03%,and influenced the constitution of soil available N. Thereinto, growing soybean, cotton, maize and sorghum significantly decreased soil inorganic N contents by 85.41%, 83.09%, 70.89% and 83.35%,but increased soil hydrolysable organic N contents by 1.41, 1.53, 2.11 and 1.28 times, respectively; growing soybean, cotton, maize and sorghum significantly decreased the rate of soil inorganic N to available N by 68.61%, 65.09%, 56.47% and 63.00%, but increased the rate of soil hydrolysable organic N to available N by 4.18, 4.21, 3.66 and 4.08 times, respectively. Compared with the control, growing soybean, cotton, maize and sorghum significantly increased the transform rate of ammonium nitrogen fertilizer by 93.66%, 38.19%, 32.58% and 38.31% respectively, and growing soybean treatment had the highest increasing range; the nitrification rates of ammo- nium nitrogen fertilizer of growing soybean, cotton, maize and sorghum treatments were negative values, and growing soybean treatment had the highest decreasing amplitude. The ammonium nitrogen fertilizer use efficiency of growing soybean, cot- ton, maize and sorghum treatments were 52.01%, 28.31%, 24.16% and 28.40% re- spectively and growing soybean treatment had the highest value. In conclusion, growing crops suppressed the soil nitrification and accelerated the development of soil hydrolysable organic nitrogen by the utilization of soil available nitrogen and the alteration of soil environment, and hence impacted the constitution of soil available nitrogen and the transform and use of ammonium nitrogen applied in soil. Legumi- nous crops had stronger ability of suppressing nitrification, making use of ammonium compared with non-Leguminous crops.

Chemically and biologically activated biochars slow down urea hydrolysis and improve nitrogen use efficiency

Biochar is considered a potential technology to enhance chemical fertilizer use efficiency through intensification of the interactions between nutrients and the functional groups on biochar surfaces.However,little is known about how the application of activated biochars mixed with urea influences nitrogen(N)mineralization and crop performance in paddy fields.Here,a sawdust-derived fresh biochar(FBC)(ca.400℃)was activated chemically with 15%hydrogen peroxide and biologically with a nutrient solution mixed with a soil inoculum to obtain a chemically activated biochar(CBC)and a biologically activated biochar(BBC),respectively.The chemical and surface properties of FBC,CBC,and BBC were evaluated using spectroscopic methods,i.e.,Fourier transform infrared spectroscopy and 13C nuclear magnetic resonance,and potentiometric charge determination.The N retention capacity of biochars and their interaction with urea hydrolysis were examined in a laboratory incubation experiment.Additionally,a field experiment was carried out in a paddy field with the biochars unmixed or mixed with urea at a 1:1 ratio.Our results showed that negative surface functional groups and negative charges were increased on both activated biochars,especially CBC.Both activated biochars contributed to a significant reduction in urea-biochar suspension pH and increased N retention in the incubation experiment.Despite the enhanced surface properties of the activated biochars,no similar increases in rice biomass and grain yield were observed for these biochars in the field experiment.However,rice biomass,grain yield,apparent N use efficiency,and agronomic N use efficiency were significantly higher with the application of the three biochars compared to no-biochar application.Altogether,the results indicate that the application of urea mixed with biochar could enhance crop performance,especially in the case of activated biochar,which would enhance N retention in the soil,reducing N loss.

Varied previous crops on improving oilseed flax productivity in semiarid Loess Plateau in China

To investigate the effects of crop rotation on oilseed flax growth and yield,three season experiments were carried out in semi-arid area of Dingxi,Gansu from 2017 to 2019.The designed 6 rotational systems were FFF(flax-flaxflax),PFF(potato-flax-flax),WPF(wheat-potato-flax),FPF(flax-potato-flax),PWF(potato-wheat-flax)and FWF(flax-wheat-flax).Flax growth and yield investigation results showed that crop rotation increased leaf area duration,dry matter accumulation,seed nitrogen accumulation,water and nitrogen used efficiency,compared with continuous cropping of flax.Flaxseed yields in rotation systems were 22.23%–44.11%greater than those of continuous cropping system.Those in wheat and potato stubbles had higher tiller number(21.43%and 29.46%),more branches(14.24%and 6.97%),effective capsules(26.35%and 28.79%),higher water use efficiency(40.26%and 33.5%),higher nitrogen partial factor productivity(33.85%and 31.46%)and dry matter(41.98%and 25.47%)than those in oilseed flax stubble.It concluded that crop rotation system was an effective measure for oilseed flax productivity in semi-arid area by improving yield components and promoting biomass.

Nitrate signaling and use efficiency in crops

Nitrate(NO3–)is not only an essential nutrient but also an important signaling molecule for plant growth.Low nitrogen use efficiency(NUE)of crops is causing increasingly serious environmental and ecological problems.Understanding the molecular mechanisms of NO3–regulation in crops is crucial for NUE improvement in agriculture.During the last several years,significant progress has been made in understanding the regulation of NO3–signaling in crops,and some key NO3–signaling factors have been shown to play important roles in NO3–utilization.However,no detailed reviews have yet summarized these advances.Here,we focus mainly on recent advances in crop NO3–signaling,including short-term signaling,long-term signaling,and the impact of environmental factors.We also review the regulation of crop NUE by crucial genes involved in NO3–signaling.This review provides useful information for further research on NO3–signaling in crops and a theoretical basis for breeding new crop varieties with high NUE,which has great significance for sustainable agriculture.

Effect of Rural Sewage Irrigation Regime on Water-Nitrogen Utilization and Crop Growth of Paddy Rice in Southern China

Reclaimed water irrigation has become an effective mean to alleviate the contradiction between water availability and its consumption worldwide.In this study,three types of irrigation water sources(rural sewage’s primary treated water R1 and secondary treated water R2,and river water R3)meeting the requirements of water quality for farmland irrigation were selected,and three types of irrigation water levels(low water levelW1 of 0–80 mm,medium water level W2 of 0–100 mm,and high water level W3 of 0–150 mm)were adopted to carry out research on the influence mechanismS of different irrigation water sources and water levels on water and nitrogen use and crop growth in paddy field.The water quantity indicators(irrigation times and irrigation volume),soil ammonium nitrogen(NH4+-N)and nitrate nitrogen(NO3−-N),rice yield indicators(thousand-grain weight,the number of grains per spike,and the number of effective spikes),and quality indicators(the amount of protein,amylose,vitamin C,nitrate and nitrite content)of rice were measured.The results showed that,the average irrigation volume under W3 was 2.4 and 1.9 times of that under W1 and W2,respectively.Compared with R3,the peak consumption of rice was lagged behind under R1 and R2,and the nitrogen form in 0–40 cm soil layers under rural sewage irrigation was mainly NH4+-N.The changes of NO3−-N and NH4+-N in the 0–40 cm soil layer showed the trend of declining and then increasing.The water level control only had a significant effect on the change of NO3−-N in the 60–80 cm soil layer.Both irrigation water use efficiency and crop water use efficiency were gradually reduced with the increase of field water level control.The nitrogen utilization efficiency under rural sewage irrigation was significantly higher than that under R3.Compared with the R3,rural sewage irrigation could significantly increase the yield of rice,and as the field water level rose,the effect of yield promotion was more obvious.It was noteworthy that the grain of rice under R1 monitored the low nitrate and nitrite content,but no nitrate and nitrite was discovered under R2 and R3.Therefore,reasonable rural sewage irrigation(R2)and medium water level(W2)were beneficial to improve nitrogen utilization efficiency,crop yield and crop quality promotion.

东北黑土区典型县域农牧系统养分流动特征分析

在保障粮食安全的前提下,东北黑土区作物和畜牧生产的耦合促进了农业绿色发展。本研究选择位于东北黑土区的吉林省农安县为研究区域,以农牧系统为研究边界,通过实地调研、统计数据和文献,结合食物链养分流动模型(NUFER:NUtrient flows in Food chains,Environment and Resources use)定量分析1990—2020年农牧系统氮磷养分流动、利用效率和环境损失,探究气候和社会经济因素对氮磷排放的驱动作用,并设置平衡施肥(减少化肥施用)和有机肥替代(提升有机物料替代)两种情景评估该县减排潜力。结果表明,相对于1990年,2020年农安县农牧体系氮磷输入量分别下降45%和23%,其中化肥施用是最大的输入项。作物和农牧系统养分利用率波动增加,而畜禽系统养分利用率下降并逐渐趋于稳定。农牧体系氮磷损失量较1990年分别减少41%和增加29%。农田氨挥发、径流侵蚀和畜禽粪便直排为主要排放途径。通过平衡施肥和有机替代,土壤氮磷积累处于较低水平,至2030年农安县化学氮肥有80%的减施潜力,化学磷肥有85%的减施潜力,且氮磷养分环境排放均减少67%,作物和农牧系统养分利用率均增长50%以上。综上,农安县农牧体系未来可通过增加秸秆和粪便还田量提升化肥减施潜力。东北黑土区应继续深化化肥零增长政策,推行有机废弃物资源化利用,实现农牧系统协同优化发展。

Integrated application of February Orchid(Orychophragmus violaceus) as green manure with chemical fertilizer for improving grain yield and reducing nitrogen losses in spring maize system in northern China

The development of more efficient management systems is crucial to achieving high grain yields with high nitrogen use efficiency（NUE）. February Orchid-spring maize rotation system is a newly established planting system with the benefits of ground cover and potential wind erosion in northern China. A field experiment was conducted to evaluate the effects of integrated application of February Orchid as green manure with reduction of chemical fertilizers（INTEGRATED） on spring maize yield, N uptake, ammonium volatilization, and soil residual mineral N in northern China. Compared to farmers＇ traditional fertilization（CON）, integrated application of February Orchid as green manure with 30% reduction of nitrogen fertilizers（INTEGRATED） increased maize grain yield and biomass by 9.9 and 10.2%, respectively. The 0–100 cm soil residual Nmin at harvest was decreased by 58.5% and thus nitrogen use efficiency was increased significantly by 26.7%. The nitrogen balance calculation further demonstrated that the INTEGRATED approach performed better than CON with lower apparent nitrogen loss（decreased by 48.9%） which evidenced by the ammonium volatilization of top-dressing fertilizer was decreased by 31.1%, the N_（min） movement to the deeper soil layers was reduced, and the apparent nitrogen leaching loss nearly equal to 0 under the INTEGRATED treatment. Therefore, in northern China, integrated application of green manure and chemical fertilizers is an efficient management approach for improving maize yields and NUE simultaneously.

Effect of Continuous Application of Controlled Release Nitrogen Fertilizer in Various Types of Soil in Dong-Ting Lake Region under Double Rice Cropping System

[Objective] This study aimed to explore the effects of continuous application of controlled release nitrogen fertilizer under double rice cropping system. [Method] By modeling three types of paddy soils in Dong-Ting Lake area, four treatments as no fertilizer （CK）, urea, controlled release nitrogen fertilizer （CRNF） and 70% controlled release nitrogen fertilizer （70% CRNF） were designed in the micro-plot trials from 2005 to 2008. [Result] The rice yield in treatment CRNF at N 150 kg/hm2 was increased by 10.3%, 8.0% and 2.4% compared with treatment of urea, in alluvial sandy loamy paddy soil （ALS）, purple calcareous clayey paddy soil （PCS）, and reddish yellow loamy paddy soil （RYS）, respectively; and the yield in treatment of 70% CRNF was increased by 6.1%, 2.6% and -0.8%, respectively. The ranking order of nitrogen uptake amount by plant in early rice and late rice was CRNF 70% CRNF urea CK in all three types of soil. Nitrogen utilization efficiency of CRNF in above three types of soil was 60.7%, 59.6% and 56.3%, increased by 23.8%, 19.4% and 16.3% compared with that in treatment of urea, respectively. Nitrogen utilization efficiency of CRNF in early rice was increased year by year, and was higher than that of 70% CRNF during the whole experiment stage, while that in late rice was increased first and then decreased from the 3rd year. [Conclusion] Continuous application CRNF could alleviate the decreasing of soil nitrogen fertility and organic carbon especially in ALS, increase rice yield and nitrogen utilization efficiency in double-rice cropping system.

Advances in Application of Biological Nitrification Inhibitors

Based on current research, the characteristics and action mechanism of biological nitrification inhibitors at home and abroad were reviewed by combining with the latest research progress. The application effects of biological nitrification inhibitors on agricultural production were summarized. Research hotspot and achievements of biological nitrification inhibitors at home and abroad were summarized. The research direction in future was forecasted.

华北高产粮区基于种植制度调整和水氮优化的节水效应

冬小麦/夏玉米一年两熟是华北平原粮食作物主要的种植方式。冬小麦生育期降水少,春季灌溉是保证其高产的必要措施。基于上述问题,在华北平原高产粮区设置田间试验,研究了调整种植制度和水氮优化等措施下的节水效应。结果表明,将一年两熟的冬小麦套种夏玉米调整为冬小麦直播夏玉米,并结合水氮优化等措施,能降低作物耗水15%,提高灌溉水利用效率52%～54%,而产量并没有下降;而将一年两熟调整为两年三熟和一年一熟,尽管能降低作物耗水24%～31%,且能提高灌溉水利用效率58%～172%,但产量却下降16%～27%。综上所述,该区将现行的一年两熟制中的套种调整为直播,并加以水氮优化等措施,是目前较为适宜的种植方式。考虑到该区水资源严重短缺的现实,两年三熟制可能是未来的种植趋势,但需要挖掘其产量潜力。

作物氮素高效利用研究与现代农业

通过对氮肥的增产作用以及不合理施肥所产生的负面影响的分析,阐明了作物氮素高效利用研究的意义;综述了作物氮素高效利用的生理机制和遗传研究进展;提出了作物氮素高效利用研究的技术途径,认为选育氮素高效利用品种是提高氮肥利用率最经济有效的途径和现代农业发展的必然要求。

Assessment of Fertilising Properties of a Solid Digestate in Comparison with Undigested Cattle Slurry Applied to an Acidic Soil

The use of digestates or cattle slurries as fertilisers could contribute to the recycling of nutrients and organic matter, thus meeting the goals of the circular economy in agriculture. This work aims at evaluating the fertilising properties of a solid digestate (DG) in comparison with undigested cattle slurry (CS) and mineral fertilisation (MF). The experiment was performed in pots with ryegrass (Lolium multiflorum Lam.) grown in an acidic soil during a 163 days crop cycle. The results showed that throughout the crop cycle neither DG nor CS increased soil organic matter. DG significantly increased (P < 0.001) the sum of the soil exchangeable bases and soil P availability compared with CS or MF. Also, DG significantly increased (P < 0.05) the apparent P recovery of ryegrass (43%) compared with MF (27%). In the first cut, the ryegrass yield was higher in DG and CS than in MF, decreasing in the second and third cuts as a consequence of a decrease in N availability. Nevertheless, the fertilisation with DG or CS could replace the half amount of mineral N fertilisation, without a significant decrease in the ryegrass forage production. In addition, DG enables greater efficiency in the use of P than CS or MF.

Residue recycling options and their implications for sustainable nitrogen management in rice-wheat agroecosystems

Background In the Indo-Gangetic Plain,rice-wheat is the most extensively practiced crop rotation.The escalating issue of crop residue burning,particularly rice straw,and the necessity to lower the exorbitant expenses associated with fertilizer inputs stand out as significant challenges for farmers in the region.A well-suited integrated nutrient management(INM)strategy that focuses on recycling crop residues can serve as a solution to address these issues.Such a strategy not only mitigates air pollution resulting from residue burning but also helps combat water pollution due to nitrate losses from agroecosystems.Field experiments were used to evaluate the suitability of eight INM-modules that included various combinations of inorganic fertilizer rates(50%,100%,150%of recommended dose),crop residues(wheat and rice stubble retention at 30 cm standing stubble equivalent to 1/3 the straw yield),rice straw compost(RSC),farmyard manure(FYM),and green manuring(GM),compared to 100%recommended dose of fertilizers(F)and no fertilizer application.Results There was a considerable improvement in nitrogen mineralization,grain yields,and nitrogen use efficiency under GM+RSC-F50 and GM+FYM-F50.These INM modules would permit a 50%reduction in the use of chemical fertilizers.There was a little yield penalty with in situ rice residue incorporation at 100%F;however,this could be overcome with 150%F fertilizer application.In situ retention of wheat straw with a full application of fertilizer resulted in steadily rising crop yields over time.Changes in the redox potential,soil pH,and soil organic carbon best accounted for the observed trajectories in nitrogen use efficiency.Conclusion The most promising INM modules for adoption by farmers in the Indo-Gangetic Plain to judiciously use crop residues and curtail chemical fertilizer inputs are green manuring with Sesbania aculeata+rice straw compost at 5 t ha^(−1)+only 50%of recommended dose of fertilizers(GM+RSC-F50),and green manuring with Sesbania aculeata+farmyard manure at 5 t ha^(−1)+only 50%of recommended dose of fertilizers(GM+FYM-F50).Sole incorporation of crop residues without nitrogen augmentation from other sources might not help curtail chemical fertilizer use.Composting rice straw,which otherwise is widely burnt,proved a useful nitrogen source and a vital component of INM.Waste rice straw composting at the community scale and its application as a nutrient source can help achieve sustainable nitrogen management in the agroecosystems of Indo-Gangetic Plain.

油烟连作对现代烟草农业建设与发展的影响

[目的]探索提高油烟连作中前茬作物经济效益对连作效应的影响。[方法]对前茬作物采取高产栽培措施,并在生长中后期进行摘顶处理。[结果]摘顶提高了油菜的分枝数、角果数和单株生产潜力;油烟连作的经济效益明显提高。[结论]油烟连作有效地提高了烟农的年均收入,实现了增产增收,对现代烟草农业的全面建设与发展具有一定参考价值。

Mitigating growth-stress tradeoffs via elevated TOR signaling in rice

Rice production accounts for approximately half of the freshwater resources utilized in agriculture,result-ing in greenhouse gas emissions such as methane(CH4)from flooded paddy fields.To address this chal-lenge,environmentally friendly and cost-effective water-saving techniques have become widely adopted in rice cultivation.However,the implementation of water-saving treatments(WsTs)in paddy-field rice has been associated with a substantial yield loss of up to 50%as well as a reduction in nitrogen use efficiency(NUE).In this study,we discovered that the target of rapamycin(TOR)signaling pathway is compromised in rice under WsT.Polysome profiling-coupled transcriptome sequencing(polysome-seq)analysis unveiled a substantial reduction in global translation in response to WST associated with the downregulation of TOR activity.Molecular,biochemical,and genetic analyses revealed new insights into the impact of the positive TOR-S6K-RPS6 and negative TOR-MAF1 modules on translation repression under WST.Intriguingly,ammonium exhibited a greater ability to alleviate growth constraints under WsT by enhancing TOR signaling,which simultaneously promoted uptake and utilization of ammonium and nitrogen allocation.We further demonstrated that TOR modulates the ammonium transporter AMT1;1 as well as the amino acid permease APP1 and dipeptide transporter NPF7.3 at the translational level through the 5'untranslated region.Collectively,these findings reveal that enhancing TOR signaling could mitigate rice yield penalty due to WST by regulating the processes involved in protein synthesis and NUE.Our study will contribute to the breeding of new rice varieties with increased water and fertilizer utilization efficiency.

Nitrogen assimilation in plants:current status and future prospects

Nitrogen(N)is the driving force for crop yields;however,excessive N application in agriculture not only increases production cost,but also causes severe environmental problems.Therefore,comprehensively understanding the molecular mechanisms of N use efficiency(NUE)and breeding crops with higher NUE is essential to tackle these problems.NUE of crops is determined by N uptake,transport,assimilation,and remobilization.In the process of N assimilation,nitrate reductase(NR),nitrite reductase(Ni R),glutamine synthetase(GS),and glutamine-2-oxoglutarate aminotransferase(GOGAT,also known as glutamate synthase)are the major enzymes.NR and Ni R mediate the initiation of inorganic N utilization,and GS/GOGAT cycle converts inorganic N to organic N,playing a vital role in N assimilation and the final NUE of crops.Besides,asparagine synthetase(ASN),glutamate dehydrogenase(GDH),and carbamoyl phosphate synthetase(CPSase)are also involved.In this review,we summarize the function and regulation of these enzymes reported in three major crops—rice,maize,and wheat,also in the model plant Arabidopsis,and we highlight their application in improving NUE of crops via manipulating N assimilation.Anticipated challenges and prospects toward fully understanding the function of N assimilation and further exploring the potential for NUE improvement are discussed.

Effects of organic fertilizers produced using different techniques on rice grain yield and ammonia volatilization in double-cropping rice fields

Ammonia(NH_(3)) volatilization from rice fields contributes to poor air quality and indicates low nitrogen use efficiency. Although organic fertilizers can meet the nitrogen requirement for rice growth, the simultaneous effects of organic fertilizers on NH_(3) volatilization and rice yield in paddy fields are poorly understood and quantified. To address this gap in our knowledge, experimental field plots were established in a conventional double-cropping paddy field in the Pearl River Delta region, southern China. Five fertilizer treatments were used besides the control with no fertilizer: fresh organic fertilizer, successively composted organic fertilizer, chemically composted organic fertilizer, mixture of chemically composted organic fertilizer with inorganic fertilizer, and chemical fertilizer. Ammonia volatilization was measured using a batch-type airflow enclosure method. No significant differences in grain yield were observed among organic and chemical fertilizer treatments. However, compared with chemical fertilizer, chemically composted organic fertilizer and successively composted organic fertilizer significantly decreased total NH_(3) volatilization by 70% and 68%, respectively. The ammonium-nitrogen concentration in field surface water correlated strongly(P < 0.01) and positively with NH_(3) volatilization across fertilization treatments. Our findings demonstrate that chemically composted organic fertilizer can sustain rice yield while reducing NH_(3) volatilization. An important future step is to promote these field measurements to similar rice cultivation areas to quantify the regional-and national-scale impact on air quality and nitrogen deposition in sensitive areas, and to design and implement better fertilizer management practices.