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Long-term excessive nitrogen (N) application does not increase or even decreases grain yield and N use efficiency (NUE) of maize, in which the roles of root morphological and physiological characteristics are not clear. The goal of this study was to explain the mechanism underlying no increment in grain yield under excessive N application from the perspective of root morpho-physiological characteristics. A 10-year long-term N fertilizer trial was conducted in Jilin Province, Northeast China, growing maize at three N fertilizer levels (zero N, N0; recommended N, N2; and high N level, N4) in 2019, 2020 and 2021. Two widely planted maize genotypes: ‘Xianyu 335’ (XY335) and ‘Zhengdan 958’ (ZD958) were used. Grain yield, N content, root morphology and other physiological characteristics were analyzed to further evaluate the relationships between N uptake, N utilization, plant growth, and root systems under different N treatments. Compared with N0, root biomass, post-silking N uptake and grain yield were significantly improved with increased N input, whereas no significant differences were observed between recommended N and high N. High N application increased root length and root surface area, but decreased root activity (measured by TTC (2,3,5-triphenyltetrazolium chloride) method), nitrate reductase activity and root activity absorbing area regardless of genotypes. Root length and root to shoot ratio negatively contributed to N uptake (by -1.2% and -24.6%), while root surface area, root activity, nitrate reductase activity and root activity absorbing area were positively contributed to N uptake. The interaction effect between cultivar and N application was significant on NUE. XY335 obtained the highest NUE (11.6%) and N recovery efficiency (18.4%) through higher root surface area (23.6%), root activity (12.5%), nitrate reductase activity (8.3%) and root activity absorbing area (6.9%) compared with other treatments. Overall, recommended N application promoted Post N uptake, NUE and grain yield by root surface area and root activity, nitrate reductase activity and root activity absorbing area, while high N application did not increase or even decreased NUE by reducing root surface area, root activity, nitrate reductase activity and root activity absorbing area. Our case study successfully revealed that root surface area, root activity, nitrate reductase activity and root activity absorbing area were the limiting factors of NUE increase under high N application.

The nitrogen (N) uptake and utilization in maize (Zea maysL.) plants are accomplished through a series of biochemical reactions and transformations involving the N assimilation enzymes. Nitrate reductase (NR) and glutamine synthetase (GS) exert important functions in the N assimilation and remobilization processes. The mechanisms underlying plant N partitioning and the associated expression patterns of NR and GS genes in maize hybrids with different N utilization efficiencies were still not clear. In this study, the expression of ZmNRand ZmGSgenes that are related to N partitioning were analyzed in two maize hybrids (XY335 and HN138). Results showed that XY335 displayed higher grain yield, kernel numbers, shoot N uptake, and physiological N utilization efficiency (NUtE) than those shown in HN138 under low‐N conditions. The higher post‐silking N uptake and N remobilization in vegetative organs in XY335 were associated with the enhanced net photosynthetic rate (Pn), the NR and GS activities in ear‐leaf. Additionally, the expression levels of ZmGS1.3and ZmGS1.4were up‐regulated when exposed to low‐N stress, showing higher values in XY335 than those in HN138. Correlation analysis showed that the expression levels of ZmNR, ZmGS1.3, and ZmGS1.4are correlated with leaf NR and GS activities, N remobilization, and grain yield. Our investigation suggested the critical roles of the N metabolism‐associated genes in the modulation of internal N translocation and plant productivity in maize. Future transgene analysis on ZmNRand ZmGScan provide insights into the molecular mechanisms underlying plant tolerance to low N stress in maize.

Straw return is an effective way to improve crop grain yield and potassium (K) use efficiency by increasing soil K content. However, the effects of straw return on soil K supplying capacity, replacement of K fertilizer, and K-use efficiency under maize (Zea maysL.)–rice (Oryza sativaL.) cropping systems are little studied. A two-year field experiment was conducted to determine the physiological determinants of K-use efficiency under straw return with four K fertilization rates. Sr33 (straw returned plus 33% of K fertilizer applied) and Sr67 (straw returned plus 67% of K fertilizer applied) increased annual crop yields by 1.5% and 3.2% and increased agronomic K-use efficiency by respectively 2.9 and 1.3-fold on average in the two years, compared with the conventional practice S0K100 (no straw returned plus normal amounts of K fertilizer applied). The Sr33 and Sr67 treatments resulted in significantly greater equilibrium K concentration ratios (CR0K) and specifically exchangeable K (KX) values according to quantity/intensity (Q/I) relationship analyses, indicating improvement of the potential soil K supply capacity. However, the Sr67 better maintained the soil exchangeable K level and K balance. The results suggested that K released from maize and rice straw can replace about half of chemical K fertilizer, depending on the available K content in maize–rice cropping system production.

Variations in weather conditions can affect winter wheat (Triticum aestivumL.) yield. This study aimed to determine the ways in which the yield formation processes of winter wheat respond to variations in weather conditions at a large range. Five sowing dates (SDs) were set at 15‐d intervals from early October to early December during the period 2015–2017 in the North China Plain (NCP). Sowing in mid‐October (SD2) produced the highest yield, which was similar to that of conventional sowing (early October, SD1). Sowing in early December (SD5) increased wheat yields by 6.1 and 14.0% averaged two year compared to sowing in early (SD3) or late (SD4) November, respectively. The increased yield for SD5 was attributed to increased dry matter accumulation (DMA) pre‐anthesis, and greater numbers of spikes and kernels. The DMA, spike number, and kernel number were mainly influenced by the pre‐anthesis plant growth rate (PGR), which was affected by temperature from sowing to anthesis. Low temperatures (maximum temperature <18.9°C, minimum temperature <7.6°C, daily mean temperature <12.8°C) from sowing to anthesis occurred following SD3 and SD4 sowings, which decreased pre‐anthesis PGR, and in turn decreased the pre‐anthesis DMA and spike and kernel number. These eventually reducing the total biomass and grain yield. We conclude that sowing wheat extremely late (early December) has the potential to increase grain yield, which may offset the negative effects of climatic factors in the NCP.

Reasonable use of water is required for the sustainable development of maize production in the North China Plain (NCP). In this study, straw mulching (SM) was evaluated in a 2‐yr field experiment to determine whether its effect on maize (Zea maysL.) yield and water use efficiency (WUE) differed under different irrigation systems. Compared with no mulching (NM) treatment, SM increased maize yield by 10.6 and 12.5% under a drip irrigation system in 2016 and 2017, respectively, which was mainly attributed to an 11.7 and 13.5% increase in total dry matter (DM). The increased soil water content in the 0‐ to 40‐cm layer at the six‐leaf (V6), silking (R1), and maturity (R6) stages for SM improved the soil mineral N content (Nmin) in that layer and then increased the N accumulation from V6 to R1 and post‐silking by 7.6 and 21.1% averaged over 2 yr compared with NM, respectively. The enhanced N accumulation for SM increased the leaf area index and DM accumulation rate, which increased the DM accumulation from V12 to R1 and post‐silking by 16.2 and 16.4% averaged over 2 yr compared with NM, respectively, and then the grain number and grain weight. Straw mulching also improved the WUE under the drip irrigation system due to the greater grain yield and 6.1% lower water consumption. This demonstrated that SM combined with the drip irrigation system effectively improved the yield and WUE of maize due to improved DM and N accumulation promoted by the increased water content and Nminin the upper soil layers.

Crop yield potential can be increased through the use of appropriate agronomic practices. Integrated agronomic practice (IAP) is an effective way to increase maize (Zea maysL.) grain yield and nitrogen use efficiency (NUE); however, the physiological processes associated with gains in yield potential obtained from IAP, particularly the different under various soil fertility conditions, remain poorly understood. An IAP strategy including optimal planting density, split fertilizer application, and subsoiling tillage was evaluated over two growing seasons to determine whether the effects of IAP on maize yield and NUE differ under different levels of soil fertility. Compared to farmers' practices (FP), IAP increased maize grain yield in 2013 and 2014 by 25% and 28%, respectively, in low soil fertility (LSF) fields and by 36% and 37%, respectively, in high soil fertility (HSF) fields. The large yield gap was attributed mainly to greater dry matter (DM) and N accumulation with IAP than with FP owing to increased leaf area index (LAI) and DM accumulation rate, which were promoted by greater soil mineral N content (Nmin) and root length. Post-silking DM and N accumulation were also greater with IAP than with FP under HSF conditions, accounting for 60% and 43%, respectively, of total biomass and N accumulation; however, no significant differences were found for post-silking DM and N accumulation between IAP and FP under LSF conditions. Thus, the increase in grain yield with IAP was greater under HSF than under LSF. Because of greater grain yield and N uptake, IAP significantly increased N partial factor productivity, agronomic N efficiency, N recovery efficiency, and physiological efficiency of applied N compared to FP, particularly in the HSF fields. These results indicate that considerable further increases in yield and NUE can be obtained by increasing effective soil N content and maize root length to promote post-silking N and DM accumulation in maize planted at high plant density, especially in fields with low soil fertility.

Conventional fertilization with most N applied before or during early maize (Zea maysL.) growth stages can negatively affect production if soil N is insufficient after silking. Here, drip irrigation with a split application of N (drip fertigation) was evaluated to determine whether the effect on yield and N use efficiency (NUE) differs with cropping practice. Compared with conventional fertilization, drip fertigation increased yield by 13 and 14% at a low planting density under a low N rate (L) and by 15% at a high planting density under a high N rate (H) in 2012 and 2013, respectively. Yield increases under drip fertigation were attributed to 18 and 17% increases in postsilking dry matter (DM) accumulation under L, and 12 and 10% increases in presilking DM accumulation, and 17 and 16% increases in postsilking DM accumulation under H in 2012 and 2013, respectively. Increased postsilking N accumulation under drip fertigation, promoted by greater root length and soil mineral N after silking, maintained increased leaf area index (LAI) and DM accumulation rate to improve postsilking DM accumulation under L. Greater N accumulation under drip fertigation from the 12‐leaf stage to silking and after silking promoted greater LAI and DM accumulation rate to increase pre‐ and postsilking DM accumulation under H. Because of greater grain yield and N uptake and less water consumption, drip irrigation improved NUE and irrigation water use efficiency. Drip fertigation can effectively improving maize grain yield and NUE resulting from improved DM accumulation with increased early‐season N uptake.

Variation in weather conditions during grain filling has substantial effects on maize kernel weight (KW). The objective of this work was to characterize variation in KW with sowing date-associated weather conditions and examine the relationship between KW, grain filling parameters, and weather factors. Maize was sown on eight sowing dates (SD) at 15–20-day intervals from mid-March to mid-July during 2012 and 2013 in the North China Plain. With sowing date delay, KW increased initially and later declined, and the greatest KW was obtained at SD6 in both years. The increased KW at SD6 was attributed mainly to kernel growth rate (Gmean), and effective grain-filling period (P). Variations in temperature and radiation were the primary factors that influenced KW and grain-filling parameters. When the effective cumulative temperature (AT) and radiation (Ra) during grain filling were 950°C and 1005.4MJm−2, respectively, P and KW were greatest. High temperatures (daily maximum temperature [Tmax]>30.2°C) during grain filling under early sowing conditions, or low temperatures (daily minimum temperature [Tmin]<20.7°C) under late sowing conditions combined with high diurnal temperature range (Tmax-min>7.1°C) decreased kernel growth rate and ultimately final KW. When sowing was performed from May 25 through June 27, higher KW and yield of maize were obtained. We conclude that variations in environmental conditions (temperature and radiation) during grain filling markedly affect growth rate and duration of grain filling and eventually affect kernel weight and yield of maize.

Variations in weather conditions could alter maize (Zea maysL.) growth and development. This study was conducted to determine the eco‐physiological determinants of variations in maize yield with weather conditions, and the relationship between grain yield, dry matter production, and climatic factors. Eight sowing dates were set at 15‐ to 20‐d intervals from mid‐March to mid‐July during 2012 and 2013 in the Huang‐Huai‐Hai region of China. When the sowing date was delayed, the yield increased initially and later declined, and the greatest yield was obtained at 12 June (SD6) sowing date for both years. The increased yield for SD6 was mainly attributed to the 1000‐kernel weight and post‐silking dry matter production, which were mainly influenced by the post‐silking plant growth rate. Variations in temperature and radiation were the primary factors that influenced the post‐silking dry matter production of maize, and eventually influenced grain yield. High temperatures (daily maximum temperature [Tmax] > 28.1°C) during post‐silking under early sowing conditions and low temperatures (daily minimum temperature [Tmin] < 17.7°C) under late sowing conditions combined with low radiation (accumulated radiation [Ra] < 1 005.4 MJ m2) decreased the post‐silking plant growth rate, thereby decreasing the dry matter production and grain yield. Therefore, when the sowing was done from 25 May to 27 June, the relatively higher maize yield would be obtained. We conclude that variations in weather conditions (temperature and radiation) from silking to maturity significantly affect the plant growth rate of maize, influence post‐silking dry matter production, and grain yield.

Plant photosynthetic rate is affected by stomatal status and internal CO2carboxylation. Understanding which process determines photosynthetic rate is essential for developing strategies for breeding crops with high photosynthetic efficiency. In this study, we identified different physiological patterns of photosynthetic rate in two different rice populations. Photosynthetic gas exchange parameters were measured during the flowering stage in two rice populations. Clustering and correlation analyses were performed on the resulting data. Five or six groups were defined by K-means clustering according to differences in net photosynthetic rates (Pn). According to differences in stomatal conductance (gs) and carboxylation efficiency (CE), each group was clustered into three subgroups characterized by physiological patterns stomatal pattern, carboxylation pattern, and intermediate pattern. Pnwas significantly correlated with gs(r=0.810) and CE (r=0.531). Pnwas also significantly correlated with gsand CE in the three physiological patterns. The correlation coefficients were highest in the stomatal pattern (0.905 and 0.957) and lowest in the carboxylation pattern (0.825 and 0.859). Higher correlation coefficients between Pnand gsor CE in the three physiological patterns indicate that clustering is very important for understanding factors limiting rice photosynthesis.