Field Crops Research

Article	Citations
How process-based modeling can help plant breeding deal with G x E x M interactions	122
Editorial Board	120
Late sowing with reduced nitrogen rate promotes relative maturation and nitrogen use efficiency without compromising yield in cotton	115
Root system architecture in a barley RIL population: Agronomic effects of seedling and adult root traits	111
Forage boost or grain blues? Legume choices shape Kernza intermediate wheatgrass dual-purpose crop performance	77
Flue-cured tobacco (Nicotiana tabacum L.) leaf quality can be improved by grafting with potassium-efficient rootstock	75
Comparing process-based wheat growth models in their simulation of yield losses caused by plant diseases	73
UAV-based indicators of crop growth are robust for distinct water and nutrient management but vary between crop development phases	71
Estimating maize LAI by exploring deep features of vegetation index map from UAV multispectral images	71
Long-term straw incorporation regulates greenhouse gas emissions from biodegradable film farmland, improves ecosystem carbon budget and sustainable maize productivity	63
Slow-release fertilizer deep placement increased rice yield and reduced the ecological and environmental impact in Southeast China: A life-cycle perspective	63
Plastic film mulch combined with adding biochar improved soil carbon budget, carbon footprint, and maize yield in a rainfed region	63
Nano-iron and AM fungi inoculation in dryland wheat field: A sustainable alternative to plastic film mulching	61
Perenniality and diversity drive output stability and resilience in a 26-year cropping systems experiment	61
System-based phosphorus management in non-flooded rice-lentil rotation in tropical alkaline soil on Gangetic plain: Crop productivity, phosphorus use efficiency and budgeting	59
Defoliation level and timing affect popcorn yield traits in the Midwestern United States	58
Establishing a water-use boundary function for potato through crop modeling	58
Real-time application of neem-coated urea for enhancing N-use efficiency and minimizing the yield gap between aerobic direct-seeded and puddled transplanted rice	57
Effects of long-term mineral fertilization on silage maize monoculture yield, phosphorus uptake and its dynamic in soil	56
Comprehensive growth monitoring index using Sentinel-2A data for large-scale cotton production	54
DPC can inhibit cotton apical dominance and increase seed yield by affecting apical part structure and hormone content	54
The dwarf gene Rht15 improved lodging resistance but differentially affected agronomic and quality traits in durum wheat	53
Effects of selenium (Se) uptake on plant growth and yield in common buckwheat (Fagopyrum esculentum Moench)	53
Effects of long-term nutrient management in semi-arid Vertisols on soil quality and crop productivity in a cotton-greengram intercropping system	52
Editorial Board	51

Traits associated with higher productivity and resilience to drought-prone Mediterranean environments of coastal-lowland quinoa (Chenopodium quinoa Willd.)	50
Optimal planting dates for diverse crops in Inner Mongolia	50
Phenotypic traits of sunflower varieties depend on the composition of cover crops	49
Enhancing precision nitrogen management for cotton cultivation in arid environments using remote sensing techniques	49
Pi-efficient wheat cultivars screened by using both functional marker CAPS-799 and field experiment	47
Long-term fertility experiments for irrigated rice in the West African Sahel: Effect on macro- and micronutrient concentrations in plant and soil	47
The critical period for yield and grain protein determination in quinoa (Chenopodium quinoa Willd.)	47
Genotype × environment interaction and selection of maize (Zea mays L.) hybrids across moisture regimes	46
Long-term no tillage straw mulching increased soil water and nitrogen storage in dryland wheat on the Loess Plateau, but may increase dissolved organic nitrogen leaching	45
Optimizing nitrogen fertilization and irrigation strategies to balance agroecosystem services in the wheat-maize double cropping system: A 21-year field study	45
Contrasted reaction norms of wheat yield in pure vs mixed stands explained by tillering plasticities and shade avoidance	45
A high yield potential ideotype for irrigated rice: Rice plant types with short culms and long, upright leaves	45
Genotype X environment interaction and yield stability of finger millet (Eleusine Coracana L.) genotypes based on AMMI, GGE and MTSI analysis in humid lowland areas of Ethiopia	44
Contrasting responses of soil microbial ecological clusters and oilseed rape production to nitrogen fertilizer in different cropping systems	44
Combining measurements and modelling to reveal long-term effects of nitrogen fertilizer application timing on N2O emissions in corn	44
Towards higher agrobiodiversity – Evaluating the effects of undersowing different flowering species on soybean productivity	43
Trends in crop yield estimation via data assimilation based on multi-interdisciplinary analysis	43
Long-term diversified cropping promotes wheat yield and sustainability across contrasting climates: Evidence from China and Switzerland	43
Regulation of 2-acetyl-1-pyrroline (2-AP) biosynthesis and grain quality in fragrant rice under salt stress	42
Layered nitrogen fertilization regulates root morphology to promote synergistic nitrogen and phosphorus absorption in maize (Zea mays L.)	41
Cover crops enhance soil health, crop yield and resilience of tropical agroecosystem	40
Key factors influencing wheat grain zinc and manganese concentration in areas with different soil available phosphorus	40
Sustainable nitrogen management in maize using optical sensor: Assessing yield, economics, and environmental impact	40
Agronomic management factors impacting yield, quality stability, and environmental footprints of barley in a mediterranean environment	40
Agronomic and economic evaluation of ratoon rice cropping systems with perennial rice varieties in West Africa	39
Increasing temperature shortened the carbon uptake period and decreased the cumulative net ecosystem productivity in a maize cropland in Northeast China	39
Influence of photothermal quotient in the critical period on yield potential of cereals–A comparison of wheat and barley	38
Direct nitrous oxide emissions from a crop rotation of maize and mung bean after different long-term fertilizer applications in Thailand	38
Modelling water productivity for ecological intensification of crop sequences in the Inner Argentinean Pampas	38
Is bunch planting suitable for wheat? An evaluation based on yield and lodging resistance	37
Mixed cropping of determinate and indeterminate soybean lines enhances productivity	37
Extended photoperiods after flowering increase the rate of dry matter production and nitrogen assimilation in mid maturing soybean cultivars	37
Carbon uptake of the sugarcane agroecosystem is profoundly impacted by climate variations due to seasonality and topography	37
Quantitative trait loci for leaf inclination angle in rice detected using reciprocal mapping populations	37
Kernel filling and desiccation in temperate maize: Breeding and environmental effects	37
Rice yield response to climate variability diverges strongly among climate zones across China and is sensitive to trait variation	37
Simultaneous enhancement of maize yield and lodging resistance via delaying plant growth retardant application	36
Integration of genome-wide association and genomic prediction for dissecting seed protein and amino acid in foxtail millet	36
Nitrogen fertilization produces divergent effects on canopy structure between indica and japonica rice reflected in leaf to panicle ratio based on deep learning	36
Agronomic adaptations to heat stress: Sowing summer crops earlier	36
Plant topping effects on growth, yield, and earliness of field-grown cotton as mediated by plant density and ecological conditions	35
Cover crops decrease maize yield variability in sloping landscapes through increased water during reproductive stages	35
Effects of cultural practices on weed community and seedbank dynamics in a potato rotation	35
Zeolite enhances phosphorus accumulation, translocation, and partitioning in rice under alternate wetting and drying	35
Coordinating lodging incidence and grain yield through wheat genetic diversity	35
Grain growth and development in wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.): Coordination between water content and source/sink ratio	35
Environmental conditions outweigh seeding rates for cover crop mixture performance across the Northeast US	35
Responses to precision planting in canola and grain legume crops	35
Changes of rice canopy structure under global dimming	34
Incorporation of rice residue and green gram cultivation saves nitrogen, improve soil health and sustainability of rice-wheat system	34

Sheep grazing increases the forage yield and reduces the yield-scaled soil CO2 emissions of sown pastures in an inland arid region	34
Crop attributes explaining current grain yield dominance of maize over sorghum	34
Improving maize nitrogen nutrition index prediction using leaf fluorescence sensor combined with environmental and management variables	34
Impact of plastic sheet mulching on grain Zn concentration, P/Zn ratio and Zn uptake in dryland grown winter wheat	34
Winter wheat genotype ability to recover nitrogen supply by precedent crops under combined nitrogen and water scenarios	34
Editorial Board	33
Impact of paclobutrazol on storage root number and yield of sweet potato (Ipomoea batatas L.)	33
Editorial Board	33
Effective Striga control and yield intensification on maize farms in western Kenya with N fertilizer and herbicide-resistant variety	32
A farmer data-driven approach for prioritization of agricultural research and development: A case study for intensive crop systems in the humid tropics	32
Increased cassava growth and yields through improved variety use and fertilizer application in the highlands of South Kivu, Democratic Republic of Congo	32
Drivers of sorghum response to fertilizer microdosing on smallholder farms across Burkina Faso	32
LINTUL-Cassava-NPK: A simulation model for nutrient-limited cassava growth	32
Editorial Board	31
Editorial Board	31
Editorial Board	31
Stability of common bean (Phaseolus vulgaris L.) genotypes for root system architecture and seed yield in multi-environments	31
Editorial Board	31
Novel Genetic Variation Through Altered zmm28 Expression Improves Maize Performance Under Abiotic Stress	31
Exploiting heterosis of semi-hybrids and heterogeneity of cultivar mixtures to enhance alfalfa crop performance	30
Editorial Board	30
Editorial Board	30
Editorial Board	30
Grain mineral concentration of Chinese winter wheat varieties released between 1970 and 2005 under diverse nutrient inputs	30
Booting stage is the key timing for split nitrogen application in improving grain yield and quality of wheat – A global meta-analysis	29
Dissecting the relationship between yield and mineral nutriome of wheat grains in double cropping as affected by preceding crops and nitrogen application	29
Feasibility of yield estimation based on leaf area dynamics measurements in rice paddy fields of farmers	29
Integrated mulching and nitrogen management strategies influence carbon footprint and sustainability of wheat production on the Loess Plateau of China	29
Quantifying pre- and post-anthesis heat waves on grain number and grain weight of contrasting wheat cultivars	29
Sustainability assessment of nitrogen nutrition index based topdressing nitrogen application	29
Is partial substitution of animal manure for synthetic fertilizer a viable N2O mitigation option? An integrative global meta-analysis	29
Management practices regulate the response of canopy and ecosystem water use efficiency in cropland ecosystems	29
Unlocking maize yield potential through exploring canopy-root interactions with nature-based nutrient management	28
Experimental and producer-reported data quantify the value of foliar fungicide to winter wheat and its dependency on genotype and environment in the U.S. central Great Plains	28
Experimental assessment of the yield gap associated with maize production in the North China Plain	28
Ozone flux-effect relationship for early and late sown Indian wheat cultivars: Growth, biomass, and yield	28
Variations in water availability and N cycling across different seasons in cover crop systems	28
Diverse water management in a preceding wheat crop does not affect maize yield but increases inter-annual variability: A six-year field study	28
Responses of soil CO2 emissions to tillage practices in a wheat maize cropping system: A 4-year field study	28
Maximising soybean productivity with late maturity groups in Mediterranean irrigated systems	28
Optimizing bioenergy sorghum productivity and nutrient removal in Illinois: Impact of nitrogen fertilization under diverse marginal conditions	28
Edaphic stress interactions: Important yet poorly understood drivers of plant production in future climates	28
Balancing phosphorus fertilization for sustainable maize yield and soil test phosphorus management: A long-term study using machine learning	28
Estimating early season growth and biomass of field pea for selection of divergent ideotypes using proximal sensing	27
Carbon dioxide and/or temperature elevation effect on yield response, nutrient partitioning and use efficiency of applied nitrogen in wheat crop in central India	27
The central role of ear nitrogen uptake in maize endosperm cell and kernel weight determination during the lag period	27
Responses of soil water supply during the wheat growing season to agricultural management practice in Northern China: A meta-analysis	27
Advantages of deep fertilizer placement in environmental footprints and net ecosystem economic benefits under the variation of precipitation year types from winter wheat fields	27
Innovative furrow ridging fertilization under a mechanical direct seeding system improves the grain yield and lodging resistance of early indica rice in South China	27
Adopting different irrigation and nitrogen management based on precipitation year types balances winter wheat yields and greenhouse gas emissions	27
Radiative transfer model inversion using high-resolution hyperspectral airborne imagery – Retrieving maize LAI to access biomass and grain yield	27
How does increasing planting density affect nitrogen use efficiency of maize: A global meta-analysis	27
Alleles of high-yielding indica rice that improve root hydraulic conductance also increase flag leaf photosynthesis, biomass, and grain production of japonica rice in the paddy field	27
MP3, a quantitative trait locus for increased panicle number, improves rice yield potential in Japan by connecting with high source and translocation traits	27
Influence of the temperature during grain filling stage and nitrogen application rate on yield and quality of indica hybrid rice	26
The roots of the rotation effect run deep	26
Yield performance, land and water use, economic profit of irrigated spring wheat/alfalfa intercropping in the inland arid area of northwestern China	26
Ecosystem level carbon and moisture fluxes from a high biomass fibre producing jute crop (Corchorus olitorius L): An eddy covariance-based analysis	26
Crop nitrogen status and yield formation: A cross-species comparison for maize, rice, and wheat field crops	26
Optimal row spacing configuration to improve cotton yield or quality is regulated by plant density and irrigation rate	26
Wheat yield progress and stability during the last five decades in Argentina	26
Intercropping and species interactions on physiological and light use characteristics of forage cereals-legumes combinations in semi-arid regions	25
Spatial and temporal variation in crop productivity and relation with soil fertility within upland agroforestry	25
Does canopy angle influence radiation use efficiency of sugar beet?	25
Editorial Board	25
No-tillage with total green manure mulching: A strategy to lower N2O emissions	25
Yield benefits from joint application of manure and inorganic fertilizer in a long-term field pea, wheat and potato crop rotation	25
Resource acquisition and interactions in spring wheat/faba bean intercropping under diverse environments	25
Bio-based fertilisers can replace conventional inorganic P fertilisers under European pedoclimatic conditions	25
Conservation agriculture practices lead to diverse weed communities and higher maize grain yield in Southern Africa	25
Corrigendum to “Assessing the impacts of cover crops on maize and soybean yield in the U.S. Midwestern agroecosystems” [Field Crops Res. 273 (2021) 108264]	25
Evaluating nitrogen fertilization strategies to optimize yield and grain nitrogen content in top winter wheat varieties across Switzerland	25
Selection of suitable type and application rate of biochar for alfalfa (Medicago sativa L.) productivity in ridge-furrow rainwater-harvesting in semiarid regions of China	25
Irrigation increases on-farm soybean yields in water-limited environments without a trade-off in seed protein concentration	24
Optimization of irrigation and nitrogen fertilization increases ash salt accumulation and ions absorption of drip-fertigated sugar beet in saline-alkali soils	24
Does straw return increase crop yield in the wheat-maize cropping system in China? A meta-analysis	24
Auxin plays a key role in nitrogen and plant density-modulated root growth and yield in different plant types of rapeseed	24
Retrieving canopy nitrogen concentration and aboveground biomass with deep learning for ryegrass and barley: Comparing models and determining waveband contribution	24
A European perspective on opportunities and demands for field-based crop phenotyping	24
Multi-source data fusion for estimating maize leaf area index over the whole growing season under different mulching and irrigation conditions	24

Coupling effect analysis of drip irrigation and mixed slow-release nitrogen fertilizer on yield and physiological characteristics of winter wheat in Guanzhong area	24
Competition-recovery and overyielding of maize in intercropping depend on species temporal complementarity and nitrogen supply	24
Seed inoculation with Azospirillum brasilense in the U.S. soybean systems	24
Adapting the CROPGRO Perennial Forage model to predict growth and development of Pensacola bahiagrass	24
Optimizing root system architecture to improve cotton drought tolerance and minimize yield loss during mild drought stress	23
Biochar effects on crop yield variability	23
Maize genetic progress in the central Pampas of Argentina: effects of contrasting sowing dates	23
Clade-dependent effects of drought on nitrogen fixation and its components – Number, size, and activity of nodules in legumes	23
Grain size variation in two-rowed malt barley under Mediterranean conditions: Phenotypic plasticity and relevant trade-offs	23
Crop response to P fertilizer omission under a changing climate - Experimental and modeling results over 115 years of a long-term fertilizer experiment	23
Navigating the trade-offs in crop production and soil quality through alternative cropping	23
Estimating the maize above-ground biomass by constructing the tridimensional concept model based on UAV-based digital and multi-spectral images	23
Boll/leaf ratio improves the source–sink relationship and lint yield during the boll setting stage of cotton	23
Quantifying physiological contributions to nitrogen-induced yield variation in field-grown cotton	23
Impact of climate variability and extreme rainfall events on sugarcane yield gap in a tropical Island	23
Evaluation of production capacity for rice-rapeseed cropping system in China	23
Optimization of water and nitrogen management to improve seed cotton yield, water productivity and economic benefit of mulched drip-irrigated cotton in southern Xinjiang, China	23
Modeling long-term nitrogen utilization under alfalfa–corn rotation in Northeast China	23
Machine learning for regional crop yield forecasting in Europe	23
Crop establishment and diversification strategies for intensification of rice-based cropping systems in rice-fallow areas in Odisha	23
Interspecific competition and nitrogen application alter soil ecoenzymatic stoichiometry, microbial nutrient status, and improve grain yield in broomcorn millet/mung bean intercropping systems	23
Consistency, variability, and predictability of on-farm nutrient responses in four grain legumes across East and West Africa	23
Developing recommendations for increased productivity in cassava-maize intercropping systems in Southern Nigeria	23
Regulation of photoassimilate transportation and nitrogen uptake to decrease greenhouse gas emissions in ratooning rice with higher economic return by optimized nitrogen supplies	22
Incorporating environmental covariates to explore genotype × environment × management (G × E × M) interactions: A one-stage predictive model	22
Optimizing tillage regimes in rice-rapeseed rotation system to enhance crop yield and environmental sustainability	22
Physiological response and agronomic performance of drought tolerance mutants of Aus rice cultivar Nagina 22 (Oryza sativa L)	22
Agronomic and physiological traits facilitating better yield performance of japonica/indica hybrids in saline fields	22
One–third substitution of nitrogen with cow manure or biochar greatly reduced N2O emission and carbon footprint in saline–alkali soils	22
Uncovering the potentials of long-term straw return and nitrogen supply on subtropical maize (Zea mays L.) photosynthesis and grain yield	22
Analysis of spatio-temporal variation of crop yield in China using stepwise multiple linear regression	22
Machine learning models fed with optimized spectral indices to advance crop nitrogen monitoring	22
Moderately deep tillage enhances rapeseed yield by improving frost resistance of seedling during overwintering	22
Cotton crop transpiration reveals opportunities to reduce yield loss when applying defoliants for efficient mechanical harvesting	22
N-loaded clinoptilolite under water-saving irrigation mitigates ammonia volatilization while increasing grain yield and water-nitrogen use efficiency	22
Quantifying the contribution of above- and below-ground residues of chickpea, faba bean, lentil, field pea and wheat to the nitrogen nutrition of a subsequent wheat crop	22
Effects of free air CO2 enrichment (FACE) on grain yield and quality of hybrid rice	22
Comparative prediction accuracy of hyperspectral bands for different soybean crop variables: From leaf area to seed composition	21
Grain yield prediction using multi-temporal UAV-based multispectral vegetation indices and endmember abundance in rice	21
Exploring the nitrogen source-sink ratio to quantify ear nitrogen accumulation in maize and wheat using critical nitrogen dilution curve	21
Genetic gains in maize yield and related traits for high-yielding cultivars released during 1980s to 2010s in China	21
Effects of enhanced-efficiency nitrogen fertilizers on CH4 and CO2 emissions in a global perspective	21
The environmental and agronomic benefits and trade-offs linked with the adoption alternate wetting and drying in temperate rice paddies	21
Biochar addition mitigates asymmetric competition of water and increases yield advantages of maize–alfalfa strip intercropping systems in a semiarid region on the Loess Plateau	21
Continuous years of biodegradable film mulching enhances the soil environment and maize yield sustainability in the dryland of northwest China	21
Combining manure with mineral N fertilizer maintains maize yields: Evidence from four long-term experiments in Kenya	21
Big data, small explanatory and predictive power: Lessons from random forest modeling of on-farm yield variability and implications for data-driven agronomy	21
An improvement in oilseed rape (Brassica napus L.) productivity through optimization of rice-straw quantity and plant density	21
Nitrogen and rice straw incorporation impact nitrogen use efficiency, soil nitrogen pools and enzyme activity in rice-wheat system in north-western India	21
Genetic progress in cotton lint and yield components in Argentina	21
Maize/soybean intercrop over time has higher yield stability relative to matched monoculture under different nitrogen-application rates	21
Editorial Board	20
Reducing cadmium accumulation and increasing grain yield with proper timing of flood irrigation in the second season of ratoon rice	20
Simulation of maize crop growth using an improved crop model considering the disintegrated area of biodegradable film	20
Quantifying contributions of leaf area and longevity to leaf area duration under increased planting density and nitrogen input regimens during maize yield improvement	20
Ultra-wide film mulching with moderate irrigation water salinity enhances cotton growth under drip irrigation in Xinjiang, China	20
Genetic improvement analysis of nitrogen uptake, utilization, translocation, and distribution in Chinese wheat in Henan Province	20
Nitrogen reduction by 20 % with green manure retention reduces soil evaporation, promotes maize transpiration and improves water productivity in arid areas	20
Controlled-release phosphate fertilizer improves soil fertility and soybean productivity by regulating soil microbial diversity and composition and increasing enzyme activities	20
Attainable yield and soil texture as drivers of maize response to nitrogen: A synthesis analysis for Argentina	20
Alternate intercropping of cotton and peanut increases productivity by increasing canopy photosynthesis and nutrient uptake under the influence of rhizobacteria	20
High-throughput physiological phenotyping of crop evapotranspiration at the plot scale	20
Greenness index profile in maize canopy: Implications for crop N status diagnosis	20
Improving maize yield estimation by assimilating UAV-based LAI into WOFOST model	19
Model-based evaluation of rainfed lowland rice responses to N fertiliser in variable hydro-edaphic wetlands of East Africa	19
Editorial Board	19
Optimum organic fertilization enhances rice productivity and ecological multifunctionality via regulating soil microbial diversity in a double rice cropping system	19
Extreme climate weakens the effect of biochar in increasing yield and reducing N2O emissions	19
Enhancing zinc and iron bioavailability through crop rotation and organic farming: Insights from a long-term study	19
Wheat breeding in China over the past 80 years has increased grain zinc but decreased grain iron concentration	19
Six years of different fertilization regimes shift weed community and competition with winter oilseed rape	19
Editorial Board	19
Optimizing cropping systems and irrigation regimes to mitigate NH3 emissions and enhance crop productivity in the Huang-Huai-Hai Plain	19
Ovary abortion in field-grown maize under water-deficit conditions is determined by photo-assimilation supply	19
Simulating plastic mulching effects on the soil water balance and maize yields using the modified RZ-SHAW model	19
In-season nitrogen status and pre-harvest potato yield assessment using air-spaceborne imagery with AI techniques	19
A new adaptive identification strategy of best crop management with farmers	19
Grazing optimizes forage production and soil GHG emissions of mixed perennial pasture in an inland arid area	19
Annual burying of pelletized straw benefits grain amino acid by increasing soil mineral elements: A case study in Northeast China	19
Ethylene modulates peanut (Arachis hypogaea L.) growth and yield in response to planting depth	19
Understanding response of yield-scaled N2O emissions to nitrogen input: Data synthesis and introducing new concepts of background yield-scaled N2O emissions and N2O emission-yield curve	19
Analysis of overwintering indexes of winter wheat in alpine regions and establishment of a cold resistance model	19
Diversifying cropping sequence reduces nitrogen leaching risks	18
15N labelling of cattle manure reveals the distribution of organic fertiliser nitrogen in a winter wheat system	18
Coordinating maize source and sink relationship to achieve yield potential of 22.5 Mg ha-1	18
Effect of grass-diet and grass-legume-diet manure applied to planting holes on smallholder maize production in Rwanda	18
Sequential submergence and drought induce yield loss in rice by affecting redox homeostasis and source-to-sink sugar transport	18
Short term fallow and partitioning effects of green manures on wheat systems in East African highlands	18
Effect of warm nights on Fusarium graminearum-bread wheat pathosystem: Impact on grain quality and rheological properties in two contrasting commercial genotypes	18
Calibrating the STICS soil-crop model to explore the impact of agroforestry parklands on millet growth	18
Manure application enhanced cotton yield by facilitating microbially mediated P bioavailability	18
Interspecies interaction for nitrogen use efficiency via up-regulated glutamine and glutamate synthase under wheat-faba bean intercropping	18
Assessing chickpea attainable yield and closing the yield gaps caused by agronomic and genetic factors	18
Effect of crop management and climatic factors on weed control in sugarcane intercropping systems	18
Editorial Board	18